Do the solvolysis reactions of secondary substrates occur by the SN1 or SN2 mechanism: or something else?
- First Online:
- 495 Downloads
Primary and methyl aliphatic halides and tosylates undergo substitution reactions with nucleophiles in one step by the classic SN2 mechanism, which is characterized by second-order kinetics and inversion of configuration at the reaction center. Tertiary aliphatic halides and tosylates undergo substitution reactions with nucleophiles in two (or more) steps by the classic SN1 mechanism, which is characterized by first-order kinetics and incomplete inversion of configuration at the reaction center due to the presence of ion pairs. When the nucleophile is also the solvent, the substitution reaction is called a solvolysis, and both the SN2 and SN1 reactions now obey first-order kinetics. Schleyer and Bentley have provided solid, but not conclusive, evidence that secondary substrates undergo solvolysis by a merged mechanism, one that blends characteristics of both the SN2 and SN1 mechanisms. The following paper presents the history of their sustained pursuit of a merged mechanism and subsequent rebuttals to this claim. Several issues related to the philosophy and sociology of science are also discussed.
KeywordsSolvolysis reaction SN1 reaction SN2 reaction Two-step mechanism One-step mechanism Ion pairing Merged mechanism Solvent ionizing power Solvent nucleophilicity 2-Adamantyl substrates Kinetics α secondary isotope effects Secondary substrates Nucleophilic solvent assistance SN2 (intermediate)
- Anslyn, E.V., Dougherty, D.A.: Modern physical organic chemistry. University Science Books, Sausalito, CA (2006)Google Scholar
- Bentley, T.W., Schleyer, P., Von, R.: Medium effects on the rates and mechanisms of solvolytic reactions. In: Gold, V., Bethell, D. (eds.) Advances in physical organic chemistry, vol. 14, pp. 1–67. Academic Press, New York (1977)Google Scholar
- Biale, G., Parker, A.J., Smith, S.G., Stevens, I.D.R., Winstein, S.: E2C mechanism in elimination reactions. Absence of an extreme form of merged mechanism for elimination and substitution. Comparison of Saytzeff versus Hofmann Tendencies and of Anti versus Syn Elimination. J. Am. Chem. Soc. 92, 115–122 (1970)CrossRefGoogle Scholar
- Hoffmann, R., Minkin, V.I., Carpenter, B.K.: Ockham’s Razor and chemistry. Bull. Chim. Soc. Fr. 133, 117–130 (1996)Google Scholar
- Hoffmann, R., Minkin, V.I., Carpenter, B.K.: Ockham’s Razor and chemistry. HYLE 3, 3–28 (1997)Google Scholar
- Reichardt, C.: Solvents and solvent effects in organic chemistry (3rd ed.). Wiley-VCH. Weinheim, Germany (2003)Google Scholar
- Schleyer, P., Von, R.: A simple preparation of Adamantane. J. Am Chem. Soc. 79, 3292 (1957)Google Scholar
- Schleyer, P., Von, R., Nichols, R.D.: The preparation and reactivity of 2-substituted derivatives of Adamantane. J. Am. Chem. Soc. 83, 182–187 (1961)Google Scholar
- Sober, E.: Simplicity. In a companion to the philosophy of science (Newton-Smith, W. H. ed.). Blackwell, Malden, MA (2001), pp 433–441Google Scholar
- Streitwieser, A.: Solvolytic displacement reactions. McGraw-Hill, New York (1962)Google Scholar