Ab initio molecular orbitals study of the conformational preference in alpha-cyano-alpha-fluorophenylacetic acid ester.
The origin of conformational preference in alpha-cyano-alpha-fluorophenylacetic acid (CFPA) methyl ester that is a model system of alpha-cyano-alpha-fluoro-p-tolylacetic acid (CFTA) esters was theoretically investigated by means of DFT and MP2 calculations. Two stable conformations having the C-F bond syn and anti to the C=O bond, respectively, were obtained for CFPA methyl ester. A small energy difference (0.9 kcal mol-1 at the MP2(fc)/6-31++G(d,p)) was found between the two conformations. From the molecular orbital analysis based on the Natural Bond Orbital analysis and supported by calculations using the Orbital Deletion Procedure technique, we found that sigma-(sigma*+pi*)(C=O) and sigma-sigma*(Ph) and pi(Ph)-sigma* hyperconjugations are the main factors responsible for the conformational preference. The role of the fluorine atom on the stereogenic center was also clarified.
Sahnoun
Riadh
R
Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan. rsahnoun@gmail.com
Fujimura
Yuichi
Y
Kabuto
Kuninobu
K
Takeuchi
Yoshio
Y
Noyori
Ryoji
R
D000085:Acetates / Q000737:chemistry*; D004952:Esters / Q000737:chemistry; D006845:Hydrocarbons, Fluorinated / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D013816:Thermodynamics; D014050:Toluene / Q000031:analogs & derivatives* / Q000737:chemistry
D000085:Acetates; D004952:Esters; D006845:Hydrocarbons, Fluorinated; C524931:alpha-cyano-alpha-fluorophenylacetic acid methyl ester; C401482:cyanofluoro-p-tolylacetic acid; D014050:Toluene