Methyl carbon-13 nuclear magnetic resonance

Instmmental methods of analysis provide information about the specific composition and purity of the amines. QuaUtative information about the identity of the product (functional groups present) and quantitative analysis (amount of various components such as nitrile, amide, acid, and deterruination of unsaturation) can be obtained by infrared analysis. Gas chromatography (gc), with a Hquid phase of either Apiezon grease or Carbowax, and high performance Hquid chromatography (hplc), using siHca columns and solvent systems such as isooctane, methyl tert-huty ether, tetrahydrofuran, and methanol, are used for quantitative analysis of fatty amine mixtures. Nuclear magnetic resonance spectroscopy (nmr), both proton ( H) and carbon-13 ( C), which can be used for quaHtative and quantitative analysis, is an important method used to analyze fatty amines (8,81). 

Abscisin II is a plant hormone which accelerates (in interaction with other factors) the abscission of young fruit of cotton. It can accelerate leaf senescence and abscission, inhibit flowering, and induce dormancy. It has no activity as an auxin or a gibberellin but counteracts the action of these hormones. Abscisin II was isolated from the acid fraction of an acetone extract by chromatographic procedures guided by an abscission bioassay. Its structure was determined from elemental analysis, mass spectrum, and infrared, ultraviolet, and nuclear magnetic resonance spectra. Comparisons of these with relevant spectra of isophorone and sorbic acid derivatives confirmed that abscisin II is 3-methyl-5-(1-hydroxy-4-oxo-2, 6, 6-trimethyl-2-cyclohexen-l-yl)-c s, trans-2, 4-pen-tadienoic acid. This carbon skeleton is shown to be unique among the known sesquiterpenes. 

The H and nuclear magnetic resonance (NMR) chemical shift of all the parent structures are fully reported in CHEC-II(1996) <1996CHEC-II(6)447>. Since then, the complete proton and carbon chemical shift assignments have been made for 2- and 3-formyl, acetyl, or methyl phenoxathiin <1996PJC36>. 

The assembly of the carbon skeletons of these unusual hydrocarbons was first studied in Carpophilus freemani Dobson, through careful GC-MS and Nuclear Magnetic Resonance (NMR) studies of the incorporation of 2H or 13C-labeled precursors (Petroski et al., 1994). Assembly of the carbon skeleton of the aggregation pheromone of C. freemani, (2 , 4 , 6ii)-5-ethyl-3-methyl-2,4,6-nonatriene, involves initiation with acetate elongation with first propionate (to provide the methyl branch), then butyrate (to provide the ethyl branch) and chain termination with a second butyrate (Figure 6.7). At some point, loss of C02 from one of the butyrate units occurs to yield the appropriate hydrocarbon, but Petroski et al. (1994) were unable to determine which of the butyrate units loses its carboxyl group. Bartelt and Weisleder (1996) studied the biosynthesis of 15 additional methyl- and/or ethyl-branched, tri- and tetraenes in the related... 

Fischer recognized the first carbene complexes in 1964. They were formed by the attack of an alkyllithium on a metal carbonyl followed by methylation (equations 1 and 2). Resonance form (2), considered as the dominant one in the heteroatom stabilized Fischer carbenes, shows the multiple character of this carbon-heteroatom bond. This effect is responsible for the restricted rotation often observed for this bond in nuclear magnetic resonance (NMR) studies. For example cis and trans isomers (6) and (7) of methoxymethyl carbenes rapidly interconvert at room temperature, but can be frozen out in the proton NMR at -40 °C. By contrast, the M-C bond is close to single and often rotates freely. 

As indicated in Section 11,4 (p. 64), direct treatment of alkyl halides with sodium cobalt tetracarbonyl, carbon monoxide, and methanol at elevated temperatures and pressures yields esters. Surprisingly, application of this reaction at 60° (using methanol instead of ether) to methyl tri-0-acetyl-2-deoxy-2-iodo-/3-D-glucopyranoside gave, almost exclusively, the elimination product (88) (in deacetylated form) and a compound presumed to be (on the basis of nuclear magnetic resonance evidence only) the branched-chain ester (87) in less than 0.5 % yield. It is thought that, in the presence of methanol, the sodium cobalt tetracarbonyl dissociates to yield sodium methoxide, and that this causes deacetylation of the substrate. 

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