S-carbon atom

Anilino vinyl derivatives of thiazolium (30, R = H) or acetanilido (30, R = C0CH3), as well as formyl methylene 30b (methods E-G), give asymmetrical dyes when condensed with a methyl reactive group of another species (Scheme 42). Mesosubstituted symmetrical or unsymmet-rical thiazolocyanines are obtainable via /S-alkylmercaptovinyl thiazolium derivatives (32) (methods H and I) (Scheme 43). a or /S carbon atoms of the trimethine chain can be substituted by acetyl when a dye is treated with acetic anhydride (method L). The hydrolysis of neocyanines lead to trimethine cyanine by fractional elimination of a composant chain (method K). 

The Michael addition of nucleophiles to a, -unsaturated sulfoxides creates initially a-sulfinyl carbanions by nucleophilic attack on the /S-carbon atom. Russell and Becker found that treatment of a mixture of diphenylmethane and anisaldehyde with potassium t-butoxide in DMSO gave at first the condensation product 170, which upon Michael addition afforded the final product 171. 

Thermal 1,5-hydrogen shifts are thus allowed and, because of the symmetry of the T.S. (39), the H atom in the product (37, x = 1) will be on the same side of the common plane of the polyene s carbon atoms as it was in the starting material (36, x = 1) this is described as a suprafacial shift. This latter point would not be experimentally verifiable in the above example, but that thermal 1,5-shifts (which are quite common) do involve strictly suprafacial migration has been demonstrated in the compound (40). This is found, on heating, to yield a mixture of (41) and (42), which are produced by suprafacial shifts in the alternative conformations (40a) and (406), respectively ... 

It is conceivable that the spherically symmetrical Is hydrogen orbital could, alternatively, overlap across the plane of the polyene s carbon atoms, when the terminal lobes of the latter s HOMO were opposite in phase—antarafacial overlap. The terminal lobes of the HOMO will be opposite in phase for (36, x = 0,2,4...), leading to a... 

Because the carbon-halogen bond is polar the OH attacks the S+ carbon atom and so the reaction is classified as a nucleophilic substitution. Reactions in which an -OH group replaces a halogen atom are also called hydrolysis reactions. 

Plus adducts from reaction at the a and S carbon atoms... 

A-Oxidation of pyrazines appears to result in increased shielding of the a and a carbon resonances by 6-11 p.p.m., whereas the /3 and /S carbon atoms are deshielded by 3-4 p.p.m., a trend similar to that observed with substituted pyridines. These results have been qualitatively explained in terms of resonance polar effects (80OMR(13)l72). 

Additional parameters Sw are required in order to calculate the chemical shift values of branched chain alkanes (standard deviation of predicted chemical shifts + 0,3 ppm, B = — 2.3 ppm) (Table 4.3). The values symbolized by Greek letters indicate the change in chemical shift due to substitution of hydrogen by a methyl group at the a to s carbon atoms. The remaining 8 correction parameters Sk, account for the effect of branching. 

The partial charges of the alkyl chain s carbon atoms are quite different (294) the C in the a-position to oxygen possesses the largest density of positive charge. As a result, the scission of Ca-Cp bonds was easier than other C-C bonds. 

The mechanism of oxidation takes place with retention of stereochemistry at the alcohol s carbon atom and so the overall... 

The spectrum you just saw is in fact of lactic acid (2-hydroxypropanoic acid). When you turned the last page, you made some lactic acid from glucose in the muscles of your arm—it is the breakdown product from glucose when you do anaerobic exercise. Each of lactic acid s carbon atoms gives a peak in a different region of the spectrum. 

Figure 5 A schematic diagram of horse heart c)ftochrome c viewed from the front of the heme crevice. The approximate positions of the /S-carbon atoms of the lysine residues are indicated by closed and dashed circles for residues located toward the front and back of Cc, respectively. The electrostatic free energy contribution of lysine i, Vi, is indicated by the number of diagonal marks in the circle, with —0.4kJM per hatch mark. The binding domain is essentially the same for CcO and cytochrome bc ...

In concerted E2 eliminations from monofluorides the orientation of elimination is controlled by the relative acidities of 3-hydrogen in a process that is consistent with a poor leaving group and a transition state with high carbanionic character of the (S-carbon atom [13] (Figure 6.8). 

Catalytic hydrocyanation of mono-olefinic compounds may serve as a very simple example. It stands to reason that HCN is likely to add to the olefinic double bond, H going to one of the latter s carbon atoms, and CN to the other ... 

Owing to this dichotomy, a, -unsaturated aldehydes, ketones, or esters can undergo a nucleophilic attack at either the carbonyl carbon or the )S-carbon atom (Scheme 2.29). The first of these reactions is a familiar addition to the carbonyl group (1,2-addition) which leads, in this case, to the valuable allylic alcohols. Even more intriguing synthetic options, however, are offered by the alternative pathway, the 1,4-addition generally known as the Michael reaction. The classic version of this reaction employed stable carbanions such as those generated in situ from malonic ester or nitromethane under the action of bases and in the presence of Michael acceptors, e.g. methyl vinyl ketone 90 ... 

Wolff et al. showed that 1-alkenes can be obtained from primary alkyl iodides that contain a disubstituted /S-carbon atom by treatment with 1.5 mol... 

Synthesis of tertiary amines.1 Mercuric acetate reacts with an enamine (1) in DMF by attack at the /S-carbon atom to afford an iminium salt (2). Reduction of the salt with sodium borohydride gives the corresponding tertiary amine (3). Yields are in the range 50-90%. 

SUFFIXES The suffix of the name for an organic compound indicates the kind of covalent bonds joining the compound s carbon atoms. If the atoms are joined by single covalent bonds, the compound s name will end in -ane. If there is a double covalent bond in the carbon chain, the compound s name ends in -ene. Similarly, if there is a triple bond in the chain, the compound s name will end in -yne. 

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