NEET Chemistry: Acidic nature electrophilic substitution reactions and Reimer Tiemann reaction Practice Questions

Correct answer: D — The phenoxide ion formed upon deprotonation is resonance stabilized, making the resulting anion more stable.

Phenol is more acidic than alcohols because the resulting phenoxide ion is highly resonance stabilized. The negative charge is delocalized across the benzene ring, increasing the stability of the anion and thus favoring the release of the proton.

Correct answer: B — o-hydroxybenzaldehyde

The Reimer-Tiemann reaction involves the electrophilic attack of dichlorocarbene (CCl₂) derived from CHCl₃ onto the activated ring, resulting in the formation of o-hydroxybenzaldehyde (salicylaldehyde).

Correct answer: A — Donate the π-electrons from the ring.

Phenol's acidic nature means it can donate the proton (H⁺) to form the phenoxide ion (C₆H₅O⁻). This reaction involves the delocalization of π-electrons from the ring structure, which is the basis for its acidic behavior.

Correct answer: C — It is a strong resonance donor, increasing the electron density of the ring.

The hydroxyl group (-OH) is highly electronegative and donates electron density into the benzene ring via resonance. This resonance donation makes the ring electron-rich, which is the primary reason why phenol is acidic compared to benzene.

Correct answer: C — Presence of the -OH group

The -OH group is a strong activating group due to resonance donation, which increases the electron density of the benzene ring, making it more susceptible to attack by electrophiles compared to benzene.

Correct answer: C — Ortho position

The -OH group is an activating group that donates electron density into the ring. This activation is strongest at the ortho and para positions relative to the -OH group.

Correct answer: C — Resonance effect allowing the OH group to delocalize electrons into the ring.

The acidity and activating nature of phenol stem from the resonance effect. The oxygen atom possesses lone pairs that can be donated into the π-system of the benzene ring, increasing the electron density on the ring, which makes it highly reactive towards electrophiles.

Correct answer: C — Resonance effect

The -OH group donates its lone pair to the ring via resonance, stabilizing the resulting phenoxide ion and facilitating proton release, making phenol more acidic than benzene.

Correct answer: A — Resonance stabilization of the phenoxide ion

The phenoxide ion formed upon deprotonation is highly stabilized by resonance across the aromatic ring, which is the primary reason for phenol's enhanced acidity.

Correct answer: A — Mixture of ortho and para products

Due to the activating and ortho/para directing nature of the -OH group, electrophilic substitution preferentially occurs at the ortho and para positions, leading to a mixture of products if substitution is not strictly controlled.

Correct answer: C — True

The phenol is acidic because the loss of H⁺ yields the phenoxide ion. The negative charge on the oxygen atom is stabilized by resonance across the entire benzene ring, making the phenoxide ion relatively stable.

Correct answer: B — CHCl₃

The reaction involves the formation of dichlorocarbene (CCl₂) derived from chloroform (CHCl₃), which acts as the electrophile attacking the aromatic ring.

Correct answer: C — A cyclohexadienyl cation stabilized by the OH group

When an electrophile attacks phenol, the resulting intermediate is a cyclohexadienyl cation. Due to the activating nature of the OH group, this cation is significantly stabilized through resonance involving the OH group, making the reaction facile.