The dipolemoment of \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}(2.05 \mathrm{D})\) is considerably larger than that for vinyl chloride \(\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{Cl}(1.44 \mathrm{D})\) This is because (a) of hyperconjugation in ethyl chloride. (b) the unshared electron pair in chlorine is in resonance with the olefinic double bond in vinyl chloride. (c) Ethane is a saturated molecule. (d) of the electromeric effect.

Hyperconjugation is an essential concept in organic chemistry that helps explain the stability and reactivity of molecules. It occurs when sigma electrons (typically from a C-H bond) adjacent to an unsaturated carbon system, such as a double bond or a carbocation, are delocalized into the empty p-orbital or pi system. This delocalization allows the charge to be spread out over several atoms, increasing the stability of the molecule.

Despite being a subtle effect compared to resonance, hyperconjugation can significantly impact molecular properties. For example, in structures with alkyl groups attached to double bonds or benzene rings, hyperconjugation can influence the boiling points, acidity, and even the dipole moments of molecules. However, it is essential to note that hyperconjugation requires the presence of a beta-hydrogen atom relative to a positively charged or electron-deficient center. Since ethyl chloride does not provide conditions for hyperconjugation to occur, it is not the correct explanation for the observed dipole moment difference compared to vinyl chloride.

The resonance effect is a critical contributor to the stability of molecules in organic chemistry. It refers to the delocalization of electrons across several atoms within a molecule, allowing the structure to be represented by two or more resonance structures or contributing forms. These forms are not real, individual structures; instead, they are used as a mental tool to explain the actual electron distribution within the molecule, which is a hybrid of these forms.

Compounds like vinyl chloride exhibit resonance because the lone pair of electrons on the chlorine atom can participate with the pi electrons of the adjacent double bond. This results in a delocalization of charge, effectively reducing the electron density on the chlorine atom and thus decreasing the overall dipole moment of the molecule. This concept provides the correct explanation for the higher dipole moment of ethyl chloride (2.05 D) when compared to vinyl chloride (1.44 D), demonstrating the impact of resonance on molecular properties.

The electromeric effect is a phenomenon involving the complete transfer of a pair of pi electrons to one end of a double bond in the presence of an attacking reagent, resulting in a polarized intermediate. This effect is temporary and reversible, as the electrons are transferred only for the duration of the reaction, after which they typically revert to their original position.

This movement of electrons leads to the formation of new electron distributions in the molecule, potentially creating a positive and negative end (a dipole) temporarily. However, the electromeric effect is different from resonance and hyperconjugation because it is not a permanent feature of the molecule's structure; it occurs only in response to a chemical reaction. In the context of dipole moments in stable molecules like ethyl chloride and vinyl chloride, the electromeric effect does not apply. Hence, it does not explain the difference in their dipole moments.