Title 



Molecular orbital constrained gas electron diffraction study of Nacetyl N'methyl alanine amide
 
Author 



 
Abstract 



Gas electron diffraction (GED) data were recorded at about 510 K for Nacetyl N'methyl alanine amide (ALA) and analysed using the Molecular Orbital Constrained Electron Diffraction procedure. The HF/631G* geometries of seven conformations were optimized (C7(eq) (1), C5 (2), beta(2) (3), C7(ax) (4), alpha(R) (5), alpha(L) 6), and alpha' (7)) and used as constraints of the GED data analysis. HF/631G'' 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 C5 form is not less populated than the global energy minimum, C7(eq); (3) the helical form, alpha(R), is not a significantly populated conformer.   
Language 



English
 
Source (journal) 



Journal of molecular structure.  Amsterdam
Theochem: applications of theoretical chemistry to organic, inorganic and biological problems.  Amsterdam, 1981  2010  
Publication 



Amsterdam : 1995
 
ISSN 



00222860
 
Volume/pages 



338(1995), p. 7182
 
ISI 



A1995RR60800008
 
Full text (Publisher's DOI) 


  
Full text (publisher's version  intranet only) 


  
