JEE Main 2014 · 6 Apr · Shift 1 · Chemistry Q57 · Dronacharya Exams

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ChemistrySingle correct+4 / -1Question 57 of 90

For which of the following molecule significant $\mu\ne0$ ?

(a) 1,4-dichlorobenzene (b) 1,4-dicyanobenzene (c) hydroquinone (benzene-1,4-diol) (d) benzene-1,4-dithiol

Four para-disubstituted benzenes: (a) Cl and Cl, (b) CN and CN, (c) OH and OH, (d) SH and SH.

A

Only (a)

B

(a) and (b)

C

Only (c)

D

(c) and (d)

Answer and worked solution

Official answer: D

In 1,4-dichloro- and 1,4-dicyanobenzene the two C-X dipoles lie along one axis and cancel: $\mu=0$ .
In hydroquinone and benzene-1,4-dithiol, the O-H and S-H bonds lie at an angle to the ring axis. In their conformations the dipoles do not cancel, so $\mu\ne0$ .

Answer: (c) and (d).

Topics:Bond parameters and dipole moment

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