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Ab initio studies of structural features not easily amenable to experiment. 42. Molecular geometries and conformational analysis of methylbutanoate

✍ Scribed by Lothar Schäfer; V. J. Klimkowski; C. Van Alsenoy; J. D. Ewbank; J. N. Scarsdale

Publisher
John Wiley and Sons
Year
1985
Tongue
English
Weight
578 KB
Volume
6
Category
Article
ISSN
0192-8651

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✦ Synopsis

Conformational energy profiles were calculated for T ~, the C-C-C=O torsion, and 7 2 , the C -C -C -C torsion, of methyl butanoate, using Pulay's ab initio gradient procedure at the 4-21G level with geometry optimization at each point. In addition, the structures of seven conformations were fully relaxed, including the energy minima ( T ~, T ~) = (0, -60), (0,1801, (120,180), (120, -601, and the maxima (0, 0), (180,180), and (60, -60). The calculated geometries confirm the previously formulated rule that, in

systems, the following rules can be formulated, incorporating results from previous studies of butanal, butanoic acid, and 2-pentanone: (1) C(S)-H, < C(S)-Ha in all the conformers in which the &methyl group is remote from the ester group; whereas, in all the conformers in which nonbonded interactions are possible between the C(G)-methyl and the ester groups, the bonding pattern is affected by a C-H...O=C interaction. (2) In the most stable conformers, (0,601, C(p)-H,, < C(p)--H., and C(y)-H, < C(y)-Hs, regardless of X. (3) The average C-C bonds in the TZ = 180" conformers are consistently shorter than those with T~ = 60" (compared at T~ constant). In the most stable conformations ( T ~ = 0", T~ = 60"or 180"), the bonding sequence is consistently C(a)-c(p) < C(p)-c(y) < c(y)-c(S); whereas, when T~ = 120", C(cu)-C(p) < C(p)-C(y) > C(y)-C(S). *Bevoegdverklaard Navorser, Belgian National Science Foundation (NFWO).

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