Good argument on the difficulty to indicate which are the molecules responsible for spectral information

"By analysing the regression coefficient of the four PLS models
(Fig. 6) it can be seen that the region between 5000 and
4000 cm 1 is the most important. This spectral region is mainly
due to C–H and C–C combination bands and is the one that contains
most information regarding the chemical composition of the defective
and non-defective beans, although, as already stated, coffee is a
combination of numerous organic molecules and therefore it is difficult
to indicate which are the molecules responsible for the information
contained in the spectral region referred to previously."

Ana Paula Craig, Adriana S. Franca, Leandro S. Oliveira, Evaluation of the potential of FTIR and chemometrics for separation between defective and non-defective coffees, Food Chemistry, Volume 132, Issue 3, 1 June 2012, Pages 1368-1374, ISSN 0308-8146,