The molecules having dipole moment are :

Options

A. 2,2-Dimethylpropane
B. trans-Pent-2-ene
C. cis-Hex-3-ene
D. 2,2,3,3-Tetramethylbutane

Answer

B

Explanation

Since the +I-effect of `CH_3CH_2` group is higher than that of `CH_3` group, therefore , the dipole moments of `C-CH_3` and `C-CH_2CH_3` bonds are unequal . Although these two dipoles oppose each other, yet they do not exactly cancel out each other and hence trans-2-pentene has small but finite dipole moment. In cis-hex-3-ene , although the dipole moment of the two `C-CH_2CH_3` bonds are equal , they are inclined to each other at angle of `60^@` and hence have a finite resultant.
Further, 2,2-dimethylpropane and 2,2,3,3-tetramethylbutane have zero dipole moments because of the following two reasons :
(i)C-C and C-H bonds in alkanes are almost non-polar and have no fixed orientations in space , therefore, their resultant dipole moment, if any , are almost negligible .
(ii)Both these are symmetrical molecules and hence their dipole moments is zero.