Search results for "carbon-13"

E-2-Benzylidenebenzocycloalkanones. IV. Studies on transmission of substituent effects on 13C NMR chemical shifts of E-2-(X-benzylidene)-1-tetralones…

2005

Abstract Single substituent parameter (SSP) and dual substituent parameter (DSP) analyses were applied to study the transmission of substituent effects on selected 13C NMR chemical shifts of the cyclic chalcone analogues, E-2-(4′-X-benzylidene)-1-tetralones (2) and E-2-(4′-X-benzylidene)-1-benzosuberones (3). In order to study how the geometry of the cyclic chalcone analogues affects the transmission of substituent effects similar investigations with the respective chalcones (4) were also performed. The results obtained earlier with the five-membered analogue E-2-(4′-X-benzylidene)-1-indanones (1) were also involved in the comparisons. Geometry optimization of the unsubstituted 1a, 2a, 3a a…

13C NMR study on the methoxy carbon chemical shifts in chloro-substituted anisoles and guaiacols

1983

The 13C NMR chemical shifts of methoxy carbons in chlorinated anisoles and guaiacols have been measured for acetone-d6 solutions. Multiple linear regression analysis, and also ‘simple sum rule’ calculations, have been used to estimate the effects of the chlorine atoms (the position and degree of substitution) on the chemical shifts. The most important effects have shown to be due to the chlorine atoms adjacent to the methoxy and hydroxy substituents. For chlorinated guaiacols, the greatest effect is due to the chlorine atom adjacent to the methoxy group. For chlorinated anisoles, the substituents adjacent to the methoxy group (2,6-disubstitution) cause large effects. For both groups of comp…

DFT calculation of structures and NMR chemical shifts of simple models of small diameter zigzag single wall carbon nanotubes (SWCNTs)

2011

Linearly conjugated benzene rings (acenes), belt-shape molecules (cyclic acenes) and model single wall carbon nanotubes (SWCNTs) were fully optimized at the unrestricted level of density functional theory (UB3LYP/6-31G*). The models of SWCNTs were selected to get some insight into the potential changes of NMR chemical shift upon systematic increase of the molecular size. The theoretical NMR chemical shifts were calculated at the B3LYP/pcS-2 level of theory using benzene as reference. In addition, the change of radial breathing mode (RBM), empirically correlated with SWCNT diameter, was directly related with the radius of cyclic acenes. Both geometrical and NMR parameters were extrapolated t…

Comparative NMR and IR spectral, X-ray structural and theoretical studies of eight 6-arylidenedibenzo[b,e]thiepin-11-one-5,5-dioxides

2007

Abstract Eight 6-arylidenedibenzo[b,e]thiepin-11-one-5,5-dioxides are characterized by NMR and IR spectroscopy. Single crystal X-ray structures for three congeners are reported. In addition, the transmission of substituent effects in conjugated double bond system of 6-arylidenedibenzo[b,e]thiepin-11-one-5,5-dioxide framework has been evaluated by calculating the correlations between selected 13C NMR chemical shifts and IR stretching wave numbers and Hammett constants of the substituents locating in the phenyl ring of the arylidene moiety.

Nitrogen-15 NMR Studies on Hydrazines. 2— Substituent Effect Analysis inortho-Substituted Phenylhydrazines and Anilines

1996

15N and 13C NMR spectra of some ortho-substituted phenylhydrazines were measured at natural isotope abundance in DMSO-d6 solutions. The substituent present exerts a larger effect on the chemical shift of the nitrogen atom directly bound to the aromatic ring (N-1), the second one (N-2) showing an attenuated trend of similar sign. Contrary to what observed for para and meta isomers, the cross-correlation between N-1 and N-2 SCS values of ortho-substituted phenylhydrazines is not satisfactory; on the other hand, N-1 SCSs show a reasonably good linear regression with the σR− constants. As expected, no correlation was found between N-1 and C-1 or H-1 SCS values. Correlations between 13C and 15N …

NMR studies of benzoannulation in lithium, sodium and potassium ortho-formylphenolates

2010

Abstract Lithium, sodium and potassium derivatives of (benzo)salicylaldehydes have been prepared and characterized by 1 H and 13 C NMR in order to see how the metal cation and benzoannulation affect spectral parameters. There is no qualitative effect of the alkali metal atom in the compounds studied (from this point of view salicylaldehydes remind β-diketones). On the other hand, 1 H chemical shifts of the hydroxyl and formyl protons and 13 C chemical shifts of C2 (bearing OX, X = H, Li, Na or K) and of that the formyl carbon show the most significant variations being the best indicators of aromatic character of the six-membered quasi-ring of salicylaldehyde. In contrast, C1 (bearing formyl…

ChemInform Abstract: Methylium Ions with OPV Chains - New NIR Dyes.

2010

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.

13C-Decoupled J-Coupling Spectroscopy Using Two-Dimensional Nuclear Magnetic Resonance at Zero-Field

2017

We present a two-dimensional method for obtaining 13C-decoupled, 1H-coupled nuclear magnetic resonance (NMR) spectra in zero magnetic field using coherent spin-decoupling. The result is a spectrum determined only by the proton–proton J-coupling network. Detection of NMR signals in zero magnetic field requires at least two different nuclear spin species, but the proton J-spectrum is independent of isotopomer, thus potentially simplifying spectra and thereby improving the analytical capabilities of zero-field NMR. The protocol does not rely on a difference in Larmor frequency between the coupled nuclei, allowing for the direct determination of J-coupling constants between chemically equivalen…

1982

Multinuclear Magnetic Resonance Study of 2,4,6-Triarylpyridines, 1-Methyl-2,4,6-Triarylpyridinium, and 2,4,6-Triarylpyrylium Cations

1995

Abstract The H, 13C, 15N, and 19F NMR spectra of 2,4,6-triarylpyridines, 1-methyl-2,4,6-triarylpyridinium and 2,4,6-triarylpyrylium perchlorates have been studied. The H NMR signals of protons 3(5) in the heteroaromatic ring are deshielded due to the polarization of C-H bonds caused by delocalization of the positive charge in pyridinium and pyrylium cations. Generally, conformational and structural variations affect the 13C NMR chemical shifts of all carbons in the heteroaromatic ring. Those of carbons 3(5) can best be related to the electron-donating or electron-accepting ability of substituents. However, both electronic character of substituents and charge of heteroatom itself are needed …