Correct calculation of ΔH°, ΔC°P, and ΔV° from temperature and pressure dependences of equilibrium constants: The importance of thermal expansion and compressibility of the solvent

Activities of solutes and compositions of solutions may be expressed corretly in terms of molarity (c), molality (m) or mole fraction (x), leading to corresponding equilibrium constants K_c, K_m, or K_x. Equations for differences between ΔG°_c, ΔG°_m, and ΔG°_x values are derived. Common errors in calculations involving (dlnK_c/dT) and (dlnK_c/dP) are identified and remedies for these errors are presented.     

Heats of melting of sodium nitrate and indium by differential scanning calorimetry: a suggestion for a new calibration substance

Measurments with a Perkin-Elmer DSC-2 differential scanning calorimeter that has been calibrated with indium, tin, and lead have yielded values for the heat of melting of sodium nitrate. Analysis of these results along with those from earlier investigations gives ΔH_m ? 3615 cal mol^?1 as a recommended “best” value for the heat of melting of NaNO₃. The consistency of our results over a period of three years in which many samples were investigated, in combination with results of earlier investigations, leads us to suggest that NaNO₃ is a useful substance for calibration of differential scanning calorimeters. Results of our measurements of the heat of melting of indium are presented and discussed in relation to earlier investigations.     

Mass spectrometry in structural and stereochemical problems. CCLVI—electron impact induced fragmentation of juvenile hormone analogs

Complete high resolution mass spectra of several analogs of the juvenile hormones have been analyzed with the aid of our recently developed INTSUM program and mass spectra of deuterated analogs. Representative compounds chosen for study included the biologically interesting (2E, 4E)-3,7,11-trimethyl-2,4-dodecadienoates (1,2), (2E,4E)-11-methoxy-3,7,-11-trimethyl-2,4-do-decadienoates (3,4) and three analogs (5-7) of the trans-trans-farnesoate skeleton. These compounds display characteristic fragmentations which can be used to detect the presence of the compounds in complex mixtures using mass fragmentography or aid in the structure elucidation of related compounds.     

The reaction of lithium phenylacetylide and phenyllithium with N-(ω-Bromoalkyl)phthalimides

Lithium phenylacetylide reacted with short-chain N-(ω-bromoalkyl)phthalimides 1b and 1c to give tricyclic products 2b and 2c in moderate yields. Likewise, tricyclic products 3a-c were obtained when short-chain imides 1a-c were treated with phenyllithium. When longer-chain imides 1d-f in this series were treated with lithium phenylacetylide only tertiary alcohols 4d-f could be isolated. Partial hydrogenation of 2b and 2c yielded the corresponding alkenes 5b and 5c , products which corroborated the structural assignment of 2b and 2c .     

Organic chemistry of C60 (Buckminsterfullerene): chromatography and osmylation

Treatment of C60 with osmium tetroxide and pyridine gives the osmate ester (2:1 adduct) establishing that oxygen functionality can be added to C60 without disrupting the carbon framework.     

Engineering the chemistry and nanostructure of porous silicon Fabry-Pérot films for loading and release of a steroid

A method for engineering the surface chemistry and pore dimensions in porous Si films for the purpose of controlling the loading and release of a hydrophobic drug is described. Loading of the steroid dexamethasone is confirmed by Fourier transform infrared spectroscopy, and the release rates are characterized by observation of the appearance of the drug in solution (UV-vis absorption spectroscopy) and by measurement of the Fabry-Perot fringes in the optical reflectivity spectrum of the porous Si film. Optical reflectivity changes provide a measure of the release rate of the drug that is amenable to in-vivo diagnostic applications. Fresh porous Si films are prepared by electrochemical etch and subsequently modified by hydrosilylation with 1-dodecene. The dodecene-modified samples are more robust in aqueous environments and exhibit slower release rates of the drug relative to freshly etched porous Si. Whereas the relatively large dexamethasone molecule is found to infiltrate the freshly etched samples, it does not enter the chemically modified films, because of steric crowding from the dodecyl species. To achieve a high degree of loading into these modified films, the pores are enlarged before hydrosilylation by treatment with an aqueous solution containing HF and dimethyl sulfoxide. The pore expanded, chemically modified samples admit approximately 70% of the dexamethasone that can be admitted into an unmodified (freshly etched) sample. Diffusion of the steroid from the modified, pore expanded films into phosphate-buffered saline solution is slower than from the unmodified sample by a factor of approximately 20, with 90% of the drug delivered in 3 days for the chemically modified films compared to 3 h for the unmodified films.     

Thermodynamics of aqueous EDTA systems: Apparent and partial molar heat capacities and volumes of aqueous strontium and barium EDTA

Apparent molar heat capacities and volumes have been determined for Na₂SrEDTA (aq) and Na₂BaEDTA (aq). Standard state partial molar heat capacities and volumes have been calculated as well as the partial molar properties at 0.1 m ionic strength that are needed for various thermodynamic calculations. Selected enthalpies and stability constants from the literature have been combined with out heat capacities to generate predicted stability constants to 200°C.     

The enthalpy of solution of ferrous chloride in water at 298 K

We have made calorimetric measurements of the enthalpy of dissolving solid ferrous chloride in water at 298 K and have derived ΔH° = −19.82 kcal mol⁻¹ for the standard enthalpy of this process. This ΔH° is related by way of some thermodynamic calculations to other properties of iron.     

Calorimetric investigations of association equilibria: the pyridine-iodine complex in cyclohexane and in carbon tetrachloride

The results of two independent calorimetric investigations of the pyridine- iodine complex are reported. “Best” values are reported as K_m = 128 1/mol and ΔH° = -8.4 kcal mol^?1 for the formation of the complex in cyclohexane at 25°C, and K_m = 104 and ΔH° = -7.9 kcal mol^?1 in carbon tetrachloride. Evidence is presented to support the contention that association constants for weak complexes determined by calorimetric methods can be as reliable as those determined by spectrometric methods, and that values of ΔH° determined by the calorimetric method are much more reliable than those derived from the temperature dependence of equilibrium constants.     

Thermal and volumetric properties of chloroform+benzene mixtures and the ideal associated solution model of complex formation

In the ideal associated solution model, activity coefficients of all species (labelled A, B, and AB here) at equilibrium are taken to be unity at all compositions and temperatures. We have applied this model to an analysis of thermodynamic properties (vapor pressures, excess enthalpies, partial molar enthalpies of solution, excess heat capacities, and excess volumes) of the chloroform+benzene system in terms of K, H, C _p , and V for the equilibrium represented by A+B=AB. It is demonstrated that there is reasonably good consistency between this simple model and all of the thermodynamic data, which shows that the model is realistic enough to be useful in assessing the properties of the not-very-stable AB complex in the chloroform+benzene system. New thermal (partial molar enthalpies of solution and excess heat capacities) and volumetric properties of the chloroform+benzene system have been measured, with results presented here.