Amino acetaldehyde conformers: structure and spectroscopic properties

ABSTRACT We present a computational study of the different conformers of amino acetaldehyde. This molecule is a precursor of glycine and also an isomer of the detected molecules acetaldehyde and methylformamide. In addition, a previous theoretical result shows that amino acetaldehyde could be formed from the gas phase reaction of formamide with CH$_{5}^{+}$. Different computational approaches, going from density functional theory (DFT) to coupled cluster (CC) calculations, are employed for the characterization of the amino acetaldehyde conformers. We locate four low-lying conformation on the singlet potential energy surface (PES), two with a synperiplanar arrangement of the carboxylic oxygen atom and the NH2 group, and the other two conformers with an anticlinal disposition. All levels of theory predict the conformer with a synperiplanar arrangement and the H atoms of the NH2 group pointing in the direction of the oxygen, denoted as in-sp-amino acetaldehyde, as the most stable. The viability of the interconversion processes between the four conformers in space is analysed. Relevant spectroscopic parameters to rotational spectroscopy with ‘spectroscopic’ accuracy at the composite level are reported. Vibrational frequencies and infrared intensities are also computed at the CC with single and double excitations (CCSD) level including anharmonic corrections. This information could help in the experimental characterization of amino acetaldehyde that could be considered as a good candidate molecule to be searched for in space.

Noncovalent interactions in 1:1 complexes of nitrogen trifluoride and nitroxyl

The computational investigations on 1:1 complexes of the nitrogen trifluoride (NF[Formula: see text] species with the nitroxyl (HNO) species have been carried out, which reveal the existence of the nine complexes on the singlet potential energy surface (PES). The atoms in molecules (AIM) theory and the electron localization function (ELF) along with the identification of noncovalent interaction (NCI) regions and the investigation of electron transfer of all the obtained complexes have been carried out to provide suitable insight into the electronic and structural properties of these complexes. The calculated results reveal that the N-atom of the NF3 species and the O-atom of the HNO species have more key roles compared with the F-atom of the NF3 species and the N-atom of the HNO species in the obtained complexes.

Quantum modeling of the reaction between ozone and hydrogen cyanide

This work consists of an investigation, using current methods of quantum chemistry and, at first, on the basis of the available experimental results, about the new mechanisms of the reaction between ozone and hydrogen cyanide (HCN) in gaseous phases. Three possible reaction pathways which we have determined as the most probable and, all three, leading exactly to the same products, are proposed here. For each of these pathways, several steps for which we performed a kinetic study were identified in the singlet potential energy surface. To confirm the proposed mechanisms, we have achieved a study including the intrinsic reaction coordinate (IRC), the topological analysis of atoms in molecule and the harmonic vibrational frequencies calculations. The obtained results reveal that the final products have considerable thermodynamic stability and this reaction is exothermic in standard conditions.

Theoretical investigation on the reaction of HS+ with CH3NH2

The singlet and triplet potential energy surfaces for the reaction of HS+ with the simplest primary amine, CH3NH2, were determined at the CCSD(T)/6-311+G(d,p) level using the B3LYP/6-311G(d,p) and QCISD/6-311G(d,p) geometries. All possible reaction channels were explored. The results show that three paths on the singlet potential energy surface and one path on the triplet potential energy surface are competitive. These four feasible paths provide products which are presented in the paper and they are consistent with previous experimental results. On the other hand, the stationary points involved in the most favourable path all lie below those of the reactant and thus the title reaction is expected to be rapid, which is also consistent with the experiment.

Prediction of Tetraoxygen Reaction Mechanism with Sulfur Atom on the Singlet Potential Energy Surface

The mechanism of S+O4(D2h) reaction has been investigated at the B3LYP/6-311+G(3df) and CCSD levels on the singlet potential energy surface. One stable complex has been found for the S+O4(D2h) reaction, IN1, on the singlet potential energy surface. For the title reaction, we obtained four kinds of products at the B3LYP level, which have enough thermodynamic stability. The results reveal that the product P3 is spontaneous and exothermic with −188.042 and −179.147 kcal/mol in Gibbs free energy and enthalpy of reaction, respectively. Because P1 adduct is produced after passing two low energy level transition states, kinetically, it is the most favorable adduct in the1S+1O4(D2h) atmospheric reactions.

Theoretical Study of the 1CF2 + 3O2 Reaction on the Singlet Potential Surface

A detailed singlet potential energy surface survey on the 1CF2 + 3O2 reaction is carried out in order to clarify the reaction mechanisms of the singlet difluorocarbene (1CF2) with oxygen (3O2) at the B3LYP/6-311++G(d,p) level. To determine the accurate energies of all stationary points, the QCISD/6-311++G(d,p) single-point calculations are done by using the B3LYP/6-311++G(d,p) optimized geometric structures. The title reaction is important in high temperature processes. Four product channels, P1(F2 + CO2), P2(F2O + CO), P3(2F + CO2) and P4(FCO + FO), have been found in the 1CF2 + 3O2 reaction. P1(F2 + CO2) and P3(2F + CO2) have comparable contributions to the title reaction and they are more favorable than the other two thermodynamically and kinetically.

Theoretical Study of the 1CHBr + 3O2 Reaction

The mechanism of the reaction of the monobromocarbene (1CHBr) with3O2was studied theoretically at the B3LYP/6-311++G(d,p) level on the singlet potential energy surface (PES). All structures of the stationary points (reactants, intermediates, transition states and products) were optimized and their energies were obtained. Three product channels, P1(HCO + BrO), P2(CO2+ HBr) and P3(CO + HOBr), are found. P2(CO2+ HBr) is the most favorable one both kinetically and thermodynamically.