Organic Compounds Containing Halogens Question 174
Question: Arrange the following compounds in order of increasing dipole moment:
(I) Toluene
(II) m-dichlorobenzene
(III) o-dichlorobenzene
(IV) p-dichlorobenzene
Options:
A) $ I \lt IV \lt II \lt III $
B) $ IV \lt I \lt II \lt III $
C) $ IV \lt I \lt III \lt II $
D) $ IV \lt II \lt I \lt III $
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Answer:
Correct Answer: B
Solution:
[b] In p-dichlorobenzene, the two equal dipoles are in opposite direction, hence the molecule has zero dipole moment. In o- and m- dichlorobenzenes, the two dipoles are at $ 60{}^\circ $ and $ 120{}^\circ $ apart respectively, and thus according to parallelogram law offerees, the dipole moment of o-dichlorobenzene is much higher than that of m-isomer. Lastly, toluene with a +I group possesses little dipole moment. Thus the overall order is
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