Vingt ans apres: To Karplus or not to Karplus?

The Karplus equation is more than twenty years old. Is that equation still worth while for the chemist today? Can it be applied to materials science? An example of its possible role in wood chemistry, for instance in the conformational analysis of cellulosic materials, macromolecules, biopolymers, carbohydrates and other wood derivatives is presented. NMR data are advantageously compared to X-ray diffraction data for the purpose of conformational assessment. However, there exists several Karplus-type equations, thus rendering its use by materials chemist more complicated: which one applies to the system under study? We therefore review some of the best fit calculations for the Karplus equation, suggest a uniform criterion to evaluate all Karplus-type equations, and include a review of ³J calculations using the Karplus equations.