摘要:

AbstractThe energy barrier to rotation about the C(sp2)C(aryl) single bond in non‐planarN,N‐dimethyl‐,N,N‐tetramethylene‐,N,N‐diisopropyl‐2,6‐difluorobenzamides and inN,N‐dimethyl‐2‐chloro‐6‐fluorobenzamide was investigated by19F{1H} NMR in the presence of an optically active shift reagent. The free energy of activation was calculated from the coalescence temperature of the fluorine signals; the calculation was accomplished using the simple, approximative equation and, also, by the graphical procedure including the (eigen) line width, i.e. without the broadening caused by two‐site exchange. A distinct effect of the size of theN‐substituents on the ΔGc‡values was observ

ISSN:0030-4921    

DOI:10.1002/mrc.1270190302

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractThe solvaton model, incorporating INDO parameters and commonly encountered perturbation procedures, is employed to obtain the variation of1J(N≡C) as a function of the dielectric of the medium (ϵ) for some cyanides and isocyanides. In all cases considered1J(N≡C) is predicted to become increasingly negative as ϵ increases. Changes of up to 2 Hz in1J(N≡C) are expected, with the isocyanides being more sensitive than the cyanides to a chan

ISSN:0030-4921    

DOI:10.1002/mrc.1270190303

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractThe13C NMR spectra of several monocyclic γ‐sultones(1,2‐oxathiolane 2,2‐dioxides) and δ‐sultones(1,2‐oxathiane 2,2‐dioxides) have been determined and are presented herein. The chemical shifts of the ring carbons of these compounds are compared in terms of conformational, electronic and anisotropic differences. Electric field effects may be responsible for the chemical shifts of the C‐α carbon, but do not appear to be important for C‐α. Anisotropic deshielding also appears to be important for the chemical shifts of C‐α, but the effects on C‐α appear to be small. Dipole changes at C‐α and C‐α, induced by back donation of electron density from the ring oxygen to sulfur, may explain the chemical shifts at C‐α. Substituent effects are readily explained in terms of well‐known effects. In general, the carbons closest to the sulfonate group are found to be the most affected, and the carbons of the δ‐sultones proximate to the sulfonate group are found to be more

ISSN:0030-4921    

DOI:10.1002/mrc.1270190304

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractThe high resolution13C NMR spectrum of an eutectic mixture ofN‐(p‐methoxybenzylidene)‐p‐n‐butylaniline andN‐(p‐ethoxybenzylidene)‐p‐n‐butylaniline has been measured as a function of the spinning angle θ between the rotor axis and the magnetic field. The influence of a strong magnetic field and rapid sample spinning gives rise to a specific orientation of this nematic mesophase; if 0<θ<54°44′; the director of the nematic phase is oriented in parallel with the rotor axis, and if 54°44′;<θ<90° it is perpendicular to the rotor axis. At the exact magic angle a nematic sample displays the chemical shifts of the corresponding isotropic liquid. Nematic order is retained at all other director‐field angle values, thus allowing chemical shift anisotropy measurements of the nematic sample or

ISSN:0030-4921    

DOI:10.1002/mrc.1270190305

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractTransmission mechanisms of long‐range FH couplings in several fluorinated derivatives of toluene are analysed carrying out partially restricted molecular orbital calculations at the INDO level of approximation. All π‐components follow the A+B sin2θ dependence, with the dihedral angle defined by the exocyclic CH (or CF) bond and the aromatic ring plane. Four‐ and five‐bond couplings show an important σ‐component, which follows the known zig‐zag rule. Both σ‐ and π‐contributions show a conspicuous insensitivity to fluorine ring substitution. Moreover, four‐bond couplings present an important through‐space component, which is negative for acisarrangement. A sign inversion is found at a dihedral angle between 70° and 80°, which is interpreted as indicating that several throug

ISSN:0030-4921    

DOI:10.1002/mrc.1270190306

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractThe13C NMR spectra oftrans‐ andcis‐fused bicyclo[4.n.0]alkanes, wheren=4, 3 and 2, were determined. The distortion of the six membered ring, which is due to the strain arising from the 1,2 fusion of cyclohexane with a smaller ring, is apparent mainly for the chemical shifts of the ring junction carbons. Both for thetrans‐and for thecis‐fused hydrocarbons the results support a cyclohexane in a chair conformation, distorted to a different degree according to the size of the other ring. The geometries of the different compounds in the series were cal

ISSN:0030-4921    

DOI:10.1002/mrc.1270190307

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractThe proton spectra of phenyltin trichloride including119Sn‐ and117Sn‐satellites have been analysed in isotropic and in oriented solvents. The indirect as well as the direct proton‐proton and proton‐tin coupling constants have been measured. From these the proton‐proton and proton‐tin internuclear distances corrected for harmonic vibrations have b

ISSN:0030-4921    

DOI:10.1002/mrc.1270190308

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractThe radical anion of bacteriochlorophyll a has been monitored by observing differential electron transfer broadening in the1H NMR spectrum of diamagnetic bacteriochlorophyll in the presence of a small amount of chemically produced anion. The use of NMR difference spectra clearly indicates which sites in the anion have greatest spin density; these data are compared with other studies on the cation and anion.

ISSN:0030-4921    

DOI:10.1002/mrc.1270190309

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractRadical species were generated from 4,4′;‐ and 2,2′;‐alkylidenebisphenols during oxidation with free and co‐ordinated [Co(III)]RO2˙Radicals. This simulates the participation of bisphenolic antioxidants in the process of stabilization of hydrocarbons. Phenoxyls are primarily formed, and, depending on the character of the alkylidene bridge, some of them are gradually transformed into phenoxy radicals of the galvinoxyl type. Oxidation of alkylidenebisphenols by oxygen complexed to Co(II) yields co‐ordinated cyclohexadienonyloxy radicals. The character of the alkyl substituents on the phenolic nuclei specifically influences the stability of the generated phenoxy radicals at the applied temperature. The ESR characteristics of the primarily formed phenoxyls, phenoxyls of the galvinoxyl type and co‐ordinated cyclohexadienonyloxyls

ISSN:0030-4921    

DOI:10.1002/mrc.1270190310

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractCarbon‐1 shifts in 1‐dimethylimino‐3‐dimethylamino‐1‐(4‐substituted)phenylprop‐2‐ene perchlorates show high correlation and negative dependence v. a σ set having highfcharacter, similar to α and carbonyl carbon shifts in 4‐substituted styrenes andN,N‐dimethylbezamides, respectively. In sharp contrast with the β‐carbons of the styrenes and the15N absorptions of benzamides, whose shifts show high positive correlations with specific ratios offandRcharacters, the C‐2 shifts remain invariant. In the correlation of the barriers about the N‐CO bond inN,N‐dimethylbenzamides v.f/R, theReffect has been reported to increase dramatically for themeta‐series when values determined in acetonitrile are exchanged with those determined in chloroform and, in theparaseries, to be higher than (normal) in both solvents. α‐Carbon shifts in tris‐para‐substituted triphenylcarbonium ions correlate with a σ set having exceptionally highRcharacter (c. 98 %). Explanations, based mainly on the like

ISSN:0030-4921    

DOI:10.1002/mrc.1270190311

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY