Long-range spin–spin coupling constants as an indicator of conformational preferences in ethyl and trifluoroethyl vinyl ethers

Schaefer, Ted; Parr, William J. E.

doi:10.1139/v77-393

Cited by 9 publications

References 8 publications

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Secondary 2‐Norbornyl Cation Intermediates Substituted at C(5) and C(7) by Electron‐withdrawing Groups. Addition of fluorosulfuric acid to unsaturated norbornane derivatives

Quarroz

Vogel

1979

Helvetica Chimica Acta

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SummaryLow temperature (-130" to -110") addition of exo-norborn-5-en-2-01 (7) to excess HS03F in S02CIF yielded a mixture of exo-5-(fluorosulfonyloxy)-exo-2-and endo-2-norbornylhydroxonium ions (9 + 10) under kinetic control that was different from the mixture of 9 + 10 obtained by addition of endo-norborn-5-en-2-01(8) to HS03F under kinetic control. These mixtures differed from the mixture of 9+ 10 observed at higher temperature (-80" to -60") (thermodynamic control). Addition of 3-nortricyclanol(23) or exo-2,3-epoxynorbornane (24) to HS03F at -120"k 10" yielded a mixture containing the exo-2-(fluorosulfonyloxy)-anti-7-and syn-7-norbornylhydroxonium ions (26+ 27) as major adducts. Qualitative rates of the isomerization of 26 + 27 to the more stable ions 9 + 10 and of the isomerization 9 % 10 were evaluated. The solvolysis of 9 + 10 in HS03F yielded the exo-2, exo-5-and exo-2, endo-5-norbornanediyl bis (fluorosulfates) (21 + 22). Norbornadiene and quadricyclane added 2 equivalents of HS03F and furnished kinetically a mixture of exo-2, anti-7-and exo-2, syn-7-norbornanediyl bis (fluorosulfates) (36 + 37) as major adducts. The latter 36+37 were isomerized into a kinetic mixture of the more stable isomers 21 + 22. The rates of these isomerizations were compared. The use of DS03F and (exo-2-D)-norborn-5-en-2-01 (15) confirmed that heterolyses of the fluorosulfates were responsible for the observed isomerization; elimination-addition processes occurred but much more slowly. The results are interpreted in terms of substituted classical and o-bridged secondary 2-norbornyl cation intermediates. It appears that the electron withdrawing substituents FSO, and H20+ (HO) destabilize the o-bridged 2-norbornyl cation more at C(5) than C(7). If the o-bridged ions 5-Z substituted at C(5) by Z=FSO, or H20+ (HO) are transition states in the isomerization of the corresponding classical ions 3-Z,4-Z, the free enthalpy difference between the 'non-classical' o-bridged ion and the classical ions is not higher than the energy barrier to the quenching of the latter intermediates by FSOj in HSO,F/SO*ClF. I) 2,Present address: Lonta AG, CH-3930 Visp, Switzerland. Author, to whom correspondence should be addressed. 336HELVETICA CHIMICA ACTA -Vol. 62, Fasc. 1 (1979) -Nr. 36 Introduction. -The nature of the secondary 2-norbornyl cation has stirred a controversy that is not yet settled [l]. A long-standing problem is whether this carbocation exists as a pair of 'rapidly equilibrating' enantiomorphic structures 1 1' (double minimum energy hypersurface) or as a 'non-classical' o-bridged carbonium ion 2 with C,-symmetry in its ground state (single minimum energy hyper~urface)~).

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Secondary 2‐Norbornyl Cation Intermediates Substituted at C(5) and C(7) by Electron‐withdrawing Groups. Addition of fluorosulfuric acid to unsaturated norbornane derivatives

Quarroz

Vogel

1979

Helvetica Chimica Acta

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Influence des interactions attractives non liees sur les stabilites relatives d'ethers et d'acetates d'enol renfermant un groupe styryle

Huet

1978

Tetrahedron

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Inductive substituent constants σji from olefinic geminal 1h, 1h nmr coupling constants

Knorr¹

1981

Tetrahedron

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Long-range spin–spin coupling constants as an indicator of conformational preferences in ethyl and trifluoroethyl vinyl ethers

Cited by 9 publications

References 8 publications

Secondary 2‐Norbornyl Cation Intermediates Substituted at C(5) and C(7) by Electron‐withdrawing Groups. Addition of fluorosulfuric acid to unsaturated norbornane derivatives

Secondary 2‐Norbornyl Cation Intermediates Substituted at C(5) and C(7) by Electron‐withdrawing Groups. Addition of fluorosulfuric acid to unsaturated norbornane derivatives

Influence des interactions attractives non liees sur les stabilites relatives d'ethers et d'acetates d'enol renfermant un groupe styryle

Inductive substituent constants σji from olefinic geminal 1h, 1h nmr coupling constants

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