Chapter 21: Ester Enolates

Active Methylenes

• In some molecules there are H atoms that are adjacent to 2 carbonyl groups (which are electron withdrawing).
• Extra resonance stabilisation of the enolate anion makes these H more acidic (i.e lower pKa) than hydrogens adjacent to a single carbonyl group.
• These type of compounds are sometimes called "active methylenes"  (recall a methylene group is a CH₂)

Some common active methylene compounds are shown below as JMOL images.... make sure you can see the acidic active methylene hydrogen atoms.....

• As we will see later is this Chapter, these compounds are useful synthetic intermediates.
• Their enolates can be formed readily and can be alkylated, then further manipulated.

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© Dr. Ian Hunt, Department of Chemistry, University of Calgary