Table 2.

Geometric parameters optimized at the B97D/aug-cc-pvTz and B97D/aug-cc-pv(T+d)z levels for methyl acetate and thioacetic acid S-methyl ester, respectively ^a.

	Gas	CHCl3	CH3CN	Exp.
CH3COOCH3, cis b
C-C	1.514(1.500)	1.511	1.510	1.496
C=O	1.212(1.212)	1.217	1.219	1.206
C-O	1.363(1.351)	1.357	1.354	1.357
TS	1.393	1.389	1.387
O-CH3	1.448(1.437)	1.453	1.454	1.438
C-C=O	125.8(125.9)	125.6	125.6
O=C-O	123.8(123.3)	123.6	123.6	123.0
C-O-CH3	115.4(114.1)	116.1	116.3	116.4
TS	114.6	114.5	114.5
HCC=O	1.1(0.2)	0.6	0.5
CH3COOCH3, trans
C-C	1.519	1.514	1.511
C=O	1.207	1.215	1.218
C-O	1.370	1.361	1.358
O-CH3	1.440	1.449	1.453
C-C=O	124.0	124.1	124.2
O=C-O	118.5	118.0	117.8
C-O-CH3	120.4	120.3	120.3
HCC=O	0.1	0.1	0.1
CH3COSCH3, cis c
C-C	1.520(1.507)	1.517	1.516	1.499
C=O	1.213(1.216)	1.218	1.220	1.214
C-S	1.797(1.769)	1.791	1.788	1.781
rot 90°	1.885	1.883	1.883
S-CH3	1.820(1.798)	1.820	1.820	1.805
C-C=O	123.4(123.6)	123.3	123.2	123.4
O=C-S	123.1(122.7)	123.1	123.1	122.8
C-S-CH3	99.9(98.5)	100.7	101.1	99.2
rot 90°	95.9	96.3	96.4
HCC=O	180.0(178.8)	178.7	178.5	143.1
CH3COSCH3, trans
C-C	1.518	1.514	1.511
C=O	1.212	1.218	1.221
C-S	1.805	1.796	1.793
S-CH3	1.829	1.828	1.828
C-C=O	123.9	124.0	124.0
O=C-S	118.1	117.9	117.8
C-S-CH3	105.1	105.2	105.3
HCC=O	0.0	0.6	0.6

^a Distances in Å, angles in degrees. Cis and trans structures correspond to O=C-X-C (X=O, S) torsional angles of very close to 0° and 180°, respectively, heavy atoms are nearly coplanar. Values in parentheses from MP2 optimization with the same basis set. B97D parameters with characteristic changes in the transition state geometry or for the X=C-Y-C = 90° structures (rot 90°) are indicated. ^b Experimental data from ref. [32]. Corrected geometric parameters based on gas electron diffraction experiment. ^c Experimental data from gas electron diffraction, ref. [33].