Replacement of alkyl groups

Steric and inductive effects determine the rate of formation of the pentacovalent siUcon reaction complex. In alkaline hydrolysis, replacement of a hydrogen by alkyl groups, which have lower electronegativity and greater steric requirements, leads to slower hydrolysis rates. Replacement of alkyl groups with bulkier alkyl substituents has the same effect. Reaction rates decrease according to ... 

Many xenobiotics contain alkyl groups, such as the methyl (-CH3) group, attached to atoms of O, N, and S. An important step in the metabolism of many of these compounds is replacement of alkyl groups by H, as shown in Figure 7.6. These reactions are carried out by mixed-function oxidase enzyme systems. Examples of these kinds of reactions with xenobiotics include O-dealky-lation of methoxychlor insecticides, N-dealkylation of carbary 1 insecticide, and S-dealkylation of dimethyl mercaptan. Organophosphate esters (see Chapter 18) also undergo hydrolysis, as shown in Reaction 7.3.12 for the plant systemic insecticide demeton ... 

Replacement of alkyl groups by substituents bearing nonbonding electrons renders the boron atom less electrophilic, and this, together with internal coordination from its own acyloxy groups, explains why the acyloxyboron intermediates become progressively less reactive towards protonolysis. 

Replacement of alkyl groups by nitro groups ArR —y ArNO ... 

The replacement of alkyl groups on R4M with electronegative substituents causes an increase in the magnitude of as the result of the greater a... 

Aluminum chloride Ketones and carboxylic acid amides with replacement of alkyl groups Anomalous Friedel-Crafts reaction... 

This section lists examples of the oxidation of methylenes (RCHpR — RCOR ), the replacement of alkyl groups by ketonic groups and the degradation of alkyl groups to ketones (R2CHR — RjCO). For the acylation of hydrocarbons (RH — RCOR ) see section 176 (Ketones from Hydrides)... 

Without additional reagents Replacement of alkyl groups by halogen s. 11, 606... 

Dealkylation (s. a. Elimination of alkyl groups. Monodealkylation, Replacement of alkyl groups by hydrogen) G-Dealkylation, quinoline ring with — 12, 948 N-Dealkylation (s. a. N-De-methylation) 14, 50, 54, 769 0-Dealkylation (s. a. Ethers, cleavage)... 

The replacement of alkyl group on the imidazolium by more flexible ether group is a way to develop ILs with low viscosity and melting point (Figure 4). This effect has been obtained both for substituents at the anion (such as sulfate), as well as the cation [43,44]. 

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