Abstract

Using ab initio molecular orbital (MO) theory to calculate the heats of formation of formyl system. Results show that, the heats of formation of formic acid (HC=O(OH)); methyl formaldehyde (HC=O(CH3)) and formyl amide (HC=O(NH2)) at CCSD(T)/6-311++G(3df,2p) // MP2/6-31G(d,p) level, were similar to the experimental results with different amount from 0.1 to 2.8 kJ/mol. The heats of formation of the rest of compounds have been calculated from four different working reactions at CCSD(T) method in conjunction with 6-311++G(3df,2p) basis set, with a probable error of ± 5 kJ/mol. This method can also be used to calculate heats of formation for compounds of the same system or others for which these quantities are not experimentally available.