Question

The kind of delocalization involving sigma bond orbitals is called?
A.Hyperconjugation
B.Mesomerism
C.Tautomerism
D.Resonance

Answer 1

Hint: Delocalization is said to happen in a compound when electric charge is distributed on more than one atom. Bonding electrons are distributed over various atoms which are bonded together. To answer this question, you must recall the properties of the terms given in the question.

Complete answer:
Of all the given options, hyperconjugation is the effect which involves the delocalization of the sigma bond electron pair. It occurs when an alkyl group is present adjacent to an unsaturated system namely a double bond or a benzene ring. The order of inductive effect is reversed in the molecule and this is known as hyperconjugation. It involves the delocalization of sigma electrons through the overlapping of the p orbitals of the bond with the sigma bond of the single bond adjacent to it. It is a permanent electron displacement and is known as no bond resonance.

Thus, the correct answer is A.

Additional Information: More are the number of alpha hydrogen atoms, more will be the amount of hyperconjugative structures and will provide more stability. The alpha carbon hydrogen bond breaks and the charge is transferred to the radical or carbocation. More the number of alpha hydrogen atoms, more will be the stability of the carbocation or free radical.

Note:
Hyperconjugation effect and inductive effects are the opposites of each other. Inductive effect involves the partial charge movement through sigma bonds while hyperconjugation occurs through total transfer of the electrons of the sigma bond pair. Mesomerism, tautomerism and resonance are all phenomenons involving the delocalization of the pi electrons of a multiple bond.