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.
Free-energy barriers of 9.85 and 11.91 +/- 0.15 kcal/mol at -70.8 degrees C were found by dynamic NMR spectroscopy for the E-to-Z and Z-to-E conversions, respectively, of methyl formate (1) enriched in 13C to 99% for the carbonyl carbon [methyl formate 13C (2)]. These barriers are higher than the literature values reported for -53 degrees C. 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.
Cain
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D
Department of Chemistry, Jackson State University, Jackson, Mississippi 39217-0510, USA.
Pawar
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DM
Stewart
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M
Billings
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H
Noe
E A
EA
D002247:Carbon Isotopes; D003198:Computer Simulation; D005563:Formic Acid Esters / Q000737:chemistry*; D006845:Hydrocarbons, Fluorinated / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008956:Models, Chemical; D008968:Molecular Conformation; D010100:Oxygen / Q000737:chemistry*
D002247:Carbon Isotopes; D005563:Formic Acid Esters; D006845:Hydrocarbons, Fluorinated; C025468:methyl formate; D010100:Oxygen