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2B-O2-M-1540 PDF
イオンモビリティー質量分析計を用いたシス－トランス異性体の構造と異性化反応機構に関する量子化学的研究
Gas phase structures of positively or negatively charged isomers were investigated using ion mobility mass spectrometry combined with quantum chemical calculation. Reaction mechanisms for isomerization from trans-form to cis-form in deprotonated urocanic acid are also discussed.
To obtain better initial 3D conformations for protonated or deprotonated isomers of urocanic acids, we calculated the optimal structure, the dominant conformers and their steric energies for all possible conformers. This was calculated utilizing the MMFF94S force field and the CONFLEX 7 software. The optimized geometries and heats of formation for the first 21 conformations of protonated and deprotonated molecules in trans- and cis-urocanic acids were calculated using the B3LYP/6-31++G(d,p) level with the Gaussian 16 program. CCSs for the above-mentioned conformers were also calculated by TM.
In both protonated and deprotonated molecules, theoretical CCS values for trans forms were found to be larger than those of cis forms. In the B3LYP/6-31++G(d,p) calculations of the deprotonated molecules, the heat of formation for the most stable cis form was 59.3 kJ/mol more stable than that of the most stable trans form. This is considered to be the reason that the peak corresponding to only cis-forms appeared in ion mobility drift grams.