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Model Paper 1 — Chemistry STD 11 Science — Question

Rajasthan BoardEnglish MediumSTD 11 ScienceChemistryModel Paper 15 Marks
Question
1. Explain hyperconjugation effect. How does hyperconjugation effect explain the stability of alkenes?
2. Draw the resonance structures of the following compounds:
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Answer

1. Hyperconjugation: The relative stability of various classes of carbonium ions may be explained by the number of no-bond resonance structures that can be written for them. Such structures are arrived by shifting the bonding electrons from an adjacent $C - H$ bond to the electron - deficient carbon. In this way, the positive charge originally on carbon is dispersed to the hydrogen. This manner of electron release by assuming no-bond character in the adjacent C - H bond is called Hyper conjugation or No-bond Resonance. The greater the hyperconjugation, the greater will be the stability of the compound. The increasing order of stability can be shown as:

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2. Resonance structure of the given compounds are as follows:
i. $CH _2= CH - Cl \leftrightarrow+ CH _2- CH = Cl ^{+}$
ii. $CH _2= CH - CH = CH _2 \leftrightarrow^{+} CH _2- CH = CH \cdot CH _2^{-} \leftrightarrow CH _2- CH = CH \cdot CH _2^{+}$
iii. $CH _2= CH \cdot CHO \leftrightarrow+ CH _2 \cdot CH = CHO ^{-}$ 

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