A¹³C NMR and density functional theory study of critical behaviour of binary water/2,6-lutidine solution

Abstract

Temperature dependences of13 C NMR shifts have been measured in binary water / 2,6-lutidine mixture close to the lower critical solution point at TCL = 306.0±0.5 K. In order to evaluate hydrogen bonding and solvent effect contributions to the measured chemical shifts, 13 C magnetic shielding tensors of non-bonded 2,6-lutidine molecule, as well as water / 2,6-lutidine H-bond complex in vacuo and in various solvents (acetonitrile, water) have been calculated using the density functional theory (DFT) with the modified hybrid functional of Perdew, Burke, and Ernzerhof (PBE1PBE). The solvent reaction field effect has been taken into account using the polarizable continuum model (PCM).13 C NMR shifts 'order parameters' (∆δ = |δ + − δ − |) and 'diameters' (φδ = |(δ + + δ − )/2 − δC|, where δ + , δ − , and δC are the chemical shifts of coexisting phases and at the critical point respectively) have been calculated for each 13 C signal close to TCL and processed using linear regression analysis of ∆δ ∼ |T − TCL| and φδ ∼ |T − TCL| in the log-log plot. It has been shown that the critical index β can be determined most correctly using temperature dependences of the 13 C NMR signals of C4 and C3,5 carbons of 2,6-lutidine. An evaluation of critical index of 'diameter' is rather imprecise because of problems of referencing of δC. The obtained φδ slope from C4 data (0.65±0.08) are closer to 2β than to 1 − α value. The results are discussed in the light of DFT data and within the concept of complete scaling.

Solid-State NMR and Impedance Spectroscopy Study of Spin Dynamics in Proton-Conducting Polymers: An Application of Anisotropic Relaxing Model

“…Our approach was proven to be adequate in various cases earlier. For example, satisfactory agreement between calculated and experimentally measured 1 H NMR chemical shifts was obtained not only for molecular systems involved in strong H-bonding but also for rather “inert” species, e.g., CH 3 protons (see refs ( 23 ) and ( 24 ), and references therein). We have analyzed isolated fragments of PMETAC composed of 2 monomers in order to support the assignment of experimentally observed signals ( Figure 2 ).…”

“…The Gaussian 16 program 22 was used for all our calculations. The 1 H and 13 C chemical shifts were obtained by subtracting the computed isotropic shielding constants of PMETAC from the corresponding shielding constants of TMS which are taken from ref ( 23 ). Our approach was proven to be adequate in various cases earlier.…”

NMR and DFT study on media effects on proton transfer in hydrogen bonding: concept of molecular probe with an application to ionic and super-polar liquids

“…the PBE1PBE functional with 6-311++G** basis set, the optimal OÁ Á ÁO distance of 2.496 A ˚was found, that is even slightly closer to the experimental X-ray bond length of 2.425(2) A ˚.34 On the other hand, PBE1PBE1 functional applied together with the polarizable continuum model (PCM) gives very good agreement between calculated and experimental 1 H, 13 C and 17 O NMR chemical shifts and perfectly reproduces many observed tendencies, for H-bonded systems in particular. [35][36][37] Therefore this functional and the same basis set were adopted in all further DFT calculations of the present work.…”

1H and13C NMR study of phase transition and molecular motion in ionic liquids forming lyotropic liquid-crystalline ionogels

“…The principal components of the 1 H and 13 C chemical shift tensors (δ ij , i, j = X, Y, Z) were obtained subtracting those of σ from the isotropic part of magnetic shielding tensor of TMS (σ iso (TMS) values for 1 H and 13 C nuclei were taken from [17]), i. e. δ = 1 σ iso (TMS) − σ and used to construct other parameters of magnetic shielding. These parameters, namely, isotropic chemical shift:…”