Ab initio studies of the conformations of methylamine and ethylenediamine: interaction forces affecting the structural stability

A theoretical study of the inversion and rotation barriers in Methyl-substituted Amines

“…Note that the B3LYP imaginary frequencies differ no more than 80 cm -1 from the CCSD(T)/cc-pVTZ results. All geometric parameters calculated using B3LYP/cc-pVQZ are, in general, in good agreement with the CCSD(T) results and also with previous theoretical calculations [7][8][9][10]13,14 and experimental data. [2][3][4] We have also carried out the IRC calculations using the B3LYP/ cc-pVTZ method and the results confirm that the first-order inversion transition state and the rotation transition state connect to the ground state, as already shown by Kim and Zeroka 13 using a more complete two-dimensional potential energy surface.…”

“…The origin of the structural stability was confirmed to be essentially due to the stereo electronic effect. As obtained by Lee et al, 8 The two CCSD(T) results of the methylamine barrier heights, the single point calculations with the geometries optimized at the B3LYP/cc-pVQZ level and those obtained with the geometries optimized with the CCSD(T), are presented in Table 1. The results obtained with B3LYP/ccpVQZ and the experimental data [1][2][3]5 are also presented.…”

“…106.8 A (1,3,8) (1,4,11) 113.3 A (1,3,9) (1,4,13) 109.8 A (1,3,10) (1,4,12) 110.1 A (9,3,10) (12,4,13) 107.7 A (11,4,13) (8,3,9) 108.0 A (11,4,12) (8,3,10) 107.8…”

“…[1][2][3][4][5][6][7] Methylamine is considered a small molecule from the theoretical point of view, therefore it is appropriate to be studied using high level theoretical quantum chemical methodologies, having received many contributions. [7][8][9][10][11][12][13][14] Lee et al 8 investigated the origin of the structural stability of methylamine concluding that the stereo electronic effect is the major interaction force affecting its stability. Csonka and Sztraka 9 using density functional and post-HartreeFock methodologies showed that the density functional BP86/6-311G(d) method provides reliable results for geometry and vibrational frequencies, as compared with the experimental results.…”

Spectroscopic and Theoretical Studies on Solid 1,2‐Ethylenediamine Dihydrochloride Salt

“…Actually, the understanding of the factors that govern the conformational preferences of these polycationic systems (namely, intra-and/ or intermolecular interactions) is of utmost importance for determining the structure-activity relationships (SARs) underlying their biological function. Nevertheless, although ab initio molecular orbital calculations have proved to be a particularly valuable tool for the conformational analysis of amines, [29][30][31][32][33][34][35][36][37] no such systematic study has, to date, been reported on biogenic polyamine salts. In fact, to the best of the authors' knowledge, only two studies can be found in the literature on the ab initio assignment of the Raman spectra of such molecules, and even these are restricted to the NÀH and CÀH stretching modes.…”