Low Resolution Mass Spectra of Some Unsaturated δ-Lactones

Abstract

Mass spectra of the δ-lactones of the following 5-hydroxy-2-enoic acids were determined: 5-hydroxyhex-2-enoic acid (I), 5-hydroxyoct-2-enoic acid (II), 5-hydroxydec-2-enoic acid (III), 5-hydroxydodec-2-enoic acid (IV), 5-hydroxy-8-methylnon-2-enoic acid (V), 5-hydroxy-6-ethyloct-2-enoic acid (VI), 5-hydroxy-5, 6, 6-trimethylhept-2-enoic acid (VII), and 5-hydroxy-5-methylnon-2-enoic acid (VIII). The following modes of fragmentation are consistent with observed m/e values, metastable peaks, and established modes of breakdown in compounds containing similar atomic groupings: -l. Loss of side chain, resulting in ions at m/e 97 for I-VI and at m/e 111 and 153 for VII and VIII (diagnostic peaks); 2. 1, 4-Rupture of the ring giving an ion at m/e 68 (diagnostic peak) which loses CO to give m/e 40; 3. Loss of CO from m/e 97 fragment to give m/e 69 which breaks down further to m/e 41→m/e 39; 4. 1, 4-Rupture of m/e 111 and m/e 153 fragments to give m/e 43 and 85, further breakdown of m/e 85→57→41→39; 5. Loss of H2O from the molecular ion providing there is a hydrogen atom on C5 and the side chain is at least 3 carbon atoms in length, further loss of H2O when the side chain is equal to C5 or C7; 6. Loss of CO2 from the molecular ion of I, IV-VIII; 7. Loss of CO from all molecular ions; 8. Loss of 2×28 from the molecular ions of III, IV, V, VI; 9. Loss of (18+28) from the molecular ion of III, IV, V, VI; 10. Loss of 60 from the molecular ion of II, III, IV, V, VI; 11. Formation of M+1 ion (169) of VII and VIII; 12. Formation of M+1 ion (143) of saturated_??_-octalactone and loss of H2O from this M+1 ion.