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. Can. J. Chem. 54, 1643 (1976). The rate constants for a number of exothermic displacement (S,,2) reactions of the type X-+ CH3Y -Y + CH3X where X-= H-, 0 -, C-, F-, S-, CI-, OH-, C,-, C N -, SH-, S,-, C,H-, NHz-. NO,-, C H F -, CH,CI-, C H , B r , C H 3 0 -, CH,S-. and C H , N H and Y = F, CI, and Br, have been measured in the gas phase at 297 f 2 K using the flowing afterglow technique. These gas-phase measurements provided an opportunity to determine the intrinsic nucleophilic reactivity of 'nude' anions and hence to assess the role of solvation in the kinetics of S,,2 reactions proceeding in solution. Comparisons of the experimental rate constants with rate constants calculated using classical theories of capture indicate that several displacement reactions may possess large inrrin.sic energies of activation, E, >> 2 kcal mol-I.Correlations were found between apparent activation energies and the heats of reaction. These correlations provided a convenient classification of the various anion nucleophiles. Displacement was observed to compete with proton transfer in reactions involving nucleophiles of high intrinsic basicity and with hydrogen atom transfer and Hz' transfer in the reactions of the 0-radical anion.

The gas phase equilibria were measured with a pi~lsed electron beam high pressure ion source mass spectrometer. The ion source contained pure ammonia or mixtures of ammonia and water vapor at pressures in the T o r r range. Determination of the temperature dependence of the equilibrium constants led to the evaluation of AGO, A H 0 , and AS0 values for the equilibria from t~ = 1 to 4 and \v = 1 to 5. The AGO values for the NH4+(NH3),, equilibria were in good agreement with previous determinations from this laboratory. Fair agreement was observed for the A H 0 and AS0 values. Comparison with the corresponding results for NH4+(HzO),, showed that the AH ,,,,,-, and AGO ,,,,,-were larger than AH , , . , -, and AGO ,,.,,-,. The difference was largest for the first step (1,O) and decreased progressively until a reversal with water values becoming larger occurred at the (5,4) step. The stronger hydrogen bonds of NH3 to N H 4 + for low ligand numbers is explained by the greater basicity of N H , . As the ionic charge becomes dispersed and more distant stronger interactions are obtained with water which gives stronger H bonds in the absence of positive ionic charge. Breaks in theAH,,.,,-values indicateexistenceof a relatively stabIeNH4+(NHJ)., symmetric ion. A much smaller and less distinct break is observed with pure water ligands.The mixed ammonia-water clusters show similar effects. The addition of a N H 3 molecule to a pure water ligand complex gives the strongest interaction. The addition of H 2 0 to a pure ammonia cluster gives the weakest interaction. The above effect is strongest at lowest ligand numbers. The difference decreases gradually and becomes reversed for more than four ligands. [Traduit par le journal]Can.

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A flash pyrolysis method has been employed, allowing the production of pyrolysis oil from Athabasca asphaltene on the multigram scale, for the identification of homologous series of n-alkylbenzenes, 9-n-alkylfluorenes, and 1-n-alkyldibenzothiophenes. These aromatic classes of compounds were concentrated from the pyrolysis oil by a sequence of selective oxidative and chromatographic steps. Identification was based on comparison of GC retention times and mass spectra with those of synthetic standards or with literature values. The 1-n-alkyldibenzothiophenes were also found in the maltene fractions of several heavy oils and bitumens of northern Alberta and the 9-n-alkylfluorenes were found before in the maltene fraction of Athabasca bitumen. These aromatic compounds all possess alkyl substitution patterns which suggest that they have been derived by the cyclization and aromatization of precursor substances which possessed a linear carbon framework. The linear carbon framework of these and other compounds previously identified in the pyrolysis oil of Athabasca asphaltene contrasts with the terpenoid carbon framework which characterizes the compounds identified in the distillable portion of the maltene of the same bitumen and points to an n-alkanoic origin of the asphaltene.