Substituent Effects in Gas Chromatography

Gas chromatographic retention characteristics of phenols with Superox-20M

“…If the data from the investigation of Karger and co-workers (35) for only the alkyl substituents are plotted without inclusion of the other substituents such as halogen and methoxy, there is no immediately evident correlation; the correlation coefficient of the linear least-squares regression line of their data is approximately 0.29. However, when the logarithm of the ratio of the activity coefficients is plotted against Karger's oa the chromatographic substituent constant, the correlation improves considerably (see Figure 4).…”

“…The slope of the least-squares lines in Figure 4 represents the Hammett p value which corresponds to the sensitivity of a specific reaction to changes in the electronic environment at the functional group (here, a phenolic hydroxyl group). Accordingly, p is a measure of the selectivity of a stationary phase for phenols (35). The larger the value of p, the more sensitive the stationary phase is to changes in the electronic environment around the phenolic hydroxyl group.…”