135388-79-3Relevant articles and documents
Stereochemical analysis of deuterated alkyl chains by MS/MS
Morizur,Taphanel,Mayer, Philip S.,Morton, Thomas Hellman
, p. 381 - 387 (2000)
Vicinally deuterated sec-alkyl phenyl ethers, CH3(CH2)(m)CH(OPh)CHD(CH2)(n)CH3, display significant differences in mass spectra between threo and erythro stereoisomers. MS/MS experiments, in which parent ions of a single mass are selected and their fragmentation patterns subsequently measured, show that alkene expulsion represents virtually the only decomposition pathway. Two types of MS/MS experiment are reported: mass- analyzed ion kinetic energy (MIKE) spectroscopy of metastable ions and collisionally activated decomposition (CAD) of stable ions. The expulsion of a deuterated alkene from a monodeuterated precursor yields ionized phenol, PhOH·+ (m/z 94). The expulsion of an undeuterated alkene yields PhOD·+ (m/z 95). Without exception, the ratios (PhOD·+/PhOH·+) from precursors in the threo series have values greater than their diastereomers in the erythro series. The ratio of ratios, r = PhOD·+/PhOH·+ for the threo divided by PhOD·+/PhOH·+ for the erythro, has a value of 1.2 for the 2- phenoxy-3-deuteriobutanes and larger values for all of the higher homologues up through the monodeuterated phenoxyoctanes (m + n = 4). The highest degree of stereoselectivity, r = 5.8, is measured for 3-phenoxy-4-deuteriohexane. Experiments with multiply deuterated analogues show that alkene elimination is highly regioselective, unlike the corresponding decompositions of ionized sec-alcohols or their acetates. The fact that a large fraction of ionized sec-alkyl phenyl ethers undergo stereospecific syn-elimination means that mass spectrometry has a useful capacity to distinguish one isotopically labeled diastereomer from another.
