Values of ( ΔfHo298.15)(g) and (S°298.15)(g) of the several N,N-ethylenebisalkaneamides calculated using RB3LYP/6-31G(D,P) AND CBS-4M approaches, and their correlation dependencies

Publication date: 1 April 2017 Source:Computational and Theoretical Chemistry, Volume 1105 Author(s): Gregory A. Poskrebyshev In the present work, the thermochemical properties of the several N,N′-ethylenbisalkaneamides are calculated using RB3LYP/6-31G(d,p), UB3LYP/6-311++G(d,p), CBS-4M and CBS-Q approaches. The values of standard enthalpies of their formation ((Δf H o 298.15)(g)) are calculated using thermochemistry of the isodesmic reactions as well as using the group additivity methods. Due to the high uncertainty in the values of (Δf H o 298.15)(g) of the high atomic molecules, calculated using different approaches, the simple methodology for determination of (Δf H o 298.15)(g) values of compounds with more than 16 “heavy” atoms (C, N and O) is proposed. This methodology is based on the extrapolation of the linear dependence of results of the CBS-4M and RB3LYP/6-31G(d,p) calculations. Reliability of the values of (Δf H o 298.15)(g), determined using this methodology, is comparable with the results of CBS-4M calculations. The following expression for the determination of (Δf H o 298.15)CBS-4M =0.45+1.023×(Δf H o 298.15)RB3LYP describes well the values of (Δf H o 298.15)(g) of amides, n-alkanes and N,N′-ethylenbisalkaneamides, calculated using the CBS-4M approach. The values of (Δf H o 298.15)CBS-4M =−578.9±7 and −1128.8±7kJ/mol, determined using this expression, and the values of (Δf H o 298.15)RB3LYP, calculated, respectively, for (C4H9C(O)NHCH...

Source: Computational and Theoretical Chemistry - March 6, 2017 Category: Chemistry Source Type: research