New methods of determining the structural groups -COOH and -CH2- have been developed. The investigation of carboxyl groups is possible both after derivatization with p-fluorophenacylbromide and by quantitative interpretation of the Fourier transform infrared (FT IR) spectra. There exists a linear relationship between the results of these two methods that is generally valid for the analysis of all brown coal components. The maximum extinction coefficient of the symmetric stretching vibration band of the CH2 groups has been determined using model substances. This allows quantification of this structural group directly from the FT IR spectrum. The results agree with the contents of methylene groups as determined by C-13-cross polarization-magic angle spinning-nuclear magnetic resonance (C-13 CPMAS NMR) spectroscopy. Using these methods, the COOH and CH2 groups contained in brown coals of the North Rhine region and in their bioconversion products have been quantified.