Electron impact and isobutane and ammonia chemical ionization mass spectrometry of some tetrahydropyranyl acetals

The electron impact induced fragmentations of 24 tetrahydropyrane ethers of different types of alcohols were studied by exact mass measurement and metastable ion analysis. The most characteristic features of the spectra were associated with the tetrahydropyrane ring, As the size of the molecule increased, the fragmentations with respect to exocyclic oxygen became more important allowing differentiation among the isomeric aliphatic alcohols. Under isobutane chemical ionization, loss of neutral alcohol from M + H]⁺ leading to the formation of a tetrahydropyranium ion was dominant for aliphatic alcohol derivatives, whereas loss of 2-hydroxy tetrahydropyrane giving rise to an alkyl ion was dominant for bicyclic alcohol derivatives. Under ammonia chemical ionization, nucleophilic substitution reactions were always most important.