Long-range Proton-proton Coupling Research Articles

Long-range coupling in cyclic silanes.

We report the synthesis of a mixed methyl- and hydro-substituted cyclosilane (1) possessing cis/trans stereoisomerism. Each diastereomer of 1 possesses distinct symmetry elements (cis-1: Cs-symmetric; trans-1: C2-symmetric). Cyclosilane 1 is a model system to probe configuration- and conformation-dependent long-range proton-proton coupling. Extensive NMR spectroscopic characterization is reported, including one-dimensional 1H NMR and 29Si DEPT and INEPT+ spectra and two-dimensional 1H-29Si and 1H-1H correlated spectroscopy (HSQC, HMBC, COSY). On the basis of these experiments, molecular connectivity consistent with four-bond 1H-1H coupling is confirmed.

Synthesis of new cyano-substituted analogues of Tröger's bases from bromo-derivatives. A stereochemical dependence of long-range (n JHH , n=4, 5, and 6) proton-proton and proton-carbon (n JCH , n=1, 2, 3, 4, and 5) coupling constants of these compounds.

A free-catalyst microwave-assisted cyanation of brominated Tröger's base derivatives (2a-f) is reported. The procedure is simple, efficient, and clean affording the nitrile compounds (3a-e, I) in very good yields. Complete assignment of 1 H and 13 C chemical shifts of 2a-f, I and 3a-d, I was achieved using gradient selected 1D nuclear magnetic resonance (NMR) techniques (1D zTOCSY, PSYCHE, DPFGSE NOE, and DEPT), homonuclear 2D NMR techniques (gCOSY and zTOCSY), and heteronuclear 2D NMR techniques (gHSQCAD/or pure-shift gHSQCAD, gHMBCAD, bsHSQCNOESY, and gHSQCAD-TOCSY) with adiabatic pulses. Determination of the long-range proton-proton coupling constants n JHH (n=4, 5, 6) was accomplished by simultaneous irradiation of two protons at appropriate power levels. In turn, determined coupling constants were tested by an iterative simulation program by calculating the 1 H NMR spectrum and comparing it to the experimental spectrum. The excitation-sculptured indirect-detection experiment (EXSIDE) and 1 H-15 N CIGARAD-HMBC (constant time inverse-detection gradient accordion rescaled heteronuclear multiple bond correlation) were applied for determination of long-range carbon-proton coupling constants n JCH (n=2, 3, and 4) and for assignment of 15 N chemical shift at natural abundance, respectively. DFT/B3LYP optimization studies were performed in order to determine the geometry of 2c using 6-31G(d,p), 6-311G(d,p), and 6-311+G(d,p) basis sets. For calculation of 1 H and 13 C chemical shifts, n JHH (n=2, 3, 4, 5, and 6), and n JCH (n=1, 2, 3, and 4) coupling constants, the GIAO method was employed at the B3LYP/6-31G(d,p), B3LYP/6-31+G(d,p), B3LYP/6-311+G(d,p), B3LYP/6-311++G(2d,2p), B3LYP/cc-pVTZ), and B3LYP/aug-cc-pVTZ) levels of theory. For the first time, a stereochemical dependence magnitude of the long-range n JHH (n=4, 5, and 6) and n JCH (n=1, 2, 3, 4, and 5) have been found in bromo-substituted analogues of Tröger's bases.

Molecular orbital calculations of the long-range proton-proton coupling constants in purine and pyrimidine nucleosides

The molecular orbital INDO method is used for the calculation of long-range NMR proton-proton coupling constants between H1, and protons of the base and between the protons of the furanose ring in purine and pyrimidine nucleosides. The computations show that the couplings between H1, and the protons of the base are negligible in the purine nucleosides and are very sensitive to the torsion angle about the glycosidic bond in pyrimidine nucleosides. For uridine and its derivatives the calculated J 1, 5 are in agreement with experiment for an anti conformation of these compounds. For α- and β-pseudouridines, J1, 6 is important and may be large for anti as well as syn conformations. The long-range couplings between the protons of the furanose ring vary little with the puckering of the sugar.

Synthesis and conformational analysis of substituted 2,6-dioxabicyclo[3.1.1]heptanes: 1,3-anhydro-2,4-di- O-benzyl-6-deoxy-β- d-glucopyranose by 1H-NMR spectroscopy and molecular mechanics calculation

A highly selective ring opening reduction of methyl 3- O-allyl-2- O-benzyl-4,6- O-benzylidene-α- d-glucopyranoside provided the 2,4-di- O-benzyl derivative. This was toluenesulfonylated or iodinated and subsequently reduced to give crystalline methyl 3- O-allyl-2,4-di- O-benzyl-6-deoxy-α- d-glucopyranoside in good yield. Acid hydrolysis followed by deallylation and acetylation afforded a 1,3-diacetate which, on treatment with hydrogen chloride in diethyl ether, gave the crystalline key intermediate 3- O-acetyl-2,4-di- O-benzyl-α- d- glucopyranosyl chloride, Ring closure of the chloride with lithium methoxide afforded 1,3-anhydro-2,4-di- O-benzyl-6-deoxy-β- d-glucopyranose ( 15). Vicinal and long-range proton-proton coupling constants suggested that the conformation of the 1,3-anhydro sugar ether is essentially B 2,5 for the pyranose ring and a chair for the 1,3-dioxane ring. Molecular mechanics calculations using program MMP2 were applied to compound 15 and its analogue, 1,3-anhydro-2,4-di- O-benzyl-β- d-rhamnopyranose, and the results were in good agreement with those calculated by a modified Karplus equation and those measured on molecular models.

Experimental and theoretical studies of long-range proton-proton coupling constants in ring-substituted styrenes

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTExperimental and theoretical studies of long-range proton-proton coupling constants in ring-substituted styrenesM. Barfield, C. J. MacDonald, I. R. Peat, and W. F. ReynoldsCite this: J. Am. Chem. Soc. 1971, 93, 17, 4195–4202Publication Date (Print):August 1, 1971Publication History Published online1 May 2002Published inissue 1 August 1971https://doi.org/10.1021/ja00746a017RIGHTS & PERMISSIONSArticle Views58Altmetric-Citations44LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (911 KB) Get e-Alerts Get e-Alerts

The mechanism of long-range proton-proton coupling

The perturbation treatment of proton-proton coupling developed in earlier papers, has been extended to allow for electron delocalization through intervening C-C and C-H bonds.