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NEET levelSingle correct optionDifficulty 1 of 3st001

Which of the following alkenes can exist as a pair of geometrical (cis/trans) isomers?

A $CH X_{3} - CH X_{2} - CH = CH X_{2}$
B $CH X_{3} - CH = C (CH X_{3}) X_{2}$
C $CH X_{3} - CH = CH - CH X_{3}$
D $CH X_{2} = CH - CH X_{3}$

Answer: C

Geometrical isomerism about

C = C

needs two different groups on each doubly bonded carbon. In but-2-ene each sp2 carbon carries

H

and

CH X_{3}

, so cis and trans forms exist. The other three have a carbon with two identical groups (

CH X_{3}

,

CH X_{3}

or

H

,

H

). Hence only

CH X_{3} - CH = CH - CH X_{3}

qualifies.

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