Carbon-13 magnetic resonance spectroscopy

The spin-spin interaction of the ring CHj group protons with the ortho-positioned protons and the protons of the CHj fragment of the (CH3)3SiCH2 group amount to 2.5 and 2 cps, while those of the ring vicinal protons, to 9 cps. 

The attempts to generate 2,6-dimethyl-4-trimethylgermylmethyl- and 2,6-dimethyl-4-trimethylstannyl-methylbenzenium ions by interaction between the derivatives of benzene and HCI/AICI3 at —80 °C in CHjClj have resulted in splitting the CHj-metal bond with the formation of the methylbenzenium ion 

The PMR spectra of methylbenzenium ions containing CHjCl, CH2C(=0)H, 

CH2C(=0H)H and CH2CgHj at the ring sp hybridized carbon atom are given in 

The methods of generating methylbenzenium ions containing the CH3 group and an electronegative substituent X at the ring sp -hybridized carbon atom are discussed in Sect. II. The influence of X on the chemical shifts of the CHj-group protons (above all those of the I-CH3 group) can be estimated from Table 21 (cf. also Table 11). 

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Use of Carbon-13 Magnetic Resonance Spectroscopy for Biosynthetic Investigations A. G. 

Nuclear magnetic resonance (NMR) spectroscopy (Section 14.1) A type of spectroscopy that uses transitions between the energy states of certain nuclei when they are in a magnetic field to supply information about the hydrocarbon part of a compound. There are two NMR techniques that are of most use to organic chemists proton magnetic resonance (lH-NMR) spectroscopy, which provides information about the hydrogens in a compound, and carbon-13 magnetic resonance spectroscopy (13C-NMR), which provides information about the carbons in a compound. 

Using carbon-13 magnetic resonance spectroscopy, Rinehart and his collaborators have shown49 that the biosynthesis of the streptovaricins is very similar to that of the rifamycins. Streptovaricin D is synthesized from a C7N unit of unknown origin to which 8 propionic acid residues and two acetic acid residues are attached, whereby the direction of growth is the same as that of the rifamycins. In contrast to the... 

One other pyridine alkaloid has been detected in dendrobatid frogs. The structure of this minor alkaloid, noranabasamine (XIII), was established by proton and carbon-13 magnetic resonance spectroscopy (14). The ultraviolet spectrum was as follows X ,ax (CH3OH) 244 nm, e 11,000, 275 nm, e 10,000. The optical rotation, [a]o, was -14.4° (CH3OH). Anabasamine, a plant alkaloid, also is levorotatory, but it is unknown whether noranabasamine, now given a code number 239J, has the same 2S configuration. 

Booth H, Everett JR. The experimental determination of the conformational free energy, enthalpy, and entropy differences for alkyl groups in alkylcyclohexanes by low temperature carbon-13 magnetic resonance spectroscopy. J Chem Soc Perkin II 1980 255-259. 

Carbon-13 magnetic resonance spectroscopy has found some use in determining the fraction of carbon atoms that are in aromatic locations (fj as well as in attempting to define the structure of the aromatic ring system, although the question of the aromatic nature of coal as determined by this method is certainly open to debate. And there is the possibility of serious under estimation of the aromatic nature of coal by this method (Snape et al., 1989). 

Given the widespreaid use and interest in ATA for the inhibition of particular cellular processes, and the well documented fact that ccmner-cial lots of ATA are impure, we felt it was necessary to structurally characterize the active con nents present in "ATA preparations. We achieved fractionation by the condtiined use of dialysis and ultrafiltration, and structural elucidation by carbon-13 magnetic resonance spectroscopy. Evidence will be presented that ATA is a mixture of polymers of the phenol-formaldehyde type whose inhibitory potency increases with the average moleculw weight of the polymer fraction. 

Dorman, D , and Bovey, F.A. (1973) Carbon-13 Magnetic Resonance Spectroscopy, The Spectrum of Proline in Oligopeptides, J. Org. Chem., 38, 2379-2383. Kessler, H. (1982) Conformation and Biological Activity of Cyclic Peptides, Angew. Chem., Int. Ed. Engl., 21, 512-523. 

Such a protocol has been used to characterize a large number of dendrobatid alkaloids. Two additional alkaloids of the histrionicotoxin class were detected and characterized. These were histrionicotoxins 235 A and 259 (see Fig. 13). The structure of histrionicotoxin 259 has been confirmed by proton and carbon-13 magnetic resonance spectroscopy (255). Histrionicotoxins as a class are characterized by a major fragment ion (CsHioN) at m/z 96. All form O-acetyl derivatives and all of the eleven... 

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