Draw the resonance structures of the following compounds.
(a) `CH_(2)= CH= underset(..)overset(..)(C )l:` (b) `CH_(2)=CH-CH= CH_(2)` (c ) `CH_(2)= CH- underset(underset(H)(|))(C )=O`

Explanation

(a) `CH_(2)= CH- underset(..)overset(..)(C )l: harr overset(+)(C )H_(2) - CH= underset(..)(C )overset(+)(l):`
In ethenal, Cl is negative atom which give the non-bonding electron pair to the adjacent C-Cl and form `pi`-bond.

In structure (A) 1-2 carbon and 3-4 carbon, `pi`-electron pair respectively more in `C_(2)-C_(3) and C_(4)` so structure (B) form.
The `pi` electron pair of `C_(3)-C_(4)` shift on `C_(2)-C_(3) and C_(1)-C_(2) pi`-electron pair shift on `C_(1)`. So negative charge on `C_(1)` and positive charge on `C_(4)` possessive structure (C ) form