Question

Arrange the following in decreasing order of their reactivity with an electrophile.

Answer 1

$\left(a\right)$ The structure in which the number of pi-bonds are more has more number of resonating structures and more sites are available for the attack of electrophile. Thus, the reactivity is more towards electrophilic addition reactions.

$\left(b\right)$ $ONa$ is more electron donating than $F$, which increases its reactivity towards electrophilic addition reaction. $N^{+}(C{H}_3{)}_3$ is electron deficient, therefore, is least reactive.

$\left(c\right)$ $N{H}_2$ is electron donating. So, it is more reactive. While $N{O}_2$ and $OMe$ are deactivating at meta-position due to their high electronegativities. $O$ being more electronegative is more deactivating. Hence, $N{O}_2$ substituted is more reactive than $OMe$ substituted.

$\left(d\right)$ Pyrrole is more reactive than benzene as pyrrole ring is activated because the lone pair of electron on $N$ take part in resonance and activate the ring. Pyridine is least reactive because the $N$ present in the ring is not involved in resonance and due to its high electronegativity its attracts the ring electrons towards itself and deactivates the ring.