Aliphatic carbon atoms

Compounds acting as coupling components must have a high electron density on the reacting carbon atom. Therefore diazonium ions react only at aliphatic carbon atoms which are activated by electron-withdrawing groups (usually acyl or nitro). There is... 

Sutton, P. W. Dahl, L. F. (1967) "The molecular structure of Co3(CO)g CCH3. A tricyclic organocobalt complex containing a metal-coordinated triply bridging aliphatic carbon atom, J. Am. Chem. Soc. 89,261-268. 

X10-6 for H bonded to C. The atomic susceptibility of diamond is — 6.00X10-6 we accept this for aliphatic carbon. Now in the aliphatic carbon atom there are four L electrons contributing to the susceptibility in all directions, whereas in the aromatic carbon atom only three remain to be considered, the fourth being involved in the calculation of AK. For aromatic carbon, aside from the pz electron, we accordingly assume the atomic susceptibility... 

With regard to the findings of the studies conducted by Eichhorn and Knepper [34], an interference with monocarboxylated DATS could be ruled out as the molecular ions of these intermediates have m/z two units lower than that of SPC with the same number of aliphatic carbon atoms.1 Moreover, they do not produce the fragment m/z 183, which was always detected along with the [M — H] of SPC.2... 

In the preceding section substituent effects on aliphatic carbon atoms, mostly in monosubstituted molecules, were examined by comparing their, 3C chemical shifts with those of the respective unsubstituted parent compounds. If one proceeds to molecules M bearing two substituents (X, Y Scheme 43) it often happens that SCS(X) (140 — 141) or SCS(Y) (139 — 141) differ considerably from the values expected for the monosubstituted prototypes (138 — 139 and 138 — 140, respectively). 

Labelling the aliphatic carbon atom with (53%) allowed comparison of the nuclear magnetic C -shifts of the covalent sp -hybridized triphenyl-C -methanol (in tetrahydrofuran solution) with that of the labelled triphenylcarbonium ions, (C8Hg)3C HS07 (triphenyl-C -methanol in sulphuric acid solution). A shift of 129-6 p.p.m. to lower shielding was observed in the triphenylcarbonium ion, as compared with the covalent triphenylmethanol. 

Oxidation Aliphatic Carbon Atoms. Oxidation at the terminal carbon atom of an alkyl substituent is co-oxidation oxidation of the carbon atom located second from the end is co-1 oxidation. Unless specifically catalyzed by an enzyme, co-1 oxidation tends to occur more frequently. The anticonvulsant drug ethosuximide is metabolized at both the CO and co-1 position. 

The stability of the complex is higher with higher basicity of the oxygen atoms. (The atoms attached to aromatic rings are less basic than the ones attached to aliphatic carbon atoms). 

A more recent kinetic study has indicated that under acidic conditions a-ketonitrosoalkanes may rearrange rapidly to the oxime [33]. Amines also bring about the isomerization of nitrosocyclohexane [34], These observations along with the older observations mentioned in Touster s review [2] imply that the whole question of the nitrosation of aliphatic carbon atoms should be reexamined with modern techniques to establish the reaction conditions under which the true aliphatic nitroso compounds (or their dimers) can be isolated. 

S. M. Parmerter, The coupling of diazonium salts with aliphatic carbon atoms. Org. React. 10, 1 (1959). 

The nitrosation of aliphatic carbon atoms, particularly of carbon atoms activated by adjacent carbonyl, carboxyl, nitrile, or nitro groups, has been reviewed in great detail [2]. Judging from this review, with few exceptions, nitrosation of active methylene compounds leads to the formation of oximes (unfortunately termed isonitroso compounds in the older literature). The few exceptional cases cited in which true nitroso compounds (or their dimers) were formed involved tertiary carbon atoms in which no hydrogen atoms were available to permit tautomerism to the oxime or involved a reaction which was carried out under neither acidic nor basic conditions. 

Box 4.14 C Chemical Shift Values for Halogenated Aliphatic Carbon Atoms... 

The results of column 3 in Table IX show that in all three macerals more than half of the aliphatic carbon atoms may be present in alicyclic or/and hydroaromatic rings. The micrinite has no range but only one value because even 2 R.i< i > is bigger than the smallest value for (CH2 + CH). There is no doubt that in the case of the micrinite even small errors in the values of the... 

There appear to be two C5-dehydrocyclizations over platinum-on-carbon catalyst. Activation energy differences suggest that the reaction involving an sp2 and an sp3 carbon atom (a cyclization in which the new bond is formed between an aliphatic and an aromatic carbon atom) is different from cyclizations involving two sp3 carbon atoms (in which the new bond is formed between aliphatic carbon atoms of two side-chains). 

Similarly, all diamine ligands with three aliphatic carbon atoms between the nitrogen donors will... 

Nucleophilic fluorinations can be performed at a primary, sometimes also at a secondary, aliphatic carbon atom [8], Good leaving-groups for the aliphatic nucleophilic fluorination are... 

The Sn2 reaction involves the attack of a nucleophile from the side opposite the leaving group and proceeds with exclusive inversion of configuration in a concerted manner. In contrast to the popular bimolecular nucleophilic substitution at the aliphatic carbon atom, the SN2 reaction at the vinylic carbon atom has been considered to be a high-energy pathway. Textbooks of organic chemistry reject this mechanism on steric grounds [175]. 

The assignments of the 13C chemical shifts of laudanosine were first made by Wenkert et al. (6) and confirmed later (15). It is now apparent that compounds 2 and 3 (14) and 3,4-dimethoxyphenethylamine (6, 15) serve as satisfactory models of the isoquinoline and benzyl moieties, respectively. The substitution of a 3,4-dimethoxybenzyl group at C-l of 3, as in laudanosine (28), caused changes to occur in the chemical shifts of the aliphatic carbon atoms of the tetrahydroisoquinoline moiety analogous to those of the compounds with substituents at C-l listed in Table II (C-l, +7.9 C-3, —6.2 C-4, —3.5 NCH3, —3.6). The chemical shift changes between 27 and 28... 

The bisbenzylisoquinoline alkaloid, isochondodendrine (33), (Fig. 5 and Table V) and its (9-methyl and O-acetyl derivatives have been studied by 13C NMR (23). The aliphatic carbon atoms of this symmetrical molecule were assigned by comparison to the benzylisoquinoline alkaloids and by the off-resonance spectrum. The oxygen substituent at C-8 caused a shielding of C-l. In the aromatic region of the spectrum C-9 and C-l2 had chemical shifts which remained essentially constant in all derivatives examined. Methylation and acetylation of the phenolic group produced characteristic shift changes which allowed the assignment of C-4a, C-6, C-7, C-8,... 

The 13C spectrum of cularine (34) (Fig. 6, Table VI), has been reported by Wenkert et al. (6). The chemical shifts of the aliphatic carbon atoms were assigned by comparison with those of laudanosine (28) and follow also from those of the simple isoquinolines (Section II). In the aromatic region the resonances of the pair of protonated carbon atoms at C-5 and C-6 were differentiated from those at C-2 and C-5 by the observation of... 

Several groups have examined the 13C spectra of the aporphine alkaloids (6, 7, 38-40) examples are found in Fig. 10. The chemical shift assignments (Table X) for the aliphatic carbon atoms of rings B and C were made by comparison to laudanosine (28) (6) and to the reduced proaporphines (41). In the case of caaverine (49) a comparison with (+)-lirmidine (50) revealed the P deshielding effect of the TV-methyl group on C-5 and C-6a and the shielding of C-7 by a y effect. 

A close examination of the chemical shifts of the aliphatic carbon atoms of the diastereomeric pairs, 81 and 82, 83 and 84, and 85 and 86, has shown that the diastereomers may be differentiated by CMR spectroscopy. The change in stereochemistry at C-T between em/iro-/i-hydrastine (81) and f/ireo-a-hydrastine (82) caused deshielding in 82 at C-3, C-4, and the A-methyl group by +2.3, +2.5 and +0.2 ppm, respectively, whereas C-T was shielded by —0.9 ppm. Chemical shift differences of similar magnitude were observed for the pairs, 83 and 84, and 85 and 86 except that in these systems C-T underwent a slightly larger shielding. 

In the meantime, new concepts for the synthesis of cyclic pentaalkylphosphoranes have been developed (88), which have proved the existence of a phosphorus atom bearing 5 aliphatic carbon atoms, 2 of which are... 

The tendency for diamond formed under nonfluid conditions to be influenced by the structure of the precursor carbon can be noted when hydrocarbons are decomposed at 12 GPa. Aliphatic hydrocarbons, which already posses tetrahedral carbon bonding, seem to slowly lose hydrogen and approach cubic diamond. Purely aromatic molecules such as anthracene change to graphite, then finally to diamond at higher temperatures. Adding aliphatic carbon atoms to the molecules or the mixture favors diamond formation at lower temperatures. 

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