Question

Which one of the following does not exhibit hyperconjugation?
A. Ethanal
B. Allylene
C. Isobutylene
D. Trifluoro acetaldehyde

Answer 1

Hint: One of the following does not exhibit hyperconjugation because positive charge cannot be formed due to high electronegativity and except one all exhibits hyperconjugation by having few hyper conjugative H atoms.

Complete answer:
Now, we need to check the given options:
A) Ethanal ( $C{H_3}CHO$ ): It exhibits hyperconjugation with having 3 hyper conjugative H atoms.
B) Allylene: It exhibits hyperconjugation by having again 3 hyper conjugative H atoms.
C) Isobutylene: It also exhibits hyperconjugation having 6 hyper conjugative H atoms.
D) Trifluoroacetaldehyde: It does not exhibit hyper conjugation as positive charge cannot be formed on F atoms because of high electronegativity of F.

Hence, Correct Option will be D.

Additional Information:
- Acetaldehyde ($C{H_3}CHO$), also known as ethanal, an aldehyde which is used as a starting material in the process of synthesis of 1-butanol (n-butyl alcohol), ethyl acetate, perfumes, flavourings, aniline dyes, plastics, synthetic rubber, and some other chemical compounds. Allylene is also called as methyl-acetylene or also by propyne. The structure of allylene is \[C{H_3} - C \equiv CH\]. It has a triple bond which informs us that it is not stable and also it is a highly reactive compound.
- Isobutylene is generally used as a monomer for the formation of various polymers like butyl rubber, polybutene and polyisobutylene. One of the most important applications of butyl rubber is the manufacturing of tyres for cars and various other vehicles.
- Trifluoroacetaldehyde is corrosive to skin, eyes and mucous membranes. It is used to make other chemicals and also as a solvent. Trifluoroacetic acid is actually a monocarboxylic acid that is the trifluoro derivative of acetic acid. It has a major role as a reagent and also as a human xenobiotic metabolite.

Note:
As we can see, trifluoroacetaldehyde does not exhibit hyper conjugation due to positive charge which cannot be formed on F atoms because of high electronegativity of F.