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Each comprehension given below is followed by some multiple choice questions. Each question has one correct option. Choose the correct option.
Comprehension 2 An organic reaction
occurs through making and breaking of
bonds. The breaking of bonds may occur
either homolytically leading to the formation
of radicals or heterolytically generating
positively and negatively charged species.
The neutral species (free radicals, carbenes,
nitrenes, etc.) and positively charged species
being electron deficient are collectively
called electrophiles while neutral and
negatively charged species which are electron
rich are called nucleophiles. An organic
reaction usually involves the attack of a
reagent (radicals, positively and negatively
charged species) on the substrate molecule).
The substrate molecule, although as a whole
electrically neutral, has centres of low and
high electron density due to displacement of
bonding electrons. These electron
displacements occur through inductive,
electromeric, resonance and hyperconjuga-
tion effects. Whereas inductive effects involve
displacement of \( \sigma \)-electrons, resonance effects
involve transfer of \( \boldsymbol{n} \) - and \( \pi \)-electrons along a
conjugated system. Hyperconjugation effects,
on the other hand, involve \( \sigma-\pi \)-conjugation.
Both inductive and hyperconjugation effects
can be used to explain the stability of
carbocations and free radicals which follow
the stability order : \( 3^{\circ}2^{\circ}1^{\circ} \). The stability
of carbanions, however, follows opposite
order.
The stability of a molecule can be judged on
the basis of contribution of its resonance
structures. Resonance structures have same
position of nuclei and have same number of
unpaired electrons. Among resonance
structures, the one which has greater number
of covalent bonds, has less separation of
opposite charges, a negative charge on more
electronegative and a positive charge on a
more electropositive atom are more stable
than others.
The \( \mathrm{C}-\mathrm{C} \) bond length in propene is little shorter
\( (1.49 \AA \) ) than the \( \mathrm{C}-\mathrm{C} \) bond length \( (1.54 \AA) \) in
ethane. This is due to
(A) +I-effect of \( \mathrm{CH}_{3} \) group
(B) mesomeric effect
(C) electromeric effect
(D) hyperconjugation effect.
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