Carbon connectivity determination

Schmitz, F.J., S.K. Agarwal, S.P. Gunasekera, P.G. Schmidt, and J.N. Shoo-lery Amphimedine, New Aromatic Alkaloid from a Pacific Sponge, Amphimedon sp. Carbon Connectivity Determination from Natural Abundance C- C Coupling Constants. J. Am. Chem. Soc. 105, 4835 (1983). 

Schmitz, P.J., Agarwal, S.K., Gimasekera, S.P., Schmidt, P.G., and Shoolery, J.N. (1983) Amphimedine new aromatic alkaloid from a Padftc sponge, Amphimedon sp., carbon connectivity determination from natural abundance C- C coupling constants. /. Am. Chem. Soc., 105, 4835 836. 

Look at the two substituents connected to each double-bond carbon, and determine their priorities using the Cahn-lngold-Prelog rules. Then see whether the two high-priority groups are on the same or opposite sides of the double bond. 

How can we determine the carbon-carbon connectivities in a molecule through a combination of homo- and heteronculear shift[Pg.259]

The 2D INADEQUATE spectrum and C-NMR data of 7-hydroxyfrulla-nolide are given. Determine the carbon-carbon connectivities, and subsequently build the entire carbon skeleton based on the 2D INADEQUATE experiment. 

Once acquired, processed, and plotted, carbon-carbon connectivity information can be extracted from a 1,1-ADEQUATE spectrum. There are multiple ways of going about this task and whichever method is used is probably best determined by the preferences of the individual investigator. 

Several structures have been corrected and elucidated with the aid of 13C-detected INADEQUATE. For example, the aH and 13C assignment of frans-3,4, 5-trihydroxystilbene was corrected.53 The structure of a dimeric mero-terpenoid, tridentorubin, was also investigated by 13C-detected INADEQUATE,54 while the structure of A-74528, an inhibitor for 20,50-phosphodiesterase isolated from Streptomyces sp., was elucidated on the basis of several crucial carbon-carbon connectivities that could not be determined from the analysis of its HMBC spectrum.55 Additional examples of the use of 13C-detected INADEQUATE to aid structure determination of small molecules can be found in the literature.25 56-61... 

Another approach to deduce carbon connectivity patterns from HSC data is to determine which hydrogen signals are coupled together, and that is our goal in the next section. 

NMR experiments, involving iH-lH-COSY, DQC-COSY, 1H- 3C-HETCOR, 1H-13C-COLOC and iR-lH-NOESY techniques, have been used in order to determine unambiguously the swainsonine structure and its 1,2,8-triacetate [162]. Four methylene and four methyne protons are evident in the spectrum of swainsonine in its IH- C-HETCOR NMR spectrum, the most downfield carbon resonance (5 75.23) is the methyne carbon connected to nitrogen (C-8a), and the chemical shift of the attached proton (H-8a) is observed at 5 1.89 (dd, J= 10.4 Hz). H-8a is coupled to H-8 (6 3.77, ddd, J= 11, 10, 4 Hz), as well as to H-1 (8... 

The INADEQUATE experiment, developed by Bax et alwill not be presented due to its lack of sensitivity, it is seldom used and this is why little will be said about its processing. A computer program called COSMIC developed by Richardz et which analyses spectra and produces carbon connectivity lists as an output is, however, worthy of mention. The introduction of pulse field gradients made it possible to design much more sensitive proton detection sequences that are quite suitable for the construction of spin networks and structure determination," even if they work only with those carbons that are directly bound to protons. 

If a one-dimensional spectrum does not provide sufficient information to determine the polymer structure, two-dimensional techniques, such as INADEQUATE, may be employed (see Sec. II.E.4). For example, this experiment was used to measure the sizes of the cyclic materials, poly(ethyl a-[(allyloxy)methyl] acrylate) and poly(allyl a-[hydroxymethyl] acrylate) carbon-carbon connectivities could be traced around the rings [100]. Such advanced techniques are particularly useful for characterizing the regiore-gularity of some polymers. Certain monomers, such as vinyl fluoride, can add to a growing chain in either a head-to-tail, ... 

Introduction of disperse fillers (metals and their oxides) has an influence on anionic polymerization. The effect is connected with the presence of reactive surface centers such as OH-groups of various degree of acidity or basicity, metal cations, oxygen anions, admixtured atoms of metals, etc. Anionic polymerization at the surface of disperse carbons is determined by the possibihty of the formation of the clathrate compounds of alkaline metals and graphite. 

The INADEQUATE experiment is designed to map out the entire carbon skeleton of a molecule by providing carbon-carbon connectivities, and offers great possibilities for organic structure determination. However, it suffers severely from the low natural abundance of covalently bound pairs. 

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