JEE Advanced 2020 · Paper 1 · Chemistry Q5 · Dronacharya Exams

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ChemistrySingle correct+3 / -1Question 23 of 54

Which one of the following structures has the IUPAC name 3-ethynyl-2-hydroxy-4-methylhex-3-en-5-ynoic acid?

A

Skeletal structure: a C=C double bond; the upper carbon bears an ethyl group and a CH(OH)CO₂H group, the lower carbon bears two ethynyl groups.

B

Skeletal structure: a C=C double bond; the upper carbon bears an ethynyl group and an ethyl group, the lower carbon bears an ethynyl group and a CH(OH)CO₂H group.

C

Skeletal structure: a C=C double bond; the upper carbon bears a methyl group and a CH(OH)CO₂H group, the lower carbon bears two ethynyl groups.

D

Skeletal structure: a C=C double bond; the upper carbon bears an ethynyl group and a CH(OH)CO₂H group, the lower carbon bears an ethynyl group and a methyl group.

Answer and worked solution

Official answer: D

Parent chain. Number hex-3-en-5-ynoic acid from the acid carbon:

C1 is $\ce{CO2H}$ and C2 carries the OH;
C3=C4 is the double bond, with an ethynyl on C3 and a methyl on C4;
C5≡C6 is the triple bond.

So C3 carries $\ce{CH(OH)CO2H}$ and $\ce{C#CH}$ , and C4 carries $\ce{CH3}$ and $\ce{C#CH}$ .

Matching the drawings.

(A) and (C) put both ethynyl groups on the same carbon.
(B) has an ethyl instead of a methyl.
(D) matches.

(D)

Topics:IUPAC nomenclature

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