Carbon-13 coupling constants

Stahl, M., Schopfer, U., Frenking, G., Hoffmann, R. W., 1997, Conformational Analysis with Carbon-Carbon Coupling Constants. A Density Functional and Molecular Mechanics Study , J. Org. Chem., 62, 3702. 

The two axes (dimensions) in our 2D spectra are thus both frequency axes. We shall see as we continue that we can adjust our experiment so as to choose different types of frequency information. An early experiment, known as the J-resolved experiment, was designed in such a way that one axis was the (proton or carbon) chemical shift axis and the other the one-bond proton-carbon coupling constant. Flowever, this experiment is not generally very useful for structural determination, so that we shall not discuss it here. 

Thus tin chemical shifts are of considerable use in structural studies. In addition, tin-element coupling constants are easily visible, and particularly in proton and carbon-13 spectra the relevant coupling constant values are of diagnostic use for example both tin-proton and tin-carbon coupling constants show a Karplus-type behaviour. 

Lead-proton and lead-carbon coupling constant values have structural uses, as with tin. Lead chemical shifts are quite sensitive to temperature variations. 

V. Wray, Carbon-carbon coupling constants a compilation of data and a practical guide. In Progress in Nuclear Magnetic Resonance Spectroscopy 1979, Vol. 13, 1979, pp. 177-256. 

T. Parella, 2D methods for the measurement of long-range proton-carbon coupling constants, in Multidimensional NMR Methods for the Solution State, G. A. Morris and J. W. Emsley (eds.), John Wiley Sons Ltd, Chichester, 2010, pp. 305-314. 

One of the propylene derivatives displays the same effects to a lesser degree. The propylene carbonate coupling constants are solvent invariant. 

Conformational analysis of oligosaccharides in solution by NMR spectroscopy is based on the study of chemical shifts, n.O.e. s, and three-bond, proton-carbon coupling constants. Generally, the experimental NMR parameters P. . , (such as n.O.e. s or... 

Until now, the determination of three-dimensional structures of oligosaccharides in solution was based primarily on proton-proton distance information obtained from n.O.e. data. Here, we discuss the application of three-bond proton-carbon coupling constants. 

Three-Bond Proton-Carbon Coupling Constants. Routine applications of the three-bond C-O-C-H proton-carbon coupling constants ( Jpu) have been coiqplicated by experimental difficulties involved in tneir measurement using classical H-coupled NMR spectroscopy and a limited knowledge of the angular dependence of for the C-O-C-H... 

Vicinal proton-carbon coupling constants in a series of conformationally rigid monosaccharide derivatives showed a satisfactory dependence of upon the torsion angles (2). The... 

Aside from NMR, general spectroscopic data have not had great impact on either the bond fixation or the reactivity question. This is probably because the magnitude of the energy necessary to cause either the reaction selectivities or bond fixation is close to the error in these methods. The NMR studies stand out from this generalization. Chemical shift data have been useful in demonstrating that the effects of strained annelations are localized to the C - and tpjo-carbons. Coupling constant... 

Synopsis of Stahl etal. (1991), Conformational Analysis with Carbon-Carbon Coupling Constants. A Density Functional and Molecular Mechanics Study . 

Pyrimidine reacts quantitatively with one equivalent of phenyllithium to yield adduct 96, which is formed by attachment of the phenyl group to position 4(6). This mode of attachment is well supported by the markedly different shifts between positions 4 and 6, by the high field absorption of C-4, and by the magnitude of the hydrogen-carbon coupling constant of C-4 [ 7(CH) = 140 Hz],... 

Measurement of Carbon-Carbon Coupling Constants Without 13C Enrichment INADEQUATE... 

F7g. 2.49. INADEQUATE spectra of the 13C—UC doublets of piperidine (neat liquid. 50 MHz), including an analysis of one-, two-and three-bond carbon-carbon coupling constants [58]. 

As shown in Fig. 2.48 (e), the vectors of C13 — C13 doublet magnetizations are aligned in opposite directions when irradiated by the 90 pulse. Thus, in the INADEQUATE spectrum the C13 —C13 doublet signals will appear with the corresponding antiphase relationship, as shown in Fig. 2.49, which also demonstrates the effective suppression of the strong 13C — 12C signals of piperidine. Analysis of carbon-carbon coupling constants can be performed easily in this simple case. 

Each pair of connected carbon atoms, CA — CB, is thus segregated according to its sum of chemical shifts, so that the actual magnitude of the carbon-carbon coupling constant is no longer required for identification of the bond. A straightforward method of tracing out the carbon skeleton of a compound is thus established. 

Moreover, INADEQUATE experiments for analysis of carbon-carbon connectivities require careful interpretation when the magnitudes of two-bond and one-bond carbon-carbon coupling constants approach each other. Large two-bond CC couplings, for example, are observed for alkynyl, cyclobutyl, cyclobutenyl substructures and for carbonyl compounds substituted by electronegative groups in an a position. 

Table 3.11 (a). One-Bond Carbon-Carbon Coupling Constants Jcc. ... 

Compound Formula 2 Jcc ( z) Table 3.11 (b). Longer-Range Carbon-Carbon Coupling Constants 2JCC and 3Jqc, Data from Ref. [133 a],... 

Two-bond carbon-carbon coupling constants (2JCC) are usually smaller than three-bond couplings (3JCC), as shown for hexanoic and (E)-2-hexenoic acid ... 

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