Suggest reasonable explanations for each of the following observations: (a) The C==O stretching frequency of ,-unsaturated ketones

Suggest reasonable explanations for each of the following observations:
(a) The C==O stretching frequency of α,β-unsaturated ketones (about 1675 cm-1) is less than that of typical dialkyl ketones (1710 - 1750 cm-1).
(b) The C==O stretching frequency of cyclopropenone (1640 cm-1) is lower than that of typical α,β-unsaturated ketones (1675 cm -1).
(c) The dipole moment of diphenylcyclopropenone (μ = 5.1 D) is substantially larger than that of benzophenone (μ = 3.0 D)
(d) The β carbon of an α,β-unsaturated ketone is less shielded than the corresponding carbon of an alkene. Typical 13C NMR chemical shift values are

Transcribed Image Text:

CH CHCR 129 ppm) CH-CHCH2R (6, (δ 114 ppm)