Question

The greater stability of trans-but-2-ene over cis-but-2-ene can be explained on the basis of hyperconjugation effect.
A.True
B.False

Answer 1

Hint: The concept of hyperconjugation as well as the role of steric factor in stability is to be used in this question. Hyperconjugation can be also called as no bond resonance. Compounds which are more stable have less steric hindrance.

Complete answer:
In order to answer our question, we need to learn about hyperconjugation. When the alkyl group is associated with an unsaturated area such as $-CH=C{{H}_{2}}$ group, the order of inductive effect gets: reversed. This behaviour of alkyl groups is explained with the help of hyperconjugation effect. Since it was noticed for the first time by Baker & Nathan, it is also called Baker Nathan effect. Let us consider the example of propene ($C{{H}_{3}}-CH=C{{H}_{2}}$) in which the carbon atom of the methyl group is called $\alpha $carbon atom and the hydrogen atoms attached to are known as$\alpha $ hydrogen atoms. The $\pi $ electron pair of the double bond causes the cleavage of the C-H bond of the methyl group and the electron pair of the bond conjugates with the pi-electron pair of the double bond.
As there is no actual bond between the a-carbon atom and the positively charged hydrogen atom (or ${{H}^{+}}$), hyper-conjugation is also called no bond resonance. It is quite obvious that greater the number of $\alpha $hydrogen atoms more will be the electron releasing tendency of the alkyl group. The number of $\alpha $hydrogen atoms decreases from methyl group (three) to ethyl group (two) followed by isopropyl group (one) and finally the tertiary butyl group has no $\alpha $hydrogen atom.
Now, let us see the structures of cis and trans 3 butene:

As we can see from the structures that in trans 2 butene, the steric factor is much less. Cis 2 butene has both bulky methyl groups on same side, so steric factor is more. Hence, the stability of trans 2 butene is more but it is based on the fact of stability and not hyperconjugation.

So, the answer is false.

NOTE: Hyperconjugation imparts partial double bond character to the C-C bond and hence, it shortens the bond. An $\alpha $ hydrogen along with unsaturation is required for hyperconjugation.