Structure and weak hydrogen bonds in liquid acetaldehyde

Abstract

Investigaram-se a estrutura e formação de pontes de hidrogênio no acetaldeído líquido por simulações de Monte Carlo. Um modelo para acetaldeído com todos os átomos explicitados foi otimizado no presente trabalho. Os valores teóricos obtidos para a entalpia de vaporização e a densidade do líquido mostram boa concordância com os dados experimentais. Os gráficos de função de distribuição radial (rdf) indicam um líquido bem estruturado comparado com outros líquidos orgânicos dipolares semelhantes. A minimização usando mecânica molecular em fase gasosa produz um trímero com uma estrutura muito estável. A geometria deste complexo apresenta boa concordância com os gráficos de rdf. A correlação sítio-sítio mais próxima observada é entre o oxigênio e o hidrogênio da carbonila, sugerindo que esta correlação possui um importante papel na estrutura do líquido e suas propriedades. A distância média O⋅⋅⋅H e o ângulo C-H⋅⋅⋅O obtidos são característicos de pontes de hidrogênio fracas.Monte Carlo simulations have been performed to investigate the structure and hydrogen bonds formation in liquid acetaldehyde. An all atom model for the acetaldehyde have been optimized in the present work. Theoretical values obtained for heat of vaporisation and density of the liquid are in good agreement with experimental data. Graphics of radial distribution function indicate a well structured liquid compared to other similar dipolar organic liquids. Molecular mechanics minimization in gas phase leads to a trimer of very stable structure. The geometry of this complex is in very good agreement with the rdf. The shortest site-site correlation is between oxygen and the carbonyl hydrogen, suggesting that this correlation play a important role in the liquid structure and properties. The O⋅⋅⋅H average distance and the C-H⋅⋅⋅O angle obtained are characteristic of weak hydrogen bonds. Keywords:Monte Carlo simulation, acetaldehyde, liquid structure, weak hydrogen bond IntroductionIn recent years, theoretical investigation of liquid state properties has become a challenging subject for theoretical chemists and physicists, since fast and high memory capability computers have become available at relatively low cost.1-3 The development of suitable computer simulation methods have made it feasible to investigate a great number of liquid state properties that would not be possible, or difficult to access, with other theoretic or experimental techniques. 4,5 However, the success of the investigations using computational methodologies depends strongly on the availability of potential functions capable of describing the intermolecular interactions adequately.6-9 Therefore, the optimisation of meaningful intermolecular potential functions is of fundamental importance for the investigation of liquid state properties using theoretical methods. This optimisation is not simple, however, due to the complexity of the liquid intermolecular interactions, and some criteria, such as pairwise additivity and consideration of dipolar interaction exclusively, have been used to s...

Neutron Diffraction Study of Liquid N-Methylformamide Using EPSR Simulation

“…Nothing was discussed up to now about the characteristics of the O−H(C) correlation brought to light from this work and what could to be said concerning the so-called weak hydrogen bond in NMF based in the present results. As may be noticed by analyzing the g ( r ) O−H(C) plot of Figure , the results show a well-defined peak for the O−H(C) correlation with maximum around 3 Å, which could be attributed to a weak hydrogen bond, taking into account what has been reported on that correlation. , This kind of hydrogen bond can play an important role in the stabilization of lots of structures, and that may be the case in liquid NMF. The correlation is shorter than the O−C one, which indicates that the O−H(C) interaction orientates the relative intermolecular correlation.…”

Electron induced chemistry for acetaldehyde

“…35, by Wiberg et al 47 and by Walsh,36 respectively. The dipole moment obtained using cc-pVDZ is slightly higher compared to the experimental value of 2.75 D reported by Paul and Cox 38 and in the CRC handbook, 39 2.69 D reported in CCCBDB database 37 (originally reported by Nelson et al 40 ) and 2.6 D reported earlier by Maria et al 41 It can be easily seen that dipole moment is very sensitive to the basis set chosen and cc-pVDZ gives better value of dipole moment. 37 The dipole moment obtained through present calculations are 3.24 D using 6-31G and 2.87 D using cc-pVDZ.…”

“…37 The dipole moment obtained through present calculations are 3.24 D using 6-31G and 2.87 D using cc-pVDZ. The dipole moment obtained using cc-pVDZ is slightly higher compared to the experimental value of 2.75 D reported by Paul and Cox 38 and in the CRC handbook, 39 2.69 D reported in CCCBDB database 37 (originally reported by Nelson et al 40 ) and 2.6 D reported earlier by Maria et al 41 It can be easily seen that dipole moment is very sensitive to the basis set chosen and cc-pVDZ gives better value of dipole moment. Also inclusion of large diffused functions can improve upon the dipole moment but we cannot use diffuse functions for the target representation as this would violate the boundary condition that the target molecular orbitals should vanish on the surface of the R-matrix sphere.…”

A Monte Carlo revisiting of N-methylformamide and acetone

“…The reasons supporting this decision have been discussed previously. 64,65 Such an approach is further justified taking into account that the molecular potential parameters are effective pair potentials, optimized at the same computational conditions of the simulations themselves. Therefore, they are a kind of mean force parameter that carries out information on Coulombic long-range corrections, many-body effects, molecule polarization and so on.…”