Degree-of-freedom activation effects in proton-transfer chemical ionization mass spectrometry of open-chain and cyclic alcohols and diols

SummaryThe temperature dependence of the isobutane chemical ionization (CI.) mass spectra of 54 open-chain, cyclic and unsaturated C5-to Clo-alcohols was studied at temperatures ranging from 60 to 250", and enthalpy changes were calculated for the corresponding main reactions of typical alcohols.The CI. reactivity is controlled by the temperature and the substrate structure as usual, and in addition, by the molecular size. The combination of thermal, structural and substrate-size effects leads to the following main conclusions.At low-reactivity conditions, i.e. at 150" or less, the alcohols with less than 11 C-atoms give four distinct types of spectra, with ( M -OH)+ usually as the base peak. The characteristic ions are MC4H$ and (M-H)' for primary, M H + and (MC4H9-H20)' for secondary, (MC4H9-H20)+ for tertiary and allyl-type alcohols. Configurational assignments of stereoisomeric alcohols are also possible, by means of steric compression and shielding effects. The MH+/(M-OH)+ ratio in the spectra of epimeric methylcyclohexanols is at least 3 to 4 times higher for the isomers with mainly axial OH-group conformation compared to the equatorial isomers. Stereospecific ( M -H)+ ions are apparently formed from trans-2-methylcyclopentanol and endo-norbornan-2-01 by a favorable abstraction of the unshielded H ((1)-atoms versus normal behavior of the other epimers.While the spectra recorded at 200" show almost exclusively ( M -OH)+ ions, those at 250" give nevertheless some C-skeleton information through the temperature dependent decomposition of the ( M -OH)+ ions.

Section: T ( M -H)+ ( M -Oh)+ Mlz 83 (M-h)+ (M-oh)+ (M-h20)' (M-h-hmentioning

confidence: 97%

Section: Helvetica~himica a C T A -V O I ~~mentioning

confidence: 97%

Section: Helvetica~himica a C T A -V O I ~~mentioning

confidence: 99%

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confidence: 97%

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confidence: 99%

See 3 more Smart Citations

Temperature Dependence of the Isobutane Chemical Ionization Mass Spectra of Open‐chain and Cyclic Alcohols; Structural, Stereochemical and Molecular‐Size Effects. A reevaluation of the isobutane chemical ionization of alcohols

Winkler

Gülaçar

Mermoud

et al. 1983

Ammonia chemical ionization mass spectrometry of alcohols: Structural, stereochemical, molecular‐size and temperature effects

Gülaçar

Mermound

Winkler

et al. 1984

SunimuryAmmonia chemical ionization (CI) mass spectra of various, open-chain, cyclic and unsaturated C,to C,,,-alcohols were obtained at source temperatures ranging from 60" to 250°C. The reactivity of the ammonia adduct ion MNH: and its fragmentation channels are characteristic for the substrate structure. Although strongly temperaturedependent, the spectra give nevertheless information on the OH-group environment as well as on the C-skeleton at any source temperature. Primary, secondary and tertiary alcohols as well as allylic and simple olefinic alcohols can be distinguished by their spectra, which show ammonium adduct ions [MNHJ, adduct dehydrogenation ions [MNH,-H2]', ammonium substitution ions [MNH,-H,O]+ and [M-OH]+-ions as the main characteristic peaks. Moreover, configurational assignments of stereoisomeric alcohols are possible for larger substrate-sizes and source-temperature ranges than with isobutane CI mass spectrometry. Homologous MNHl-ions show molecular-size control of fragmentation and linear MNH,'-ions are less stable than branched isoiners due to incomplete energy randomization.

Gas‐Phase Basicities of Open‐Chain and Cyclic Diols from Dissociations of Ammonium Adducts, Protonated Mixed Dimers and ICR Experiments. Structural and Stereochemical Effects

Guenat

Houriet

Ståhl

et al. 1985

Dedicated to Prof. Tino Gaumann on the occasion of his 60" birthday (12.VIII.85 )The gas-phase basicity (GB) of open-chain and cyclic diols and triols has been determined by the method of dissociation of proton-bound adducts using 1 ,Cbutanediol and cis-and trans-1,3-cyclohexanediol as reference compounds. The GB and proton affinity (PA) of the two cyclic reference diols have been obtained in ion-cyclotronresonance experiments. The unimolecular and the collision-activated dissociations of the ammonium adducts of the polyols allow a ranking of their GB and PA values which reflects the various structural and stereochemical effects. The possibility of internal H-bonding between the two OH groups leads to a strong increase of the PA values. The incremental effect of chain length on the PA of open-chain diols is evidenced, as well as the detailed influence of the configuration and conformation for cyclopentane-and cyclohexanediols, and -trials. These experiments also emphasized the predominant role of doubly H-bound ammonium/diol chelate conformations as opposed to singly proton-bound species.Introduction. -The chemical ionization (C1) spectra of aliphatic diols show distinct features according to the structure and configuration of the molecular system. Internal stabilization of the product ions has been evidenced both under positive-CI [I] and negative-CI [2] conditions.