The Conformational Equilibrium of 1,2,3-Tribromopropane in Solution

Abstract

The p.m.r. spectra of dilute solutions of 1,2,3-tribromopropane in carbon tetrachloride, acetonitrile, and dimethylsulfoxide as well as of the neat compound are examined. From the three-and four-bond spin-spin coupling constants and from a comparison between observed and calculated dipole moments it is concluded that in nonpolar solvents the title compound exists preferably in the enantiomeric conformations a and i. In polar solvents other rotamers contribute to the equilibrium but still seem to play only a minor role. Semiempirical calculations of conformational energies rule out contributions to the conformational equilibrium from rotamers having (1 :3) bromine-bromine interactions, but otherwise are only in moderate agreement with experiment.Les spectres r.m.p. de solutions dilukes de tribromo-1,2,3 propane dans le tktrachlorure de carbone, I'acCtonitrile, et le dimethylsulfoxide aussi bien que ceux du composk pur ont etC etudiks. A partir des constantes de couplage spin-spin a trois et a quatre liaisons et a partir d'une comparaison entre les moments dipolaires calcul6s et observes, on a conclu au fait que dans des solvants non-polaires, le compose etudie existe preferentiellement dans les conformations CnantiomCriques a et i. Dans les solvants polaires, les autres rotameres contribuent a I'equilibre mais ne jouent, meme la, qu'un rBle mineur. Des calculs semiempiriques des energies conformationnelles refutent les contributions a I'equilibre conformationnel des rotameres possedant des interactions brome-brome (1 :3), mais autrement ceux-ci ne sont qu'en accord partiel seulement avec I'expkrience.[Traduit par le journal]Can. J. Chem., 51. 565 (1973)

Reaction of polyfluoroarenesulfonyl bromides with allyl bromide. Synthesis of allyl polyfluoroaryl sulfones

“…The residue was a dark solid containing (according to the 1 H NMR data) allyl polyfluoroaryl sulfone IIIa-IIIe and 1,2,3-tribromopropane (IV) at a ratio of ~1 : 1. The structure of compound IV was confirmed by comparing the 1 H NMR spectrum of the reaction mixture with the spectrum of an authentic sample of IV [14] prepared as described in [15]. Tribromopropane IV was removed by washing with hexane (3 × 10 ml), and the crude product was purified by vacuum sublimation at 80-100°C (2 mm).…”

Nuclear magnetic resonance spectrometry

“…The low barrier of inversion of tetraphenylene (1165), chirality of triarylmethyl cations (1166), ring rotation in [2.2]met.aparacyclophane (1167), hindered rotation in tertbutyl groups (1168), styryl cations (1169), acyclic hydrocarbons (1170) and 1,1,2,2-tetrachloropropane (1171), conformational studies of 1,2,3-tribromopropane (1172), nbutane (1173), 1-butene (1174), straight chain hydrocarbons (1175), polyethylene (1176), O-substituted 1,1-diphenylethanes (1177), compounds with secondary methyl groups (1178) cyclohexene (1179), highly substituted cyclohexenes (1180), bridged cyclobutanes (1181), dimethylcycloheptanes (1182), cyclopentanes, cyclopentenes, and cyclopentene oxides (1183), dibenzocycloocta-1,5-diene (1184), monosubstituted alkyl-benzenes (1185), neopentylbenzenes (1186), polyacenes (1187), benzohexahelicenes (1188), meso-and rac-2,2'-bis(hexahelicyl) (1189) have been reported. A method for assigning dihedral angles to hydrocarbons adjacent to a methylene groups using computer analyzed NMR coupling constants in a modified Karplus equation has been presented (1190).…”

Calculation of gauche coupling constants from substituent electronegativities

“…2) yielding a straight line (correlation coefficient = 0.997) described by Eqn. (6). readily illustrated by considering the case of cis-4-tbutylcyclohexanol (5).…”