Chemistry - GOC Question with Solution | TestHub
Identify the correct order :
Options:(select one or more)
Answer:
Solution:
(A) Heat of combustion
The first molecule (spiro[2.2]pentane) has more ring strain than the second (spiro[2.3]hexane) because of the smaller cyclopropane rings. Higher ring strain leads to higher potential energy, and thus a higher heat of combustion per CH₂ unit. The order shown is correct.
(B) Heat of hydrogenation
The first alkene (cyclobutene) is less substituted than the second (1,2-dimethylcyclobutene). Less substituted alkenes are less stable (higher energy) and have a higher heat of hydrogenation compared to more substituted, more stable alkenes. The order shown is correct.
(C) Stability of carbocation
The carbocation on the left has an adjacent nitrogen atom with a lone pair, which can stabilize the positive charge through resonance (p-orbital overlap). This is a very strong stabilizing effect. The carbocation on the right is a tertiary carbocation, stabilized only by hyperconjugation and induction. Resonance stabilization is much more significant than hyperconjugation, so the left carbocation is more stable than the right. The order should be the reverse.
(D) Stability of carbanion
The carbanion on the right is stabilized by the electron-withdrawing NO₂ group through resonance and inductive effects, which delocalize the negative charge. The carbanion on the left has an electron-donating OCH₃ group, which destabilizes the negative charge. Therefore, the carbanion with the NO₂ group is more stable. The order shown is correct.
