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
D. Cain et al., 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, J ORG CHEM, 66(18), 2001, pp. 6092-6095
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, r
espectively, 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 liter
ature values reported for -53 degreesC. The free-energy barrier to 1,3 oxyg
en-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 ob
tained at the MP2/6-311+G (df,pd) level was compared to a literature barrie
r 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 t
he CF3 group in trifluoromethyl formate (3) was calculated at the MP2/6-31G* level.