The Structure of the Bicyclo[2,2,1]2-Heptyl (Norbornyl) Carbonium Ion

Winstein, S.; Trifan, Daniel S.

doi:10.1021/ja01176a536

Cited by 160 publications

(68 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Of the inany systems studied none has been the subject of such intensive investigation as the reactions of 2-substituted norbornanes. These detailed kinetic (4) and isotopic (5) studies of solvolysis and deamination reactions reveal the operation of 3,2 and 6,2 hydride shifts, respectively, and Wagner-iueerwein rearrangements and imply the intermediacy of several different carbonium ions. Hitherto these rearrangements have been observed in irreversible systems.…”

Section: Abstract Nuclear Magnetic Resonance Spectra Have Beenmentioning

confidence: 88%

FAST REARRANGEMENT OF exo-NORBORNANOL IN STRONG ACID SOLUTIONS

Fraenkel¹,

Ralph²,

Kim³

1965

Can. J. Chem.

View full text Add to dashboard Cite

A B S T R A C T Nuclear magnetic resonance spectra have been obtained a t several temperatures for solutions o f 2-exo-norbornanol in strong acids. T h e spectra change with temperature reversibly. I t isconcluded that the 2-era-norbornanol undergoes very rapid rearrangement, the fast steps being 2,6 and 3,2 hydride shifts, respectively. I N T R O D U C T I O NThere is a vast literature which concerns carbonium ion rearrangements of bicyclic compounds (1-3). Of the inany systems studied none has been the subject of such intensive investigation as the reactions of 2-substituted norbornanes. These detailed kinetic (4) and isotopic (5) studies of solvolysis and deamination reactions reveal the operation of 3,2 and 6,2 hydride shifts, respectively, and Wagner-iueerwein rearrangements and imply the intermediacy of several different carbonium ions. Hitherto these rearrangements have been observed in irreversible systems. In this work it will be shown by the methods of nuclear magnetic resonance (n.1n.r.) spectroscopy that 2-exo-norbornanol is stable in strong acid solutions and a t the same time undergoes fast skeletal rearrangements. R E S U L T S A N D DISCUSSIONThe n.m.r. spectruln of 2-exo-norbornanol in Inethylene chloride is shown in Fig. I. The absorptions a t 6.19 tau and 7.87 tau arise froin CHOH and the bridgehead hydrogens respectively. The remaining hydrogens on C3, C3, C6, and C7 give the multiplets in the region of 8.8 tau; the line for OH appears a t 8.21 tau. The same spectrum is obtained using dimethyl sulfate and methanol as solvents with the exception that the chemical shift of the OH proton changes with solvents due to differences in hydrogen bonding. The chemical shifts of the solvent protons are as listed in the literature (6). In all these solutions the n.m.r. absorption for the OH hydrogen consisted of a single line. Thus 0-H exchange was too fast to permit observation of CzH, OH coupling. However, using trifluoroacetic acid as solvent, the line for C2H appears a t 5.40 tau and the rest of the spectrum ( Fig. 2A) has a slightly different appearance froin those obtained with the other solvents. Furthermore, due to fast proton exchange, the OH resonances in the acid and alcohol are merged. Since 2-exo-norbornanol was quantitatively recovered from trifluoroacetic solution, these changes must be due to a specific solvent effect.When 2-exo-norbornanol is dissolved in 97% sulfuric acid or mixtures of trifluoroacetic acid and sulfuric acid the peak due to CHOH disappears and the remaining spectrum consists of two broad lines a t 7.8 tau and 8.8 tau (Fig. 2E). The starting material was quantitatively recovered from these solutions also. Hence the effects found here do not arise from unusual chemical reactions. On heating the solutions of 2-exo-norbornanol in H2SO4-CF3C02H between 0 and 60" the resonance due to CHOH broadens and disappears

show abstract

Section: Abstract Nuclear Magnetic Resonance Spectra Have Beenmentioning

confidence: 88%

FAST REARRANGEMENT OF exo-NORBORNANOL IN STRONG ACID SOLUTIONS

Fraenkel¹,

Ralph²,

Kim³

1965

Can. J. Chem.

View full text Add to dashboard Cite

show abstract

“…313-333 K) 377-379K [lit. 377-378K (Winstein & Trifan, 1949)]. Colourless, weakly diffracting needles were obtained by diffusion of petroleum ether (b.p.…”

mentioning

confidence: 99%

Bond length and reactivity. Structure of 2-endo-bornyl p-toluenesulfonate

Jones¹,

Schmidt‐Bäse²,

Edwards³

et al. 1992

Acta Crystallogr C

View full text Add to dashboard Cite

show abstract

“…(4,5) and these The postulate of a symmetrical 2-norbornyl results have also been interpreted in terms of cation 1 is mainly due to Winstein (1). Following the symmetrical static structure.…”

Section: Introductionmentioning

confidence: 88%

A Kinetic and Thermodynamic Behavioral Comparison of Observable Secondary and Tertiary 2-Norbornyl Cations

Haseltine¹,

Wong²,

Sorensen³

et al. 1975

Can. J. Chem.

View full text Add to dashboard Cite

. Can. J. Chem. 53,1891Chem. 53, (1975. By analyzing various rearrangement processes, one can deduce the relative stabilities of the following 2-norbornyl cations (kcal/mol): 1,2-dimethyl, 0; 2-methyl, 1 ; 1-methyl, 6.5; and the parent 2-norbornyl, 8.5. Secondary 2-norbornyl cations have been assigned a "carbonium ion" structure and tertiary a "carbenium ion" structure. Using suitable model systems, an absolute rate comparison has been made of all three common rearrangement processes in the tertiary systems ("carbenium") with those already measured for the 2-norbornyl cation ("carbonium"). The activation free energies, AG*, (in kcal/mol) were: Wagner-Meerwein (WM) shift: tertiary, < 4; secondary, < 4; endo-6,2-hydride shift : tertiary, 7.2; secondary, 5.8; exo-3,2-hydride shift: tertiary, 6.6; secondary, 11.4. A discussion of the structure of tertiary and secondary 2-norbornyl cations emphasizes the following points: (i) a rationalization of the rapid endo-6,2-hydride shift observed in norbornyl cations does not necessitate a protonated nortricyclene ("carbonium ion") postulate; (ii) on the basis of the results for acyclic cations and the 1,2-dimethyl-2-norbornyl cation, one would not expect to "freeze out" the WM shift in an equilibrating 2-norbornyl cation structure; (iii) the formation of nortricyclenes may be related to a partial C G C 2 bond in the ions; and (iu) the structure of the observable secondary 2-norbornyl cation probably involves partial C G C 2 bonding but, in our opinion, this does not require a symmetrical static formulation. R. HASELTINE, N. WONG, T. S. SORENSEN et A. J. JONES. Can. J. Chem. 53,1891Chem. 53, (1975. En faisant I'analyse des divers processus de rearrangements, on peut deduire les stabilitks relatives des cations norbornyl-2 suivants (kcal/mol): dimethyl-1,2, 0; mkthyl-2, 1; methyl-1, 6.5; et le norbornyl-2 non-substituk, 8.5. On a attribuk au cation 'norbornyl-2 secondaire une structure de "carbocation" et au cation tertiaire une structure d"'ion carbenium". Faisant appel a des systemes modeles approprib, on a fait une comparaison entre les vitesses absolues des trois processus de rbrrangement commun dans les systemes tertiaires ("carb8nium") avec celles qui ont deja kt6 mesurees pour le cation norbornyl-2 ("carbocation"). Les knergies libres d'activation AG* (en kcal/mol) sont: rearrangements de Wagner-Meerwein (WM): tertiaire, < 4 ; secondaire, < 4 ; deplacement d'hydrure 6,2-endo: tertiaire, 7.2; secondaire, 5.8; dkplacement d'hydrure 3,2-exo: tertiaire, 6.6; secondaire, 11.4. Une discussion de la structure des cations norbornyl-2 tertiaires et secondaires met en bidence les points suivants: (i) une rationalisation du rkarrangement rapide d'hydrure 6,2-endo observe dans les cations norbornyles n'implique pas necessairement que I'on doive postuler I'existence d'un nortricyclene protone ("carbocation"); (ii) sur la base des rksultats obtenus avec des cations acycliques et ceux obtenus avec le cation dimkthyl-1,2 norbornyl-2, on ne devrait pas esp6er eliminer ("freeze-out") l...

show abstract

The Structure of the Bicyclo[2,2,1]2-Heptyl (Norbornyl) Carbonium Ion

Cited by 160 publications

References 0 publications

FAST REARRANGEMENT OF exo-NORBORNANOL IN STRONG ACID SOLUTIONS

FAST REARRANGEMENT OF exo-NORBORNANOL IN STRONG ACID SOLUTIONS

Bond length and reactivity. Structure of 2-endo-bornyl p-toluenesulfonate

A Kinetic and Thermodynamic Behavioral Comparison of Observable Secondary and Tertiary 2-Norbornyl Cations

Contact Info

Product

Resources

About