Studies in organic mass spectrometry. XVII The fragmentation of methyl enol ethers of 1,3‐cyclohexanediones and 1,3‐cyclopentanediones

Abstract

thyl enol ethers of 1,3-cyclohexanediones and 1,3-cyclopentanediones is studied. Six membered rino; compounds behave quite straithforwardly and in accordance with the fragmentation suggested f o r 1,3-cyclohexanediones in the enol form. Some fragmentations are supported by deuterium labelling. tuted isomers display identical spectra. This isomerisation is studied by metastable transitions, low energy spectra and deuterium labelling; a possible mechanism is advanced.The influence of alkyl substituents on the mass spectral behaviour of meIn the case of enol ethers of 1,3-~yclopentanediones the 4-or 5-substi-The mass spectral behaviour of acyclic 1,3-diones1 to 4, 1,3-~yclohexane-diones5 to and 1,3-cycl~pentanediones~ has already been discussed. It could be proven that both tautomeric forms display different fragmentation patterns.It is therefore of interest to investigate corresponding enol ethers. The fragmentation behaviour of some enol derivatives of dirnedone'l and acyclic 1,3-diketones" has been published.ethers of alkyl substituted 1,3-cyclohexanediones and 1,3-cyclopentanediones.It appears, as well from the published data as from the present work that the most important ions are formed by initial cleavage 0 to the carbonyl function.The fragmentation of the cyclic enol ethers is discussed in function of the length and the position of the alkyl substituent; the mechanisms are in all cases, supported by high resolution measurements.We now present the fragmentation of methyl en01 I; R = H 11; R = Et 111; R = n.Pr IV; R = n.Bu).Holder of a bursary of V; R = Et VIII; R = Me VI; R = n.Pr IX; R = n.Pr VII; R = n.Bu X; R = n.Bu C. Van