Explain how the hybrid structure is related to the structures of each of the following pairs of contributing resonance structures?
(a) `overset(oplus)(C )H_(2) underset((i))- underset(..)overset(Θ)C H_(2) harr CH_(2) underset((ii))= CH_(2)`
(b) `H_(2)C underset((iii))= overset(..)(O): harr H_(2)C underset((iv))- underset(..)overset(..)O:^(-)`
(c ) `R_(2) overset(+)C- underset(underset(underset((v))(R ))(|))C= overset(..)O: harr underset((vi))(R_(2)C = underset(underset(R )(|))(C) - overset(..)O:^(+))`
(d) `underset((VII)) (R-C^(+) = overset(..)(O): )harr underset((VIII))(R-C-= O:^(+))`
(e ) `underset((IX))(R- underset(underset( :O: )(||))(C)- underset(..)overset(..)OH) harr underset((IX))(R- underset(underset( :underset(..)(O): )(|))(C) - ""^(oplus")underset(..)OH)`

Explanation

(a) Since the charged structure I has high energy, the hybrid is the same as II and has practically no delocalization energy. Factors responsible for the high energy of I are: fewer number of covalent bonds, less than an octet on the `C^(+)`, and charge separation.
(b) Even though IV show charge separation, this is reasonable because .O. is much more electronegative than C and strongly attracts the `pi` electrons. THe hybrid is a good blend of both.
(c ) The hybrid more resembles V, the major contributor, because VI has a higher energy. A + charge on an atom with less than an octet is better on the less electronegative atom, in this case C.
(d) The hybrid more resembles VIII, the principal contributing structure, because both C and O have an octet and there is one more covalent bond. A + charge on an electronegative atom is not bad if the atom has an octet. VII is possible, but has high energy because C has only six electrons.
(e ) Both have the same number of covalent bonds and make significant contribution to the hybrid. The hybrid more resembles IX because X exhibits charge spearation and has higher energy.