Heats of formation of organic molecules by ab initio calculations. 1. Aliphatic amines

Abstract

A bond energy scheme has been developed and two previously existing schemes have been extended for the calculation of heats of formation of aliphatic amines using ab initio 6-31G" energies in place of experimental data. The results are in good agreement with those obtained experimentally and suggest that this method can be used to predict heats of formation of molecules of this class with an accuracy competitive with good quality experiments, and with probable errors of less than 1 kcal mol-'.

Heats of formation of organic molecules by ab initio methods: Thiaalkanes

“…The accuracy of the calculated heats of formation of the sulfides herein, together with similar earlier calculations on a variety of compounds [3,4], shows that, at least for many routine cases, it is not necessary to measure experimental heats of combustion. The heats of formation for ordinary monofunctional (unconjugated) compounds (so far, only for the classes indicated) can be determined with approximately experimental accuracy by HartreeFock calculations at the 6-3 1 G* level.…”

“…(Primary carbons are taken as a zero of reference.) The necessary input information is given in Table 1, including the Hartree-Fock energies calculated in the present work, the value of SUMH (which is the heat of formation contributions from the hydrocarbon part of the molecule), and the other quantities, which have the usual definitions [3,4,13]. Also in Table 1 are given the number of times each of these units occurs for each molecule studied.…”

“…Other values were carried over from earlier calculations on hydrocarbons [3]. The five values required are two bond energies (C-S and S-H) and three substitution increments (S-SE, S-TE, and S-ME), where these latter represent bonds from the sulfur to secondary carbons, tertiary carbons, and methyl groups, respectively.…”

“…The general procedures have been described previously [3,4]. The bond energy units for the hydrocarbon portion of the molecule have been previously determined [3], and it is only necessary to find bond energy increments for C-S and S-H bonds, and for methyl, secondary, and tertiary carbons attached to sulfur.…”

“…The bond energy units for the hydrocarbon portion of the molecule have been previously determined [3], and it is only necessary to find bond energy increments for C-S and S-H bonds, and for methyl, secondary, and tertiary carbons attached to sulfur. We therefore want to establish values for these five parameters using available experimental data, and to fit the data as best as we can using least squares methods.…”