Dichlorocarbene is an electrophile. Its addition to para-substituted styrenes p-X-C6H4-CH=CH2 is faster when the ring is electron-rich. Which is the correct order of decreasing rate of addition?

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JEE Advanced levelSingle correct optionDifficulty 3 of 3g3104

Dichlorocarbene is an electrophile. Its addition to para-substituted styrenes $p - X - C X_{6} H X_{4} - CH = CH X_{2}$ is faster when the ring is electron-rich. Which is the correct order of decreasing rate of addition?

A $X = CH X_{3} > X = OCH X_{3} > X = NO X_{2} > X = H$
B $X = OCH X_{3} > X = CH X_{3} > X = H > X = NO X_{2}$
C $X = H > X = OCH X_{3} > X = CH X_{3} > X = NO X_{2}$
D $X = NO X_{2} > X = H > X = CH X_{3} > X = OCH X_{3}$

Answer: B

The carbene is attacked by the pi electrons of the vinyl group, and a donor substituent on the ring releases electron density into the double bond (+M, +I).

OCH X_{3}

is the strongest donor, then

CH X_{3}

, then H, while the

- M

- I

nitro group withdraws and slows the reaction most. This gives

OCH X_{3} > CH X_{3} > H > NO X_{2}

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Dichlorocarbene is an electrophile. Its addition to para-substituted styrenes p-X−CX6​HX4​−CH=CHX2​ is faster when the ring is electron-rich. Which is the correct order of decreasing rate of addition?

Answer: B

More questions on Carbenes and nitrenes

Dichlorocarbene is an electrophile. Its addition to para-substituted styrenes $p - X - C X_{6} H X_{4} - CH = CH X_{2}$ is faster when the ring is electron-rich. Which is the correct order of decreasing rate of addition?