Title 



Methacrolein in the gas phase, investigated by electron diffraction, microwave and vibrational spectroscopy, supplemented with ab initio calculations of geometries and force fields
 
Author 



 
Abstract 



The structure of methacrolein was studied by the analysis of gasphase electron diffraction, Microwave and infrared (IR) data. The experimental data are supported with geometrical constraints taken from geometry relaxed ab initio calculations and vibrational constraints taken from force field calculations, both at the 42 1 G level. All data are in accord with the gas phase consisting of ap and sp conformers. An independent vibrational analysis was performed leading to an improved assignment of the IR frequencies. Assignments were found to depend upon the scaling of the ab initio force field, particularly on the grouping of the symmetry coordinates. The scaled force field reproduced the IR spectra with rootmeansquare deviations of 15.5 cm1 (ap) and 18.5 cm1 (sp), and largest discrepancies of 36 cm1 (ap) and 39 cm1 (sp). Differences between individual force constants of the two forms could be rationalized. At room temperature the ratio ap: sp = 89 : 11 was found, but we consider the resulting energy (enthalpy) difference of DELTAH = 1.15 kcal mol1 as a lower limit and the experimental value of 2.17 kcal mol1 [Durig et al., Spectrochim. Acta, Part A, 42 (1986) 891 as an upper limit to the true value. The data are in accord with planar heavy atom skeletons for both the ap and sp forms. Subject to the ab initio constraints, the r(alpha)degrees and r(g) geometry are reported. Leastsquares refinements showed equal applicability of two approaches to bring 421 G geometries to an r(g) basis, one using individual, additive correction parameters and the other using regressionbased correction parameters.   
Language 



English
 
Source (journal) 



Journal of molecular structure.  Amsterdam  
Publication 



Amsterdam : 1993
 
ISSN 



00222860
 
Volume/pages 



299(1993), p. 4359
 
ISI 



A1993MB73900005
 
Full text (Publishers DOI) 


  
Full text (publishers version  intranet only) 


  
