¹H NMR spectra of alcohols and diols in chloroform: DFT/GIAO calculation of chemical shifts

Abstract

Proton nuclear magnetic resonance (NMR) shifts of aliphatic alcohols in chloroform have been computed on the basis of density functional theory, the solvent being included by the integral-equation-formalism polarisable continuum model of Gaussian 09. Relative energies of all conformers are calculated at the Perdew, Burke and Ernzerhof (PBE)0/6-311+G(d,p) level, and NMR shifts by the gauge-including atomic orbital method with the PBE0/6-311+G(d,p) geometry and the cc-pVTZ basis set. The 208 computed CH proton NMR shifts for 34 alcohols correlate very well with the experimental values, with a gradient of 1.00 ± 0.01 and intercept close to zero; the overall root mean square difference (RMSD) is 0.08 ppm. Shifts for CH protons of diols in chloroform are well correlated with the theoretical values for (isotropic) benzene, with similar gradient and intercept (1.02 ± 0.01, -0.13 ppm), but the overall RMSD is slightly higher, 0.12 ppm. This approach generally gives slightly better results than the CHARGE model of Abraham et al. The shifts of unsaturated alcohols in benzene have been re-examined with Gaussian 09, but the overall fit for CH protons is not improved, and OH proton shifts are worse. Shifts of vinyl protons in alkenols are systematically overestimated, and the correlation of computed shifts against the experimental data for unsaturated alcohols follows a quadratic equation. Splitting the 20 compounds studied into two sets, and applying empirical scaling based on the quadratic for the first set to the second set, gives an RMSD of 0.10 ppm. A multi-standard approach gives a similar result.

Stereochemical analysis of menthol and menthylamine isomers using calculated and experimental optical rotation data

“…Likewise, at low temperature (À193 C) Pekh et al observed only one chair conformer in dichloromethane [16].With the assumption that all three OH rotamers of the dominant conformer are populated, we calculated the trans, g þ and g e rotamers of the OH eq chair of (þ)-menthol with the isopropyl group in the g þ position (Table 1). In agreement of our analysis, Lomas [32] investigated (À)-menthol and found the g e rotamer of the isopropyl group as dominant conformer, with the crystal structure revealing the isopropyl group in the gauche position [7]. However, pure computational results differ even between similar levels of theory (Table 2).…”

Unique adsorption behaviors of carboxylic acids at rutile TiO2(110)

“…Additionally, calculations for HCO 3 , CO 3 , CH 3 COO, and HCOO radicals were performed employing the Gaussian 09 computational software package [34]. B3LYP functional in combination with the 6-311 + G (2d, p) basis set were used [35][36][37].…”

Exploration of the chlorpyrifos escape pathway from acylpeptide hydrolases using steered molecular dynamics simulations

“…The three-dimensional structure (3D) of chlorpyrifos was downloaded from the ChemSpider database and the B3LYP/6-31G** level was used with Gaussian 09 (Lomas, 2014;Premkumar et al, 2015). Figure 2(b) and (c) shows the HOMO and LUMO orbits of chlorpyrifos using the Multiwfn program (Lu & Chen, 2012).…”

“…The initial model of the chlorpyrifos was extracted from the ChemSpider database. Geometric optimization of the chlorpyrifos was conducted at the B3LYP/6-31G** level using Gaussian 09 (Lomas, 2014;Premkumar, Jawahar, Mathavan, Kumara Dhas, & Milton Franklin Benial, 2015).…”

“…For, P1 we pulled 5 nm out as the tunnel length is around 4 nm, and the pulling velocity was set to .0005 nm ps −1 . SMD simulations were carried out with the software package Exploration of the chlorpyrifos escape pathway from acylpeptide hydrolases using steered molecular dynamics simulations 3 GROMACS 4.5.2 (Lomas, 2014), starting from the snapshot structure at 10 ns for the two passageways. The free energy change along a reaction coordinate is termed the potential of mean force (PMF).…”