F. Van Gaever

Differentiation between regio- and stereoisomers of bicyclo[3,2,0]heptanone-2 derivatives by chemical ionization mass spectrometry

Abstract The c.i. (isobutane) mass spectral behaviour was examined for a series of bicyclo[3,2,0]heptanone 2 derivatives, produced by (2π+2π) photocycloaddition reactions. The c.i. (isobutane) data allow unequivocal differentiation between hh- and ht-regioisomers. In some cases, a further assignment of the syn or anti form can also be made on the basis of the intensity of the protonated molecule ion.

Transalkylierung und protonenkatalysierte C-C-Spaltung bei n-Butyl-und n-Pentylbenzol in der Gasphase / Transalkylation and Proton Catalyzed C-C-Cleavage of Gaseous n-Butyl and w-Pentyl Benzenes

Abstract The investigation of several 13carbon and deuterium labelled n-butyl and n-pentyl benzenes demonstrate that chemical ionization (reagent gas: methane) induces specific carbon-carbon bond cleavages of the alkyl group. The extent of competing reaction channels as for instance direct alkene elimination versus dealkylation/reprotonation is analyzed. Partial hydrogen exchange processes between reagent ions and substrate molecules are restricted to the phenyl ring. Intramolecular exchange reactions between the side chain and the aromatic ring which are typical for the open shell molecular ions of alkyl benzenes are not observed for analogous closed shell cations.

Chemical Ionization Mass Spectrometry: A Useful Stereochemistry Probe

The helium charge exchange and the isobutane chemical ionization spectra of 4-methoxy cyclohexanecarboxylic acid ethyl esters (1c and 1t), 2,6-dimethyl-4-hydroxytetrahydropyranes (2c and 2t), 2,4,6-trimethyl-4-hydroxytetrahydropyranes (8c and 3t), and 2,7-dimethoxy-cis-decalins (4c and 4t) have been screened for correlations with the stereochemistry of these molecules. From these data it appears that chemical ionization is especially suited for configurational assignments in epimeric molecules.

Correlations between the Stereochemistry and the Chemical Ionization Spectra of Epimeric 3,4-Dimethyl-1,2-cyclopentanediols

The eight epimeric 3,4-dimethyl-l,2-cyclopentanediols have been investigated as bistrimethylsilyl (TMS) ethers and as diacetates by means of isobutane chemical ionization (CI). Correlations between stereochemistry and CI spectra appear to be limited in the case of the TMS ethers. All eight diacetates, however, can be unequivocally identified from their isobutane CI spectra.