Choosing Models in Organic Chemistry

Conceptual, mathematical, and physical models are essential tools in organic chemistry because they help rationalize the results of experiments (observables) with theory (nonobservables). Yet the paradox is that these models may be most useful to us when they are oversimplified to the point of being incorrect in some way. Without a straight line or pair of dots to represent a chemical bond, we would find it difficult to describe chemistry in a practical way. Yet in some cases we find it advantageous to draw those lines curved instead of straight, and sp hybrid orbitals cannot be relied on even to predict all of the properties of methane. A more detailed description of that line and of those orbitals can be made only with the help of computers and high level mathematics. 

If any one of our models is asked to give a more correct answer to a problem, it quickly becomes more complex. Electronegativity is useful in a qualitative sense, but attempts to make it more quantitative lead to different conclusiorrs about what it means and how it should be determined. Elementary VB theory and MO theory are intuitively reasonable, but further development obscures the simple mental pictures each provides. We feel a need to retain these simple pictures, therefore, even when we know that they cannot be totally accmate. 

One solution to the use of oversimplified models in organic chemistry is to hybridize complementary conceptual models, just as we hybridize the two Kekule structures for benzene in our minds in order to imderstand and describe aromaticity. The (x,n and bent bond descriptions represent a peiir of models that serve as useful begiiming points or approaches to the description of the double bond. Visualizing a hybrid of these two mental pictures may be more nearly correct than is thinking in terms of either model alone. 

Kuhn (reference 3) wrote that scientists are little better than laymen at characterizing the established bases of their field. Briefly summarize the physical phenomena that support your belief in atomic and molecular theory. 

For provocative comments on language and models, see Bent, H. A. /, Ghent. Educ. 1984,61,774. In particular. Bent noted that indeed, to be useful, a model must be wrong, in some respects—else it would be the thing itself. The trick is to see—with the help of a teacher—where it s right.  

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