Carbon atoms chain selection

Closer examination of the cyclobutanol t/c ratios from homologous and isomeric n-alkanones in the same zeolites reveals some interesting trends (Table 12). The t/c ratios from all of the alkanones in the Na-X and Na-Y zeolites are as expected from reaction in a large or flexible reaction cavity which is very polar (like that provided by an alcohol solution). The t/c ratios in the ZSM zeolites indicate that selectivity depends upon the total ketone length and the position of the odd electron centers of the BR along the chain. Ratios of 60 or more are reported from 4-alkanones with 9 or more carbon atoms the t/c ratios from 4-octanone in ZSM-5 and ZSM-11, 15 and 18 respectively, mark 8 carbon atom chains as being critical to a c-BR occupying... 

A selection of important anionic surfactants is displayed in table C2.3.1. Carboxylic acid salts or tire soaps are tire best known anionic surfactants. These materials were originally derived from animal fats by saponification. The ionized carboxyl group provides tire anionic charge. Examples witlr hydrocarbon chains of fewer tlran ten carbon atoms are too soluble and tliose witlr chains longer tlran 20 carbon atoms are too insoluble to be useful in aqueous applications. They may be prepared witlr cations otlrer tlran sodium. 

The hydrogenolyaia of cyclopropane rings (C—C bond cleavage) has been described on p, 105. In syntheses of complex molecules reductive cleavage of alcohols, epoxides, and enol ethers of 5-keto esters are the most important examples, and some selectivity rules will be given. Primary alcohols are converted into tosylates much faster than secondary alcohols. The tosylate group is substituted by hydrogen upon treatment with LiAlH (W. Zorbach, 1961). Epoxides are also easily opened by LiAlH. The hydride ion attacks the less hindered carbon atom of the epoxide (H.B. Henhest, 1956). The reduction of sterically hindered enol ethers of 9-keto esters with lithium in ammonia leads to the a,/S-unsaturated ester and subsequently to the saturated ester in reasonable yields (R.M. Coates, 1970). Tributyltin hydride reduces halides to hydrocarbons stereoselectively in a free-radical chain reaction (L.W. Menapace, 1964) and reacts only slowly with C 0 and C—C double bonds (W.T. Brady, 1970 H.G. Kuivila, 1968). 

Should there be a choice for the fundamental straight chain of a radical, that chain is selected which contains (1) the maximum number of double and triple bonds, (2) the largest number of carbon atoms, and (3) the largest number of double bonds. These are in descending priority. 

A mechanism has been proposed to rationalize the results shown in Figure 23. The relative proportion of the A -pyrazolines obtained by the reduction of pyrazolium salts depends on steric and electronic effects. When all the substituents are alkyl groups, the hydride ion attacks the less hindered carbon atom for example when = Bu only C-5 is attacked. The smaller deuterohydride ion is less sensitive to steric effects and consequently the reaction is less selective (73BSF288). Phenyl substituents, both on the nitrogen atom and on the carbon atoms, direct the hydride attack selectively to one carbon atom and the isolated A -pyrazoline has the C—C double bond conjugated with the phenyl (328 R or R = Ph). Open-chain compounds are always formed during the reduction of pyrazolium salts, becoming predominant in the reduction of amino substituted pyrazoliums. 

Bis(tnfluoromethyl)-subsntuted hetero-1,3-dienes and acetylenes react to give open-chain tnfluoromethyl-substituted N-propargylic amides, 4//-1.3 oxazines, and 2-oxazohnes [42,144] The formation of 2-oxazolmes is an example of pathway 2 (equabon 25), where only one carbon atom of the acetylene moiety IS incorporated into the new nng system The selectivity of this reaction can be controlled efficiently in favor of the five-membered nng system by altering the reaction conditions In the presence of 4-dimethylaminopyndine, the five-mem-... 

The oxidation described here was performed in 80% (v/v) acetonitrile — 20 % water (mole fraction of water = 0.42) at 35.0 °C. Figure 2 shows the selectivity as a function of the number of carbon atoms in R2. In the case of oxidation of la and 2a (R2 = branched alkyl groups), the selectivity reaches a sharp maximum (r = 2.4) at the isopentyl group (j = 2)l8). For R2 = straight-chain alkyl groups, alternation in the selectivity is clearly observed 18). The difference between the r value for la and 2a2 and that for la and 2h2 reaches up to 3.7. 

A (Figure 4.9). The diameter of such a neck, 2.3 A, is sufficiently large for a linear C-C chain to pass, but too small to also be an equilibrium adsorption position. The largest compound allowed inside the pores is a linear molecule limited in length to four carbon atoms due to the distance between two subsequent necks [103]. Another example of shape-selective behavior is found in a Zn-based MOF able to encapsulate linear hexane while branched hexanes are blocked [104]. 

The nucleophilic substitution on poly(vinyl chloroformate) with phenol under phase transfer catalysis conditions has been studied. The 13c-NMR spectra of partly modified polymers have been examined in detail in the region of the tertiary carbon atoms of the main chain. The results have shown that the substitution reaction proceeds without degradation of the polymer and selectively with the chloroformate functions belonging to the different triads, isotactic sequences being the most reactive ones. 

TSF [Texaco Selective Finishing] A process for separating linear from branched-chain aliphatic hydrocarbons by PSA, using zeolite 5A as the adsorbent. The desorbent is a hydrocarbon having two to four carbon atoms less than the feed. Developed by Texaco in the late 1950s. Believed to be still in operation in its Trinidad refinery as of 1990. 

Selective ring closure of cyclic secondary alkyl radicals onto the central carbon atom of allenes have been investigated in the course of pyrrolizidine alkaloid syntheses [69]. Thus, reduction of the phenylselenyl-substituted N-(l,2-buten-4-yl)pyrroli-done 42 with Bu3SnH via a radical chain mechanism provides 51% of target compound 44 as a 78 22 mixture of diastereomers (Scheme 11.14). The stereoselectivity... 

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