Electron impact and chemical ionization mass spectra of alkyldiphenylphosphine oxides

In the 70 e V electron impact mass spectra of a series of alkyldiphenylphosphine oxides (R?₂PO, R = Me, Et, n-Pr, i-Pr, n-Bu, i-Bu, t-Bu, neopentyl, n-decyl), molecular ions of low abundance are observed and M + H]⁺ ions are formed to a small extent at high sample pressures. The major ions include ?₂PO]⁺, ?₂POH]⁺; ?₂CH₂PO]⁺ and ?₂CH₂POH]⁺ which are formed by rearrangement and cleavage processes. The chemical ionization mass spectra obtained with methane and isobutane reagents consist of M + H]⁺ ions. The proton affinity of R?₂PO was found to be 219 ± 2.5 kcal mol^?1.