Nuclear magnetic resonance studies of ligand-exchange processes. I. Ligand-exchange equilibria for some gallium(III) .beta.-diketonates

1969 ◽  
Vol 8 (3) ◽  
pp. 639-643 ◽  
Author(s):  
Thomas J. Pinnavaia ◽  
S. Oguzie Nweke
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Ligand Exchange ◽  
Magnetic Resonance Studies ◽  
Exchange Processes ◽  
Nuclear Magnetic

Nuclear magnetic resonance studies. XL. Tricyclooctanone rearrangement, [3.2.1.0] → [3.3.0.0], via γ-enolization and a 2Hmr study of H/D exchange in tricyclic ketones

1984 ◽  
Vol 62 (7) ◽  
pp. 1385-1391 ◽  
Author(s):  
A. K. Cheng ◽  
Ashim K. Ghosh ◽  
J. B. Stothers
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Membered Ring ◽  
Deuterium Incorporation ◽  
Magnetic Resonance Studies ◽  
Endo Isomer ◽  
Exchange Processes ◽  
Initial Transformation ◽  
Nuclear Magnetic

The effect of strongly basic conditions (t-BuO−/t-BuOH/185 °C) on the exo and endo isomers of 7,7-dimethyltri-cyclo[3.2.1.02.4]octan-6-one has been examined. While the exo isomer is stable, the endo isomer readily rearranges to 4,4-dimethyltricyclo[3.3.0.02.8]octan-3-one (6) which subsequently undergoes reduction of the three-membered ring. The initial transformation is one of very few examples of γ-enolate rearrangement. Experiments in tert-buiyl alcohol-O-d1 were carried out to establish the several sites of deuterium incorporation in the initial ketones and in 6 using 2Hmr. These results reveal the stereochemistry of γ-enolate formation and cleavage as well as the stereoselectivities and relative rates of the exchange processes.

Nuclear magnetic resonance studies of ketone•BF3 complexes. II. The boron trifluoride catalyzed condensation of acetone

1968 ◽  
Vol 46 (24) ◽  
pp. 3799-3811 ◽  
Author(s):  
R. J. Gillespie ◽  
J. S. Hartman
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Boron Trifluoride ◽  
Methylene Chloride ◽  
Aldol Condensation ◽  
Condensation Reaction ◽  
Magnetic Resonance Studies ◽  
Exchange Processes ◽  
Donor Acceptor ◽  
Nuclear Magnetic

A detailed study of the reactions of the acetone•BF3 complex in excess acetone has been carried out by "F nuclear magnetic resonance (n.m.r.) spectroscopy. It is shown that rapid reversible fluorine exchange processes occur in solution, in addition to the slower aldol condensation–dehydration reaction. Two of the new 19F absorptions which appear during the reaction are shown to arise from BF3 complexes of donors which are formed by condensation and dehydration of acetone. The rate of the aldol condensation reaction is shown to fall off markedly as an increasing proportion of the BF3 becomes complexed with water; thus BF3 catalysis of the reaction appears to depend on the existence of a ketone–BF3 donor–acceptor bond. 1H and 19F n.m.r. studies of the acetone•BF3 complex in methylene chloride throw some light on the apparent greatly decreased reactivity of the complex in this solvent. Evidence is presented for the reversibility of the first step of the condensation reaction.

Nuclear Magnetic Resonance Studies. XXVII. Homoenolization of Fenchone. A Mechanistic Study Utilizing C And H Nuclear Magnetic Resonance

1975 ◽  
Vol 53 (2) ◽  
pp. 212-223 ◽  
Author(s):  
A. L. Johnson ◽  
J. B. Stothers ◽  
C. T. Tan
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Deuterium Exchange ◽  
Mechanistic Study ◽  
Deuterium Incorporation ◽  
Magnetic Resonance Studies ◽  
Exchange Processes ◽  
Nuclear Magnetic

Deuterium exchange occurs at five β positions in fenchone under homoenolization conditions (t-BuO−–t-BuOD, 185°), C-6(exo and endo), C-8, C-9, and C-10. Both13C and 2H n.m.r. methods were employed to monitor deuterium incorporation and the particular advantages of the latter are illustrated. The relative rates of the five exchange processes were determined directly by 2H n.m.r. in contrast to the earlier homoenolization studies for which the stereoselectivity of exchange was established indirectly. The intermediate homoenolate ion can lead to rearrangement and the rearrangement products have been characterized by 13C n.m.r. as the 3,3,6-trimethyl-norcamphors. Homoenolization of this mixture gave further evidence on the stereochemistry of homoenolate formation.

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