Energetic vs structural effects of aminoalkyl substituents in the morpholine

Abstract

Abstract Experimental and computational studies were performed in this work with the aim of evaluating and understanding the energetic effect inherent to the substitution of the hydrogen of the morpholine amino group by aminoalkyl substituents: N -(2-aminoethyl)morpholine and N -(3-aminopropyl)morpholine. The standard enthalpies of vaporization and the standard energies of combustion of the two morpholine derivatives obtained, respectively, from Calvet microcalorimetry and combustion calorimetry measurements, are reported. These data were used to derive the standard enthalpies of formation of the morpholine derivatives, in the liquid and gaseous phases, at T = 298.15 K. The computational study involved the energetic analysis of the most stable conformers on the potential energy surfaces and the determination of their gas-phase standard enthalpies of formation at the reference temperature of 298.15 K. All the computational calculations were performed using the G3(MP2)//B3LYP composite method. The combination of experimental and computational data determined in this work for morpholine derivatives, together with other available in the literature for related molecules, enabled the analyses of the energetic effects associated with the substitution of the hydrogen of the morpholine amino group by substituents aminoalkyl and alkyl, as well as the establishment of incremental schemes for the determination of the gas-phase enthalpies of formation.