Correlation Of Proton Chemical Shifts Research Articles

Carbon−Proton Chemical Shift Correlation in Solid-State NMR by Through-Bond Multiple-Quantum Spectroscopy

A new two-dimensional NMR carbon-proton chemical shift correlation experiment, the MAS-J-HMQC experiment, is proposed for natural abundance rotating solids. The magnetization transfer used to obtain the correlations is based on scaler heteronuclear J couplings. The 2D map provides through-bend chemical shift correlations between directly bonded proton-carbon pairs in a way similar to that in corresponding high-resolution liquid-state experiments. The transfer through J coupling is shown to be efficient and more selective than those based on heteronuclear dipolar couplings. The experiment, which works at high MAS spinning frequencies, yields the unambiguous assignment of the proton resonances. The experiment is demonstrated on several organic compounds.

A study of petroleum alkylcarbazoles using 1H NMR spectroscopy

A precision method for measuring proton chemical shift calculations of methylcarbazoles has been developed. For other abundant substituents the proton chemical shift correlation diagrams are reported. The method makes it possible to identify a number of carbazole structures present in petroleums. General structural regularities of petroleum carbazoles have been defined from 1H NMR data. Methylcarbazole isomers with 1- and 1,8-substituents were found to be most abundant in crude oils. Structures with three or more adjacent Me-groups and with substituents in both 4,5-positions are absent. The distribution of methyl substituents is likely to be controlled partly by migration processes. On the other hand the distribution of non-methyl substituents is of a different character and can vary with chain length.

Two-dimensional POMMIE carbon–proton chemical shift correlated 13C NMR spectrum editing

Two pulse sequences are described for acquisition of two-dimensional, carbon–proton chemical shift correlated 13C NMR spectra by the "phase oscillations to maximize editing technique". One of these sequences provides two-dimensional, carbon–proton chemical shift correlated spectra in which the 1H–1H coupling constants are present in the 1H chemical shift dimension, whereas the other sequence includes a bilinear rotation decoupling unit that removes the vicinal 1H–1H couplings in this dimension. Extensions of these techniques to generation of two-dimensional, carbon–proton chemical shift correlated CH, CH2, and CH313C NMR subspectra from linear combinations of three two-dimensional data sets are described. Decreased residual signals in the edited 2D subspectra have been achieved by Pascal programs that include six floating point coefficients, and a method for their calibration is discussed. Results are reported for troleandomycin (1). Keywords: 13C nuclear magnetic resonance, carbon–proton chemical shift correlation, DEPT, Pascal programs, POMMIE, two-dimensional NMR spectrum editing, troleandomycin.

Identification of C‐glycopyranosides and C‐glycofuranosides by 13C NMR and 1H NMR. Complete assignment of their spectral data using carbon–proton chemical shift correlation spectroscopy

AbstractC‐Glycopyranosides and C‐glycofuranosides were identified using 13C and 1H chemical shift and coupling constant data. Full assignments for all α‐ and β‐anomers were made possible by recourse to carbon–proton chemical shift correlation spectroscopy. Greater steric shielding effects were observed on the carbon atoms in cis‐1,2‐substituted compounds compared with their trans counterparts. Consistent proton chemical shift differences were also noted in that the anomeric protons resonate at lower field in all cis‐1,2‐isomers.

Applications of zero field and 2-dimensional n.m.r. methods to fossil fuels

Three new two-dimensional (2D) solid-state n.m.r. methods are described which have much potential for increasing our knowledge of coal structure. A version of carbon-13/proton chemical shift correlation spectroscopy adapted for solids is outlined and results for one coal examined. A variant of dipolar shift correlation spectroscopy is described which is very convenient for determining the relative amounts of methylene, methine and methyl or non-protonated carbons in a complex mixture such as coal. The results for one hvA coal are presented and shown to be in agreement with its ultimate analysis. The principles underlying zero field n.m.r. are also presented, with an emphasis on deuterium ZF-n.m.r. This technique is assessed as a potentially powerful method in coal structure analysis for the future.

Complete assignment of the 13C NMR spectra of the ring forms of digitoxose by DEPT spectrum editing and two‐dimensional proton chemical shift correlation spectroscopy

AbstractThe 13C chemical shifts of the four isomeric ring forms of D‐digitoxose in dimethyl sulfoxide‐d6 solution have been assigned completely by DEPT 13C NMR spectrum editing and two‐dimensional carbon–proton chemical shift correlation spectroscopy. The 13C chemical shifts are discussed in terms of their dependence on ring size and on anomeric configuration. The equilibrated mixture of four ring forms of D‐digitoxose in dimethyl sulfoxide‐d6 solution has been analysed quantitatively by 13C NMR spectroscopy, and the results compared with those obtained previously by 1H NMR.

ChemInform Abstract: ASSIGNMENT OF THE PROTON NMR SPECTRUM OF HEPTAMETHYL DICYANOCOBYRINATE IN CHLOROFORM SOLUTION BY TWO‐DIMENSIONAL CARBON‐13/PROTON CHEMICAL SHIFT CORRELATION SPECTROSCOPY

Chemischer InformationsdienstVolume 16, Issue 4 Physical Organic Chemistry ChemInform Abstract: ASSIGNMENT OF THE PROTON NMR SPECTRUM OF HEPTAMETHYL DICYANOCOBYRINATE IN CHLOROFORM SOLUTION BY TWO-DIMENSIONAL CARBON-13/PROTON CHEMICAL SHIFT CORRELATION SPECTROSCOPY L. ERNST, L. ERNSTSearch for more papers by this author L. ERNST, L. ERNSTSearch for more papers by this author First published: January 29, 1985 https://doi.org/10.1002/chin.198504050AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume16, Issue4January 29, 1985 RelatedInformation

Correlation of proton chemical shifts with substituent constant: A study in anionic σ complexes based on the bicyclo [3,3,1] nonane skeleton

The PMR spectra of a number of bicyclo [3,3,1] nonane derivatives from 1,3,5-trinitrobenzene, acetoacetanilide and triethylamine were measured in DMSO-d6. The chemical shifts of the NH and enolic OH protons exhibit a linear correlation with Hammett's σ and σn values, respectively.

Assignment of resonances in the Escherichia coli 5 S RNA fragment proton NMR spectrum using uniform nitrogen-15 enrichment

The downfield proton NMR spectrum of aqueous uniformly nitrogen-15 enriched 5 S RNA fragment is presented. Selective nitrogen-15 decoupling difference proton spectroscopy revealed nitrogen-15 chemical shifts of fragment imino nitrogens. Nitrogen chemical shifts of nucleic acid guanine and uracil imino nitrogens have separate small ranges. Nitrogen-15 and proton chemical shift correlation by the heteronuclear decoupling permitted the identification of the base type of some previously unassigned imino proton resonances in the 5 S RNA fragment spectrum. Corresponding resonances in the natural isotopic abundance 5 S RNA fragment spectrum are assigned to base types by comparison with the enriched sample spectrum. 5 S RNA fragment Proton NMR Uniform 15N enrichment Heteronuclear decoupling Chemical shift correlation Assignment strategy

Correlation of proton chemical shifts in proteins using two-dimensional exchange correlated spectroscopy

The full utilization of the information contained in protein NMR spectra requires the assignment of resonances to specific residues. Many one-dimensional and twodimensional NMR experiments can be used to give assignments to amino acid type (1-5) but, with the exception of relatively small proteins, assignments to specific residues can only be obtained by the use of chemical modification or from prior knowledge of the three-dimensional structure of the protein. In some cases, such considerations lead to a considerable simplification of the assignment procedure. A simplification is also possible where the study requires the protein to be compared in two or more different states, such as the native or nonnative states (6, 7) or the ligand-free and ligand-bound states (8). In such cases, provided the spectrum of one of the states has been previously characterized and there is exchange between the two states, the spectrum of the second state can be assigned. Tuna cytochrome c is a heme-containing electron transfer protein of 103 amino acids that may exist in either a diamagnetic oxidation state, ferrocytochrome c or a paramagnetic oxidation state, ferricytochrome c. The iron is low-spin in both oxidation states, and in ferricytochrome c it acts as a shift probe with a highly anisotropic magnetic moment. Consequently, the NMR spectra of ferricytochrome c and ferrocytochrome care very different (9). Because of the paramagnetism of ferricytochrome c, its ‘H NMR spectrum is relatively well resolved, and this has allowed resonances of approximately 45% of its carbon-bonded protons to be specifically assigned using a combination of one-dimensional NMR techniques and specific chemical modification (IO, 1Z). In contrast, the ‘H NMR spectrum of ferrocytochrome c has a considerably smaller chemical-shift dispersion, which allows fewer selective double-resonance experiments, and consequently there are fewer specific assignments available. In the present communication, making use of the assignments of ferricytochrome c, we demonstrate the utility of chemical exchange NMR to assign the corresponding resonances of ferrocytochrome c. An equimolar mixture of ferricytochrome c (CIII) and ferrocytochrome c (CII) undergoes electron exchange according to km *c111 + CII z=t *c11 + CIII. ill

Correlation of proton chemical shifts in proteins using two-dimensional double-quantum spectroscopy

La spectroscopie a 2 quanta et 2 dimensions correles offre des avantages nombreux sur la spectroscopie a 2 dimensions correlees: 1) la multiplicite des pics est tres facile a distinguer; 2) les experiences a 2 quanta permettent l'identification de pics couples avec des differences de deplacements chimiques extremement faibles

Correlation of proton chemical shifts by two-dimensional Fourier transform NMR

Correlation of proton chemical shifts by two-dimensional Fourier transform NMR

Nuclear magnetic resonance spectrum of cis-5,6-disubstituted norbornenes. Correlation of proton chemical shifts with the Taft inductive substituent constant

Nuclear magnetic resonance spectrum of cis-5,6-disubstituted norbornenes. Correlation of proton chemical shifts with the Taft inductive substituent constant