In the which of the following compounds mesomerie effect is possible? Vinyl chloride , b) Allyl chloride and c) 3- Butenal

Explanation

Structure of the given substances :
a) Vinyl chloride is `CH_(2)=CH-underset(..)overset(..)(Cl):`
b) Allyl chloride is `CH_(2)=CH-CH_(2)-underset(..)overset(..)(Cl):`
c) = 3- Butenal is `CH_(2)=CH-CH_(2)-underset(H)underset(|)C=O`
In vinyl chloride , lone pair and `pi` bond are in conjugation. Hence + M effect is possible chloride , lone pair is not in conjunction is in allyl chloride and 3 - butenal, mesomerie effect is abscent.