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- Author or Editor: James P. Lodge Jr. x
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Abstract
The ice nucleating ability of a series of substituted phenols and benzoic acids was determined. Two different measures of activity were utilized: the onset temperature of freezing, as determined on a cold stage microscope; and the relative number of ice nuclei formed at a fixed temperature in a cold chamber. Reactivity was generally found to vary with the potential strength of a hydrogen bond between the hydroxyl or carboxyl group and a water molecule. In a given series of compounds (i.e., either the phenols or the benzoic acids), it was found that the onset temperature could be predicted from the sigma value of Hammett for the individual substituent, so long as the substituent was in the meta and para position, and was not more strongly hydrogen bonding than the functional group of the parent compound. This suggests a free-energy relationship between molecular structure and nucleating power. These observations are offered for further discussion; it is clearly premature to offer a detailed mechanism for the effect.
Abstract
The ice nucleating ability of a series of substituted phenols and benzoic acids was determined. Two different measures of activity were utilized: the onset temperature of freezing, as determined on a cold stage microscope; and the relative number of ice nuclei formed at a fixed temperature in a cold chamber. Reactivity was generally found to vary with the potential strength of a hydrogen bond between the hydroxyl or carboxyl group and a water molecule. In a given series of compounds (i.e., either the phenols or the benzoic acids), it was found that the onset temperature could be predicted from the sigma value of Hammett for the individual substituent, so long as the substituent was in the meta and para position, and was not more strongly hydrogen bonding than the functional group of the parent compound. This suggests a free-energy relationship between molecular structure and nucleating power. These observations are offered for further discussion; it is clearly premature to offer a detailed mechanism for the effect.
Abstract
The authors' recent studies on phenols and benzoic adds suggest that the ability of solid organic compounds to nucleate freezing of supercooled water may be predicted, at least in a limited number of cases, from purely thermodynamic considerations. A report that pure, optically active amino acids nucleate freezing at temperatures different from their inactive forms suggests that a quantitative study of the differences might be revealing.
It was found that differences in nucleation temperature were related in a linear manner to differences in heat of solution of active and racemic forms. Tyrosine is an exception to the above behavior. It is suggested that nucleation on one of the forms may occur at the phenolic group.
Abstract
The authors' recent studies on phenols and benzoic adds suggest that the ability of solid organic compounds to nucleate freezing of supercooled water may be predicted, at least in a limited number of cases, from purely thermodynamic considerations. A report that pure, optically active amino acids nucleate freezing at temperatures different from their inactive forms suggests that a quantitative study of the differences might be revealing.
It was found that differences in nucleation temperature were related in a linear manner to differences in heat of solution of active and racemic forms. Tyrosine is an exception to the above behavior. It is suggested that nucleation on one of the forms may occur at the phenolic group.
