Sensitivity of infrared spectra to chemical functional groups

Spectral features from specific regions in infrared spectra of organic molecules can consistently be attributed to certain functional groups. Artificial neural networks were employed as a pattern recognition tool to elucidate the relationships between functional groups and spectral features. The ability of these network models to predict the presence and absence of a variety of functional groups was evaluated. The sensitivity of the artificial neural network over the entire infrared spectral region was used to generate a spectral factor representation of the major information associated with each functional group. The resulting sensitivity factors were utilized in a much simpler model for functional group prediction. Ultimately, the presence of a functional group was predicted based on the dot product of an unknown spectrum with the corresponding sensitivity factor. A probability based on Bayes' theorem was assigned to each of the predictions. The prediction accuracies were greater than 90% for all 13 functional groups considered in the investigation.