Keiichi Ohnishi

Ab initio 13C and 19F NMR chemical shifts calculations for halogenated propanes

Abstract Ab initio GIAO calculations were carried out on halogenated propanes, CClF2–CF2–CXYZ (X, Y, Z; H, Cl or F) and CF3–CXY–CHCl2 (X, Y; H, Cl or F), to estimate their 19F and 13C NMR chemical shifts values, considering all their rotamers. Although, the calculated values tend to be larger for the 19F NMR chemical shifts and smaller for the 13C NMR chemical shifts than the observed values, the calculated values show fairly good linear relationships with the observed values. The Hartree–Fock 6-31G(d) level of theory is of sufficient accuracy for application of assignment and prediction of 13C and 19F NMR chemical shifts of halogenated propanes.

19F nuclear magnetic resonance studies of halogenated propanes

Abstract The relationship between 19 F chemical shifts in halogenated propanes and their structures are elucidated using MNDO calculations to determine the population of rotamers. The pairs of atoms gauche to a fluorine atom and van der Waals interaction between the two terminal substituents are responsible for the 19 F chemical shifts. The differences among chemical shifts in diastereomers are also discussed in terms of the conformation of the molecule.

Comparative studies in the 19F and 1H NMR chemical shifts in 2,2-difluorohalogenated propanes

Abstract Fluorine-19 chemical shifts were compared with 1H chemical shifts in CF3-CF2-R versus CH3-CF2-R, CF2Cl-CF2-R versus CH2Cl-CF2-R and CFCl2-CF2-R versus CHCl2-CF2-R, where R is a substituted methyl group containing all combinations of H, Cl and F. A good linear relationship was found between the 19F and 1H NMR chemical shifts. Conformational analysis using MNDO calculations was applied to the CF3-CF2-R and CH3-CF2-R series to clarify the interaction between the terminal substituents. In halogenated propanes, 19F and 1H chemical shifts are mainly affected by the through-space interaction between the terminal substituents rather than the electronegativity.

13C NMR STUDIES OF HYDROCHLOROFLUOROPROPANES AND CHLOROFLUOROPROPANES

Abstract 13C NMR chemical shifts of 3,3-dichloro-1,1,1-trifluoropropanes (CF3-CXY-CHCl2), 3-chloro-2,2,3,3-tetrafluoropropanes (CClF2-CF2-R), and diastereomers of 1,3-dichloro-1,1,2,3-tetrafluoropropane were studied by analysis using MNDO calculations. In CF3-CXY-CHCl2, 13C NMR chemical shifts of the methylene group are dependent on the electronegativity of the atoms attached to the methylene carbon, and those of the trifluoromethyl group depend on the magnetic anisotropy of neighboring halogen atoms X and Y. In CClF2-CF2-R, the magnetic anisotropy of the atoms gauche to the terminal group and the steric effect of the terminal group are responsible for the 13C NMR chemical shift of a terminal halogenated methyl group, and the inductive effect of the substituent R mainly determines the 13C NMR chemical shift of the difluoromethylene group.

Development of CFC Alternatives

Hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) play a key role as CFC alternatives in many fields to realize the complete phaseout of the regulated CFCs by 1996. The key concept for CFC alternatives, proposed HCFCs and HFCs, their properties and applications, and their future programs will be described.

19FNMR study of HCFC propanes

Abstract Asahi Glass has developed HCFC225ca and HCFC225cb as the promising alternatives to CFC113. CF 3 CF 2 CHCl 2 CClF 2 CF 2 CHClF HCFC225ca HCFC225cb During the preliminary survey for the alternatives to CFC113, we have prepared a number of halogenated propanes and found an interesting relationship between 19 FNMR and the structure of those halogenated propanes. For example, the 19 FNMR chemical shift of CF 3 group in the series of CF 3 CF 2 R is affected by the size of R group as shown in Table 1. Those steric effect will be discussed on the basis of MNDO calculation. 1 . CF 3 chemical shift of CF 3 CF 2 R R Chemical shift CF 3 CH 3 −87.2 ppm CH 2 F −85 ppm CH 2 Cl −84.1 ppm CHF 2 −82.8 ppm CF 3 −83.0 ppm CHClF −81.9 ppm CClF 2 −80.9 ppm CHCl 2 −80.1 ppm CCl 2 F −78.1 ppm CCl 3 −75.6 ppm