Question

The arrangement of $(C{H}_3{)}_{3}C-,(C{H}_3{)}_{2}CH-,C{H}_{3}C{H}_2-$ When attached to a benzene or an unsaturated group in increasing order of inductive effect is:

• A.
• B.
• C.
• D.

Answer 1

The correct option is A

Conditions of Resonating structures: Resonance structures should fulfill following conditions:

(i) All resonating structures must have the same arrangement of atomic nuclei. Resonance differs from tautomerism in this very important aspect.

$R-\stackrel{O}{\stackrel{||}{C}}-\stackrel{..}{\underset{..}{O}}⟷R-\stackrel{\ominus }{\stackrel{O}{\stackrel{|}{C}}}=\stackrel{\oplus }{O}-H$

Position of atomic nuclei in (I) and (II) are same.

$C{H}_3-\stackrel{O}{\stackrel{||}{C}}-\underset{1}{C}{H}_3$ $C{H}_3-\stackrel{3}{\stackrel{OH}{\stackrel{||}{C}}}=\underset{1}{C}{H}_2$

(I) (II)

Position of hydrogen nuclei in (I) and (II) are different hence (I) and (II) are not the resonating structures.

(ii) The resonating structures must have the same numbers of paired and unpaired electrons. However, they differ in the way of distribution of electrons.

$\stackrel{..}{\underset{..}{O}}=\stackrel{.}{\underset{\oplus }{N}}-\stackrel{\ominus }{\stackrel{..}{\underset{..}{O}:}}⟷\underset{\ominus }{:}\stackrel{..}{\underset{..}{O}}-\stackrel{.}{\underset{\oplus }{N}}=\stackrel{..}{\underset{..}{O}}$

(iii) The energies of the different remaining structures must be the same or nearly the same.

(iv) All atoms that are part of the delocalization system must be in a plane or be nearly planar.

(v) All atoms of the resonating structure should follow the octet rule. For example:

All atoms follow octet rule.