1 / 14

NEIGHBORING GROUP PARTICIPATION

NEIGHBORING GROUP PARTICIPATION. WHEN YOU NEIGHBOR HELPS OUT. a -Bromopropionate Ion. -. -. S N 2. -. neither S N 1 or S N 2. Two different results!. REACTION IN CONCENTRATED BASE. straightforward S N 2 displacement. S N 2 ( rate = k[RBr] [OH] ) is favored by high [OH].

chelsa
Download Presentation

NEIGHBORING GROUP PARTICIPATION

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. NEIGHBORING GROUP PARTICIPATION WHEN YOU NEIGHBOR HELPS OUT

  2. a-Bromopropionate Ion - - SN2 - neither SN1 or SN2 Two different results!

  3. REACTION IN CONCENTRATED BASE straightforward SN2 displacement SN2 ( rate = k[RBr] [OH] ) is favored by high [OH]

  4. REACTION IN DILUTE BASE neighboring group participation In dilute base the internal displacement has a competing rate. Two inversions give a product with retention.

  5. SOLVOLYSIS OF BROSYLATES

  6. PREPARING A BROSYLATE LEAVING GROUP p-bromobenzenesulfonyl chloride Brosyl Chloride BsCl resonance stabilized good leaving group a brosylate (R-OBs)

  7. THE METHYL BROSYLATE GIVES 50/50 CIS + TRANS + SN1

  8. THE ACETOXY BROSYLATE GIVES 100% TRANS

  9. INTERMEDIATE ION Bridged ion, OAc attacks equally on either side, but always anti + + - O-Ac trans diacetate

  10. REARRANGEMENTS CAN ASSIST A REACTION ALSO To be added …...

  11. NGP IS COMMON IN BIOLOGICAL REACTIONS

  12. AN IMPORTANT BIOLOGICAL REACTION IN THE SYNTHESIS OF TERPENES isopentenyl pyrophosphate TERPENES ENZYME 3,3-dimethylallyl pyrophosphate USES NEIGHBORING GROUP PARTICIPATION

  13. SOME TERPENES (C10) geraniol menthol rose and other flowers peppermint camphor a-pinene camphor tree turpentine

  14. ANCHIMERIC ASSISTANCE BY HISTIDINE good nucleophile assisted by proximity + ENZYMES KNOW ALL THE TRICKS : SN2 - - enzyme double bond could never displace without the imidizole trick easily displaced weak base SN2 + elimination :B

More Related