Question

Which of the following is not a meta directing group?

• A. $-\stackrel{\oplus }{N}{H}_3$
• B. $H_{3}C-O-\stackrel{O}{\stackrel{||}{\underset{OC{H}_3}{\underset{|}{P}}}}-O-$
• C. $-B(OH{)}_2$
• D. $-C{H}_3$

Answer 1

The correct option is D $-C{H}_3$

(a) $-\stackrel{\oplus }{N}{H}_3$ is meta directing group due to strong -I effect.

(b) Dimethyl phenyl phosphate always exists in polar form.
$H_{3}C-O-\stackrel{O}{\stackrel{||}{\underset{OC{H}_3}{\underset{|}{P}}}}-\stackrel{..}{O}-Ph⟷H_{3}C-O-\stackrel{O^{-}}{\stackrel{|}{\underset{OC{H}_3}{\underset{|}{P}}}}=\stackrel{\oplus }{O}-Ph$
Hence it is an electron withdrawing group.

(c) $-B(OH{)}_2$ has incomplete octet so it is also an electron withdrawing group through -R and -I effect.

(d) $-C{H}_3$ is ortho and para directing group through hyperconjugation.