SNi

Source: Wikipedia, the free encyclopedia.
For other uses, see SNI (disambiguation).

In

nucleophilic reactions which occur with retention of configuration,[1]
but later was employed to describe various reactions that proceed with a similar mechanism.

A typical representative

stereochemical configuration. Some examples for this reaction were reported by Edward S. Lewis and Charles E. Boozer in 1952.[2] Mechanistic and kinetic studies were reported few years later by various researchers.[3][4]

Thionyl chloride first reacts with the alcohol to form an alkyl chloro sulfite, actually forming an intimate ion pair. The second step is the concerted loss of a sulfur dioxide molecule and its replacement by the chloride, which was attached to the sulphite group. The difference between SN1 and SNi is actually that the ion pair is not completely dissociated, and therefore no real carbocation is formed, which else would lead to a racemisation.

This reaction type is linked to many forms of

cationic intermediate
.

This reaction mechanism is supported by the observation that addition of pyridine to the reaction leads to inversion. The reasoning behind this finding is that pyridine reacts with the intermediate sulfite replacing chlorine. The dislodged chlorine has to resort to nucleophilic attack from the rear as in a regular nucleophilic substitution.[3]

In the complete picture for this reaction the sulfite reacts with a chlorine ion in a standard

dioxane two successive SN2 reactions take place and the stereochemistry is again retention. With standard SN1 reaction conditions the reaction outcome is retention via a competing SNi mechanism and not racemization and with pyridine added the result is again inversion.[5][3]

SNi reaction mechanism Sn1 occurs in tertiary carbon while Sn2 occurs in primary carbon
SNi reaction mechanism Sn1 occurs in tertiary carbon while Sn2 occurs in primary carbon

See also

References

  1. doi:10.1039/JR9370001271
    .
  2. doi:10.1021/ja01122a005
    .
  3. ^
    doi:10.1021/ja01098a024
    .
  4. doi:10.1016/S0040-4020(01)99294-4
    .
  5. ISBN 9780470084946
    .
Retrieved from "https://en.wikipedia.org/w/index.php?title=SNi&oldid=1197445824"
This page is based on the copyrighted Wikipedia article: SNi. Articles is available under the CC BY-SA 3.0 license; additional terms may apply.Privacy Policy