Thorpe–Ingold effect
A flawed assertion that nevertheless proved useful in synthesis
Most organic chemists are familiar with the geminal dialkyl effect, whereby intramolecular ring-forming reactions happen faster when the linking chain between reactive sites includes a tetrahedral carbon atom bearing two alkyl substituents. The corresponding cyclisation with only hydrogen substituents at the same position occurs more slowly. The gem-dialkyl effect has often been exploited in synthesis, but Jocelyn Thorpe and Christopher Ingold’s theory based on bond angle compression – although it fit the available evidence – turns out to be only a ‘limited truth’.