Thorpe-Ingold Effect

Thorpe-Ingold Effect

Overall Score4.5
  • Generality
  • Importance in Conformational Studies
  • Criteria #3
  • Criteria #4
  • Criteria #5
  • General Characteristics

The effect of geminal substitution in linear molecules that promotes cyclization is referred to as the Thorpe-Ingold effect (aka. gem-dialkyl effect).

  • General References

  • Reaction Mechanism

There are two main factors that are used to explain the Thorpe-Ingold effect.

  1. Compressed bond angle: Geminal alkyl substitution makes the bond angle between the two reacting groups narrower than 109.5˚(regular tetrahedral angle), which promotes cyclization (especially the formation of small rings).

thorpe_ingold_5.gif

  1. Decreased conformational freedom: The steric repulsion caused by the geminal substituents increases the probability of the molecule taking the conformation that favors cyclization.

thorpe_ingold_6.gif

  • Examples

The Thorpe-Ingold concept can also be used to rationalize equilibrium constants (thermodynamic phenomenon).

thorpe_ingold_2.gif

Cyclization of thioacetal-protected compounds tends to be much faster than that of unprotected ketone counterparts.

thorpe_ingold_4.gif

The “trimethyl lock” system, in which the lactonization is extremely fast due to the repulsions between three methyl groups, has been designed as a new tool for pro-drug and protecting group development.[1]

thorpe_ingold_3.gif

  • Experimental Tips

  • References

[1] Levine, M. N.; Raines, R. T. Chem. Sci. 2012, 3, 2412. DOI: 10.1039/C2SC20536J

  • Related Reactions

  • Related Books

[amazonjs asin=”B00RYSPPFG” locale=”US” title=”Synthesis of Saturated Oxygenated Heterocycles II: 7- to 16-Membered Rings (Topics in Heterocyclic Chemistry)”]

  • External Links

, ,