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Theoretical studies on nitrile‐forming elimination reactions
Author(s) -
Lee Ikchoon,
Park Hyoung Yeon,
Lee BonSu,
Kong Byung Hoo,
Lee Byung Choon
Publication year - 1992
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.610050507
Subject(s) - chemistry , substituent , nitrile , elimination reaction , leaving group , delocalized electron , medicinal chemistry , polar effect , stereochemistry , reductive elimination , organic chemistry , catalysis
The base‐promoted nitrile‐forming elimination reactions of YCH=CHC β H=NOCH=CHZ (Y=OCH 3 , H or Cl and Z=H or NO 2 ) were studied by the AM1 MO theoretical method with Cl − as a base. The reaction is found to proceed by an E 1 cB ‐like E2 mechanism in which C β —H bond cleavage is more advanced than N—O bond breaking. The syn ‐elimination has a more E 1 cB ‐like transition state (TS) than the anti elimination, which is attributed to the structurally favourable n N—ó * (C β —H) charge‐transfer interaction. An electron‐withdrawing Y substituent lowers the activation barrier by stabilizing negative charge developed on C β in the TS. An electron‐withdrawing substituent in the leaving group (Z = NO 2 ) tends to enhance the anti relative to the syn elimination process by depressing the δ * (N—O) level, which in turn makes the nć—δ * (N—O) interaction more effective. The YCH=CH— and —C β H=N fragments are perpendicular in the TS, which is stabilized by delocalization of negative charge developed on the C β atom.