Barriers to rotation in methyl formate by dynamic NMR spectroscopy and barriers to 1,3 oxygen-to-oxygen migration in methyl formate and trifluoromethyl formate by ab initio calculations

被引:20
作者
Cain, D [1 ]
Pawar, DM [1 ]
Stewart, M [1 ]
Billings, H [1 ]
Noe, EA [1 ]
机构
[1] Jackson State Univ, Dept Chem, Jackson, MS 39217 USA
关键词
D O I
10.1021/jo0103726
中图分类号
O62 [有机化学];
学科分类号
070303 ; 081704 ;
摘要
Free-energy barriers of 9.85 and 11.91 0.15 kcal/mol at -70.8 degreesC were found by dynamic NMR spectroscopy for the E-to-Z and Z-to-E conversions, respectively, of methyl formate (1) enriched in C-13 to 99% for the carbonyl carbon [methyl formate C-13 (2)]. These barriers are higher than the literature values reported for -53 degreesC. The free-energy barrier to 1,3 oxygen-to-oxygen migration of the methyl group in methyl formate was determined by ab initio calculations at several levels. The value of 58.7 kcal/mol obtained at the MP2/6-311+G (df,pd) level was compared to a literature barrier for this process (MINDO/3) and to barriers for related compounds. A free-energy barrier of 63.0 kcal/mol for the oxygen - to - oxygen migration of the CF3 group in trifluoromethyl formate (3) was calculated at the MP2/6-31+G* level.
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页码:6092 / 6095
页数:4
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