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Organic Chemistry: Some Basic Principles and Techniques — Chemistry STD 11 Science — Question

Rajasthan BoardEnglish MediumSTD 11 ScienceChemistryOrganic Chemistry: Some Basic Principles and Techniques5 Marks
Question
  1. Write two important differences between inductive effect and resonance effect.
  2. Give reasons to explain the following observations:
  1. Carbon atom number 2 in CH3CH2Cl has more positive charge than that in CH3-CH2-Br.
  2. CH3-CH=CH-CH=CH2(I) is more stable than CH3-CH=CH-CH2-CH=CH2(II)
✓

Answer

  1.  
S. No
Inductive effect
Resonance effect
1.
It involves o electrons.
It involves $\pi-$ electrons or lone pair of electrons.
2.
It decreases with distance and vanishes after 4th carbon atom.
It is all along the length if system is conjugated (alternate double bonds).
3.
It is shown by even non-planar compounds.
It is shown by only planar compounds.
  1.  
  1. Polarisation of CH3CH2Cl and CH3CH2 Br can be shown as follows.

$\stackrel{\delta\delta+}{\text{CH}_3}-\stackrel{\delta+}{\text{CH}_2}-\stackrel{\delta-}{\text{Cl}}\ \ \ \ \ \ \ \ \stackrel{\delta\delta+}{\text{CH}_3}-\stackrel{\delta+}{\text{CH}_2}-\stackrel{\delta-}{\text{Br}}$

Chlorine is more electronegative than Bromine. C-Cl bond is more polar than C-Br bond. Hence, inductive effect of 'Cl' is greater on the second carbon than Br.

  1. Resonating structures of (I)

It is more stable due to resonance effect due to conjugation i.e., alternate double bonds than II in which there is no resonance due to absence of conjugation.

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