Electron donating alkyl group

Induction The negative charge on the left is destabilized by an electron-donating alkyl group. The one on the right is not destabilized in this way. 

The effect of introducing electron-donating alkyl groups into the benzene nucleus is found to be small ... 

If we consider protonation of 2-methylbut-2-ene, then two different carbocations might be formed. One of these is tertiary, and thus favourable, because three electron-donating alkyl groups help to stabilize the cation by dispersing the charge (see Section 6.2.1). The alternative carbocation intermediate is less favourable, in that it is secondary, with just two alkyl... 

SCHEME 7. The electrophilic substitution of Et2Zn by PhHgCl follows a second order rate law with an activation barrier of AG = 16.2 kcal mol (0 °C). This barrier can be lowered by replacing the ethyl groups at the zinc by more electron-donating alkyl groups, indicating an electronically deficient transition state... 

Ethene does not polymerize by the cationic mechanism because it does not have sufficiently effective electron-donating groups to permit easy formation of the intermediate growing-chain cation. 2-Methylpropene has electron-donating alkyl groups and polymerizes much more easily than ethene by this type of mechanism. The usual catalysts for cationic polymerization of 2-methylpropene are sulfuric acid, hydrogen fluoride, or a complex of boron... 

Oxidation of alkyl phenyl sulfides by pyridinium bromochromate (PBC) is accelerated by electron-donating alkyl groups or aryl substituents, indicating an electron-deficient sulfur centre in the transition state this is accounted for in terms of rate-determining electrophilic oxygen attack from PBC to the sulfide in an. S -like process.7... 

As expected for an electrophilic addition, the reaction rate increases as alkyl groups are substituted on the double bond. The electron-donating alkyl groups make the alkene more nucleophilic. Table 11.1 lists the relative rates of bromination of a series of alkenes. As can be seen from this table, replacing all four of the hydrogens of ethene with methyl groups results in an increase in the rate of the reaction by a factor of 2 million. 

An important example of this effect is the decrease in equilibrium constants for ketones as compared to aldehydes. The replacement of the aldehyde hydrogen of acetaldehyde (K = 1.3) with a methyl group, to produce acetone (K = 2 X 10-3), results in a decrease in the equilibrium constant for hydration by a factor of approximately 1000. The inductive effect of the electron-donating alkyl group also helps shift the equilibrium for ketones toward the reactant. 

Aldehydes are more likely than ketones to form stable hydrates. The electrophilic carbonyl group of a ketone is stabilized by its two electron-donating alkyl groups, but an aldehyde carbonyl has only one stabilizing alkyl group. The partial positive charge of the aldehyde is not as well stabilized. Aldehydes are thus more electrophilic and less... 

The use of a Cp or other alkylated Cp ligand instead of unsubstituted Cp in CpCo chemistry is preferred for two reasons. First, there is less of a tendency to form oUgomers and polymers with type I and III compounds, which ensures higher solubility secondly, there seems to be a favorable electronic effect. Electron-donating alkyl groups on the Cp... 

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