Mass spectra of some acetals

The electron impact (El), methane chemical ionisation (CH4 Cl) and ammonia chemical ionisation (NH3 Cl) mass spectra of five acetals have been obtained. The [graphic omitted] ions dominate the total ion current under El (70 and 14 eV). In the CH4 Cl mode, the [(M+ 1)–CH3OH]+ ions form the base peaks, except for methyl 2-(dimethoxymethyl)-5-(2-hydroxyethyl)-cyclopent-3-en-1-ylacetate, compound (V), which yields [(M+ 1)–2CH3OH]+ as the base peak. The [M+ 1]+ ion is absent from the NH3 Cl mode, but the fragmentation patterns are still complicated. The main fragmentation pathways include fragmentation from the cluster adduct ions, from the charge-transfer products and from the aldehyde, a product from the reversed reaction of the acetal. The difference in energy gained by the molecular ions during the ionisation process leads to this feature.