2-Methylhexa-2,4-dienoic acid is HOOC-C(CH3)=CH-CH=CH-CH3 (C1 is the carboxyl carbon). Which statements are correct?

It has four geometrical isomers.

In the isomer in which COOH and C4 are on the same side of the C2=C3 bond, the descriptor of that bond is Z.

In the isomer in which the C2-methyl group and C4 are on the same side of the C2=C3 bond, the descriptor of that bond is Z.

It has four geometrical isomers.

Replacing the C2-methyl by H (hexa-2,4-dienoic acid) reduces the number of geometrical isomers.

In the isomer in which COOH and C4 are on the same side of the C2=C3 bond, the descriptor of that bond is Z.

JEE Advanced levelOne or more correct optionsDifficulty 3 of 3st041

2-Methylhexa-2,4-dienoic acid is $HOOC - C (CH X_{3}) = CH - CH = CH - CH X_{3}$ (C1 is the carboxyl carbon). Which statements are correct?

AIn the isomer in which the C2-methyl group and C4 are on the same side of the C2=C3 bond, the descriptor of that bond is $Z$ .
BIt has four geometrical isomers.
CReplacing the C2-methyl by $H$ (hexa-2,4-dienoic acid) reduces the number of geometrical isomers.
DIn the isomer in which $COOH$ and C4 are on the same side of the C2=C3 bond, the descriptor of that bond is $Z$ .

C2=C3: C2 has

COOH

and

CH X_{3}

, C3 has C4 and

H

. C4=C5: C4 has C3 and

H

, C5 has

CH X_{3}

and

H

. Both bonds are stereogenic and the compound is unsymmetrical, so

2^{2} = 4

isomers: A is correct. On C2,

COOH

(O, O, O)

outranks

CH X_{3}

; on C3, C4 outranks

H

COOH

cis to C4 is therefore

Z

: B is correct. If the methyl is cis to C4, then

COOH

is trans to C4, which is

E

: C is wrong. Hexa-2,4-dienoic acid is also unsymmetrical with two stereogenic bonds, so still

4

isomers: D is wrong.