Question

The following groups are ortho-para directors. (a) \(-\mathrm{OH}\) (b) \(-\mathrm{OCCH}_{3}\) (c) \(-\mathrm{N}\left(\mathrm{CH}_{3}\right)_{2}\) (d) \(-\mathrm{NHCCH}_{3}\) (e) Ic1ccccc1 Draw a contributing structure for the resonance-stabilized cation formed during electrophilic aromatic substitution that shows the role of each group in stabilizing the intermediate by further delocalizing its positive charge.

Short answer

Question: Draw contributing resonance structures for the resonance-stabilized cation formed during electrophilic aromatic substitution for each of the following ortho-para directing groups: -OH, -OCCH3, -N(CH3)2, -NHCCH3, and Ic1ccccc1.

Step-by-step solution

1. Understand ortho-para directors and electrophilic aromatic substitution

Ortho-para directors are groups that donate electron density to the aromatic ring, activating the ring towards electrophilic aromatic substitution reactions. They stabilize the resonance-stabilized cation intermediate (also called sigma-complex or arenium ion) formed during the reaction by delocalizing the positive charge through resonance structures. The ortho and para positions are the ones most stabilized during this process. Let's draw the resonance structures for each of the given groups.

2. Draw resonance structures for the -OH group

For the case of the -OH group, the oxygen has a lone electron pair that can donate electron density to the ring, creating resonance structures that stabilize the sigma complex. Draw the -OH group attached to a benzene ring and draw resonance structures that involve pushing the lone electron pair on oxygen into the ring system, resulting in a positive charge on the oxygen and moving the positive charge to the ortho and para carbon positions.

3. Draw resonance structures for the -OCCH3 group

For the -OCCH3 group, a similar process occurs. The oxygen atom has a lone electron pair that donates electron density to the ring. Draw the -OCCH3 group attached to the benzene ring, and then push the lone electron pair on oxygen into the ring system, creating resonance structures. This will result in a positive charge on the oxygen and delocalizing the positive charge to the ortho and para carbon positions.

4. Draw resonance structures for the -N(CH3)2 group

The -N(CH3)2 group acts as an electron-donating group through the nitrogen atom, which possesses a lone electron pair. Attach the -N(CH3)2 group to the benzene ring, and then push the lone electron pair on nitrogen into the ring system. Draw resonance structures to show the delocalization of the positive charge. The positive charge will move to the ortho and para carbon positions with a positive charge on the nitrogen atom.

5. Draw resonance structures for the -NHCCH3 group

The -NHCCH3 group also acts as an electron-donating group through the nitrogen atom, which has a lone electron pair. Attach the -NHCCH3 group to the benzene ring, and then push the lone electron pair on nitrogen into the ring system. Draw resonance structures to show the delocalization of the positive charge. The positive charge will again move to the ortho and para carbon positions with a positive charge on the nitrogen atom.

6. Draw resonance structures for the Ic1ccccc1 group

The Ic1ccccc1 represents a benzene ring with an iodine atom attached to it. Iodine can donate electron density to the ring through its lone electron pairs. Attach the iodine atom to the benzene ring, and then push one of the lone electron pairs on iodine into the ring system. Draw resonance structures to show the delocalization of the positive charge. The positive charge will move to the ortho and para carbon positions with a positive charge on the iodine atom.