Proton and fluorine magnetic resonance studies of some benzoyl fluoride derivatives. Sensitivity of the fluorine shifts to intramolecular van der Waals interactions and steric effects

Abstract

. Can. J. Chem. 55,3936 (1977).The syntheses and the analyses of the high resolution proton and fluorine magnetic resonance spectra of the 3-fluoro-4-methyl-, 2-fluoro-5-chloro-, 2-fluoro-6-chloro-, 2,6-difluoro-, and of the pentafluorobenzoyl fluorides are reported. The spin-spin coupling constants over five bonds between the sidechain fluorine-19 and the ring protons are sensilive to intrinsic substituent perturbations. Their use in the deduction of conformational preferences is much more problematical than is the use of the corresponding proton-proton couplings in benzaldehyde derivatives. The 2-iluoro-6-chloro compound is nonplanar, as indicated by a finite magnitude of the longrange proton-fluorine coupling over six bonds. The nonplanarity is also indicated by a comparison of the through-space fluorine-fluorine coupling to those in the other compounds. The chemical shift of the sidechain fluorine moves to low field by over 35 ppm as the size of the two ortho substituents increases. The individual shifts are discussed in terms of intramolecular van der Waals interactions and of out-of-plane twisting of the COF group. IntroductionThe long-range coupling constants between the aldehydic proton and ring protons or fluorine nuclei in benzaldehyde (1) and its derivatives (2-7) indicate that 5~mH,CH0, the coupling involving protons in the meta position to the aldehyde group, is not very sensitive to intrinsic substituent effects but that it is highly stereospecific. In 1,

Some unique properties of in 2-fluorotoluene derivatives. Conformational dependence

“…The 4,5-dinitro and the 4,6-dinitro derivatives were made (12), although in decent agreement with experiment for 6~i.C"3 by nitration of 4-nitro-2-fluorotoluene. The synthesis of the 4-(3) and 5~:ft'" (8, apparently (14) overemphasize the proxcarbonyl fluoride derivative has been described (17). The 6-nitro and imate and/or a mechanisms in 2-fluorotoluene.…”

Theoretical and experimental conformational preferences of the aldehyde and fluoroaldehyde groups in 2-methylbenzaldehyde, 2-trifluoromethylbenzaldehyde, and 4-chloro-2-methylbenzoyl fluoride. Proximate couplings

“…The latter are not always in number of their derivatives by a variety of tech-agreement with those found at room temperature, a niques (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). In solution at least (1,14), the fact perhaps attributable to varying solvent effects twofold barrier to rotation about the exocyclic car- (20) in the experiments; particularly if the conforbon-carbon bond is 31.4 kJImol for benzaldehyde mational isomers have rather different dipole m0-and 29.3 kJImol for benzoyl fluoride, so that at am-merits (1 1).…”