Title
Molecular orbital constrained gas electron diffraction study of N-acetyl N'methyl alanine amide Molecular orbital constrained gas electron diffraction study of N-acetyl N'methyl alanine amide
Author
Faculty/Department
Faculty of Sciences. Chemistry
Publication type
article
Publication
Amsterdam ,
Subject
Chemistry
Source (journal)
Journal of molecular structure. - Amsterdam
Theochem: applications of theoretical chemistry to organic, inorganic and biological problems. - Amsterdam, 1981 - 2010
Volume/pages
338(1995) , p. 71-82
ISSN
0166-1280
ISI
A1995RR60800008
Carrier
E
Target language
English (eng)
Full text (Publishers DOI)
Affiliation
University of Antwerp
Abstract
Gas electron diffraction (GED) data were recorded at about 510 K for N-acetyl N'-methyl alanine amide (ALA) and analysed using the Molecular Orbital Constrained Electron Diffraction procedure. The HF/6-31G* geometries of seven conformations were optimized (C-7(eq) (1), C-5 (2), beta(2) (3), C-7(ax) (4), alpha(R) (5), alpha(L) 6), and alpha' (7)) and used as constraints of the GED data analysis. HF/6-31G'' force constants were determined for each conformation and used to calculate mean amplitudes of vibration and shrinkage corrections. It is found that, in the case of ALA, the customarily applied linear approximation for calculating shrinkages yields values which are unacceptably large. Therefore data analyses were performed both without shrinkage and with shrinkages calculated at a lower temperature. Subject to the selected constraints our interpretation of the GED data supports the following conclusions for vapors of ALA at about 500 K: (1) the compound exists in a conformational equilibrium with several significantly populated states; (2) the C-5 form is not less populated than the global energy minimum, C-7(eq); (3) the helical form, alpha(R), is not a significantly populated conformer.
E-info
https://repository.uantwerpen.be/docman/iruaauth/8cf256/0c64228.pdf
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