Arrange the following compounds in order of increasing dipole moment:Toluene (I),m-dichlorobenzene (II), O-dichlorobenzene (III), p-dichlorobenzene (IV)
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a
I < IV < II < III
b
IV < I < II < III
c
IV < I < III < II
d
IV < II < I < III
answer is A.
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Detailed Solution
The dipole moment of p-dichlorobenzene is zero since the two equal dipoles oppose each other. The two dipoles are at 60º apart in o-dichlorobenzene but at 120º is m-dichlorobenzene, therefore, according to parallelogram law of forces, the dipole moment of o-dichlorobenzene is much higher than that of m-isomer. Toluene due to + I-effect of the CH3 group has a small but finite dipole moment, therefore, the overall order is p-dichlorobenzene (IV) < toluene (I) < m-dichlorobenzene (II) < o-dichlorobenzene (III). i.e, option (b) it is correct.