12.0: Prelude to Reactions at the α-carbon, part I There is a connection between the killer platypus in Australia and the 'hunting magic' in the Amazon, and it has to do with the structure and reactivity of what organic chemists refer to as the α -carbon: the carbon atom positioned adjacent to a carbonyl or imine group in an organic molecule. 12.1: Review of Acidity at the α-Carbon Let's review what we learned in section 7.6 about the acidity of a proton on an a-carbon and the structure of the relevant conjugate base, the enolate ion. Remember that this acidity can be explained by the fact that the negative charge on the enolate conjugate base is delocalized by resonance to both the α -carbon and the carbonyl oxygen. 12.2: Isomerization at the α-Carbon Enolate ions are the key reactive intermediates in many biochemical isomerization reactions. Isomerizations can involve either the interconversion of constitutional isomers, in which bond connectivity is altered, or of stereoisomers, where the stereochemical configuration is changed. Enzymes that interconvert constitutional isomers are usually called isomerases, while those that interconvert the configuration of a chiral carbon are usually referred to as racemases or epimerases. 12.3: Aldol Addition Along with Claisen condensation reactions, which we will study in the next chapter, aldol additions are responsible for most of the carbon-carbon bond forming events that occur in a living cell. Because biomolecules are built upon a framework of carbon-carbon bonds, it is difficult to overstate the importance of aldol addition and Claisen condensation reactions in the chemistry of living things! 12.4: α-Carbon Reactions in the Synthesis Lab - Kinetic vs. Thermodynamic Alkylation Products While aldol addition reactions are widespread in biochemical pathways as a way of forming carbon-carbon bonds, synthetic organic chemists working the lab also make use of aldol-like reactions for the same purpose. 12.5: Nitrosation In organic chemistry, nitrosamines are organic compounds with a nitroso group (-N=O) bonded to an amine. Most nitrosamines are carcinogenic. There are significant levels of nitrosamines in many foodstuffs, especially meat and cheese products preserved with nitrite compounds. 12.E: Reactions at the α-Carbon, Part I (Exercises) 12.S: Reactions at the α-Carbon, Part I (Summary)