An experimental and theoretical study of the preferred hydrogen bonding site of methyl isothiocyanate

Abstract

The hydrogen‐bond acceptor properties of MeNCS were investigated in vacuo with theoretical (MP2 and DFT) calculations, in CCl4 and (CF3)2CHOH solutions by Fourier transform infrared spectrometry and in the solid state through the Cambridge Structural Database. These methods show that MeNCS is a sulfur base in hydrogen bonding. The electrostatic potential at the molecular surface is more negative by 36 kJ mol−1 around S than around N. The hydrogen bonding of HF is more favorable to sulfur than to nitrogen by ca 5, 4 and 7 kJ mol−1, respectively, on the dissociation energy, enthalpy and Gibbs energy scales (B3LYP calculations). The selectivity of hydrogen bonding sites appears to be governed by a push–pull mechanism (electrons going from N to S) rather than by hardness. Towards a phenol, the order of sulfur basicity is . Copyright © 2003 John Wiley & Sons, Ltd.

An Enthalpic Scale of Hydrogen-Bond Basicity. 4. Carbon π Bases, Oxygen Bases, and Miscellaneous Second-Row, Third-Row, and Fourth-Row Bases and a Survey of the 4-Fluorophenol Affinity Scale

“…A paper devoted to the theoretical estimation of the 4-fluorophenol affinity of nitrogen bases contains about 100 experimental values. 21 A few data for new fluoroalkanes, 22 new chloroalkanes, 23 double-bonded sulfur bases, 24 and pyrrolines 25 are scattered in several papers. This paper first reports the 4-fluorophenol affinity scale for carbon π bases (aromatics, alkenes, and alkynes), oxygen bases with many functionalities (N-oxides, phosphine oxides, JOCArticle sulfoxides, selenoxides, carbonyl bases, ethers, and nitro compounds), new sulfur bases (thiocarbonyl bases and phosphine sulfides), and miscellaneous first-, second-, third-, and fourthrow bases (new nitrogen bases, phosphine, selenide, telluride, arsine, and stibine).…”

“…Hydrogen-bond formation to oxygen is driven by the interaction of the positive charge on hydrogen with the negative charge on oxygen, whereas with sulfur the main interaction is between the hydrogen charge and the dipole and quadrupole of sulfur. 70 In the isothiocyanate function, the electron-withdrawing effect of the NdC moiety, with its electronegative sp carbon atom, 24 might account for this function having the lowest HB affinity of the O, N, and S bases studied.…”

“…A paper devoted to the theoretical estimation of the 4-fluorophenol affinity of nitrogen bases contains about 100 experimental values . A few data for new fluoroalkanes, new chloroalkanes, double-bonded sulfur bases, and pyrrolines are scattered in several papers.…”

Hydrogen‐Bond Accepting Strength of Five‐Membered N‐Heterocycles:The Case of Substituted Phenylpyrrolines and Myosmines

“…[1] Accurate enthalpy measurements were carried out by following the absorbance of a single solution as a function of temperature. [44,45] In a typical measurement, the spectra of a solution containing approximately 4 mmol dm -3 of pFP and a base concentration adjusted so that about 50 % of the phenol was complexed at 25°C were recorded at five temperatures between -5 and +55°C. The enthalpy ∆H°B HX and the entropy relative to molar fractions and ∆S°B HX were obtained through the vanЈt Hoff equation.…”

Thermodynamic and Spectroscopic Scales of Hydrogen‐Bond Basicity and Affinity

“…Table 4.11 -Nitrogen bases: imines, oximes [94,96]. Table 4.23 -Sulfur bases: thioketone, thioamides, thioureas [73] and isothiocyanates [87]. Table 4.13 -Oxygen bases: water, alcohols, phenols [61].…”