Abstract
The standard molar enthalpies of formation of β-alanine, sarcosine, and 4-aminobutanoic acid in the gaseous phase at T = 298.15 K were calculated by the high-level Gaussian-4 method. The agreement with available experimental data is good for β-alanine and 4-aminobutanoic acid, while a significant discrepancy between theoretical and experimental enthalpy of formation values for sarcosine suggests the inaccuracy of experimental data for this compound. These results were also supported by isodesmic reaction calculations. The recommended values of Δ f H m ∘ (β-alanine, g, 298.15 K) = (−419.7 ± 4.0) kJ · mol −1, Δ f H m ∘ (sarcosine, g, 298.15 K) = (−389.0 ± 4.0) kJ · mol −1, and Δ f H m ∘ (4-aminobutanoic acid, g, 298.15 K) = (−436.7 ± 5.0) kJ · mol −1 together with those obtained earlier for glycine and alanine, enable one to determine the group additivity values (GAVs) for some groups with nitrogen bound to carbon. These GAVs were used to estimate the enthalpies of formation of 5-aminopentanoic acid, 6-aminohexanoic acid, and 8-aminooctanoic acid. For the two first species, the experimental and calculated values agree well. A large deviation observed for 8-aminooctanoic acid suggests that experimental Δ f H m ∘ ( cr ) value for this compound is not reliable.
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