JEE Main · 2025 · 24 Jan 2025 · Shift 2 · General Organic Chemistry

The possible number of stereoisomers for 5-phenylpent-4-en-2-ol is ____ .

Answer: 4

Solution

5-Phenylpent-4-en-2-ol is

Ph - CH = CH - C H_{2} - CH (OH) - C H_{3}

. Carbon-2 bears four different groups —

- O H

- C H_{3}

- H

and

- C H_{2} C H = C H P h

— making it a stereocentre with

R

S

isomerism.

The

C 4 = C 5

double bond also carries two different substituents on each sp

^{2}

carbon (

H

and

C H_{2} C H (O H) C H_{3}

on one end,

H

and

P h

on the other), so it supports

E

Z

geometric isomerism as well.

With two independent stereogenic elements, the total number of stereoisomers is

2^{2} = 4

(R, E)

(R, Z)

(S, E)

and

(S, Z)

JEE Main · 2025 · 24 Jan 2025 · Shift 2 · Integer answer