Question

Are the following substituents ortho–para directors or meta directors?

a.$\mathbf{CH}\mathbf{=}\mathbf{CHC}\equiv \mathbf{N}$

b.${\mathbf{NO}}_2$

c.${\mathbf{CH}}_2\mathbf{OH}$

d.$\mathbf{COOH}$

e.${\mathbf{CF}}_3$

f.$\mathbf{N}\mathbf{=}\mathbf{O}$

Short answer

a)

$\text{-CH=CHC}\equiv \text{N}$is a meta director.

b)

${\text{NO}}_{\text{2}}$is a meta director.

c)

${\text{CH}}_{\text{2}}\text{OH}$is a meta director.

d)

COOH is a meta director

e)

${\text{CF}}_{\text{3}}$ is a meta director.

f)

$\text{N=O}$is a meta director

Step-by-step solution

Step-by-step-solutionStep 1: Reactivity of the benzene ring

The electron-with drawing substituents decrease the reactivity of the benzene ring. The substituents, which are attached to the benzene having partial positive charge or positive charge, will withdraw the electrons from the benzene ring and forms a most stable carbocation, then the incoming electrophile is directed towards the meta position.

Identification of the given molecules

a)

In this structure, a partial positive charge is present on the carbon atom, which is attached to the benzene ring. So, the incoming electrophile is directed towards the meta position. Thus, $\text{-CH=CHC}\equiv \text{N}$is a meta director.

$\text{-CH=CHC}\equiv \text{N}$is a meta director (a)

b)

In this structure, a positive charge is present on the nitrogen atom, which is attached to the benzene ring. So, the incoming electrophile is directed towards the meta position. Thus,${\text{NO}}_{\text{2}}$is a meta director.

${\text{NO}}_{\text{2}}$is a meta director (b)

c)

In this, structure, a partial positive charge is present on the carbon atom, which is attached to the benzene ring. So, the incoming electrophile is directed towards the meta position. Thus,${\text{CH}}_{\text{2}}\text{OH}$is a meta director.

${\text{CH}}_{\text{2}}\text{OH}$is a meta director (c)

d)

In this structure, a partial positive charge is present on the carbon atom, which is attached to the benzene ring. So, the incoming nucleophile is directed towards the meta position. Thus, COOH is a meta director.

COOH is a meta director (d)

e)

In this structure, a partial positive charge is present on the carbon atom, which is attached to the benzene ring. So, the incoming electrophile is directed towards the meta position. Thus, ${\text{CF}}_{\text{3}}$is a meta director.

${\text{CF}}_{\text{3}}$is a meta director (e)

f)

In this structure, a partial positive charge is present on the nitrogen atom, which is attached to the benzene ring. So, the incoming electrophile is directed towards the meta position. Thus,$\text{N=O}$ is a meta director.

$\text{N=O}$ is a meta director (f)