is more pronounced thanThe dipolar resonance form of diphenylcyclopropenone has aromatic character. Its stabilityleads to increased charge separation and a larger dipole moment.(d)Decreased electron density at the carbon atom of an ,-unsaturated ketone is responsiblefor its decreased shielding. The decreased electron density arises from the polarization of itselectrons as represented by a significant contribution of the dipolar resonance form.18.39Bromination can occur at either of the two -carbon atoms.The1H NMR spectrum of the major product, compoundA, is consistent with the structure of 1-bromo-3-methyl-2-butanone. The minor product B is identified as 3-bromo-3-methyl-2-butanone on thebasis of its NMR spectrum.18.40Three dibromination products are possible from halogenation of 2-butanone.The product is 1,3-dibromo-2-butanone,on the basis of its observed 1H NMR spectrum, which
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