The Calculation of Effective Pair Potentials in Solution from Activity Coefficient Data: Nitrobenzene in Benzene

Abstract

SAUL GOLDMAN. Can. J. Chem. 53,2608 (1975).The stoichiometric activity coefficients of nitrobenzene in benzene at low concentrations over the range 5.5-25 "C were represented by a temperature-dependent dimerization constant. Constant Pressure Solution Theory was used to derive a relationship between this dimerization constant and the sum of two cluster integrals. One of these integrals involves an effective nitrobenzene-nitrobenzene pair potential in benzene, and the other, an effective nitrobenzenebenzene pair potential in benzene. Two approximate mathematical models, each involving dipole-dipole and square-well potentials were used to evaluate the cluster integrals. The resultant expressions were fitted to the data. It was found that unique expressions for the pair potentials could not be obtained, and therefore ranges of solutions were reported. These solutions indicated (i) that the effective pair potentials in solution were of the same order of magnitude as those determined for comparable systems from gas-phase second virial coefficient data and (ii) that there existed a relatively short-range stabilizing effect in the nitrobenzene-benzene pair potential that was absent in the nonelectrostatic part of the nitrobenzene-nitrobenzene pair potential. This was explained in terms of a charge-transfer interaction between nitrobenzene and benzene, an explanation that is consistent with n.m.r. shift data. SAUL GOLDMAN. Can. J. Chem. 53,2608 (1975).A basses concentrations et a des tempkratures allant de 5.5 a 25 "C, les coefficients d'activitk stoichiomktriques du nitrobenzene dans le benzene peuvent Ctre reprksentks par une constante de dimkrisation dependante sur la tempkrature. On a utilisk la thkorie de solutions a pression constante pour ktablir une relation entre cette constante de dimkisation et la somme des deux intkgrales d'agglomkrations. Un de ces intkgrales implique une paire potentielle effective nitro-benzene-nitrobenzene dans le benzene, et I'autre unepairepotentielle effective nitrobenzene-benzene dans le benzene. On a utilise deux modeles mathkmatiques approchks pour evaluer les intkgrales d'agglomkration; chacun implique des potentiels dipole-dipole et point-carrk. On a trouvk que I'on ne peut obtenir des expressions uniques pour les paires de potentiels; on rapporte donc des limites pour les solutions. Ces solutions indiquent (i) que les potentiels des paires effectives en solution sont du mCme ordre de grandeur que ceux determinks en phase gazeuse pour des systemes comparables a partir de coefficients seconds virials; (ii) qu'il existe un effet stabilisant agissant a courte portke dans le potentiel de la paire nitrobenzene-benzene mais qui est absent de la partie nonklectrostatique du potentiel de la paire nitrobenzene-nitrobenzene. On explique ceci en termes d'une interaction de transfert de charge entre le nitrobenzene et le benztne; cette explication est en accord avec les donnkes des dkplacements chimiques en r.m.n.[Traduit par le journal]

Dielectric Study of the Solvent Effect on Molecular Interaction in Nitrobenzene, Pentan-3-one, and Octan-1-ol

“…From the point of view of the molecular structure, it can be suspected that the molecules of benzene can more easily interact with the molecules of nitrobenzene (weak charge-transfer interaction between benzene and nitrobenzene molecules has been found). 24 However, Figure 1 demonstrates that cyclohexylbenzene disturbs nitrobenzene interaction more effectively than cyclohexane or benzene. In cyclohexylbenzene the interaction of the phenyl substituent (corresponding to benzene molecules) with nitrobenzene molecules is hindered because cyclohexylbenzene occurs in solution in the form of the chair-equatorial conformer, which is energetically most favorable.…”

“…The nonpolar solvent disturbs the interaction of neighboring molecules, and Δε/ E 2 strongly decreases as a result of dissolving of nitrobenzene. From the point of view of the molecular structure, it can be suspected that the molecules of benzene can more easily interact with the molecules of nitrobenzene (weak charge-transfer interaction between benzene and nitrobenzene molecules has been found) . However, Figure demonstrates that cyclohexylbenzene disturbs nitrobenzene interaction more effectively than cyclohexane or benzene.…”