Unknowns chemical classification tests

The classification tests (summarized in Table 31.2), when properly done, can distinguish between various types of aldehydes and ketones. However, these tests alone may not allow for the identification of a specific unknown aldehyde or ketone. A way to correctly identify an unknown compound is by using a known chemical reaction to convert it into another compound that is known. The new compound is referred to as a derivative. Then, by comparing the physical properties of the unknown and the derivative to the physical properties of known compounds listed in a table, an identification can be made. 

The importance of validation has been generally acknowledged, and most QSAR models in the literature are validated either by cross validation or external test sets [13,46]. Model validation for classification models is typically specified by statistical quality measures of overall quality such as sensitivity, specificity, false positives, false negatives, and overall prediction. Unfortunately, it is often impossible to specify accuracy and prediction confidence for individual unknown chemicals, specifically those unknown chemicals with structures requiring the model to extend to, or beyond, the limits of chemistry space defined by the training set. 

In addition. Experiment 53 (Identification of Unknowns) offers a "green" alternative procedure. This procedure avoids the use of toxic chemicals for classification tests and substitutes the use of spectroscopy, which does not require any chemical reagents (except a small amount of organic solvent). 

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