The Barbier–Wieland degradation is a procedure for shortening the

carbon chain In chemistry, catenation is the bonding of atoms of the same element into a series, called a ''chain''. A chain or a ring shape may be ''open'' if its ends are not bonded to each other (an open-chain compound), or ''closed'' if they are bonde ...

of a carboxylic acid by one carbon. It only works when the carbon adjacent to the carboxyl is a simple

methylene bridge In organic chemistry, a methylene bridge, methylene spacer, or methanediyl group is any part of a molecule with formula ; namely, a carbon atom bound to two hydrogen atoms and connected by single bonds to two other distinct atoms in the rest of t ...

(an

aliphatic In organic chemistry, hydrocarbons ( compounds composed solely of carbon and hydrogen) are divided into two classes: aromatic compounds and aliphatic compounds (; G. ''aleiphar'', fat, oil). Aliphatic compounds can be saturated, like hexane, ...

carbon with no substituents). The reaction sequence involves conversion of the carboxyl and

alpha carbon In the nomenclature of organic chemistry, a locant is a term to indicate the position of a functional group or substituent within a molecule. Numeric locants The International Union of Pure and Applied Chemistry (IUPAC) recommends the us ...

into an

alkene In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond. Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...

, which is then cleaved by

oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...

to convert the former alpha position into a carboxyl itself. BWc

References

Name reactions Carboxylic acids Degradation reactions {{organic-chemistry-stub