Protonation thermochemistry of aminoacetonitrile.
The gas-phase basicity (GB) of aminoacetonitrile (NH2CH2CN, 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 x mol(-1)). Molecular orbital calculations up to the G2 level demonstrate that protonation occurs preferentially on the nitrogen atom of the NH2 group, and provide a theoretical proton affinity (PA(1)) of 824.0 kJ x 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 degrees (1H+) - S degrees (1) = 8.6 J x mol(-1) x K(-1). Combining this value with experimental GB(1) leads to an 'experimental' proton affinity of 819.2 kJ x mol(-1), in close agreement with the G2 expectation.
Bouchoux
Guy
G
Laboratoire des Mécanismes Réactionnels, UMR CNRS 7651, Département de Chimie, Ecole Polytechnique, 91128 Palaiseau Cedex, France. bouchoux@dcmr.polytechnique.fr
Guillemin
Jean-Claude
JC
Lemahieu
Nadège
N
McMahon
Terrance B
TB
D000465:Algorithms; D000607:Aminoacetonitrile / Q000737:chemistry*; D017357:Cyclotrons; D005583:Fourier Analysis; D013058:Mass Spectrometry; D008958:Models, Molecular; D011522:Protons; D013816:Thermodynamics
D011522:Protons; D000607:Aminoacetonitrile