The dipole moment of vinyl chloride is less than that of methyl chloride due to:

1. Resonance effect:
Resonance refers to the delocalization of electrons within a molecule, resulting in the stabilization of the molecule. In the case of vinyl chloride (CH2=CHCl), the double bond between the carbon atoms allows for resonance to occur. The pi electrons in the double bond can delocalize onto the chlorine atom, resulting in a partial negative charge on the chlorine and a partial positive charge on the adjacent carbon atom. This charge distribution contributes to the dipole moment of the molecule. However, in methyl chloride (CH3Cl), there is no such resonance effect as there is no double bond present.

2. Inductive effect:
The inductive effect refers to the polarization of sigma bonds due to differences in electronegativity between atoms. In the case of vinyl chloride, the chlorine atom is more electronegative than the adjacent carbon atom, causing a partial positive charge on the carbon atom and a partial negative charge on the chlorine atom. This charge separation creates a dipole moment. In methyl chloride, the inductive effect is also present, but to a lesser extent due to the difference in electronegativity between carbon and chlorine being smaller than that between carbon and chlorine in vinyl chloride.

3. Electromeric effect:
The electromeric effect involves the movement of electrons in response to the presence of an electric field. In vinyl chloride, the presence of the double bond allows for the movement of pi electrons towards the chlorine atom, resulting in a dipole moment. However, in methyl chloride, the absence of a double bond restricts the movement of electrons, leading to a smaller dipole moment.

4. Hyperconjugation:
Hyperconjugation refers to the delocalization of sigma electrons into adjacent pi systems or empty p orbitals. In vinyl chloride, the presence of the double bond allows for hyperconjugation to occur, resulting in partial electron density being shifted towards the chlorine atom, contributing to the dipole moment. However, in methyl chloride, the absence of a double bond restricts hyperconjugation, leading to a smaller dipole moment.

In summary, the dipole moment of vinyl chloride is less than that of methyl chloride due to the presence of resonance, inductive effect, electromeric effect, and hyperconjugation in vinyl chloride. These factors contribute to a larger charge separation and dipole moment in vinyl chloride compared to methyl chloride.

Inductive effect