Search results for "Carbon-13 NMR"
showing 10 items of 262 documents
Substituted methyl 5β-cholan-24-oates II.13C NMR spectral assignment
1994
The 13C NMR spectra were recorded and assigned for nine derivatives of methyl 5β-cholan-24-oates (esters of bile acids) including hydroxy, oxo and/or acetyloxy groups. Assignments were based on the empirical substituent-induced chemical shifts (SCS), spectral comparison with compounds of similar structure, distortionless enhancement by polarization transfer (DEPT) and proton coupled 13C NMR measurements.
Direct determination of tautomerism in purine derivatives by low-temperature NMR spectroscopy
2004
An investigation of the purine derivatives N,N-dimethyl-N'-(7(9)-H-purin-6-yl)-formamidine, 6-chloropurine and 6-methoxy purine at low temperatures by NMR spectroscopy has been carried out. Low temperature enabled us in two cases to detect the separate NMR signals of N7-H and N9-H tautomers.
Synthesis, spectroscopic (Mössbauer, IR and NMR) and X-ray structural studies of diorganotin complexes of 2,2′-bipyrimidine and further NMR studies o…
1996
Abstract The ligand 2,2′-bipyrimidine (bipym) was reacted with diorganotins R 2 SnCl 2 (R = methyl, ethyl) and complexes of the types R 2 SnCl 2 bipym, R 2 SnCl 2 bipym · bipym and (R 2 SnCl 2 ) 2 bipym were synthesized and studied by 1 H and 13 C NMR spectroscopy in solution, and by IR and Mossbauer spectroscopy in the solid state and frozen solutions. The complexes Et 2 SnCl 2 bipym · bipym and (Et 2 SnCl 2 ) 2 bipym were characterized by X-ray diffraction methods. In both complexes the tin environment is octahedral with chloro atoms in a cis disposition, the ethyl groups in a trans disposition and two N atoms from the ligand bipym. the second complex is a centrosymmetric binuclear specie…
ChemInform Abstract: 1,2-Methyl Shift in the Reaction of 4,7-Dihydro-4,5-dimethyl-7-phenyl-(1,2,4)-triazolo[1,5-a]pyrimidine with Tosyl Azide.
2010
The reaction of the heterocyclic enamine 1 with tosyl azide (2) leads to the tosylimino derivative 4 of 1,2,4-triazolo[1,5-a]pyrimidine. The extrusion of nitrogen from the primary adduct 3 is followed by a 1,2-shift of a methyl group. The structure determination of 4 is based on 1H and 13C nmr spectra including NOE measurements.
Why benchmark-quality computations are needed to reproduce 1-adamantyl cation NMR chemical shifts accurately.
2011
While the experimental (1)H NMR chemical shiftsof the 1-adamantyl cation can be computed within reasonably small error bounds, the usual Hartree-Fock and density functional quantum-chemical computations, as well as those based on rather elaborate second-order Møller-Plesset perturbation theory, fail to reproduce its experimental (13)C NMR chemical shifts satisfactorily. This also is true even if the NMR shielding calculations treat electron correlation adequately by the coupled-cluster singles and doubles model augmented by a perturbative correction for triple excitations (i.e., at the CCSD(T) level) with quadruple-ζ basis sets. We demonstrate that good agreement can be achieved if highly a…
E-2-Benzylidenebenzocycloalkanones III. Studies on transmission of substituent effects on IR carbonyl stretching frequencies and 13C NMR chemical shi…
2004
Abstract Single substituent parameter and dual substituent parameter analysis was applied to study transmission of substituent effects on IR carbonyl stretching frequencies of E -2-(X-benzylidene)-1-indanones ( 3 ), -tetralones ( 4 ), and -benzosuberones ( 5 ). Similar analyses were performed for selected 13 C NMR chemical shifts of some E -2-(X-benzylidene)-1-indanones ( 3 ). For a better understanding of the results semiempirical and ab initio quantum chemical calculations were performed to determine the preferred geometry and to calculate the theoretical 13 C NMR chemical shifts of the selected compounds ( 3 ). The differences among the regression coefficients were discussed in terms of …
Using neural networks for (13)c NMR chemical shift prediction-comparison with traditional methods.
2002
Abstract Interpretation of 13 C chemical shifts is essential for structure elucidation of organic molecules by NMR. In this article, we present an improved neural network approach and compare its performance to that of commonly used approaches. Specifically, our recently proposed neural network ( J. Chem. Inf. Comput. Sci. 2000, 40, 1169–1176) is improved by introducing an extended hybrid numerical description of the carbon atom environment, resulting in a standard deviation (std. dev.) of 2.4 ppm for an independent test data set of ∼42,500 carbons. Thus, this neural network allows fast and accurate 13 C NMR chemical shift prediction without the necessity of access to molecule or fragment d…
Billion-Fold Enhancement in Sensitivity of Nuclear Magnetic Resonance Spectroscopy for Magnesium Ions in Solution
2014
Beta-nuclear magnetic resonance (NMR) spectroscopy is highly sensitive compared to conventional NMR spectroscopy, and may be applied for several elements across the periodic table. Beta-NMR has previously been successfully applied in the fields of nuclear and solid-state physics. In this work, beta-NMR is applied, for the first time, to record an NMR spectrum for a species in solution. 31Mg b-NMR spectra are measured for as few as 10^7 magnesium ions in ionic liquid (EMIM-Ac) within minutes, as a prototypical test case. Resonances are observed at 3882.9 and 3887.2 kHz in an external field of 0.3 T. The key achievement of the current work is to demonstrate that beta-NMR is applicable for the…
Kinetic study of methoxide-promoted elimination reactions of some 1,1,1-trichloro-2,2-bis(phenyl-substituted)ethanes
2001
The methoxide-promoted elimination reaction of some 1,1,1-trichloro-2,2-bis(phenyl-substituted)ethanes (1) was investigated. The ortho-substituted derivatives were found to be less reactive than the corresponding ortho-unsubstituted derivatives, irrespective of the nature of their substituent. The reactivity data were correlated with the 13C NMR chemical shift values of C-β of either 1,1,1-trichloro-2,2-bis(phenyl-substituted)ethanes or 1,1-dichloro-2,2-bis(phenyl-substituted)ethenes and the better result was obtained for the former correlation. Activation parameters for the methoxide-promoted elimination of 1 show very similar values for ortho-substituted derivatives. The total data set se…