Methine C atom

In contrast, for R = C6H3Pr2-2,6, H transfer and an unusual coupling of two Pr methine C atoms resulted in a linked formamidinate complex as illustrated in Scheme 193. °° ... 

COjEt R"" = COPh, = COPh R = Bu", R = H, R = COPh Z = As, R = Ph, R2 = H, R3 = COPh or COjMe MejSCHCOPh CsHjNCHCOPh), in contrast to the dinuclear complexes [Hg2(Ylide)2Cl4] formed with HgCl2. It was found that v(CO) for the complexes exhibits a blue shift relative to the free ylide, the values approaching those of completely protonated onium salts, indicative of coordination via the methine C atom. Similar thiocyanato-complexes showed both N and S bonding modes with N co-ordination favoured by complexes of the least basic ylides. 

Oxidation of porphyrins was used to elucidate its structure. It leads (e.g. with KMn04) the formation of pyrrole-2,5-dicarboxylic acids with retention of the methine C-atoms, or (e.g. with Cr03) to maleimides with loss of the methine C-atoms ... 

Biological degradation of haemoglobin to bilirubin (see p 98) starts (expressed in a simplified manner) with oxidation at a methine C-atom forming iron oxyphlorin which exists as enol 29 in an acidic and as ketone 30 in a basic medium. Further oxidation of 30 leads to biliverdin with extrusion of the methine bridge which, on reduction, yields bilirubin. 

Synthesis and characterization of triphyrins, a new family of porphyri-noids containing three pyrrole rings and more than three methine C atoms 13H(87)1209. 

In this simplified example of phenylalanine, in the first iteration the methyl groups arc given a value of I in the first classification step because they contain a primaiy C-atom, The methylene group obtains a value of 2, and the methine carbon atom a value of 3. In the second step, the carbon atom of the methyl group on the left-hand side obtains an extended connectivity (EC) value of 2 because its neighboring atom had a value of 2 in the first classification step. 

The methine carbon atom also obtains an EC value of 4 (= 1 -h 1 + 2) in the second iteration. This process is repeated iteratively until the number of different EC values (c) is lower than or equal to the number of EC values in the previous iteration. Then the relaxation procc.ss is terminated. Next, the EC numbers of the previous iteration are taken for a canonical numbering and for the determination of constitutional symmetry (Figure 2-44),... 

In the case of partly modified polymers the spectra B, C and D show more complicated structures which can be presumably due to significant neighbouring-groups effects between phenyl carbonate groups and modified or unmodified groups linked to the next aliphatic methine carbon atoms. 

In trans 2-butene, the chemical shift variations are almost identical, which could correspond to a general intermolecular interaction. However, if the comparison is made with liquid trans 2-butene, specific interactions are clearly shown again by the greater change in the methinic C carbon atom. 

In chlorophyll iron as complex-forming metal is replaced by magnesium (Willstatter). The structure of chlorophyll differs from that of haemin as follows. In chlorophyll one propionic acid chain (a) in oxidised form has condensed with a methine carbon atom to form a cyclopentane ring which takes the position at (c) of the vinyl ethyl. Further the two carbonyl groups are esterified and one of the four pyrrole rings is partially hydrogenated... 

This chapter, therefore, ends the monograph with a potpourri of reactions all of which occur without a change in oxidation state. In many cases, the reaction is one of nucleophilic attack at an electrophilic C-atom. The result is often hydrolytic bond cleavage (e.g., in carbohydrate conjugates, disubstitut-ed methylene and methine groups, imines, oximes, isocyanates, and nitriles, and various ring systems) or a nucleophilic substitution (e.g., hydrolytic de-halogenation of halocarbons and chloroplatin derivatives, and cyclization reactions). The formation of multiple bonds by dehydration is a special case to be discussed separately. 

With heterocycles containing an sp--nitrogen atom, a totally different problem can occur, namely nucleophilic addition of the base to the azo-methine (C=N) bond. The use of very sterically hindered bases such as lithium tetramethylpiperidide (LiTMP) can prevent this type of addition in certain cases, but bases of this sort tend to be expensive and not suitable for general use. However, two different approaches to overcoming the problem of azomethine addition have been developed over the years, both relying on the fact that the addition is temperature dependent, and that by enabling metalation reactions to be performed at low temperatures, the desired carbanion formation can often be achieved. 

In the side chain of cholesteryl chloride C atoms with the same number of attached protons are found to behave similarly [166] the methyl carbon atoms C-26 and C-27 relax more slowly than C-21, the methylene carbon C-24 slower than C-23, and the methine carbon atom C-25 slower than C-20. The mobility of the side chain thus increases with increasing distance from the steroidal skeleton. 

Tridentate bonding involving both acetyl oxygen atoms and the methine carbon atom occurs in dimeric [Pt(C,0,0-C3 H7 COCHCOC, H7)Me3 ]2, whose structure, shown schematically in (5) is established by both X-ray55 and neutron diffraction studies.56... 

Fig. 7. C-NMR spectrum of 1,3-Bd and n-BuLi, DP — 10-12. The signal at 99.6 ppm in curve A was split into a doublet upon coupling with proton nucleus. This suggests that this absorption is that of a methine carbon atom.

As expected, [2-13C]glucose leads to the labelling of the methylpyrazines almost exclusively in the quaternary C atoms. There was evidence of a small amount (about 5%) of label in the methine groups and this was attributed to retroaldolisation of glucose or the glucosylamine (see ref. 92). 

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