Aliphatic Amines: A Critical Analysis of the Experimental Enthalpies of Formation by Comparison with Theoretical Calculations

Abstract

The accuracy of experimental data on enthalpies of formation and vaporization of aliphatic amines (primary, secondary, and tertiary amines, di-, tri-, and tetramines, and cycloalkylamines) was assessed by theoretical calculations. The gas-phase enthalpies of formation were calculated using the Gaussian 4 (G4) method combined with isodesmic reactions. Three amines, CH 3 NH 2 , CH 3 NHCH 3 , and (CH 3 ) 3 N, were used as the main reference species in the isodesmic reactions; their experimental enthalpies of formation were recently revisited in the Active Thermochemical Tables. The enthalpies of vaporization were estimated by three group additivity and molecular electrostatic potential models and then were used to calculate the enthalpies of formation in the liquid state. When the deviations of experimental values from those provided by the theoretical methods were analyzed, a set of accurate and consistent values of enthalpy of formation of aliphatic amines was recommended for use in thermochemical calculations and as benchmarks for theoretical chemistry.

Strained Small Nitrogen Heterocycles‐Azabicyclobutanes and Azirines

“…Unless explicitly said to the contrary, the recent literature study [41] will likewise always be used as the source of information for the enthalpy of formation of acyclic amines. In particular, we accept their recommended value of −76 kJ/mol for the enthalpy of formation of diethylamine.…”

“…For the tertiary N-methylaziridine, the secondary 2-methylaziridine, and the primary cyclopropylamine, the enthalpies of formation are 120, 89 and 77 kJ/mol, respectively. [39,41] As a general rule, we find the isomerization transformation [Eq (21)] of isostructural tertiary to secondary to primary amines is exothermic, of increasingly N-alkylated to C-alkylated amines, by ca. 20 kJ/mol.…”

“…The simplest example is that of 2butylamine, CH 3 CH(NH 2 )CH 2 CH 3 , and 2-methyl-n-propylamine, CH 3 CH(CH 3 )CH 2 NH 2 , both isostructural with 2-methylbutane. With the recommended enthalpies of formation of these two primary amines from [41] of À 105 and À 98 kJ/mol, the difference is 7 kJ/mol. Let us take a consensus ofÀ 101 kJ/mol for the enthalpy of formation of the primary amine to be compared with 2-methylbutane.…”

Thermodynamic Analysis of Chemical Hydrogen Storage: Energetics of Liquid Organic Hydrogen Carrier Systems Based on Methyl-Substituted Indoles

“…Refs. [ 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 ] are mentioned in the Supplementary Materials.…”

Accurate prediction of norbornadiene cycle enthalpies by DLPNO‐CCSD(T1)/CBS method

“…show that the proposed DLPNO−CCSD(T)-based atom equivalents methodology is more efficient than the G4 method. In our previous studies of amines, amino acids, hydrazines, azides, ureas, nitro compounds, and phenols (see Reference [26] and references therein) it was shown that the G4 method, especially combined with isodesmic reactions, can give reliable theoretical estimates of the gas-phase enthalpies of formation. At the same time, for polycyclic adamantane T A B L E 1 Experimental and theoretical enthalpies of formation (kJ/mol) of adamantane and molecules of norbornadiene cycle we could not get a good agreement with the experiment either for atomization or isodesmic reaction.…”