Functional group reaction dependence

Diastereoselectivities in complex systems are determined by conformation of the transition states which are affected by chelation and steric effects of substituents and reaction conditions. For example, the stereochemistry of a hydroxyl group derived from a ketone is determined by coordination of hydroxyl and other functional groups, and depends on the presence or absence of HMPA (Equation (42)). 

We noticed that the reactivity of the silane and silanol (alkoxysilane) components in the condensation was very much dependent on the steric environment of the silicon atom bearing the functional group. Reaction of M,H-B 10 with M.OH-B 10, or i-B,OH-Bio also proceeded without any big problem. For example, M,H-Bio (0.97 g, 10.9 X lO mol) and an isomeric mixture of i-B,OH-Bio (0.1 g, 1.8 x 10 " mol), and TFB (0.0074 g, 1.5 x 10 mol, 2 mol%) were reacted in toluene (5 mL) at room temperature for 24 h. The resulting solution after filtration through a Horisil column was reduced in volume under vacuum and precipitated slowly via slow addition into methanol (40 mL) to obtain a white polymeric solid (0.98 g). 

Reactions of Thiols, Selenols, and Tellurols.—Many of the reactions of thiols depend on the high nucleophilicity of the thiolate anion, and lead to sulphides or other sulphur-containing functional groups. Reactions of this type are therefore discussed in later sections of this Chapter. 

Chemical modification refers to the modification process in which chemical reactions occur between the backbone, branched chain, and side chain of a macro-molecular chain. The modification principle depends mainly on the structural changes of the main chain, branched chain, or side chain. Chemical modifications include copolymerization between different monomers, grafting reaction of macromolecular chains, crosslinking reaction within macromolecular chains, functional group reactions on the macromolecular chains, and so forth. For example. 

The success of the last reaction depends upon the inertness of the ester carbonyl groups towards the organocadmium compound with its aid and the use of various ester acid chlorides, a carbon chain can be built up to any reasonable length whilst retaining a reactive functional group (the ester group) at one end of the chain. Experimental details are given for l-chloro-2-hexanone and propiophenone. The complete reaction (formation of ketones or keto-esters) can be carried out in one flask without isolation of intermediates, so that the preparation is really equivalent to one step. 

The intramolecular reaction oF allcenes with various O and N functional groups offers useful synthetic methods for heterocycles[13,14,166]. The reaction of unsaturated carboxylic acids affords lactones by either exo- or endo-cyclization depending on the positions of the double bond. The reaction of sodium salts of the 3-alkenoic acid 143 and 4-alkenoic acid 144 with Li2PdCl4 affords mostly five-membcrcd lactones in 30-40% yields[167]. Both 5-hexe-noic acid (145) and 4-hexenoic acid (146) are converted to five- or six-mem-bered lactones depending on the solvents and bases[168]. Conjugated 2,4-pentadienoic acid (147) is cyclized with Li2PdCl4 to give 2-pyrone (148) in water[i69]. 

AH corrosion inhibitors in use as of this writing are oil-soluble surfactants (qv) which consist of a hydrophobic hydrocarbon backbone and a hydrophilic functional group. Oil-soluble surfactant-type additives were first used in 1946 by the Sinclair Oil Co. (38). Most corrosion inhibitors are carboxyhc acids (qv), amines, or amine salts (39), depending on the types of water bottoms encountered in the whole distribution system. The wrong choice of inhibitors can lead to unwanted reactions. Eor instance, use of an acidic corrosion inhibitor when the water bottoms are caustic can result in the formation of insoluble salts that can plug filters in the distribution system or in customers vehicles. Because these additives form a strongly adsorbed impervious film at the metal Hquid interface, low Hquid concentrations are usually adequate. Concentrations typically range up to 5 ppm. In many situations, pipeline companies add their own corrosion inhibitors on top of that added by refiners. 

Since the stereochemical course of a catalytic hydrogenation is dependent on several factors, " an understanding of the mechanism of the reaction can help in the selection of optimal reaction conditions more reliably than mere copying of a published recipe . In the first section the factors which can influence the product stereochemistry will be discussed from a mechanistic viewpoint. In subsequent sections the hydrogenation of various functional groups in the steroid ring system will be considered. In these sections both mechanistic and empirical correlations will be utilized with the primary emphasis being placed on selective and stereospecific reactions. 

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