Biphenyl is two benzene rings joined by a single bond. The site of substitution for a biphenyl is determined by (1) which phenyl ring is more activated (or less deactivated), and (2) which position on that ring is most reactive, using the fact that a phenyl substituent is activating and ortho, para-directing.
b. Predict the mononitration products of the following compounds
(v)

Verified step by step guidance

1. Analyze the structure of the compound: The molecule consists of two benzene rings connected by a single bond, forming a biphenyl system. Additionally, one of the benzene rings has a ketone group attached to it, which is an electron-withdrawing group.
2. Determine the activation/deactivation of the rings: The benzene ring with the ketone group is deactivated due to the electron-withdrawing nature of the ketone group. The other benzene ring is relatively more activated because it does not have any electron-withdrawing substituents.
3. Identify the directing effects: The phenyl substituent (the benzene ring without the ketone group) is activating and ortho, para-directing. This means that nitration will preferentially occur at the ortho or para positions relative to the phenyl substituent on the activated ring.
4. Consider steric hindrance: The ortho positions on the activated benzene ring may experience steric hindrance due to the proximity of the phenyl substituent. Therefore, the para position is likely to be the most reactive site for nitration.
5. Predict the mononitration product: The nitro group (-NO₂) will be added to the para position of the activated benzene ring, relative to the phenyl substituent, as this position is both electronically favorable and less sterically hindered.

Key Concepts

Electrophilic Aromatic Substitution (EAS)

Electrophilic Aromatic Substitution is a fundamental reaction in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. In biphenyl, the presence of two benzene rings allows for substitution reactions at various positions, influenced by the electronic effects of substituents. Understanding EAS is crucial for predicting the products of nitration in biphenyl.

Activating and Deactivating Groups

Substituents on an aromatic ring can either activate or deactivate the ring towards electrophilic substitution. Activating groups, such as alkyl groups, increase the electron density of the ring, making it more reactive, while deactivating groups, like nitro groups, withdraw electron density and reduce reactivity. In biphenyl, the relative activation of each phenyl ring will determine the site of substitution during nitration.

Ortho/Para-Directing Effects

Ortho and para directing effects refer to the positions on an aromatic ring where electrophilic substitution is most likely to occur, influenced by the nature of substituents. Activating groups typically direct new substituents to the ortho and para positions relative to themselves, while deactivating groups direct to the meta position. In biphenyl, understanding these directing effects is essential for predicting the specific nitration products.