A new empirical relation between liquid dynamic viscosity, temperature, and chemical constitution of organic compounds is proposed. The method is based on the De Guzman-Andrade equation and the introduction of a new property, the equivalent chain length of a compound, defined as the chain length (in carbon atoms) of the hypothetical n-alkane having a viscosity equal to 1 cP at the same temperature as the compound in question. Cumulative constitutional correction factors for the equivalent chain length and the slope of the log viscosity-temperature curve are proposed. With the aid of these data, the viscosity between boiling and melting points of many compounds can be predicted. The method proves to be more accurate than the existing ones and it does not make use of any other physical property.

In many instances, particularly when preparing plant designs, the enthalpy of combustion of compounds must be estimated. We present in this note a simple and accurate method to obtain such enthalpies at 298.15 K. Basically, we develop correction factors for a wide variety of functional groups and branching modes to correct simple relationships for alkane combustion. The method has been shown to apply to gaseous, liquid, and solid compounds with errors less than 1%. In addition, the enthalpy of combustion can be converted to a standard enthalpy of formation; as such, the method compares favorably to the best estimation techniques now available for the property. Enthalpy of CombustionIt is well known that for most homologous series, there is a first-order correspondence between the total number of carbon atoms and the enthalpy of combustion (Handrick, 1956). We have utilized this concept to estimate enthalpies of combustion by developing correction factors to determine an equivalent alkane chain length, N , such that, with this parameter, one can then utilize simple relations developed for n-alkanes. Thus we define N asHere C is the total number of carbon atoms in the molecule, while AN, values are correction factors for functional groups and chain branching. Values of ANi vary depending upon whether the compound is a gas (g), liquid (I), or solid (s). In Table 1 we show values of AN, applicable to many compound types. In cases where there may be an ambiguity, clarifying remarks are given with the table. It can be seen that a wide variety of organic compounds may be treated, including aliphatic, naphthenic, and aromatic materials.With values of AN, for the compound of interest, N can be found from Eq. 1 and the enthalpy of combustion AHzfrom Eqs. 2 through 4. Here AH: is defined as the difference between the enthalpy of a compound and that of its products of combustion in the gaseous state, all a t the standard state of 298.1 5 K and 10' Pa (1 bar). The products of combustion are H,O(g), C 0 2 , SO2, N,, and HX(g) with X = halogen. AHXg) = -198.42-615.14 N (kJ/mol) (2) AH:(l) = -196.98-610.13 N (kJ/mol) (3) AH:(s) = -206.21-606.56 N (kJ/mol)In Appendix I we illustrate the applicability of the method to a number of compound types, both simple and quite complex. (A more detailed statistical comparison between calculated and literature values of AH: is available upon request from the author.)The method was applied to a large number of compounds for which the equivalent alkane chain length N ranged from 1 to 66. Further limitations were an upper limit equal to one for the ratio between the number of corrections and the number of carbon atoms and, for halides, an upper limit equal to one for the ratio between halogen and hydrogen atoms. These limitations were fixed because it was noted that beyond the indicated limits the application of the method yielded low estimates. This is illustrated by the following results for chlorinated gaseous ethanes, using calculated and literature values as indicated. AH: calc.

R e p le 2 octobre 1990 R. SABBAH et E. N. L. E. BULUKU. Can. J. Chem. 69,481 (1991). Le prtsent travail porte sur 1'Ctude thermodynamique des trois isomeres du dihydroxybenzene. Cette ttude a permis la dCtermination des enthalpies de combustion, de sublimation, de fusion et de transition des 1,2-, 1,3-et 1,4-dihydroxybenzenes. Les techniques utilisCes ont Ct C la calorimCtrie de combustion de faibles quantitCs de substances, la calorimCtrie de changement d'Ctat (sublimation), l'analyse thermique differentielle et la mesure des capacitts calorifiques. L'ensemble des rCsultats expCrimentaux a permis de : mettre en Cvidence l'existence d'une liaison hydrogkne intramolCculaire dans l'isomkre ortho; prkciser la stabilitk relative des trois molCcules de dihydrobenzenes; et determiner : i partir de l'enthalpie de sublimation, une valeur CnergCtique pour les liaisons intermolCculaires; 1'Cnergie de conjugaison expkrimentale et de la comparer i la valeur thtorique; l'enthalpie d'atomisation 3 partir de laquelle a Ct C calculCe I'enthalpie de la liaison intramolCculaire Cb-OH. Mots clts : thermodynamique, calorimCtrie, analyse thermique differentielle, 1,2-dihydroxybenzkne ou catCcho1; 1,3-di-hydroxybenzkne ou rCsorcino1; 1,4-dihydroxybenzene ou hydroquinone ou quinol; enthalpies de combustion, de sublimation, de fusion, de transition; Cnergie de conjugaison; enthalpies d'atomisation, de liaisons inter-et intra-molCculaires; temperature du point triple et de transition. R. SABBAH and E. N. L. E. BULUKU. Can. J. Chem. 69,481 (1991). The present work is concerned with a thermodynamic study of the three isomers of dihydroxybenzene. By combustion calorimetry of small amounts of substance, sublimation calorimetry, differential thermal analysis, and heat capacity measurements, it was possible to determine the enthalpies of formation of 1,2-, 1 3 , and 1,4-dihydroxybenzene in the condensed and gaseous phases, their enthalpies of fusion and transition, and the temperature of their triple point and transition. The experimental results are used to discuss the relative stability and determine the conjugation energy of the three compounds. The values are in good agreement with the theoretical values obtained from a quantum chemical calculation. The enthalpies of atomization enabled us to determine an energy value for the intramolecular Cb-OH bond in dihydroxybenzenes and to correlate it with previous results obtained from a study of alkane-diols. The enthalpies of sublimation were discussed. An intramolecular hydrogen bond was displayed in the ortho isomer. Intermolecular hydrogen bonds associated with van der Waals interactions exist in dihydroxybenzenes. Their energy contributions were determined.

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