The work of adhesion between water and a series of immiscible organic liquids has been found to obey a linear solvation free energy relationship (LSER) on the basis of solute parameters for the organic compound. This relationship, together with the surface tensions of water and of the pure organic liquids, allows reasonably accurate estimation of the corresponding interfacial tensions and provides insight into the nature of intermolecular forces at the water−organic interface. Furthermore, the similarity of this multiparametric LSER to that for partitioning of organic solutes between water and the gas phase (log L W) leads to a much simpler two-parameter relationship. Estimation of the interfacial tension with this latter relationship requires a knowledge of only two parameters, log L W and the surface tension of the pure organic liquid. Since reasonably accurate group contribution methods are available for estimating both log L W and surface tensions from molecular structure, this result provides a novel approach for a priori estimation of the water−organic interfacial tension directly from the chemical structure of the organic compound itself.

Flash points (T FP ) of hydrocarbons are calculated from their flash point numbers, N FP , with the relationshipIn turn, the N FP values can be predicted from experimental boiling point numbers (Y BP ) and molecular structure with the equationwhere D is the number of olefinic double bonds in the structure, T is the number of triple bonds, and B is the number of aromatic rings. For a data set consisting of 300 diverse hydrocarbons, the average absolute deviation between the literature and predicted flash points was 2.9 K.

3D printing was used to prepare models of the calculated geometries of unsaturated organic structures. Incorporation of p orbital isosurfaces into the models enables students in introductory organic chemistry courses to have hands-on experience with the concept of orbital alignment in strained and unstrained π systems.

Flash points (T FP ) of organic compounds are calculated from their flash point numbers, N FP , with the relationshipIn turn, the N FP values can be predicted from boiling point numbers (Y BP ) and functional group counts with the equation095 where G i is a functional group-specific contribution to the value of N FP and n i is the number of such functional groups in the structure. For a data set consisting of 1000 diverse organic compounds, the average absolute deviation between reported and predicted flash points was less than 2.5 K.

An investigation of the chemistry and interconversion of tin(II) and tin(IV) porphyrins is reported. Tin(IV) porphyrins photoredu'ce with SnCl2• 2H20 in pyridine to yield first the tin(IV) chlorin and subsequently the corresponding r/c-tetrahydroporphyrin or bacteriochlorin. The mechanism of the photoreduction evidently involves electron transfer from SnCl2 to the porphyrin excited triplet and subsequent protonation of the resulting tin(IV) porphyrin dianion. Preparation of heretofore unknown tin(II) porphyrins by introduction of anhydrous SnCl2 into the porphyrin in degassed solutions is described. The tin(II) porphyrin is extremely reactive and oxidizes readily to the stable tin(IV) porphyrin on exposure to air or water. Analysis of absorption and nmr spectra of tin(II) octaethylporphyrin indicates that the tin may be relatively far out of the porphyrin plane. Activation of the tin(II) porphyrin by heat or light yields ring-reduced porphyrintin(IV) species. This transformation may proceed via intramolecular electron transfer. he structures, reactivity, and biological functions of metalloporphyrins and their complexes con-

A 3D printer is used to prepare a variety of models representing potential energy as a function of two geometric coordinates. These models facilitate the teaching of structure–energy relationships in molecular conformations and in chemical reactions.

3D printing was used to prepare space-filling models of electron density isosurfaces and high-resolution molecular models on the basis of the van der Waals radii of atoms. Both model types provide students with kinesthetic simulations of steric effects in bimolecular substitution and elimination reactions. The models can be printed in small sizes for individual student use or large sizes for classroom demonstrations. These space-filling models can also enable visually impaired students to experience tangible representations of theoretical surfaces.

The classical Kinney method for predicting the boiling points of acyclic alkanes is taken as the starting point for the development of a much more accurate group contribution method developed using multiparametric linear regression. The procedure involves calculating a revised "boiling point number" (Y R ) from a count of structural features, including the length of the longest carbon chain, the nature and location of substituents, and the overall shape of the molecule. For a combined data set of 198 acyclic alkanes having from 6 to 30 carbon atoms, the correlation of predicted and literature boiling points has an R 2 of 0.999 and an average absolute deviation of 1.45 K. Thus, the method reported here is comparable in accuracy to, but much easier to apply than, more elaborate molecular connectivity, nonlinear regression, and neural network methods that were developed for narrower ranges of molecular weights.