$\text{HCHO}$ and $\text{HCOOH}$ are detected by:
- ✓$ \mathrm{NaHCO}_3 $
- B$ \mathrm{CuSO}_4 / \mathrm{NaOH} $
- C$ \mathrm{AgNO}_3 / \mathrm{NH}_4 \mathrm{OH}$
- DAll of these
Answer: A.
View full solution →Question types
Organic Chemistry: Some Basic Principles and Techniques question types
435 questions across 7 question groups — pick any mix to generate a Chemistry paper with step-by-step answer keys.
435
Questions
7
Question groups
5
Question types
01
M.C.Q (1 Marks)
182 Q→02Assertion (A) & Reason (B) MCQ
7 Q→031 Marks Question
85 Q→042 Marks Questions
67 Q→053 Marks Question
49 Q→06Case study (4 Marks)
5 Q→075 Marks Questions
40 Q→Sample Questions
Organic Chemistry: Some Basic Principles and Techniques questions
One sample from each question group in this chapter. Select any group above to see the full set with answer keys.
$\sigma_{\text{C}-\text{C}} :4 ;\ \sigma_{\text{C}-\text{H}}:6;\ \pi_{\text{C}=\text{C}}:1; \ \pi_{\text{C}\equiv\text{C}}:2$ These number of $\sigma$ and $\pi$-bonds are present in which of the following molecule?
- ✓$\text{CH}\equiv\text{C} -\text{CH}=\text{CH}-\text{CH}_{3}$
- B$\text{CH}_{2}=\text{C}=\text{CH}-\text{CH}_{3}$
- C$\text{CH}_{2}=\text{CH}-\text{CH}=\text{CH}_{3}$
- DNone of the above.
Answer: A.
View full solution →In which of the following inductive effect is possible:
- AButane
- BBenzene
- CCyclohexane
- ✓Butanal
Answer: D.
View full solution →Sodium nitroprusside reacts with sodium sulphide formed in lassaigne's test to detect presence of sulphur gives violet colour due to:
- A$\text{Na}_2\big[\text{Fe}(\text{CN})_5\text{NO}\big]$
- ✓$\text{Na}_4\big[\text{Fe}(\text{CN})_5\text{NOS}\big]$
- C$\text{Na}_2\big[\text{Fe}(\text{CN})_5\text{COS}\big]$
- DNone of these.
Answer: B.
View full solution →Consider the following compounds,
Which of the following statements is$/$ are true regarding $I$ and $II$?
Which of the following statements is$/$ are true regarding $I$ and $II$?
- ✓I shows $+R-$effect, whereas $II$ shows $-R-$effect.
- BI shows $-R-$effect, whereas $II$ shows $+R-$effect.
- CBoth $I$ and $II$ show $+R-$effect.
- DBoth $I$ and $II$ show $-R-$effect.
Answer: A.
View full solution →Note : In the following questions a statement of Assertion $(A)$ followed by a statement of Reason $(R)$ is given. Choose the correct option out of the choices given below each question.
Assertion $(A)$ : Sulphur present in an organic compound can be estimated quantitatively by Carius method.
Reason $(R)$ : Sulphur is separated easily from other atoms in the molecule and gets precipitated as light yellow solid.
Assertion $(A)$ : Sulphur present in an organic compound can be estimated quantitatively by Carius method.
Reason $(R)$ : Sulphur is separated easily from other atoms in the molecule and gets precipitated as light yellow solid.
- ABoth $A$ and $R$ are correct and $R$ is the correct explanation of $A.$
- BBoth $A$ and $R$ are correct but $R$ is not the correct explanation of $A.$
- ✓Both $A$ and $R$ are not correct.
- D$A$ is not correct but $R$ is correct.
Answer: C.
View full solution →Note : In the following questions a statement of Assertion $(A)$ followed by a statement of Reason $(R)$ is given. Choose the correct option out of the choices given below each question.
Assertion $(A)$ : All the carbon atoms in $\ce{H_2C = C = CH_2}$ are $sp^2$ hybridised
Reason $(R)$ : In this molecule all the carbon atoms are attached to each other by double bonds.
Assertion $(A)$ : All the carbon atoms in $\ce{H_2C = C = CH_2}$ are $sp^2$ hybridised
Reason $(R)$ : In this molecule all the carbon atoms are attached to each other by double bonds.
- ABoth $A$ and $R$ are correct and $R$ is the correct explanation of $A$.
- BBoth $A$ and $R$ are correct but $R$ is not the correct explanation of $A.$
- CBoth $A$ and $R$ are not correct.
- ✓$A$ is not correct but $R$ is correct.
Answer: D.
View full solution →Note : In the following questions a statement of Assertion $(A)$ followed by a statement of Reason $(R)$ is given. Choose the correct option out of the choices given below each question.
Assertion $(A)$ : Simple distillation can help in separating a mixture of propan $-1-\text{ol}\ ($boiling point $97^\circ C)$ and propanone $($boiling point $56^\circ C).$
Reason $(R)$ : Liquids with a difference of more than $20^\circ C$ in their boiling points can be separated by simple distillation.
Assertion $(A)$ : Simple distillation can help in separating a mixture of propan $-1-\text{ol}\ ($boiling point $97^\circ C)$ and propanone $($boiling point $56^\circ C).$
Reason $(R)$ : Liquids with a difference of more than $20^\circ C$ in their boiling points can be separated by simple distillation.
- ✓$A$ and $R$ both are correct, and $R$ is the correct explanation of $A.$
- B$A$ and $R$ both are correct, but $R$ is not the correct explanation of $A$.
- C$A$ is true but $R$ is false.
- D$A$ and $R$ both are false.
Answer: A.
View full solution →Note : In the following questions a statement of Assertion $(A)$ followed by a statement of Reason $(R)$ is given. Choose the correct option out of the choices given below each question.
Assertion $(A)$ : Pent $- 1-$ ene and pent $- 2 -$ ene are position isomers.
Reason $(R)$ : Position isomers differ in the position of functional group or a substituent.
Assertion $(A)$ : Pent $- 1-$ ene and pent $- 2 -$ ene are position isomers.
Reason $(R)$ : Position isomers differ in the position of functional group or a substituent.
- ✓$A$ and $R$ both are correct, and $R$ is the correct explanation of $A.$
- B$A$ and $R$ both are correct, but $R$ is not the correct explanation of $A$.
- C$A$ is true but $R$ is false.
- D$A$ and $R$ both are false.
Answer: A.
View full solution →In the following Questions, the Assertion and Reason hrve been put forfiird. Read the statements csrefully end choose the correct alternative from the following:
Assertion : A Mixture of $o-$ nitrophenol and $p-$ nitrophenol can be separated by steam distillation.
Reason : $p-$ nitrophenol is steam volatile while $o-$ nitrophenol is not steam volatile.
Assertion : A Mixture of $o-$ nitrophenol and $p-$ nitrophenol can be separated by steam distillation.
Reason : $p-$ nitrophenol is steam volatile while $o-$ nitrophenol is not steam volatile.
- ABoth Assertion and Reason are true and Reason is the correct explanation of Assertion.
- BBoth Assertion rnd Reason are true but Reason is not the correct explenatlon of Assertion.
- ✓Assertion is true but Reason is false.
- DBoth Assertion and Reason arc false.
Answer: C.
View full solution →Identify the functional groups in the following compounds:
Give the IUPAC names of the following compounds: 
Draw the resonance structures for the following compounds. Show the electron shift using curved-arrow notation. $\mathrm{C}_6 \mathrm{H}_5 \mathrm{NO}_2$.
View full solution →Identify the functional groups in the following compounds:
Draw the resonance structures for the following compounds. Show the electron shift using curved-arrow notation. $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ + \\ \text{CH}_3\text{H}=\text{CHCH}_2$
View full solution →Will $\mathrm{CCl}_4$ give white precipitate of AgCl on heating it with silver nitrate? Give reason for your answer.
View full solution →Identify the functional groups in the following compounds:
Draw formulas for the first five members of homologous series beginning with the following compounds.
H-COOH.
H-COOH.
Draw formulas for the first five members of homologous series beginning with the following compounds.
$\mathrm{CH}_3 \mathrm{COCH}_3$.
View full solution →$\mathrm{CH}_3 \mathrm{COCH}_3$.
Draw formulas for the first five members of homologous series beginning with the following compounds.
$\mathrm{H}-\mathrm{CH}=\mathrm{CH}_2$.
View full solution →$\mathrm{H}-\mathrm{CH}=\mathrm{CH}_2$.
For the following bond cleavages, use curved-arrows to show the electron flow and classify each as homolysis or heterolysis. Identify reactive intermediate produced as free radical, carbocation and carbanion.
For the following bond cleavages, use curved-arrows to show the electron flow and classify each as homolysis or heterolysis. Identify reactive intermediate produced as free radical, carbocation and carbanion.
What is the relationship between the members of following pairs of structures? Are they structural or geometrical isomers or resonance contributors?
Write bond line formulas for: Isopropyl alcohol, 2,3-Dimethylbutanal, Heptan-4- one.
Why is nitric acid added to sodium extract before adding silver nitrate for testing halogens?
Read the passage given below and answer the following questions from 1 to 5.
Hyperconjugation is a general stabilising interaction. It involves delocalisation of σ electrons of C—H bond of an alkyl group directly attached to an atom of unsaturated system or to an atom with an unshared p orbital. The σ electrons of C—H bond of the alkyl group enter into partial conjugation with the attached unsaturated system or with the unshared p orbital. Hyperconjugation is a permanent effect. To understand hyperconjugation effect, let us take an example of CH 32 + (ethyl cation) in which the positively charged carbon atom has an empty p orbital. One of the C-H bonds of the methyl group can align in the plane of this empty p orbital and the electrons constituting the C-H bond in plane with this p orbital can then be delocalised into the empty p orbital as depicted in Figure.
This type of overlap stabilises the carbocation because electron density from the adjacent σ bond helps in dispersing the positive charge.
In general, greater the number of alkyl groups attached to a positively charged carbon atom, the greater is the hyperconjugation interaction and stabilisation of the cation. Thus, we have the following relative stability of carbocations:
Hyperconjugation is also possible in alkenes and alkylarenes. Delocalisation of electrons by hyperconjugation in the case of alkene can be depicted as in Figure.
There are various ways of looking at the hyperconjugative effect. One of the way is to regard C—H bond as possessing partial ionic character due to resonance.
The hyperconjugation may also be regarded as no bond resonance.
The hyperconjugation may also be regarded as no bond resonance.
Methods of purification of organic compounds Once an organic compound is extracted from a natural source or synthesised in the laboratory, it is essential to purify it. Various methods used for the purification of organic compounds are based on the nature of the compound and the impurity present in it. The common techniques used for purification are as follows :
i) Sublimation
ii) Crystallisation
iii) Distillation
iv) Differential extraction and
v) Chromatography
Finally, the purity of a compound is ascertained by determining its melting or boiling point. Most of the pure compounds have sharp melting points and boiling points. New methods of checking the purity of an organic compound are based on different types of chromatographic and spectroscopic techniques.
Sublimation On heating, some solid substances change from solid to vapour state without passing through liquid state. The purification technique based on the above principle is known as sublimation and is used to separate sublimable compounds from non- sublimable impurities.
Crystallisation This is one of the most commonly used techniques for the purification of solid organic compounds. It is based on the difference in the solubilities of the compound and the impurities in a suitable solvent. The impure compound is dissolved in a solvent in which it is sparingly soluble at room temperature but appreciably soluble at higher temperature. The solution is concentrated to get a nearly saturated solution. On cooling the solution, pure compound crystallises out and is removed by filtration. The filtrate (mother liquor) contains impurities and small quantity of the compound. If the compound is highly soluble in one solvent and very little soluble in another solvent, crystallisation can be satisfactorily carried out in a mixture of these solvents. Impurities, which impart colour to the solution are removed by adsorbing over activated charcoal. Repeated crystallisation becomes necessary for the purification of compounds containing impurities of comparable solubilities.
Distillation This important method is used to separate
i) volatile liquids from nonvolatile impurities and
ii) the liquids having sufficient difference in their boiling points.
Liquids having different boiling points vaporise at different temperatures. The vapours are cooled and the liquids so formed are collected separately. Chloroform (b.p 334 K) and aniline (b.p. 457 K) are easily separated by the technique of distillation (Fig 12.5). The liquid mixture is taken in a round bottom flask and heated carefully. On boiling, the vapours of lower boiling component are formed first. The vapours are condensed by using a condenser and the liquid is collected in a receiver. The vapours of higher boiling component form later and the liquid can be collected separately.
Partition Chromatography: Partition chromatography is based on continuous differential partitioning of components of a mixture between stationary and mobile phases. Paper chromatography is a type of partition chromatography. In paper chromatography, a special quality paper known as chromatography paper is used. Chromatography paper contains water trapped in it, which acts as the stationary phase. A strip of chromatography paper spotted at the base with the solution of the mixture is suspended in a suitable solvent or a mixture of solvents (Fig. 12.13). This solvent acts as the mobile phase. The solvent rises up the paper by capillary action and flows over the spot. The paper selectively retains different components according to their differing partition in the two phases. The paper strip so developed is known as a chromatogram. The spots of the separated coloured compounds are visible at different heights from the position of initial spot on the chromatogram. The spots of the separated colourless compounds may be observed either under ultraviolet light or by the use of an appropriate spray reagent as discussed under thin layer chromatography.
- Hyperconjunction involves delocalisation of … electrons of C—H bond of an alkyl group directly attached to an atom of unsaturated system or to an atom with an unshared p orbital.
- $\sigma$
- $\pi$
- $\delta$
- $\eta$
- Which of the is an example of technique used for purification.
- Distillation
- Differential extraction
- Chromatography
- All the above
- On heating, some solid substances change from solid to vapour state without passing through liquid state is known as …
- Melting
- Boiling
- Sublimation
- Condensation
- The hyperconjugation may also be regarded as ….
- bonding resonance
- no bond resonance
- no bond induction
- bonding induction
- Chromatography paper contains water trapped in it, which acts as the … phase.
- mobile
- stationery
- Secondary
- quaternary
Read the passage given below and answer the following questions from 1 to 5.
A reagent that brings an electron pair to the reactive site is called a nucleophile (Nu:) i.e., nucleus seeking and the reaction is then called nucleophilic. A reagent that takes away an electron pair from reactive site is called electrophile (E+) i.e., electron seeking and the reaction is called electrophilic.
Electron Displacement Effects in Covalent Bonds The electron displacement in an organic molecule may take place either in the ground state under the influence of an atom or a substituent group or in the presence of an appropriate attacking reagent. The electron displacements due to the influence of an atom or a substituent group present in the molecule cause permanent polarlisation of the bond. Inductive effect and resonance effects are examples of this type of electron displacements. Temporary electron displacement effects are seen in a molecule when a reagent approaches to attack it. This type of electron displacement is called electrometric effect or polarisability effect.
Inductive Effect When a covalent bond is formed between atoms of different electronegativity, the electron density is more towards the more electronegative atom of the bond. Such a shift of electron density results in a polar covalent bond. Bond polarity leads to various electronic effects in organic compounds. Let us consider cholorethane $(CH_3CH_2Cl)$ in which the C–Cl bond is a polar covalent bond. It is polarised in such a way that the carbon-1 gains some positive charge $(\delta+)$ and the chlorine some negative charge $(\delta-)$ The fractional electronic charges on the two atoms in a polar covalent bond are denoted by symbol (delta) and the shift of electron density is shown by an arrow that points from$(\delta+)$ to $(\delta-)$ end of the polar bond.
In turn carbon-1, which has developed partial positive charge $(\delta+)$draws some electron density towards it from the adjacent C-C bond. Consequently, some positive charge$(\delta\delta+)$develops on carbon-2 also, where $(\delta\delta+)$ symbolises relatively smaller positive charge as compared to that on carbon – 1. In other words, the polar C – Cl bond induces polarity in the adjacent bonds. Such polarisation of σ- bond caused by the polarisation of adjacent $σ-$bond is referred to as the inductive effect.
Resonance Structure There are many organic molecules whose behaviour cannot be explained by a single Lewis structure. An example is that of benzene. Its cyclic structure containing alternating C–C single and C=C double bonds shown is inadequate for explaining its characteristic properties.
As per the above representation, benzene should exhibit two different bond lengths, due to C–C single and C=C double bonds. However, as determined experimentally benzene has a uniform C–C bond distances of 139 pm, a value intermediate between the C–C single(154 pm) and C=C double (134 pm) bonds. Thus, the structure of benzene cannot be represented adequately by the above structure. Further, benzene can be represented equally well by the energetically identical structures I and II.
Therefore, according to the resonance theory the actual structure of benzene cannot be adequately represented by any of these structures, rather it is a hybrid of the two structures (I and II) called resonance structures. The resonance structures (canonical structures or contributing structures) are hypothetical and individually do not represent any real molecule. They contribute to the actual structure in proportion to their stability.
Resonance Effect The resonance effect is defined as ‘the polarity produced in the molecule by the interaction of two π-bonds or between a π-bond and lone pair of electrons present on an adjacent atom’. The effect is transmitted through the chain. There are two types of resonance or mesomeric effect designated as R or M effect. (i) Positive Resonance Effect (+R effect) In this effect, the transfer of electrons is away from an atom or substituent group attached to the conjugated system. This electron displacement makes certain positions in the molecule of high electron densities. This effect in aniline is shown as : (ii) Negative Resonance Effect (- R effect) This effect is observed when the transfer of Electrons is towards the atom or substituent Group attached to the conjugated system. For Example in nitrobenzene this electron Displacement can be depicted as : The atoms or substituent groups, which represent +R or –R electron displacement effects are as follows: +R effect: – halogen, –OH, –OR, –OCOR, –NH2, –NHR, –NR2, –NHCOR, – R effect: $– COOH, –CHO, > C = O, – CN, – NO_2$ The presence of alternate single and double bonds in an open chain or cyclic system is termed as a conjugated system. These systems often show abnormal behaviour. The examples are 1,3- butadiene, aniline and nitrobenzene etc. In such systems, the π-electrons are delocalised and the system develops polarity.
Electromeric Effect (E effect) It is a temporary effect. The organic compounds having a multiple bond (a double or triple bond) show this effect in the presence of an attacking reagent only. It is defined as the complete transfer of a shared pair of π-electrons to one of the atoms joined by a multiple bond on the demand of an attacking reagent. The effect is annulled as soon as the attacking reagent is removed from the domain of the reaction. It is represented by E and the shifting of the electrons is shown by a curved arrow ( ). There are two distinct types of electromeric effect.
a) Positive Electrometric Effect (+E effect)- In this effect the π−electrons of the multiple bond are transferred to that atom to which the reagent gets attached. For example
b) Negative Electromeric Effect (–E effect) -In this effect the $\pi-$ electrons of the multiple bond are transferred to that atom to which the attacking reagent does not get attached. For example: When inductive and electromeric effects operate in opposite directions, the electomeric effect predominates.
View full solution →A reagent that brings an electron pair to the reactive site is called a nucleophile (Nu:) i.e., nucleus seeking and the reaction is then called nucleophilic. A reagent that takes away an electron pair from reactive site is called electrophile (E+) i.e., electron seeking and the reaction is called electrophilic.
Electron Displacement Effects in Covalent Bonds The electron displacement in an organic molecule may take place either in the ground state under the influence of an atom or a substituent group or in the presence of an appropriate attacking reagent. The electron displacements due to the influence of an atom or a substituent group present in the molecule cause permanent polarlisation of the bond. Inductive effect and resonance effects are examples of this type of electron displacements. Temporary electron displacement effects are seen in a molecule when a reagent approaches to attack it. This type of electron displacement is called electrometric effect or polarisability effect.
Inductive Effect When a covalent bond is formed between atoms of different electronegativity, the electron density is more towards the more electronegative atom of the bond. Such a shift of electron density results in a polar covalent bond. Bond polarity leads to various electronic effects in organic compounds. Let us consider cholorethane $(CH_3CH_2Cl)$ in which the C–Cl bond is a polar covalent bond. It is polarised in such a way that the carbon-1 gains some positive charge $(\delta+)$ and the chlorine some negative charge $(\delta-)$ The fractional electronic charges on the two atoms in a polar covalent bond are denoted by symbol (delta) and the shift of electron density is shown by an arrow that points from$(\delta+)$ to $(\delta-)$ end of the polar bond.
In turn carbon-1, which has developed partial positive charge $(\delta+)$draws some electron density towards it from the adjacent C-C bond. Consequently, some positive charge$(\delta\delta+)$develops on carbon-2 also, where $(\delta\delta+)$ symbolises relatively smaller positive charge as compared to that on carbon – 1. In other words, the polar C – Cl bond induces polarity in the adjacent bonds. Such polarisation of σ- bond caused by the polarisation of adjacent $σ-$bond is referred to as the inductive effect.
Resonance Structure There are many organic molecules whose behaviour cannot be explained by a single Lewis structure. An example is that of benzene. Its cyclic structure containing alternating C–C single and C=C double bonds shown is inadequate for explaining its characteristic properties.
As per the above representation, benzene should exhibit two different bond lengths, due to C–C single and C=C double bonds. However, as determined experimentally benzene has a uniform C–C bond distances of 139 pm, a value intermediate between the C–C single(154 pm) and C=C double (134 pm) bonds. Thus, the structure of benzene cannot be represented adequately by the above structure. Further, benzene can be represented equally well by the energetically identical structures I and II.
Therefore, according to the resonance theory the actual structure of benzene cannot be adequately represented by any of these structures, rather it is a hybrid of the two structures (I and II) called resonance structures. The resonance structures (canonical structures or contributing structures) are hypothetical and individually do not represent any real molecule. They contribute to the actual structure in proportion to their stability.
Resonance Effect The resonance effect is defined as ‘the polarity produced in the molecule by the interaction of two π-bonds or between a π-bond and lone pair of electrons present on an adjacent atom’. The effect is transmitted through the chain. There are two types of resonance or mesomeric effect designated as R or M effect. (i) Positive Resonance Effect (+R effect) In this effect, the transfer of electrons is away from an atom or substituent group attached to the conjugated system. This electron displacement makes certain positions in the molecule of high electron densities. This effect in aniline is shown as : (ii) Negative Resonance Effect (- R effect) This effect is observed when the transfer of Electrons is towards the atom or substituent Group attached to the conjugated system. For Example in nitrobenzene this electron Displacement can be depicted as : The atoms or substituent groups, which represent +R or –R electron displacement effects are as follows: +R effect: – halogen, –OH, –OR, –OCOR, –NH2, –NHR, –NR2, –NHCOR, – R effect: $– COOH, –CHO, > C = O, – CN, – NO_2$ The presence of alternate single and double bonds in an open chain or cyclic system is termed as a conjugated system. These systems often show abnormal behaviour. The examples are 1,3- butadiene, aniline and nitrobenzene etc. In such systems, the π-electrons are delocalised and the system develops polarity.
Electromeric Effect (E effect) It is a temporary effect. The organic compounds having a multiple bond (a double or triple bond) show this effect in the presence of an attacking reagent only. It is defined as the complete transfer of a shared pair of π-electrons to one of the atoms joined by a multiple bond on the demand of an attacking reagent. The effect is annulled as soon as the attacking reagent is removed from the domain of the reaction. It is represented by E and the shifting of the electrons is shown by a curved arrow ( ). There are two distinct types of electromeric effect.
a) Positive Electrometric Effect (+E effect)- In this effect the π−electrons of the multiple bond are transferred to that atom to which the reagent gets attached. For example
b) Negative Electromeric Effect (–E effect) -In this effect the $\pi-$ electrons of the multiple bond are transferred to that atom to which the attacking reagent does not get attached. For example: When inductive and electromeric effects operate in opposite directions, the electomeric effect predominates.
- A reagent that brings an electron pair to the reactive site is called a …
- nucleophile
- electrophile
- amphoteric
- amphophillic
- A reagent that takes away an electron pair from reactive site is called ..
- nucleophile
- electrophile
- amphoteric
- amphophillic
- The … effect is defined as the polarity produced in the molecule by the interaction of two π-bonds or between a π-bond and lone pair of electrons present on an adjacent atom.
- hindrance
- inductive
- resonance
- hyperconjunction
- –OH group, represent … electron displacement effect.
- M+
- M-
- R-
- R+
- – COOH group, represent … electron displacement effect.
- M+
- M-
- R-
- R+
Read the passage given below and answer the following questions from 1 to 5.
Branched chain hydrocarbons: In a branched chain compound small chains of carbon atoms are attached at one or more carbon atoms of the parent chain. The small carbon chains (branches) are called alkyl groups. For example:
In order to name such compounds, the names of alkyl groups are prefixed to the name of parent alkane. An alkyl group is derived from a saturated hydrocarbon by removing a hydrogen atom from carbon. Thus, $CH_4$becomes$ – CH_3 $and is called methyl group. An alkyl group is named by substituting ‘yl’ for ‘ane’ in the corresponding alkane. Some alkyl groups are listed in Table
Abbreviations are used for some alkyl groups. For example, methyl is abbreviated as Me, ethyl as Et, propyl as Pr and butyl as Bu. The alkyl groups can be branched also. Thus, propyl and butyl groups can have branched structures as shown below .
Common branched groups have specific trivial names. For example, the propyl groups can either be n-propyl group or isopropyl group. The branched butyl groups are called sec- butyl, isobutyl and tert-butyl group. We also encounter the structural unit, – $CH_2C(CH_3)_3$, which is called neopentyl group.
For Nomenclature of branched chain alkanes ,longest carbon chain in the molecule is identified. The numbering is done in such a way that the branched carbon atoms get the lowest possible numbers. lower number is given to the one coming first in the alphabetical listing. Carbon atom of the branch that attaches to the root alkane. in alphabetical order, the prefixes iso- and neo- are considered to be the part of the fundamental name of alkyl group. The prefixes sec- and tert- are not considered to be the part of the fundamental name.
Cyclic Compounds: A saturated monocyclic compound is named by prefixing ‘cyclo’ to the corresponding straight chain alkane. If side chains are present, then the rules given above are applied. Names of some cyclic compounds are given below.
The phenomenon of existence of two or more compounds possessing the same molecular formula but different properties is known as isomerism. Such compounds are called as isomers. The following flow chart shows different types of isomerism.
Structural Isomerism Compounds having the same molecular formula but different structures (manners in which atoms are linked) are classified as structural isomers. Some typical examples of different types of structural isomerism are given below:
(i) Chain isomerism: When two or more compounds have similar molecular formula but different carbon skeletons, these are referred to as chain isomers and the phenomenon is termed as chain isomerism. For example, $C_5H_{12}$ represents three compounds:
(ii) Position isomerism: When two or more compounds differ in the position of substituent atom or functional group on the carbon skeleton, they are called position isomers and this phenomenon is termed as position isomerism. For example, the molecular formula $C_3H_8O$ represents two alcohols:
(iii) Functional group isomerism: Two or more compounds having the same molecular formula but different functional groups are called functional isomers and this phenomenon is termed as functional group isomerism. For example, the molecular formula $C_3H_6O$ represents an aldehyde and a ketone:
(iv) Metamerism: It arises due to different alkyl chains on either side of the functional group in the molecule. For example, $C_4H_{10}O$ represents methoxy propane $(CH_3OC_3H_7)$ and ethoxyethane $(C_2H_5OC_2H_5).$
Stereoisomerism The compounds that have the same constitution and sequence of covalent bonds but differ in relative positions of their atoms or groups in space are called stereoisomers. This special type of isomerism is called as stereoisomerism and can be classified as geometrical and optical isomerism.
Substrate and Reagent Ions are generally not formed in the reactions of organic compounds. Molecules as such participate in the reaction. It is convenient to name one reagent as substrate and other as reagent. In general, a molecule whose carbon is involved in new bond formation is called substrate and the other one is called reagent. When carbon-carbon bond is formed, the choice of naming the reactants as substrate and reagent is arbitrary and depends on molecule under observation. Example:
View full solution →Branched chain hydrocarbons: In a branched chain compound small chains of carbon atoms are attached at one or more carbon atoms of the parent chain. The small carbon chains (branches) are called alkyl groups. For example:
In order to name such compounds, the names of alkyl groups are prefixed to the name of parent alkane. An alkyl group is derived from a saturated hydrocarbon by removing a hydrogen atom from carbon. Thus, $CH_4$becomes$ – CH_3 $and is called methyl group. An alkyl group is named by substituting ‘yl’ for ‘ane’ in the corresponding alkane. Some alkyl groups are listed in Table
| Alkane | Alkyl Group | ||
| Molecular formula | Name of alkane | Structural formula | Name of alkyl group |
| $CH_4$ | Methane | $-CH_3$ | Methyl |
| $C_2H_6$ | Ethane | $-CH_2CH_3$ | Ethyl |
| $C_3H_8$ | Propane | $-CH_2CH_2CH_3$ | Propyl |
| $C_4H_{10}$ | Butane | $-CH_2CH_2CH_2CH_3$ | Butyl |
| $C_{10}H_{22}$ | Decane | $-CH_2(CH_2)_8CH_3$ | Decyl |
Common branched groups have specific trivial names. For example, the propyl groups can either be n-propyl group or isopropyl group. The branched butyl groups are called sec- butyl, isobutyl and tert-butyl group. We also encounter the structural unit, – $CH_2C(CH_3)_3$, which is called neopentyl group.
For Nomenclature of branched chain alkanes ,longest carbon chain in the molecule is identified. The numbering is done in such a way that the branched carbon atoms get the lowest possible numbers. lower number is given to the one coming first in the alphabetical listing. Carbon atom of the branch that attaches to the root alkane. in alphabetical order, the prefixes iso- and neo- are considered to be the part of the fundamental name of alkyl group. The prefixes sec- and tert- are not considered to be the part of the fundamental name.
Cyclic Compounds: A saturated monocyclic compound is named by prefixing ‘cyclo’ to the corresponding straight chain alkane. If side chains are present, then the rules given above are applied. Names of some cyclic compounds are given below.
The phenomenon of existence of two or more compounds possessing the same molecular formula but different properties is known as isomerism. Such compounds are called as isomers. The following flow chart shows different types of isomerism.
Structural Isomerism Compounds having the same molecular formula but different structures (manners in which atoms are linked) are classified as structural isomers. Some typical examples of different types of structural isomerism are given below:
(i) Chain isomerism: When two or more compounds have similar molecular formula but different carbon skeletons, these are referred to as chain isomers and the phenomenon is termed as chain isomerism. For example, $C_5H_{12}$ represents three compounds:
(ii) Position isomerism: When two or more compounds differ in the position of substituent atom or functional group on the carbon skeleton, they are called position isomers and this phenomenon is termed as position isomerism. For example, the molecular formula $C_3H_8O$ represents two alcohols:
(iii) Functional group isomerism: Two or more compounds having the same molecular formula but different functional groups are called functional isomers and this phenomenon is termed as functional group isomerism. For example, the molecular formula $C_3H_6O$ represents an aldehyde and a ketone:
(iv) Metamerism: It arises due to different alkyl chains on either side of the functional group in the molecule. For example, $C_4H_{10}O$ represents methoxy propane $(CH_3OC_3H_7)$ and ethoxyethane $(C_2H_5OC_2H_5).$
Stereoisomerism The compounds that have the same constitution and sequence of covalent bonds but differ in relative positions of their atoms or groups in space are called stereoisomers. This special type of isomerism is called as stereoisomerism and can be classified as geometrical and optical isomerism.
Substrate and Reagent Ions are generally not formed in the reactions of organic compounds. Molecules as such participate in the reaction. It is convenient to name one reagent as substrate and other as reagent. In general, a molecule whose carbon is involved in new bond formation is called substrate and the other one is called reagent. When carbon-carbon bond is formed, the choice of naming the reactants as substrate and reagent is arbitrary and depends on molecule under observation. Example:
- $CH_4$ becomes –$ CH_3$, is called … group.
- methyl
- ethyl
- propyl
- butyl
- For the Nomenclature of branched chain alkanes …. carbon chain in the molecule is identified.
- shortest
- longest
- smallest
- none of above
- when two or more compounds possessing the same molecular formula but different properties is known as ….
- Allotrops
- Isotops
- Isomers
- Isobars
- For the Nomenclature of branched chain alkanes, the numbering is done in such a way that the branched carbon atoms get the … possible numbers.
- biggest
- Lower
- Highest
- lowest
- Which of the following is not an example of isomerisim?
- Functional
- Positional
- Chain
- Preconditional
Read the passage given below and answer the following questions from 1 to 5.
The three-dimensional (3-D) structure of organic molecules can be represented on paper by using certain conventions. For example, by using solid ( ) and dashed ( ) wedge formula, the 3-D image of a molecule from a two-dimensional picture can be perceived. In these formulas the solid-wedge is used to indicate a bond projecting out of the plane of paper, towards the observer. The dashed-wedge is used to depict the bond projecting out of the plane of the paper and away from the observer. Wedges are shown in such a way that the broad end of the wedge is towards the observer. The bonds lying in plane of the paper are depicted by using a normal line (—). 3-D representation of methane molecule on paper has been shown in Figure.
A cyclic or open chain componds these compounds are also called as aliphatic componds and consist of staright or branched chain componds for example:
Cyclic or closed chain or ring compounds
a) Alicyclic compounds Alicyclic (aliphatic cyclic) compounds contain carbon atoms joined in the form of a ring (homocyclic).
Someetimes atoms other than carbon are also present in the ring (heterocylic). Tetrahydrofuran given below is an example of this types of compound:
These exhibit some of the properties similar to those of aliphatic compounds.
b) Aromatic compounds Aromatic compounds are special types of compounds. These include benzene and other related ring compounds (benzenoid). Like alicyclic compounds, aromatic comounds may also have hetero atom in the ring. Such compounds are called hetrocyclic aromatic compounds. Some of the examples of various types of aromatic compounds are:
Benzenoid aromatic compounds .
Organic compounds can also be classified on the basis of functional groups, into families or homologous series.
Functional Group The functional group is an atom or a group of atoms joined to the carbon chain which is responsible for the characteristic chemical properties of the organic compounds. The examples are hydroxyl group (–OH), aldehyde group (–CHO) and carboxylic acid group (–COOH) etc.
Homologous Series A group or a series of organic compounds each containing a characteristic functional group forms a homologous series and the members of the series are called homologues. The members of a homologous series can be represented by general molecular formula and the successive members differ from each other in molecular formula by a $–CH^2$ unit. There are a number of homologous series of organic compounds. Some of these are alkanes, alkenes, alkynes, haloalkanes, alkanols, alkanals, alkanones, alkanoic acids, amines etc. It is also possible that a compound contains two or more identical or different functional groups. This gives rise to polyfunctional compounds.
A systematic name of an organic compound is generally derived by identifying the parent hydrocarbon and the functional group(s) attached to it. See the example given below.
By further using prefixes and suffixes, the parent name can be modified to obtain the actual name. Compounds containing carbon and hydrogen only are called hydrocarbons. A hydrocarbon is termed saturated if it contains only carbon-carbon single bonds.
The IUPAC name for a homologous series of such compounds is alkane. Paraffin (Latin: little affinity) was the earlier name given to these compounds. Unsaturated hydrocarbons are those, which contain at least one carbon- carbon double or triple bond. IUPAC Nomenclature of Alkanes Straight chain hydrocarbons: The names of such compounds are based on their chain structure, and end with suffix ‘-ane’ and carry a prefix indicating the number of carbon atoms present in the chain (except from $CH_4$ to $C_4H_{10}$, where the prefixes are derived from trivial names). The IUPAC names of some straight chain saturated hydrocarbons are given in Table. The alkanes in table differ from each other by merely the number of $– CH_2$ groups in the chain. They are homologues of alkane series.
View full solution →The three-dimensional (3-D) structure of organic molecules can be represented on paper by using certain conventions. For example, by using solid ( ) and dashed ( ) wedge formula, the 3-D image of a molecule from a two-dimensional picture can be perceived. In these formulas the solid-wedge is used to indicate a bond projecting out of the plane of paper, towards the observer. The dashed-wedge is used to depict the bond projecting out of the plane of the paper and away from the observer. Wedges are shown in such a way that the broad end of the wedge is towards the observer. The bonds lying in plane of the paper are depicted by using a normal line (—). 3-D representation of methane molecule on paper has been shown in Figure.
A cyclic or open chain componds these compounds are also called as aliphatic componds and consist of staright or branched chain componds for example:
Cyclic or closed chain or ring compounds
a) Alicyclic compounds Alicyclic (aliphatic cyclic) compounds contain carbon atoms joined in the form of a ring (homocyclic).
Someetimes atoms other than carbon are also present in the ring (heterocylic). Tetrahydrofuran given below is an example of this types of compound:
These exhibit some of the properties similar to those of aliphatic compounds.
b) Aromatic compounds Aromatic compounds are special types of compounds. These include benzene and other related ring compounds (benzenoid). Like alicyclic compounds, aromatic comounds may also have hetero atom in the ring. Such compounds are called hetrocyclic aromatic compounds. Some of the examples of various types of aromatic compounds are:
Benzenoid aromatic compounds .
Organic compounds can also be classified on the basis of functional groups, into families or homologous series.
Functional Group The functional group is an atom or a group of atoms joined to the carbon chain which is responsible for the characteristic chemical properties of the organic compounds. The examples are hydroxyl group (–OH), aldehyde group (–CHO) and carboxylic acid group (–COOH) etc.
Homologous Series A group or a series of organic compounds each containing a characteristic functional group forms a homologous series and the members of the series are called homologues. The members of a homologous series can be represented by general molecular formula and the successive members differ from each other in molecular formula by a $–CH^2$ unit. There are a number of homologous series of organic compounds. Some of these are alkanes, alkenes, alkynes, haloalkanes, alkanols, alkanals, alkanones, alkanoic acids, amines etc. It is also possible that a compound contains two or more identical or different functional groups. This gives rise to polyfunctional compounds.
A systematic name of an organic compound is generally derived by identifying the parent hydrocarbon and the functional group(s) attached to it. See the example given below.
By further using prefixes and suffixes, the parent name can be modified to obtain the actual name. Compounds containing carbon and hydrogen only are called hydrocarbons. A hydrocarbon is termed saturated if it contains only carbon-carbon single bonds.
The IUPAC name for a homologous series of such compounds is alkane. Paraffin (Latin: little affinity) was the earlier name given to these compounds. Unsaturated hydrocarbons are those, which contain at least one carbon- carbon double or triple bond. IUPAC Nomenclature of Alkanes Straight chain hydrocarbons: The names of such compounds are based on their chain structure, and end with suffix ‘-ane’ and carry a prefix indicating the number of carbon atoms present in the chain (except from $CH_4$ to $C_4H_{10}$, where the prefixes are derived from trivial names). The IUPAC names of some straight chain saturated hydrocarbons are given in Table. The alkanes in table differ from each other by merely the number of $– CH_2$ groups in the chain. They are homologues of alkane series.
| Name | Molecular formula | Name | Molecular Formula |
| Methane | $CH_4$ | Heptane | $C_7H_{16}$ |
| Ethane | $C_2H_6$ | Octane | $C_8H_{18}$ |
| Propane | $C_3H_8$ | Nonane | $C_9H_{20}$ |
| Butane | $C_4H_{10}$ | Decane | $C_{10}H_{22}$ |
| Pentane | $C_5H_{12}$ | Icosane | $C_{20}H_{42}$ |
| Hexane | $C_6H_{14}$ | Triacontane | $C_{30}H_{62}$ |
- IUPAC is an acronym for …
- International Union of Pure and Applied Chemistry
- International units of proteins and carbohydrates
- International understandings on physical aspects of chemistry
- Iodine under packings
- In homologous series, the successive members differ from each other in molecular formula by a … unit.
- $CH_3$
- $CH_2$
- $CH$
- $CH_4$
- A hydrocarbon is termed saturated if it contains only carbon-carbon … bonds.
- Triple
- Double
- Single
- Zero
- From ….., where the prefixes are derived from… trivial names.
- $CH_4$ to $C_2H_6$
- $CH_4$ to $C_3H_8$
- $CH_4$ to $C_6H_{14}$
- $CH_4$ to $C_4H_{10}$
- Molecular formula of octane is …
- $C_4H_{10}$
- $C_6H_{14}$
- $C_2H_6$
- $C_8H_{18}$
Read the passage given below and answer the following questions from 1 to 5.
F Wohler synthesised an organic compound, urea from an inorganic compound, ammonium cyanate.
The knowledge of fundamental concepts of molecular structure helps in understanding and predicting the properties of organic compounds. You have already learnt theories of valency and molecular structure. Also, you already know that tetravalence of carbon and the formation of covalent bonds by it are explained in terms of its electronic configuration and the hybridisation of s and p orbitals. It may be recalled that formation and the shapes of molecules like methane $(CH_4)$, ethene $(C_2H_4)$, ethyne $(C_2H_2)$ are explained in terms of the use of $sp^3, sp^2$ and sp hybrid orbitals by carbon atoms in the respective molecules. Hybridisation influences the bond length and bond enthalpy (strength) in compounds. The sp hybrid orbital contains more s character and hence it is closer to its nucleus and forms shorter and stronger bonds than the sp3 hybrid orbital.The sp2 hybrid orbital is intermediate in s character between sp and sp3 and, hence, the length and enthalpy of the bonds it forms, are also intermediate between them. The change in hybridisation affects the electronegativity of carbon. The greater the s character of the hybrid orbitals, the greater is the electronegativity. Thus, a carbon atom having an sp hybrid orbital with 50% s character is more electronegative than that possessing sp2 or sp3 hybridised orbitals. This relative electronegativity is reflected in several physical and chemical properties of the molecules concerned, about which you will learn in later units.
Characteristic Features of π Bonds In a π (pi) bond formation, parallel orientation of the two p orbitals on adjacent atoms is necessary for a proper sideways overlap. Thus, in $H_2C=CH_2$ molecule all the atoms must be in the same plane. The p orbitals are mutually parallel and both the p orbitals are perpendicular to the plane of the molecule. Rotation of one $CH_2$ fragment with respect to other interferes with maximum overlap of p orbitals and, therefore, such rotation about carbon-carbon double bond (C=C) is restricted. The electron charge cloud of the π bond is located above and below the plane of bonding atoms. This results in the electrons being easily available to the attacking reagents. In general, π bonds provide the most reactive centres in the molecules containing multiple bonds.
Structures of organic compounds are represented in several ways. The Lewis structure or dot structure, dash structure, condensed structure and bond line structural formulas are some of the specific types. The Lewis structures, however, can be simplified by representing the two-electron covalent bond by a dash (–). Such a structural formula focuses on the electrons involved in bond formation. A single dash represents a single bond, double dash is used for double bond and a triple dash represents triple bond. Lone- pairs of electrons on heteroatoms (e.g., oxygen, nitrogen, sulphur, halogens etc.) may or may not be shown. Thus, ethane $(C_2H_6)$, ethene $(C_2H_4)$, ethyne $(C_2H_2)$ and methanol $(CH_3OH)$ can be represented by the following structural formulas. Such structural representations are called complete structural formulas.
These structural formulas can be further abbreviated by omitting some or all of the dashes representing covalent bonds and by indicating the number of identical groups attached to an atom by a subscript. The resulting expression of the compound is called a condensed structural formula. Thus, ethane, ethene, ethyne and methanol can be written as:
Similarly, $CH_3CH_2CH_2CH_2CH_2CH_2CH_2CH_3$ can be further condensed to $CH_3(CH_2)_6CH_3$. For further simplification, organic chemists use another way of representing the structures, in which only lines are used. In this bond-line structural representation of organic compounds, carbon and hydrogen atoms are not shown and the lines representing carbon-carbon bonds are drawn in a zig-zag fashion. The only atoms specifically written are oxygen, chlorine, nitrogen etc. The terminals denote methyl $(–CH_3)$ groups (unless indicated otherwise by a functional group), while the line junctions denote carbon atoms bonded to appropriate number of hydrogens required to satisfy the valency of the carbon atoms. Some of the examples are represented as follows: (i) 3-Methyloctane can be represented in various forms as:
View full solution →F Wohler synthesised an organic compound, urea from an inorganic compound, ammonium cyanate.
The knowledge of fundamental concepts of molecular structure helps in understanding and predicting the properties of organic compounds. You have already learnt theories of valency and molecular structure. Also, you already know that tetravalence of carbon and the formation of covalent bonds by it are explained in terms of its electronic configuration and the hybridisation of s and p orbitals. It may be recalled that formation and the shapes of molecules like methane $(CH_4)$, ethene $(C_2H_4)$, ethyne $(C_2H_2)$ are explained in terms of the use of $sp^3, sp^2$ and sp hybrid orbitals by carbon atoms in the respective molecules. Hybridisation influences the bond length and bond enthalpy (strength) in compounds. The sp hybrid orbital contains more s character and hence it is closer to its nucleus and forms shorter and stronger bonds than the sp3 hybrid orbital.The sp2 hybrid orbital is intermediate in s character between sp and sp3 and, hence, the length and enthalpy of the bonds it forms, are also intermediate between them. The change in hybridisation affects the electronegativity of carbon. The greater the s character of the hybrid orbitals, the greater is the electronegativity. Thus, a carbon atom having an sp hybrid orbital with 50% s character is more electronegative than that possessing sp2 or sp3 hybridised orbitals. This relative electronegativity is reflected in several physical and chemical properties of the molecules concerned, about which you will learn in later units.
Characteristic Features of π Bonds In a π (pi) bond formation, parallel orientation of the two p orbitals on adjacent atoms is necessary for a proper sideways overlap. Thus, in $H_2C=CH_2$ molecule all the atoms must be in the same plane. The p orbitals are mutually parallel and both the p orbitals are perpendicular to the plane of the molecule. Rotation of one $CH_2$ fragment with respect to other interferes with maximum overlap of p orbitals and, therefore, such rotation about carbon-carbon double bond (C=C) is restricted. The electron charge cloud of the π bond is located above and below the plane of bonding atoms. This results in the electrons being easily available to the attacking reagents. In general, π bonds provide the most reactive centres in the molecules containing multiple bonds.
Structures of organic compounds are represented in several ways. The Lewis structure or dot structure, dash structure, condensed structure and bond line structural formulas are some of the specific types. The Lewis structures, however, can be simplified by representing the two-electron covalent bond by a dash (–). Such a structural formula focuses on the electrons involved in bond formation. A single dash represents a single bond, double dash is used for double bond and a triple dash represents triple bond. Lone- pairs of electrons on heteroatoms (e.g., oxygen, nitrogen, sulphur, halogens etc.) may or may not be shown. Thus, ethane $(C_2H_6)$, ethene $(C_2H_4)$, ethyne $(C_2H_2)$ and methanol $(CH_3OH)$ can be represented by the following structural formulas. Such structural representations are called complete structural formulas.
These structural formulas can be further abbreviated by omitting some or all of the dashes representing covalent bonds and by indicating the number of identical groups attached to an atom by a subscript. The resulting expression of the compound is called a condensed structural formula. Thus, ethane, ethene, ethyne and methanol can be written as:
Similarly, $CH_3CH_2CH_2CH_2CH_2CH_2CH_2CH_3$ can be further condensed to $CH_3(CH_2)_6CH_3$. For further simplification, organic chemists use another way of representing the structures, in which only lines are used. In this bond-line structural representation of organic compounds, carbon and hydrogen atoms are not shown and the lines representing carbon-carbon bonds are drawn in a zig-zag fashion. The only atoms specifically written are oxygen, chlorine, nitrogen etc. The terminals denote methyl $(–CH_3)$ groups (unless indicated otherwise by a functional group), while the line junctions denote carbon atoms bonded to appropriate number of hydrogens required to satisfy the valency of the carbon atoms. Some of the examples are represented as follows: (i) 3-Methyloctane can be represented in various forms as:
- … synthesised an organic compound, urea from an inorganic compound, ammonium cyanate.
- Wohler
- Adams
- Roger
- William Evans
- Dot structure is also known as …
- Zig zag structure
- Lewis structure
- Line structure
- Bond line structure
- Terminals in zigzig structure denotes … Group.
- Bromyl
- Propyl
- Methyl
- Pentyl
- Triple dash represents …
- Single bond
- Double bond
- Triple bond
- Equivalent bond
- Lewis structures representing the two-electron covalent bond by …
- .
- :
- ?
- –
Discuss the principle of estimation of halogens, sulphur and phosphorus present in an organic compound.
Explain the terms Inductive and Electromeric effects. Which electron displacement effect explains the following correct orders of acidity of the carboxylic acids?
View full solution →- $Cl_3CCOOH > Cl_2CHCOOH > ClCH_2COOH$.
- $CH_3CH_2COOH > (CH_3)_2CHCOOH > (CH_3)_3C.COOH$.
Discuss the chemistry of Lassaigne's test.
Describe the method, which can be used to separate two compounds with different solubilities in a solvent S.
Explain why alkyl groups act as electron donors when attached to a $\pi$ system.
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