A general procedure is presented for computing the gas phase heats of formation of a wide variety of organic compounds. A E for the formation of the molecule from its elements at 0 K is obtained from density functional calculations (Gaussian 92/DFT) for optimized geometries. This result is converted to AH at 298 K by assuming ideal behavior and adding the translational, rotational, and vibrational energies. Additive correction terms corresponding to the various coordination states of the carbons, nitrogens, and oxygens were developed using a database of 54 compounds. The experimental AH; values of these compounds are then reproduced with an average absolute error of 3 kcal/mol and a standard deviation of 4 kcal/mol. For a group of 10 test cases that were not part of the database, the average absolute error is 3.5 kcal/mol and the standard deviation is 4.1 kcal/mol. 0 1995 by John Wiley & Sons, Inc.

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A nonlocal density functional procedure is used to compute the dissociation energies of some N–F and O–F bonds that show an anomalous relationship between force constants and bond lengths. The dissociation energies are found to increase in the same direction as the force constants. The trend in the bond lengths is interpreted in terms of the quantities of charge in the N–F and O–F bond regions.

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