The proximate spin–spin coupling, ⁵J(F,CH₃), as a quantitative conformational indicator in alkylfluorobenzenes and related compounds

Abstract

The through-space or proximate nuclear spin-spin coupling constant, 'J(F,CH3) = 'J, between methyl protons and ring fluorine nuclei in alkylfluorobenzenes is postulated as 'J/HZ = A(cos4 0) + sin^ (0/2)), 0 being the torsional angle for the C, 2-C, , bond. A and B are obtained from the known internal rotational behaviour in 2,6-difluoroethylbenzene and the corresponding cumene derivative. The parameterization is tested on the observed ' 5 in derivatives of 2,4,6-tri-tert-butyl-and 2,4,6-tri-isopropyl-fluorobenzene, in 2-chloro-6-fluoroisopropylbenzene, 2,6-difluoro-a-methylstyrene, and N-methyl-8-fluoroquinolinium halides. A prediction is made for ' J in 2,6-difluoro-tert-butylbenzene. It appears that the present parameterization allows the derivation of approximate torsional potentials from proximate couplings, for example in a , adimethyl-2,6-difluorobenzyl alcohol.

Novel Cr (III), Fe (III) and Ru (III) Vanillin Based Metallo‐Pharmaceuticals for Cancer and Inflammation Treatment: Experimental and Theoretical Studies

“…All computations were performed by Gaussian 09 W software package . B3LYP/GENECP method utilizing 6–311++G** basis set for C, H, N, and O‐atoms and LANL2DZ basis set for trivalent (Cr, Fe and Ru) atoms to compute the geometries of the ligand and the desired complexes . By utilizing HOMO and LUMO energies values for the ligand and its as‐prepared complexes computed at the same level, its electronegativity, χ, can be computed from: χ = (I + A)/2, chemical hardness, η = (I‐A)/2, ω = μ 2 /2𝛈 (electrophilicity) and global softness S = 1/2η where I and A are ionization potential and electron affinity, and I = −E HOMO and A = −E LUMO, respectively .…”

Conformation and Stereodynamics of Symmetrically Ortho-Disubstituted Aryl Carbinols and Aryl Ethers

“…The low-temperature 19 F spectra of 1 (Figure ) show indeed how the single signal of the two ortho fluorine atoms broadens on cooling and eventually decoalesces at −169 °C into a pair of partially overlapping signals exhibiting a quite different line width: their integrated intensities indicate that the ratio is 1:1 the free energy of activation (Δ G ⧧ = 4.6 ± 0.3 kcal mol -1 ) for the rotation that makes the ortho positions equivalent (homotopic) could be obtained .…”

“…Ab initio computations (and Molecular Mechanics as well) of 1 (X = F, R = Me) indicate that the conformations of type C (anticlinal) and D (synclinal 13 ) do not correspond to energy minima (actually they represent transition states) and that the minimum corresponding to conformation A (synperiplanar 13 ) has an energy higher (by 0.65 kcal mol -1 , according to ab initio) than that of conformation B (synclinal 13 ), indicating that the latter should be the more populated species at low temperature. The asymmetry of the most stable conformer B implies the existence of two enantiomeric forms (+sc and −sc), but the barrier for their interconversion, involving the passage through the scarcely populated conformer A (sp), is predicted to be very low: for instance, the ab initio computed value for 1 is 3.15 kcal mol -1 , as shown in Scheme…”