Acetonitrile (CH3CN) has resonance at 1.97 ppm, whereas methyl chloride (CH3CI) has resonance at 3.05 ppm,...

 

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Acetonitrile (CH3CN) has resonance at 1.97 ppm, whereas methyl chloride (CH3CI) has resonance at 3.05 ppm, even though the dipole moment of acetonitrile is 3.92 D and that of methyl chloride is only 1.85 D. The larger dipole moment for the cyano group suggests that the electronegativity of this group is greater than that of the chlorine atom. Explain why the methyl hydrogens on acetonitrile are actually more shielded than those in methyl chloride, in contrast with the results expected on the basis of electronegativity. (Hint: What kind of spatial pattern would you expect for the magnetic anisotropy of the cyano group, CN?) Acetonitrile (CH3CN) has resonance at 1.97 ppm, whereas methyl chloride (CH3CI) has resonance at 3.05 ppm, even though the dipole moment of acetonitrile is 3.92 D and that of methyl chloride is only 1.85 D. The larger dipole moment for the cyano group suggests that the electronegativity of this group is greater than that of the chlorine atom. Explain why the methyl hydrogens on acetonitrile are actually more shielded than those in methyl chloride, in contrast with the results expected on the basis of electronegativity. (Hint: What kind of spatial pattern would you expect for the magnetic anisotropy of the cyano group, CN?)