The C - C bond in acetaldehyde `(CH_(3)CHO))` is shorter than that in ethane while the C - C bond in trifluoracetaldehyde `(CF_(3)CHO))` is essentially the same as that in ethane. Explain.

Explanation

Acetaldehyde molecule contains three `alpha` - H - atoms. These H - atoms are involved in hyperconjugation with the double bond of the carbonyl group. So C - C bonds in acetadehyde has partial double bond character. In ethane the C - C bond has pure single bond character. Thus C - C bond in acetadehyde is shorter than that in ethane.
Trifluroaacetaldhyde does not have `alpha` - H atoms, So hyper - conjugation is not possible in `CF_(3)CHO`. Thus, the C - C bond in `CF_(3)CHO` is essentially the same as that in ethane.