Search results for "IFT"

Comparison of epimeric methyl lithocholate and methyl iso-lithocholate molecules: single crystal X-ray structure of methyl lithocholate, ab initio HF…

2003

Abstract 13 C NMR chemical shifts have been measured and assigned for epimeric methyl 3α/β-hydroxy-5β-cholan-24-oates (methyl lithocholate [3α-OH epimer] and methyl iso-lithocholate [3β-OH epimer]). Their molecular dynamics simulations suggest that for both epimers there exists two predominant gas phase conformations, which have been further forwarded for ab initio/HF optimizations and DFT/GIAO based 13 C NMR chemical shift calculations. Excellent linear relationships have been observed between experimental and calculated 13 C NMR chemical shifts for both epimers. For methyl lithocholate (MeLC), the other minimum energy conformation equates very well with the single crystal X-ray structure …

Corrigendum to “Comparison of epimeric methyl lithocholate and methyl iso-lithocholate molecules: Single crystal X-ray structure of methyl lithochola…

2003

Simulation of13C NMR chemical shifts for polychlorinated and polybrominated oxybenzenes with two-particle increment scheme

1994

A two-particle system of OY-Cl and OY-Br mixed increments for predicting13C NMR chemical shifts of polyhalogenated polyoxybenzenes has been developed. It has been found that only theortho- and para-interactions of the OY and Hal substituents contribute significantly to the13C chemical shifts and that theortho-effects of the OY located between Ha1 and H and those of the OY located between two Ha1 atoms are different. Additional effects are due to solvating solvents. The increment scheme is predictive over the whole class of compounds under consideration and may be realized on personal computers.

17O NMR study of chlorinated anisoles

1988

The 17O NMR chemical shifts of anisole and all 19 chlorinated anisoles measured in CDCI3 at ambient temperature show a dispersion of approximately 40 ppm. The substituent chemical shifts (SCS) of di- or more highly chlorinated compounds cannot be reproduced by addition of single substituent effects. Theoretical calculations of the 17O NMR chemical shifts have been attempted by molecular mechanical and semi-empirical molecular orbital methods at the INDO level, but the results are not satisfactory.

DFT calculations of structures, 13C NMR chemical shifts, and Raman RBM mode of simple models of small-diameter zigzag (4,0) carboxylated single-walle…

2012

Linearly conjugated benzene rings (acenes), belt-shaped molecules (cyclic acenes), and models of single-walled carbon nanotubes (SWCNTs) with one carboxylic group at the open end were fully optimized at the B3LYP/6-31G* level of theory. These models were selected to obtain some insight into the nuclear isotropic changes resulting from systematically increasing the basic building units of open-tip-monocarboxylated SWCNTs. In addition, the position of radial breathing mode (RBM), empirically correlated with the SWCNT diameter, was directly related with the radius of model cyclic acene rings. A regular convergence of selected structural, NMR, and Raman parameters with the molecular system size…

GIAO/DFT calculated chemical shifts of tautomeric species. 2-Phenacylpyridines and (Z)-2-(2-hydroxy-2-phenylvinyl)pyridines

2001

1H, 13C and 15N NMR chemical shifts for 28 substituted 2-phenacylpyridines (ketimine forms) and their enolimine tautomers, (Z)-2-(2-hydroxy-2-phenylvinyl)pyridines, were calculated via the GIAO/DFT approach. Among four tested methods at the B3LYP level of theory, the 6–311G, 6–311++G and 6–311G** basis sets gave acceptable result for 13C NMR chemical shifts whereas the 6–311++G** basis set was the minimum needed for reproduction of 15N NMR chemical shifts. Satisfactory reproduction of 13C and 15N NMR chemical shifts for different tautomers revealed that intramolecular hydrogen bonding could be modeled reliably by these calculations when the geometry optimizations were done with the HF/3–21G…

NMR spectroscopy in environmental chemistry:1H and13C NMR parameters of tricyclic polychlorinated C10 hydrocarbons and their oxy derivatives based on…

1999

Two-dimensional homo- and heteronuclear NMR chemical shift correlation techniques were applied in the characterization of five tricyclic polychlorinated C10 hydrocarbons, chlordene (1), heptachlor (2), trans-nonachlor (3), α-chlordene (4) and γ-chlordene (5), which are spread globally in the environment owing to their use as insecticides. Approximate and partly contradictory 1H and 13C NMR chemical shifts reported in the literature were corrected in this work. The chemical shift assignments of 1–5 were based on DQF COSY, HMQC and HMBC experiments. In addition, an INADEQUATE experiment was needed to ascertain the 13C chemical shifts assignment of 2. The nJ(H,H)s of 1–5 were solved by compute…

ChemInform Abstract: Tetraarylmethane Analogues in Group 14. Part 2. Ph4-nSi(p-Tol)n and Ph4-nSn(p-Tol)n (n = 0-4): Effect of the p-Tolyl Substituent…

2010

Methylium Ions with OPV Chains − New NIR Dyes

2001

Carbinols, which contain three OPV chains, were generated in convergent syntheses. The extension of the conjugation leads to a bathochromic effect that shifts the absorption from the UV into the visible region. The carbinol series has a convergence limit of the absorption at λmax = 415 nm. The corresponding carbenium ions exhibit a stronger bathochromic shift with the increasing number of repeating units in each chain. Thus, NIR dyes were obtained which show a convergence limit at λmax = 879 nm. The charge distribution in the ground state of the carbocations is discussed on the basis of 13C NMR spectroscopic data.

Extension of Conjugation Leading to Bathochromic or Hypsochromic Effects in OPV Series

2004

Four OPV series 1-4 (a-d) with a terminal dialkylamino group as electron donor were prepared by Wittig-Horner reactions. To study the influence of the push-pull effect on the long-wavelength absorption, three of the four series contained terminal acceptor groups (CN, CHO, NO(2)). The length of the chromophores strongly affects the intramolecular charge transfer (ICT)-an effect which superimposes upon the extension of the conjugation. Increasing numbers n of repeat units cause an overall bathochromic shift for the purely donor-substituted series 1 a-4 a and the series 1 b-4 b with CN as weak acceptor. The two effects annihilate each other in the series 1 c-4 c with terminal CHO groups, so th…