Thorpe–Ingold effect
The Thorpe–Ingold effect, gem-dimethyl effect, or angle compression is an effect observed in
The comparative rates of lactone formation (lactonization) of various 2-hydroxybenzenepropionic acids illustrate the effect. The placement of an increasing number of methyl groups accelerates the cyclization process.[3]
One application of this effect is addition of a
One proposed explanation for this effect is that the increased size of the substituents increases the angle between them. As a result, the angle between the other two substituents decreases. By moving them closer together, reactions between them are accelerated. It is thus a kinetic effect.
The effect also has some thermodynamic contribution as the in silico strain energy decreases on going from cyclobutane to 1-methylcyclobutane and 1,1-dimethylcyclobutane by a value between 8 kcal/mole[6] and 1.5 kcal/mole.[7] A noteworthy example of the Thorpe-Ingold effect in supramolecular catalysis is given by diphenylmethane derivatives provided with guanidinium groups.[8] These compounds are active in the cleavage of the RNA model compound HPNP. Substitution of the methylene group of the parent diphenylmethane spacer with cyclohexylidene and adamantylidene moieties enhances catalytic efficiency, with gem dialkyl effect accelerations of 4.5 and 9.1, respectively.
See also
- Chelate effect
- Flippin-Lodge angle