Secondary carbon atoms

The nitroparaffiiis in which the nitro group is attached to a primary or secondary carbon atom exist in tautomeric forms, for example ... 

Freudenberg has obtained one nitrogen-free product, C13H24O, b.p. 215-220°, by the distillation of aconitine or amorphous aconitine with barium hydroxide or zinc dust. He suggests that the fundamental hydrocarbon, C20H33, may contain two five-membered and four six-membered rings, which will include nine secondary carbon atoms. 

An isopropyl group is a secondary alkyl group. Its point of attachment is to a secondary carbon atom, one that is directly bonded to two other carbons. 

Perhaps the earliest report of the replacement of a sulfonate ester attached to a secondary carbon atom in a sugar derivative was that of Helferich (53). Under quite drastic conditions (sodium iodide in acetone, 105°C., 72 hours, sealed system) the 4-mesylate derivative 9 was converted into a crystalline 4-deoxy-4-iodo sugar derivative 10 in 46% yield. Although the position of the iodine atom was established, the configuration at C-4 was not known. 

Paraformaldehyde/DMSO dissolves cellulose rapidly, with neghgible degradation, and forms the hydoxymethyl (methylol) derivative at Ce [ 140-142]. Therefore, cellulose derivatives at the secondary carbon atoms are easily obtained after (ready) hydrolysis of the methylol residue. Additionally, fresh formaldehyde may add to the methylol group, resulting in longer methylene oxide chains, that can be functionahzed at the terminal OH group, akin to non-ionic, ethylene oxide-based surfactants [143,144]. 

It may be well to state at this point that the reagents used in any of the syntheses which follow are sufficiently mild to preclude the possibility of rearrangement of the hydrogen atoms on the carbon chain. Thus in the compounds which lead to allitol, those hydrogen atoms which are attached to secondary carbon atoms all lie on the same side of the carbon chain, just as they do in allitol. 

The formation of the product by attack at the secondary carbon atom was not due to a concurrent S 1 reaction since the isomer ratio was not affected by changes in methoxide ion concentration. Saturated epoxides differ from this example in that bimolecular attack always takes place at the less substituted carbon atom. 

These differences in the course of the reaction of Grignard and sodium compounds are not limited to carbonations but are also observed in carbonyl addition reactions. Whereas cinnamylmagnesium bromide always reacts at the secondary carbon atom next to the benzene ring, the sodium compound may react at either the secondary or the primary position, depending on the electrophilic reagent.403... 

Let us now have a closer look at three basic types of the relative probabilities appearing in the model for an isomerization vs. another isomerization, the 1,2-insertion vs. 2,1-insertion, and an isomerization vs. an insertion. The right-hand part of Figure 11 summarizes the equations for the macroscopic reaction rates for the alternative reactive events starting from an alkyl complex p0 let us assume that the secondary carbon atom is attached to the metal, so that two isomerization reactions have to be considered. 

The polymerization process is characterized by an average probability ratio of isomerization vs. insertion steps of 2.6. A closer look at the simulation results shows that for this catalyst the insertions practically occur only at the primary carbon, the insertion from the secondary carbon happen very rarely. To illustrate this point, the values of the probabilities of alternative events may be helpful. If the primary carbon is attached to the metal, the probabilities of the 1,2-insertion, 2,1-insertion and the isomerization (to secondary or tertiary carbon) are 0.700, 0.286, and 0.014, respectively. If the secondary carbon, neighboring with the two secondary carbon atoms is attached to the metal, the corresponding values are 0.002 (1, 2- ins.), 0.001 (2,1-ins.), and 0.499 (two equivalent isomerizations). And if the secondary carbon, neighboring with one primary C and one secondary C... 

The Pt/C catalyst, compared with Pd/C, showed not only enhanced activity (vide supra) but also reduced selectivity for glyceric acid (only 55% at 90% conversion), favoring dihydroxyacetone formation up to 12%, compared with 8% for the Pd case [48]. The Pt/C catalyst promoted with Bi showed superior yields of dihydroxyacetone (up to 33%), at lower pHs. Glyceric and hydroxypyruvic acids, apparently, are formed as by-product and secondary product, respectively [48], The addition of Bi seems to switch the susceptibility of glycerol oxidation from the primary towards the secondary carbon atoms. 

Biradical I would yield cyclopentene plus ethylene, biradical II the hepta-1,6-diene. Process I may have a lower energy of activation because of the stabilization of the free electron by the secondary carbon atom and also because less energy is required to compress the appropriate carbon-carbon bond, in the cyclopentane ring to yield the cyclopentene, than to rupture the ring to give the diene. 

The theories give no exact predictions as far as the structure of the ring produced is concerned. Electronic factors [such as partial carbonization of the surface (5) or the difference between the partial charge of the primary and that of the secondary carbon atom (75)] have been proposed to explain the predominance of C5 or Cg cyclic production, respectively. 

The reagent most commonly used for oxidation of ethers is RuO. The subject is well summarized in an early review by Gore [75], Primary methyl ethers RCHjOCHj are oxidised to esters RCOOCH, and secondary methyl ethers R R CjHjOCHj to ketones R COR while with benzyl ethers PhCH OR the esters PhCOOR are formed. For cyclic ethers, the carbon atoms adjacent to the O atom are oxidised, and if there are two secondary carbon atoms the main products are lactones, sometimes with partial hydrolysis to carboxylic acids [75], There is a short review on oxidation of ethers by RuO, principally on the mechanisms involved [76],... 

Table represent the louest values found in various experiments. The degree of racemization at carbon atom 2 is strongly affected by the alkyl group R (see Table). Racemization is more pronounced in the case of less hindered primary and secondary carbon atoms adjacent to the stereocenter. It is interesting to note that the degree of racemization observed in the diazotization reaction runs parallel to the degree of racemization observed in aqueous solutions of... 

Epoxides also undergo the Ritter reaction in good yields with retention of configuration via a episulfonium intermediate 190a (double-inversion process). For monosubstituted epoxides, the yields of oxazolines are lower due to nondis-criminatory attack of the nitrile on both the primary and the secondary carbon atom of the episulfonium intermediate. Complete retention of configuration is still observed despite the lower yield (Scheme 8.54). 

A similar conclusion applies to a Mg-V-O catalyst in which Mg3(V04)2 is the active component. The relative rates of reaction for different alkanes on this catalyst follow the order ethane < propane < butane 2-methylpropane < cyclohexane (Table I) [12-14]. This order parallels the order of the strength of C-H bonds present in the molecule, which is primary C-H > secondary C-H > tertiary C-H. Ethane, which contains only primary C-H bonds, reacts the slowest, whereas propane, butane, and cyclohexane react faster with rates related to the number of secondary carbon atoms in the molecule, and 2-methylpropane, with only one tertiary carbon and the rest primary carbons, reacts faster than propane which contains only one secondary carbon. Similar to a Mg-V-O catalyst, the relative rates of oxidation of light alkanes on a Mg2V207 catalyst follow the same order (Table I). 

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