ISSN:
0192-8651
Keywords:
Computational Chemistry and Molecular Modeling
;
Biochemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Computer Science
Notes:
Conformational energy profiles were calculated for τ1, the C—C—C=O torsion, and τ2, 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 (τ1, τ2) = (0, -60), (0, 180), (120, 180), (120, -60), and the maxima (0, 0), (180, 180), and (60, -60). The calculated geometries confirm the previously formulated rule that, in saturated hydrocarbons, a C—H bond trans to a C—C bond (C—Hs) is consistently shorter than a C—H bond (C—Ha) trans to another C—H bond. Specifically, for X—C(α) (= O)—C(β)—C(γ)—C(δ) systems, the following rules can be formulated, incorporating results from previous studies of butanal, butanoic acid, and 2-pentanone: (1) C(δ)—Hs 〈 C(δ)—Ha in all the conformers in which the δ-methyl group is remote from the ester group; whereas, in all the conformers in which nonbonded interactions are possible between the C(δ)-methyl and the ester groups, the bonding pattern is affected by a C—H⃛O=C interaction. (2) In the most stable conformers, (0, 60), C(β)—Ha 〈 C(β)—Hs, and C(γ)—Ha 〈 C(γ)—Hs, regardless of X. (3) The average C—C bonds in the τ2 = 180° conformers are consistently shorter than those with τ2 = 60° (compared at τ1 constant). In the most stable conformations (τ1 = 0°, τ2 = 60° or 180°), the bonding sequence is consistently C(α)—C(β) 〈 C(β)—C(γ) 〈 C(γ)—C(δ); whereas, when τ1 = 120°, C(α)—C(β) 〈 C(β)—C(γ) 〉 C(γ)—C(δ).
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jcc.540060110
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