Question

20. Match the substituent to
the stated orientation and
activation effects. Which set is
incorrect? *
O Cl; activating; o- and p-directing.
O NO2; deactivating; m-directing.
O OH; activating; o- and p-directing,
O Me; activating; o- and p-directing.
​

Answer 1

Answer:

The correct answer is option A

Explanation:

a) Cl: The Cl- substituent (as the other halogen substituents), given the high electronegativity of chlorine, has an electron-withdrawal effect on the aromatic ring, therefore reducing the electron density on it and making the ring less nucleophile, deactivating it. But the halogen groups have some lone pairs of non-bonding electrons, that can be added to the pi bonds, causing resonance of the carbocation. This effect overcomes the inductive effect of the group that destabilizes the ortho- carbocation with chlorine, bromine, and iodine. The resonance stabilizes only the ortho and para carbocations, as can be seen in the picture below, therefore directing the substitution.

b) NO2:

Any group with decreases in the rate (relative to H) is called a deactivating group. Common activating groups (not a complete list): Alkyl, NH2, NR2, OH, OCH3, SR. Common deactivating groups (not a complete list): NO2, CF3, CN, halogens, COOH, SO3H.

C) OH:

The OH group behaves as an electron activating (means enriches the benzene ring with electrons, thus making it feasible to undergo the reaction) and Cl behaves as electron deactivating (takes up electrons from the ring and slows down the reaction).

d)Me: E is an activating group because it has nitrogen with a lone pair. F is a deactivating group because C = O is directly attached to the benzene ring.