Question

Hyperconjugation phenomenon is possible in:
A.\[C{H_2} = C{H_2}\]
B.\[C{H_3} - C{H_2}CH = C{H_2}\]
C.\[{C_6}{H_5}CH = C{H_2}\]
D.\[{\left( {C{H_3}} \right)_3}C - CH = C{H_2}\]

Answer 1

Hint: Hyperconjugation is the permanent effect in which the localization of \[\sigma \] electrons take place. These sigma electrons belong to the \[C - H\] bond of an alkyl group directly attached to an atom of an unsaturated system or may be an atom with a lone pair or any charge. The presence of alpha hydrogen is the condition for the hyperconjugation effect.

Complete answer:
A molecule with the presence of alpha hydrogens can undergo hyperconjugation. This alpha hydrogen must attach to an unsaturated system or an atom with an unshared pair of electrons like a lone pair of electrons.
In option A, there are no alpha hydrogen atoms. Thus, it will not show hyperconjugation.
In option B there are two alpha hydrogen atoms. Thus, it will exhibit hyperconjugation.
The structure or molecule contains an unsaturated system means there is a presence of alkenes. To the double bonded carbon, one carbon with two hydrogen atoms is there and that carbon can be called alpha carbon.
In the option C, there are no alpha hydrogen atoms. Thus, it will not show hyperconjugation.
In option D, there are no alpha hydrogen atoms. Thus, it will not show hyperconjugation.
Option B is the correct one.

Note:
In order to contain an unsaturated system or lone pair of electrons on hetero atoms like nitrogen, oxygen. The alpha carbon must be involved in the hybridization of \[s{p^3}\]. In the given option C, there is a benzene ring with hydrogen atoms, but the carbon is in \[s{p^2}\] hybridization. Thus, it does not exhibit hyperconjugation.