Since chemistry deals with events that happen below the threshold of direct human perception, all concepts and theories must, by necessity, be couched in terms that relate them to events that are observed directly. Thus, scientists turn to metaphor to describe the models they propose for chemical reactions and molecular structures. The fact that metaphors underlie our scientific models may seem irrelevant as long as they are useful and facilitate communication. However, teachers particularly need to sharpen their awareness of this underpinning of models: unsophisticated students can mistake metaphor for literal description and the teacher may be conveying unintentionally a skewed version of science. Bhushan and Rosenfeld (page 578) explore this entire complex subject in their thought-provoking article "Metaphorical Models in Chemistry". They examine the metaphors underlying much of modern science and discuss the implications for teaching. This article should be valuable to teachers at any level, stimulating them to reexamine how they explain ideas and how they read student responses.

This issue contains many articles that utilize familiar models, some that suggest new ones, and some that provide literal information. In the latter category are two articles that are resources for information about polymers--a topic that many chemists feel is neglected in the undergraduate curriculum. A thorough review of thermosetting resins is offered by Peng and Riedl (page 587), who describe the chemistry of their production and also their practical applications as commercial products. For teachers looking for help in acquiring polymer information and products to use in the classroom, Meister (page 593) gives an extensive bibliography of sources, both of literature and actual samples.

Spectroscopy is a powerful laboratory tool and the models used to explain it are rich with metaphor, as Bhushan and Rosenfeld demonstrate for NMR. Several articles in this issue involve this important technique. On the theoretical side, Thomsen (page 616) examines why spectral lines have a linewidth. This fact is confusing to students who have been introduced to the simple model of spectra, and many practicing chemists themselves do not understand the subtleties involved. He gives a pedagogically useful introduction to the topic using only basic physics to explain the various phenomena causing line broadening. Once the spectra are obtained and reduced to lines, another model must come into play for the chemist to interpret their meaning. Mann (page 614) points out that the way the theory of first-order coupling is presented in textbooks leads students to derive and use a cumbersome and difficult process for NMR spectra analysis, when in fact it can be a trivial exercise. He presents a set of simple rules to make analysis easy and illustrates them with three examples of increasing complexity. For students, the next step in complexity from first-order coupling is 2D-NMR involving proton-proton COSY. A practical introduction to the power as well as the practice of 2D-NMR is made possible by an integrated experiment developed by Branz, Miele, Okuda, and Straus (page 659) for the undergraduate course.

Infrared spectroscopy is among the most fundamental and easily understood spectroscopic techniques according to Hess, Smith, Thomsen, and Yoder (page 655), and they have thus devised an experiment to introduce it as a structure-determination technique in the beginning chemistry course. The project involves familiarizing the students with the fundamentals of IR spectroscopy through the analyses an unknown. Since the compound cannot be identified unambiguously in all cases, students also learn that multiple methods are necessary for real world situations. Infrared spectroscopy has gained in utility with the advent of instruments with integrated Fourier transform. Anderson, Hayes, and Werner (page 653) have found it is an ideal technique for an exercise in cooperative learning in introductory chemistry. The project involves several parts carried out by different groups; when results are combined students have learned a great deal about the experimental properties of the chemical bond as they relate to the model of the bond as seen in computer simulation programs.