Hyperfine coupling constants of CH 2 protons in paramagnetic aromatic systems

Comparisons of 'H chemical shifts and charge densities (determined by C N D 0 / 2 MO calculations) for 4-substituted derivatives of styrene, toluene, benzylchloride, and N,N,N-trimethylphenylammonium ion indicate that the chemical shifts primarily reflect intramolecular electronic effects. These effects are reflected by correlations of 'H chemical shifts with the F and R reactivity parameters of Swain and Lupton. It is concluded that it is valid to correlate substituent-induced chemical shifts for aromatic derivatives with divided reactivity parameters provided that ( I ) chemical shifts are measured at infinite dilution in a non-polar medium and'(2) at least ten derivatives of each family are investigated.Calculations for 4-substituted toluenes indicate that there will be a small conformational dependence for substituent-induced benzylic proton chemical shifts.La comparaison des deplacements chimiques ' H et des densites de charge (dktermintes par la mkthode CNDO/2 MO) pour des derives substitues en position 4 du styrene, du toluene, du chlorure de benzyle et de I'ion N,N,N-trimkthylphinyl ammonium indiquent que les deplacements chimiques refletent principalement les effets Clectroniques intramolCculaires. Ces effets apparaissent sous forme de correlation entre les deplacements chimiques 'H avec les parametres de rkactivite F e t R de Swain et Lupton. On en conclut qu'il est valide de faire une correlation entre le substituant et les diplacements chimiques induits dans les derives aromatiques possedant des parametres de reactivite divises pourvu (I) q u e les deplacements chimiques soient mesurks dilution infinie dans un solvant non-polaire et (2) qu'au moins dix derives de la famille soient etudits.Les calculs pour les toluenes substituCs en position 4 indiquent qu'il y a une petite dependance conformationnelle pour les dkplacements chi~niques des protons benzyliques qui ont ett induits p a r les substituants.[ (1) derivatives) should reflect resonance effects since R = 0 for the N(CH,),+ group (3). They also [I]

supporting

confidence: 89%

A Reconsideration of the Validity of Correlating Substituent-induced Proton Chemical Shifts in Aromatic Derivatives with Reactivity Parameters

Dawson¹,

Hamer²,

Reynolds³

1974

“…This is an alkyl substituted naphthalene and the coupling constants of its e.p.r. spectrum are consistent with those of a number of other such species including 1,8-dimethylnaphthalene (3,4), trihydropyrenyl (I), and acenaphthene (5). The dynamic aspects of this radical as reflected in the alternating linewidth of the p protons are consistent with those of the related species trihydropyrenyl (1 ) and the hexahydropyrene anion (6,7).…”

Section: Introductionsupporting

confidence: 79%

The Electron Paramagnetic Resonance Spectrum of the Phenalane Anion

Paskovich¹,

Reddoch²

1972

The phenalane anion has been prepared by the reaction of alkali metals in ether solutions of both phenalane and phenalene. The electron paramagnetic resonance spectra of both the radical and of its ion pairs with sodium and with lithium in THF are reported. At room temperature there is an alternating linewidth involving the /I protons caused by conformational interconversion of the axial and equatorial positions. At -80 "C they protons are not equivalent and the corresponding coupling constants are resolved.L'anion phenalane a Ct C prepart par l'actionedes metaux alcalins sur des solutionsCtherees de phtnalaneet de phtnaltne. Les spectres r.p.e. du radical ainsi que cew des paires d'ions formees entre celui-ci et le sodium ou le lithium dans le THF, sont rapportes. A la temperature de la pitce, il se produit une alternation de largeur de raie impliquant les protons en /I et provoqute par une interconversion conformationnelle des positions axiales et Cquatoriales. A -80 "C les protons en y ne sont pas equivalents et les constantes correspondantes de couplage peuvent &tre rtsolues.

“…spectrum of p-dimethoxybenzene in conce~ltrated sulfuric acid. The isotropic splitting constants of the OCI-I3 protons are considered t o be positive, since a hyperconjugative mechanism is favored (22,23).…”

Section: V Jlolecular Orbital Calcz~laf Ionsmentioning

confidence: 99%

ORGANIC AND BIOLOGICAL SPECTROCHEMICAL STUDIES: XXIII. CONFORMATION OF THE p-DIMETHOXYBENZENE CATION RADICAL IN CONCENTRATED SULFURIC ACID

Forbes¹,

Sullivan²

1966

The electron spin resonance spectrum of the p-dimetlioxybelizerie cation radical in concentrated sulfuric acid is interpreted in terms of cis-trans isomerislii. En~pirical molecular orbital ca,l,c;i,htions support these assignments. 'l'he two isomers are found to possess slightly different g values, Ag (cis -trans) being ca. 1.5 X Nuclear magnetic resonance and clltraviolet data show that the radical exists in equilibrium wit11 the neutral non-radical species a t room temperature, but that sulfonation occurs a t higher temperatures. Suclear magnetic resonance and electron spin resonance data of solutiol~s of p-dimethoxyber~zene in D?SOd show that rapid exchange of the ring protons occurs.