Conformational preferences and orbital interactions for methyl haloacetates.
Conformational preferences and orbital interactions of methyl chloroacetate (1), methyl bromoacetate (2) and methyl iodo-acetate (3) were analyzed using experimental infra-red data, theoretical calculations and NBO analyses. The conformational equilibria of compounds 1-3 can be represented by their cis and gauche rotamers. The gauche form of 1 is stable in the vapour phase and in a non-polar solvent, but the cis is predominant in a polar solvent. For 2 the gauche form is more stable than the cis, in both the vapour and liquid phases, but for compound 3 only the gauche form was observed both in vapour phase as in solution. These conformational preferences were attributed to the orbital interaction between two antibonding orbitals pi(C=O)(*)-->sigma(C-X)(*). This unexpected interaction was possibly due to the high (0.2) electron density on pi(C=O)(*), which results from the interaction between ether oxygen lone pair and pi(C=O)(*).
Tormena
Cláudio F
CF
Chemistry Department, FFCLRP, São Paulo University, Av. Bandeirantes 3900, 14040-901 Ribeirão Preto, SP, Brazil. tormena@ffclrp.usp.br
Yoshinaga
Fabiana
F
Doi
Telma R
TR
Rittner
Roberto
R
D000085:Acetates / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry; D002251:Carbon Tetrachloride / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D012997:Solvents; D013053:Spectrophotometry / Q000379:methods; D013055:Spectrophotometry, Infrared; D013237:Stereoisomerism
D000085:Acetates; D012997:Solvents; D002244:Carbon; D002251:Carbon Tetrachloride