Edexcel IAL Chemistry 18.5 benzene electrophilic substitution mechanisms

Ignore omission or incorrect placement of methyl groups in M2 and M3

$\mathrm{HNO}_{3}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{NO}_{2}{ }^{+}+\mathrm{HSO}_{4}{ }^{-}+\mathrm{H}_{2} \mathrm{O}$

OR

$\mathrm{HNO}_{3}+2 \mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{NO}_{2}{ }^{+}+2 \mathrm{HSO}_{4}{ }^{-}+\mathrm{H}_{3} \mathrm{O}^{+}$

OR

$\mathrm{HNO}_{3}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{H}_{2} \mathrm{NO}_{3}{ }^{+}+\mathrm{HSO}_{4}{ }^{-}$and $\mathrm{H}_{2} \mathrm{NO}_{3}{ }^{+} \rightarrow \mathrm{NO}_{2}{ }^{+}+\mathrm{H}_{2} \mathrm{O}$

(4)

Expert

TE on electrophile from M1 provided positively charged

Do not award lone pair on N of $\mathrm{NO}_{2}{ }^{+}$

An answer that makes reference to the following points:

- equation for formation of nitronium ion

(1)

- curly arrow from within hexagon to

(1) anywhere on $\mathrm{NO}_{2}{ }^{+}$

- structure of intermediate ion

(1)

- curly arrow from C-H bond to within ring and

correct product

and

$\mathrm{H}^{+}$

(1)