Heats of Formation of Organic Compounds by a Simple Calculation

Heats (enthalpies) of formation of organic compounds are obtained by adding a constant for a functional group to the heat of formation of its hydrocarbon precursor obtained by counting hydrogens, as previously described. A single molecule is used to obtain the contribution of each functional group. Unlike all other empirical schemes, no global fitting is used. The calculation is done with pencil and paper or a hand calculator. The accuracy of the results is demonstrated by their agreement with more than 360 species of experimentally known heats of formation with a mean average deviation of 0.75 kcal mol−1, very nearly equal to the mean experimental uncertainty. Alcohols, hydroperoxides, ethers, amines, ketones, aldehydes, carboxylic acids, esters, chlorides, phenols, anilines, aryl ethers, nitriles, amides, and alkyl radicals are used as examples of the method. This success allows the calculation of experimentally unknown heats of formation. The method is limited to compounds that are not subject to strain or effects of conjugation. In such cases, the experimental heat of formation of the hydrocarbon precursor may be used. The method can be extended to functional groups not treated here.