Guidelines

Can ketones form enolates?

Can ketones form enolates?

In aqueous solution, an aldehyde or ketone which has an alpha type hydrogen can lose it to water, giving hydronium ion and the conjugate base of the carbonyl compound, which is called an enolate.

How are enolates formed?

Although the reaction of carbonyl compounds with sodium hydride is heterogeneous and slow, sodium enolates are formed with the loss of hydrogen, and no other organic compounds are produced. If the formed enolate is stabilized by more than one carbonyl it is possible to use a weaker base such as sodium ethoxide.

How many enolates can form?

Enolates have two resonance forms – we can put the negative charge on the oxygen or the carbon. Now here’s a complication. When we have a simple ketone (like dimethyl ketone, above!) it’s easy – it doesn’t matter which carbon we take the hydrogen from.

What are enolates give examples?

Deprotonation of enolizable ketones, aldehydes, and esters gives enolates. Typically enolates are generated from using lithium diisopropylamide (LDA). Often, as in conventional Claisen condensations, Mannich reactions, and aldol condensations, enolates are generated in low concentrations with alkoxide bases.

When to use LDA to form enolate from ketones?

For example, when using LDA to deprotonate an alpha carbon of a ketone with two differing alpha carbons (secondary vs tertiary), the deprotonation of the less substituted (subsequently forming of a less stable enolate) is favored at low temperatures.

How are enolate ions formed from aldehydes and ketones?

Enolate ions are formed by treating aldehydes or ketones with a base. A proton has to be present on the α-carbon. Enolate ions are formed by treating aldehydes or ketones with a base. A proton has to be present on the α-carbon. Enolate ions can be alkylated with an alkyl halide.

Can a ketone be alkylated with an alkyl halide?

Enolate ions can be alkylated with an alkyl halide. O-Alkylation and C-alky-lation are both possible, but the latter is more likely and more useful. The reaction allows the introduction of alkyl groups to the α-carbon of alde-hydes and ketones. If there are two α-protons present, two different alkyla-tions can be carried out in succession.

Which is an enolate ion in the aldol reaction?

The Aldol reaction involves the dimerization of an aldehyde or a ketone. In the presence of sodium hydroxide, aldehyde or ketone is converted to an enolate ion, but not all the carbonyl molecules are converted and so the enolate ion can undergo a nucleophilic addition on ‘free’ aldehyde or ketone.