Examines the phenomenon of water drops that float on water at room temperature. Describes experiments that have been done to study this phenomenon. (MA)

Reviews the areas of laser chemistry, photochemistry, infrared lasers, and laser induced molecular reactions. (SL)

This is part two in a series on classroom demonstrations of polymer principles. Described is how large molecules can be assembled from subunits (the process of polymerization). Examples chosen include both linear and branched or cross-linked molecules. (RH)

Discusses how a metal ion is bound to a particular enzyme, focusing the blue copper centers found in a variety of organisms. Coordination geometry of the blue copper site, donor set, direct structural studies, and single-crystal spectroscopy are the major topic headings. (JN)

Compares the differences in coverage and utility of three substructure databases--Chemical Abstracts, Index Chemicus, and Chemical Information System's Nomenclature Search System. The differences between Chemical Abstracts with two different vendors--STN International and Questel--are described and a summary guide for choosing between databases is…

Compares the coulumbic point charge model for hydrogen chloride with the valence bond model. It is not possible to assign either a nonpolar or ionic canonical form of the valence bond model, while the covalent-ionic bond distribution does conform to the point charge model. (JM)

Shows that electronic structure diagrams make more accurate predictions of spectral properties and chemical reactivity for simple pi systems than do either Huckel molecular orbital or valence bond theory alone. Topics addressed include absorption and photoelectron spectra, spin density distribution in radicals, and several problems regarding…

The immune system includes the most diverse proteins known because they are encoded by hundreds of scattered gene fragments which can be combined in millions or billions of ways. Events of immune response, binding of antigens, antibody structure, T-cell receptors, and other immunologically-oriented topics are discussed. (DH)

Only a few substances serve as signals within cells; this indicates that internal signal pathways are remarkably universal. The variety of physiological and biochemical processes regulated by known messengers is discussed along with chemical structures, pathways, inositol-lipid cycles, and cell growth regulation. (DH)

Discovery that mutations accumulate at steady rates over time in the genes of all lineages of plants and animals has led to new insights into evolution at the molecular and organismal levels. Discusses molecular evolution, examining deoxyribonuclei acid (DNA) sequences, morphological distances, and codon rate of change. (DH)

Describes a bonding theory which provides a framework for the description of a wide range of substances and provides quantitative information of remarkable accuracy with far less computational effort than that required of other approaches. Includes applications, such as calculation of bond energies of two binary hydrides (methane and diborane).…

The valence-shell electron-pair repulsion (VSEPR) theory is a useful tool for predicting molecular structures. The major stumbling block in teaching VSEPR theory for coordination numbers two through six is in explaining the arrangement of five electron pairs. The dilemma of five-coordination and implications for instruction in introductory…

Presents a new view of the electronic structure of pi systems that unifies molecular orbital and valence bond theories. Describes construction of electronic structure diagrams (central to this new view) which demonstrate how configuration interaction can improve qualitative predictions made from simple Huckel theory. (JN)

Pi-CI theory is a simple, semi-empirical procedure which (like Huckel theory) treats pi and pseudo-pi orbitals; in addition, electron repulsion is explicitly included and molecular configurations are mixed. Results obtained from application of pi-CI to ethylene are superior to either the Huckel molecular orbital or valence bond theories. (JN)

Examines the current debate concerning molecular structure, providing an overall assessment of the debate, discussing the development and relationship of successive concepts of molecular structure, and considering what students should be taught about molecular structure and quantum mechanics. Also addresses the tension between continuity and…