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Protonation thermochemistry of aminoacetonitrile
Author(s) -
Bouchoux Guy,
Guillemin JeanClaude,
Lemahieu Nadège,
McMahon Terrance B.
Publication year - 2006
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.2437
Subject(s) - chemistry , protonation , proton affinity , thermochemistry , proton , conformational isomerism , mass spectrometry , fourier transform ion cyclotron resonance , ion , computational chemistry , analytical chemistry (journal) , molecule , organic chemistry , chromatography , physics , quantum mechanics
Abstract The gas‐phase basicity (GB) of aminoacetonitrile (NH 2 CH 2 CN, 1) has been determined from measurement of proton transfer equilibrium constants in an ion cyclotron resonance mass spectrometer (GB(1) = 789.3 ± 1.0 kJ · mol −1 ). Molecular orbital calculations up to the G2 level demonstrate that protonation occurs preferentially on the nitrogen atom of the NH 2 group, and provide a theoretical proton affinity (PA(1)) of 824.0 kJ · mol −1 . Exact calculation of the entropy associated with hindered rotations and consideration of Boltzman distribution of conformers allow a theoretical estimate of the molar protonation entropy S°(1H + ) − S°(1) = 8.6 J · mol −1 · K −1 . Combining this value with experimental GB(1) leads to an ‘experimental’ proton affinity of 819.2 kJ · mol −1 , in close agreement with the G2 expectation. Copyright © 2006 John Wiley & Sons, Ltd.