ggonoa2egiahdaonsshstne keoneepoeleemeaiatanaealnetodesand Elctrnic Tranitions fAcetone and 3-Buten--one 网gm6g3G CH.CCH CH-CHecH, 调 M-CHy The symmetric ketone generates a single acylium peak 4 4 Conjugation of carbonyl groups with double bonds shifts the absorption to longer wavelengths: Mass spectral fragmentation of aldehydes and ketones provides structural information. 2-Pentanone, 3-pentanone and 3-methyl-2-butanone all fragment by α cleavage yielding the corresponding acylium cation and an alkyl radical. Note that the two acylium fragments identify the composition of the ketone. The peak at mass 58 results from a McLafferty rearrangement. This occurs in compounds having a hydrogen atom γ to the carbonyl oxygen and enough flexibility to allow them to get close together. This extra peak allows 2-pentanone to be distinguished from 3-methyl-2- butanone, which give otherwise identical fragments. The symmetric ketone generates a single acylium peak. Note the absence of a peak at 58, which is present in the mass spectrum of 2-pentanone