Carbon atom trivalent

Chiral carbon atoms are common, but they are not the only possible centers of chirality. Other possible chiral tetravalent atoms are Si, Ge, Sn, N, S, and P, while potential trivalent chiral atoms, in which non-bonding electrons occupy the position of the fourth ligand, are N, P, As, Sb, S, Se, and Te. Furthermore, a center of chirality does not even have to be an atom, as shown in the structure represented in Figure 2-70b, where the center of chirality is at the center of the achiral skeleton of adamantane. 

Trivalent ( classical carbenium ions contain an sp -hybridized electron-deficient carbon atom, which tends to be planar in the absence of constraining skeletal rigidity or steric interference. The carbenium carbon contains six valence electrons thus it is highly electron deficient. The structure of trivalent carbocations can always be adequately described by using only two-electron two-center bonds (Lewis valence bond structures). CH3 is the parent for trivalent ions. 

The C-NMR chemical shift of the trivalent carbon is a sensitive indicator of carbocation structure. Given below are the data for three carbocations with varying aryl substituents. Generally, the larger the chemical shift, the lower is the electron density at the carbon atom. 

Almost all stable organic species have tetravalent carbon atoms, but species with trivalent carbon atoms also exist. Carbocatiom are one such class of compounds. 

Carbocations, ions that contain a trivalent, positively charged carbon atom, react with water to give alcohols ... 

Carbanion (Section 19.7) A carbon anion, or substance that contains a trivalent, negatively charged carbon atom (R3C -). Carbanions are s/Ahybridized and have eight electrons in the outer shell of the negatively charged carbon. 

Carbocation (Sections 5.5, 6.9) A carbon cation, or substance that contains a trivalent, positively charged carbon atom having six electrons in its outer shell (R3C+). 

The intracellular and plasma membranes have a complex structure. The main components of a membrane are lipids (or phospholipids) and different proteins. Lipids are fatlike substances representing the esters of one di- or trivalent alcohol and two aliphatic fatty acid molecules (with 14 to 24 carbon atoms). In phospholipids, phosphoric acid residues, -0-P0(0 )-O-, are located close to the ester links, -C0-0-. The lipid or phospholipid molecules have the form of a compact polar head (the ester and phosphate groups) and two parallel, long nonpolar tails (the hydrocarbon chains of the fatty acids). The polar head is hydrophihc and readily interacts with water the hydrocarbon tails to the... 

These differences were explained by solvation effects in the liquid phase. The carbenium ions are more efficiently stabilized by solvation than carbonium ions, because the former have unsaturated trivalent carbon atoms. In this way, the energy barrier between the (solvated) carbenium ion and the carbonium ion transition state increases. 

We have recently characterized the heptacyclic alkaloid chilocorine from the ladybird (coccinellid) beetle Chilocorus cacti (23). In spite of its superficial complexity, this structure is easily dissected into two tricyclic moieties, A and B, each of which can be regarded as an acetogenin which has been elaborated from a straight chain of 13 carbon atoms stitched together at three points by a trivalent nitrogen atom. 

Intermediates such as 224 resulting from the nudeophilic addition of C,H-acidic compounds to allenyl ketones such as 222 do not only yield simple addition products such as 225 by proton transfer (Scheme 7.34) [259]. If the C,H-acidic compound contains at least one carbonyl group, a ring dosure is also possible to give pyran derivatives such as 226. The reaction of a similar allenyl ketone with dimethyl mal-onate, methyl acetoacetate or methyl cyanoacetate leads to a-pyrones by an analogous route however, the yields are low (20-32%) [260], The formation of oxaphos-pholenes 229 from ketones 227 and trivalent phosphorus compounds 228 can similarly be explained by nucleophilic attack at the central carbon atom of the allene followed by a second attack of the oxygen atom of the ketone at the phosphorus atom [261, 262], Treatment of the allenic ester 230 with copper(I) chloride and tributyltin hydride in N-methylpyrrolidone (NMP) affords the cephalosporin derivative 232 [263], The authors postulated a Michael addition of copper(I) hydride to the electron-... 

A term for a positively-charged trivalent carbon atom (a carbocation). RsC is a carbenium ion. The term car-... 

Our choice was the two series of dendritic polymers 5 and 6, depicted in Figure 4, which have all their open-shell centers (or trivalent carbon atoms) sterically shielded by an encapsulation with six bulky chlorine atoms in order to increase their life expectancies and thermal and chemical stabilities. Indeed, it is very well known that the monoradical counterpart of both series of polyradicals, the perchlo-rotriphenyl methyl radical, shows an astonishing thermal and chemical stability for which the term of inert free radical was coined. The series of dendrimer polymers 5 and 6 differ in the nature and multiplicity (or branching) of their central core unit, N, as well as in their branch-juncture multiplicities, N Thus, series 5 has a hyperbranched topology with = 3 and = 4, while dendrimer series 6 has a lower level of branching with = 3 and = 2, and the topology of a three-coordinated Cayley tree. 

After Gomberg had discovered triphenylmethyl in 1900, this body has been the subject of great interest. Gomberg already from the beginning stated the view that this was a compound which contained a trivalent carbon atom, i.e. a free radical . This immediately raised objections, and Gomberg himself found himself forced to give up his idea, if only for a while. 

It is well known that iraras-bicyclo[3,3,0]octane is a rigid and strained system, whereas the cis-isomer is almost strain-free. Pyrrolizidine differs in that one of the carbon atoms is substituted by a trivalent nitrogen atom which does not rigidly fix the bicyclic system. For this reason, pyrrolizidine, although it probably occurs in the preferred cia-conformation,74 has no stereoisomers. The two rings of the pyrrolizidine system form a dihedral angle with the axis along the C(8)—N bond. 

The products contain a trivalent, positively charged carbon atom surrounded by a solvent shell and a bromide ion which carries a negative charge and is surrounded and hydrogen bonded to a shell of solvent molecules. The distance between the carbon and the bromine atom in the products is much greater than in the reactants. The bond between carbon and bromine is broken as the bromide moves away from the carbon and the pair of bonding electrons ends up in the valence shell of the bromide ion. We can depict this reaction using curved-arrow notation which tracks electron movement. 

The grafting of CMPO moieties on the narrow rim affords a strong decrease of extracting ability toward lanthanides, trivalent actinides, and tetravalent plutonium from acidic solutions. The distribution ratios for the different calixarenes in NPHE are low, except for CPn3 for which the number of carbon atoms in the spacer is four, but even for this compound, the distribution ratios are lower than those obtained with their wide-rim counterparts (Figure 4.11). 

Similarly the introduction of alkyl substituents into the radical has only a small effect. Table 2 illustrates the effect that alkyl substituents attached to the trivalent carbon atom have on the rate of addition to ethylene. The variation in rate is very small and in fact the apparently regular decrease in rate of the more branched radicals is always within possible experimental error (the data for CH3CH2CH2- gives a relative rate of 0.25). In general both Tables 1 and 2 show that the introduction of methyl substituents into either the alkene or the alkyl radical reduces the rate of addition. This could be accounted for either by polar forces or by steric hindrance. 

The natural conclusion to be drawn from Table 12 is that steric effects play a very big part indeed in determining the rate and orientation of radical addition. We believe this conclusion to be correct, but, just as it is impossible to separate bond strength effects from polar effects, so it is impossible to separate steric effects in radical addition from polar effects. Any steric hindrance in the addition of a radical to an olefin will depend to a major extent on the shape of the radical. However, the shape of the radical is directly connected to the electron density at the trivalent carbon atom. 

A fullerene is a geometrically closed trivalent polyhedral network in which n carbon atoms are arranged in 12 pentagonal and n—10) hexagonal rings. Such a... 

Fats and oils are triesters of the trivalent alcohol glycerol and three (different) even-numbered aliphatic carboxylic acids, the fatty acids. Fats and oils differ in the length and the number of unsaturated bonds in the carbon chain. The shorter Cio-Ci4-fatty acids are obtained from coconut oil and palm kernel oil. These fatty acids are mostly saturated, and they are used in the manufacture of detergents. Cig-fatty acids are more widely used. Oleic acid, a Cig-fatty acid with an unsaturated bond on the ninth carbon atom, can be produced from many crops. Specific varieties or genetically modified plants, such as rape, have a content of over 90% oleic acid [4]. 

We note upon inspection of the data in Table XIV that the chemical shifts in these carbonium ions (Via, b, and c) follow the normal order observed when substituents on a fully substituted carbon atom are varied from R = H (most shielded) to CH3 to C6H5 (least shielded), rather than for substituents on an electron-deficient trivalent carbon atom, where the CH3-substituted carbon atom is less shielded than the analogous phenyl-substituted carbon atom (58). This is a rather clear-cut indication that the carbinyl carbon atoms in complexes Via, b, and c are nearly fully bonded and only slightly electron-deficient. The slight increase in shielding of the CH3 carbon when VIb is formed from the alcohol and of the C-l carbon of the phenyl group of Vic provides further confirmation of this. 

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