An ab-initio study of the C3H6-HX, C2H4-HX and C2H2-HX hydrogen-bonded complexes with X=F or Cl.
MP2/6-31G** ab-initio molecular orbital calculations have been performed to obtain geometries, H-bond energies and vibrational properties of the C3H6-HX, C2H4-HX and C2H2-HX H-bonded complexes with X=F or Cl. The more pronounced effects on the structural parameters of the isolated molecules due to complexation are verified to the CC and HX bond lengths, which are directly involved in the H-bond formation. They are increased after complexation. The calculated H-bond lengths for the hydrogen complexes for X=F are shorter than those for x-Cl by about 0.55 A, whereas the corresponding experimental value is 0.58 A. The H-bond energies are essentially determined by the nature of the proton donor molecule. For X=F, the AE mean value is 20 kJ/mol, whereas it is approximately 14.5 kJ/mol for X-Cl. The H-bond energies including zero-point corrections show a good correlation with the H-bond lengths. The more pronounced effect on the normal modes of the isolated molecules after complexation occurs to the H-X stretching mode. The H-X stretching frequency is shifted downward, whereas its IR intensity is much enhanced upon H-bond formation. The new vibrational modes arising from complexation show several interesting features.
Lopes
K C
KC
Departamento de Química, Universidade Federal da Paraiba, João Pessoa, Brazil.
Pereira
F S
FS
Ramos
M N
MN
de Arauijo
R C
RC
D002712:Chlorides / Q000737:chemistry*; D005459:Fluorides / Q000737:chemistry*; D006860:Hydrogen Bonding; D008956:Models, Chemical; D013055:Spectrophotometry, Infrared; D014732:Vibration
D002712:Chlorides; D005459:Fluorides