Wendel J. Shuely

Hydrogen bonding: XVI. A new solute salvation parameter, π2H, from gas chromatographic data

Abstract The general salvation equation, log VG0 (or log L) = c + rR2 + sπ2H + aα2H + bβ2H + l log L16 has been used to set up a new π2H parameter of solute dipolarity-polarisability, mainly through the extensive data of McReynolds and Patte et al. Values of π2H are tabulated for several hundred solutes, and two simple rules have been formulated to enable π2H to be estimated for many types of aliphatic functionally substituted compounds. A coherent set of effective solvation parameters, Σπ2H, Σα2H, Σβ2H, and also R2 and log L16, allows the application of the general solvation equation to the characterisation of any gas-liquid chromatographic stationary phase.

Hydrogen bonding. Part 13. A new method for the characterisation of GLC stationary phases—the laffort data set

A number of equations for the correlation of retention data for a series of solutes on a given stationary phase (or solvent) have been investigated with the aim of characterising stationary phases. The two most successful equations are, SP =c+dδ2+sπ2*+aα2H+bβ2H+I log L16(a), SP =c+rR2+sπ2*+aα2H+bβ2H+I log L16(b) In the present case the dependent variable SP is log L– log LDecane and the explanatory variables are solute parameters as follows: δ2 is an empirical polarisability correction term, R2 is a polarisability parameter that reflects the ability of a solute to interact with a solvent through π and n electron pairs, α2H is the solute hydrogen–bond acidity, β2H is the solute hydrogen–bond basicity, π2* is the solute dipolarity/polarisability, and L16 is the Ostwald solubility coefficient of the solute on n-hexadecane at 298 K. The constants c, r, s, a, b, and l in the more useful equation (b) are found by the method of multiple linear regression analysis, and serve to characterise a solvent phase in terms of specific solute/solvent interactions. Application of equation (b) to the five stationary phases examined by Laffort et al. shows that the magnitude of these constants is in accord with general chemical principles, and that the present procedure constitutes a new, general method for the characterisation of gas chromatographic stationary phases.

Hydrogen bonding. XV, A new characterisation of the McReynolds 77-stationary phase set

Abstract The following equation has been applied to all the phases in the McReynolds 77-stationary phase set. In this equation, V0G is the specific retention volume for a series of solutes on a given stationary phase, and the explanatory variables are R2 a modified solute molar refraction, π*2 the solute dipolarity, αH2 the solute hydrogen-bond acidity, βH2 the solute hydrogen-bond basicity, and log L16 where L16 is the solute Ostwald absorption coefficient on hexadecane at 25°c. The constants in the equation are obtained by multiple linear regression analysis, using about 150 data points in eacy regression, and values of r, s, a, b and l are regarded as characteristic constants of the phases that serve to classify the 77-phase set. It is shown that the classification of the phases into clusters is in accord with chemical principles, and is in excellent agreement with previous work using hierarchical clustering, minimum spanning tree techniques, and pattern cognition methods. The above equation allows the factors that lead to gas-liquid chromatographic separations to be identified, and provides quantitative information on the various solute-solvent interactions that give rise to these factors.

Hydrogen bonding: XVII. The characterisation of 24 gas-liquid chromatographic stationary phases studied by Poole and co-workers. including molten salts, and evaluation of solute-stationary phase interactions

Abstract The general solvation equation log K = c + rR 2 + s π 2 H + a α 2 H + b β 2 H + l log L 16 has been used to characterise 24 gas-liquid chromatographic stationary phases for which Poole and co-workers have determined log K values for a series of solutes at 121.4°C. The explanatory variables are R 2 , asolute excess molar refraction, π 2 H , the solute dipolarity, α 2 H and β 2 H , the solute hydrogen-bond acidity and basicity, and log L 16 , where L 16 is the solute gas-liquid partition coefficient on hexadecane at 25°C. It is shown that the b β 2 H term is not significant for any phase, and that the molten salts are all strongly dipolar and basic, with large s and a constants. A term-by-term analysis of the solvation equation yields a quantitative measure of the contribution to log K of various solute-stationary phase interactions, and leads to an understanding of how these interactions affect solute retention. The use of the characteristic constants c, r, s, a, b and l in the selection of stationary phases for particular separations is described.

Hydrogen bonding. Part 14. The characterisation of some N-substituted amides as solvents: comparison with gas–liquid chromatography stationary phases

Equations previously used for the characterisation of GLC stationary phases have been found to be equally suitable for the characterisation of common solvents. Thus equation (a) has been applied to solubility data for series of solutes on N-formylmorpholine (NFM), N-methylpyrrolidinone (NMP), N,N-dimethylformamide (DMF), and N,N-dimethylace amide (DMA).SP =c+r·R2+s·π2*+a·α2H+b·β2H+I· log L16(a)In equation (a), SP can be log V°G or log L for a series of solutes on a given solvent where V°G is the specific retention volume and L is the Ostwald solubility coefficient. The solte parameters are R2, a polarisability parameter; π2*, the solute dipolarity; α2H, the solute hydrogen-bond acidity; β2H, the solute hydrogen-bond basicity; and log L16 where L16 is the solute Ostwald solubility coefficient on n-hexadecane at 298 K.It is shown that at 298 K all four amides have about the same dipolarity, as judged by the s-constant, and have nearly the same hydrogen-bond basicity, as judged by the a·α2H term: all have zero hydrogen-bond acidity so that b= 0 in equation (a). Comparison can be made between results for NFM and NMP at 393 K and results for some GLC stationary phases. The two amides are less dipolar than tricyano(ethoxy) propane and diethyleneglycol succinate, about the same as Zonyl E-7®and Carbowax®, and more dipolar than poly(phenyl ether). The amides, however, have rather more hydrogen-bond basicity than any of the above five GLC phases. It is suggeted that equation (a) can be used as the basis of method for characterising condensed phases, such that common solvents as well as GLC stationary phases can be included within the scope of the method.

An analysis of polymer-probe interactions in some hydrocarbon polymers using a new solvation equation

The new solvation equation: log L= c + rR2 + sπH22 + aαH2 + bβH2 + l log L16 has been applied to the solubility of 43 gaseous probes on each of nine hydrocarbon polymers using the data of Munk et al.. In this equation, L is the gas-liquid partition coefficient of a series of probes on a given polymer, and the explanatory variables are solute properties as follows: R2 is an excess molar refraction, πH2 is the probe dipolarity-polarizability, αH2 and βH2 are the probe hydrogen-bond acidity and basicity, and L16 is the gas-liquid partition coefficient of the probe on hexadecane at 25°C. Each of the nine equations, one for each polymer, had correlation coefficients of around 0.999 and standard derivations of around 0.025 log units. The solubility of the gaseous probes, as log L values, as well as the polymer-probe interaction parameter χ calculated by Munk, have been analysed in terms of particular polymer-probe interactions.

Comparison of uncorrected retention data on a capillary and a packed hexadecane column with corrected retention data on a packed squalane column

Abstract Retention data obtained previously at 25°C on a hexadecane capillary column by Zhang et al. and a packed hexadecane column by Abraham et al., both uncorrected for any effects due to interfacial adsorption, were compared with retention data obtained by Poole et al. on a packed squalane column at 120°C, with the latter fully corrected for such effects. It is shown that for most solutes, the capillary and packed column data are equally compatible with the squalene corrected data, but for the solutes dimethyl sulfoxide, dimethylformamide and dimethylacetamide the packed column data are in much better accord with the corrected data than are the capillary column data. It is further shown that both sets of results at 25°C for carboxylic acids are in error, owing to dimerization. Retention volumes on Chromosorb G AW DMCS are reported at 25 and at 93°C. It is shown that at 25°C, there could be some contribution to solute retention from adsorption on the support, but that this is almost impossible at 93°C.

Fullerene as an adsorbent for gases and vapours

Gas–solid partition coefficients of 22 solute gases and vapours on a sample of fullerene have been obtained by a chromatographic method, elution by characteristic point. Analysis of these coefficients by the solvation equation of Abraham shows that solute dipolarity/polarisability, and hydrogen-bond acidity, as well as general dispersion interactions can influence adsorption; the fullerene is weakly polarisable, and has some hydrogen-bond basicity, commensurate with its behaviour as a giant closed-cage alkene rather than an aromatic molecule.

On the prediction of polymer-probe χ and Ω values from inverse gas-chromatographic data

Abstract The solvation equation Log V G =c+rR 2 +s π 2 H +a α 2 H +b β 2 H +1 log L 16 has been applied to the solubility of 24 probes on poly(butadiene) at 353, 363 and 373 K using VG values obtained by Romdhane and Danner by inverse gas-chromatography. In the above equation the explanatory variables are solute probe parameters as follows: R2 is an excess molar refraction, π2H is the probe dipolarity/polarizability, α2H and β2H are the probe hydrogen-bond acidity and basicity, and L16 is the probe gas-liquid partition coefficient on hexadecane at 298 K. It is shown that log VG can be predicted to ± 0.04 log units, using this equation, and that from the predicted log VG values, the weight fraction activity coefficient, Ω ∞ , can be predicted to around ± 0.04 log units, and the Flory-Huggins polymer-probe χ coefficient to within ± 0.10 units. The same general equation has also been applied to literature data on the solubility of 50 probes on poly(trifluoropropyl)methyl siloxane at 298 K, with similar results.