Suggest reasonable explanations for each of the following observations: (a) The C═O stretching frequency of a, ß -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 a, ß-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 carbon of an a, ß -unsaturated ketone is less shielded than the corresponding carbon of an alkene. Typical 13C NMR chemical shift values are