Question

The molecules having dipole moments are __________.

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

Answer 1

Answer: (C), (D)

$trans-Pent-2-ene$


Analysing the given options-

Option A : 2,2-Dimethylpropane


Option D : 2,2,3,3 – Tetramethylbutane


$2,2$-Dimethylpropane and $2,2,3,3$-tetramethylbutane have zero net 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 are symmetrical molecules. Hence, their net dipole moments are zero because their individual bond moments (if present any) will cancel out each other.

Option B : trans-Pent-2-ene



The $+I$ effect of the $C{H}_{3}C{H}_2$ group is higher than that of $C{H}_3$ group, therefore, the dipole moments of $C-C{H}_3$ and $C-C{H}_{2}C{H}_3$ bonds are unequal.

Although these two dipoles oppose each other, they do not exactly cancel out each other due to differences in carbon chain length.

So, the molecule possess some dipole moment.

Option C : cis-Hex-3-ene


Although the dipole moments of the two $C-C{H}_{2}C{H}_3$ bonds are equal, but they are inclined to each other at an angle of ${60}^{\circ }$ and hence this structure have a finite net dipole moment.