Molecular structure and conformational composition of methyl chloroacetate: An electron-diffraction and ab initio molecular orbital investigation

作者：Aarset Kirsten^*; Boldermo Kjell Gunnar; Hagen Kolbjorn

来源：Journal of Molecular Structure, 2010, 978(1-3): 104-107.

DOI：10.1016/j.molstruc.2010.02.020

• Gas-phase electron-diffraction
• Ab initio calculation
• Structure
• Conformation
• Methyl chloroacetate

The molecular structure and conformational composition of methyl chloroacetate, H(2)ClC-C(=O) -O-CH(3), have been determined by gas-phase electron-diffraction (CEO), using results from ab initio molecular orbital calculations (HF, MP2 and MP3/6-311+G(d,p)) to obtain constraints on some of the structural parameters. The molecules exist in the gas-phase at 25 C as a mixture of two stable conformers: syn with C-Cl eclipsing C=O and gauche with C-H approximately eclipsing C=O. In both of these conformers O-CH(3) is also eclipsing C=O. The experimentally observed conformational composition at 25 degrees C was 36(8)% syn and 64(8)% gauche (parenthesised values are 2u), corresponding to a free energy difference between conformers of Delta G(exp)degrees, = 1.4(9) kilmol. The corresponding theoretical values obtained for Delta G degrees are 1.1 kJ/mol (HF), 2.3 kJ/mol (MP2), and 2.4 kJ/mol (MP3). The results for the principal distances (r(h1)) and angles (41) for the major gauche conformer obtained from the combined GED/ab initio study (2 sigma uncertainties) are r(CO-CCl)= 1.502(9)angstrom, r(C-H)= 1.084(6)angstrom (average value), r(C-Cl) = 1.782(4) A, r(C=O)= 1.213(4)angstrom, r(CO-O)= 1.346(4)angstrom, r(CH(3)-O)= 1.468(10)angstrom, <C-C-Cl = 110.0(6), <C-C=O= 124.7(6)degrees, <C-C-O = 108.3(10)degrees, <C-O-C= 115.9(8)degrees, phi(Cl-C-C=O)= 111(2)degrees, phi(C-O-C=O) = 3(3)degrees. C) 2010 Elsevier B.V.

• 出版日期2010-8-20