We performed guided backpropagation on the optimized MLP-IR model for molecules that were both predicted with an MPR of 1 and has the greatest activation in the neuron corresponding to the respective functional group (Figure ). Several backpropagation plots reveal a known chemical association between peaks in IR spectroscopy and functional group assignment. This is encouraging as the model was trained without any 'expert' or chemical information about the location of the peaks corresponding to each functional group. Specifically, we discuss several functional group cases for our selected set of molecules. The alkane functional group backpropagation shows the use of peaks near 3000 cm -1 , matching the known location of alkane CH peaks tabulated in the literature. The remaining peaks, however, do not provide any additional chemical intuition with regards to the alkane functional group. Aromatic compounds are identified by a peak between 1400-1600 cm -1 , and the model selected peaks within this region. In addition, the model was able to identify the alkene bending motion around 900 cm -1 .