Question

why is the dipolar moment of CH3Cl at 1.87D whereas CH2Cl has a lower dipole moment of 1.14 D

Answer 1

In reality, the CH2Cl2 molecule is in a tetrahedral shape, so the angle between the two C-Cl bonds is 109.5deg:As you can see, the vertical parts of the dipole moment vector are additive, but the horizontal parts are subtractive, and since the horizontal components attribute more to the resultant vector (because the angle is greater than 90deg), it causes a lower dipole moment for CH2Cl2.