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JEE Main levelSingle correct optionDifficulty 2 of 3st252

The compound shown is 3-methylpent-2-ene drawn with a definite geometry. Its configuration is

A $(Z)$
B $(E)$
Ccis and $(E)$
Dit has no geometrical isomers because C3 carries two alkyl groups

Answer: A

On C2 the groups are

CH X_{3}

and

H

;

CH X_{3}

has priority. On C3 the groups are

C X_{2} H X_{5}

and

CH X_{3}

; ethyl (C attached to C,H,H) outranks methyl (H,H,H). In the drawing the C2 methyl and the C3 ethyl are on the same side of the double bond, so the configuration is

(Z)

. A trisubstituted alkene does show geometrical isomerism as long as the two groups on each carbon are different.

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