Chapter 18: 19 P (page 700)

Draw all resonance structures for the carbocation formed by ortho attack of the electrophile ${}^{+}{NO}_{2}$ on each starting material. Label any resonance structures that are especially stable or unstable.

Short Answer

Expert verified

Step by step solution

Ortho-para directing groups

The ortho-para directing groups substitute the electrophile at ortho and para positions. The electron-donating groups stabilize the positive charge (delocalizing in the ring) by donating electrons.

The electron-withdrawing groups destabilize the positive charge (delocalizing in the ring) by donating electrons.

Examples of ortho-para and meta-directing groups

Ortho-para directing groups: OH, R-, -OR, ${NH}_{2}$ , etc.

Meta directing groups: CHO, COOH, ${NO}_{2}$ , etc.

Explanation

a. The substituent on the benzene ring is $C {({CH}_{3})}_{3}$ , which is electron-donating. The positive charge obtained by the substitution of the electrophile is stabilized by $C {({CH}_{3})}_{3}$ .

b. The substituent on the benzene ring is OH, which is electron-donating. The positive charge obtained by the substitution of the electrophile is stabilized by OH.

c. The substituent on the benzene ring is CHO, which is electron-withdrawing. The positive charge obtained by the substitution of the electrophile is not stabilized by CHO.