how does resonance affect dipole moment of vinyl chloride
Answers
Answer:
Explanation:
Consider a resonance structure where the chlorine donates electrons to the alkene. ... Since the electronegativity of chlorine will be closer to the electronegativity of the carbons in vinyl chloride than the carbons of ethyl chloride, the C–Cl bond will be less polarized in vinyl chloride, giving a smaller dipole
Consider a resonance structure where the chlorine donates electrons to the alkene. This puts a formal positive charge on chlorine:
Resonance forms of vinyl chloride
This would be a very minor contributor given the electronegativities and the mismatch in orbital size. However, this is not possible in ethyl chloride at all.
The more likely explanation is that an sp2-hybridized carbon is more electronegative than an sp3-hybridized carbon. Since the electronegativity of chlorine will be closer to the electronegativity of the carbons in vinyl chloride than the carbons of ethyl chloride, the C–Cl bond will be less polarized in vinyl chloride, giving a smaller dipole.
The bonding orbital of carbon in C2H3Cl is an sp2 hybrid orbital while C2H5Cl’s is an sp3 one. The former has a higher s-content and a lower p-content resulting in it being closer to the atom resulting in a shorter bond. A shorter bond means less charge separation.
sp2 carbons are also more electronegative than sp3 carbons; see the discussion on how to interpret the high acidity of
Don't forget that dipole moment depends not only on electronegativity differences but also bond lengths. All other factors held equal, the longer the bond, the greater the dipole moment.
Why would dipole moment depend on bond length? Consider an extreme example in which, say, sodium ion were in exactly the same place as fluoride ion. Obviously the two differ tremendously in electronegativities. However, there cannot be a dipole moment; there are no poles of opposite charge since the two are directly on top of each other.
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