Infrared spectroscopy was used to examine the O-alkylation and O-acetylation of two bituminous coals with a series of reagents. Two related aspects were investigated: We attempted to apply quantitative methods to calculate the reactivity using the hydroxyl absorption bands and to calculate the total alkyl or acyl groups incorporated using specific coal bands. The latter work showed that the use of IR coal bands to determine the amount of added groups can only be used qualitatively due to unpredictable changes in the coal band intensities. Quantitative monitoring of the hydroxyl groups showed that, in some reactions, more hydroxyl was found in the coal after reaction, suggesting that there was little reaction and mostly trapping of hydrolyzed reagent into the coal.