Conformational study of a series of 6-substituted 5,6,7,12-tetrahydrodibenzo[a,d]-cyclooctenes by nuclear magnetic resonance spectroscopy

The conformational properties of seven 5,6,7,12-tetrahydrodibenzo[a,d]cyclooctenes bearing substituents at C-6 have been studied using variable temperature proton nmr spectroscopy. The position of the equilibrium between boat-chair (BC) and twist-boat (TB) conformers has been measured in several solvents. In contrast to the unsubstituted dibenzocyclooctene, appreciable amounts of TB conformer are present when C-6 is substituted by alkyl, hydroxy, or cyano substituents. Measurements at different temperatures showed the TB form to possess the greater entropy. Barriers to the BC → TB interconversion were determined by coalescence studies, using both approximate and complete line shape methods. Barriers ranged from 10.1 kcal/mol for the 6-keto derivative to 16.7 kcal/mol for the 6-hydroxy-6-methyl derivative.

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Conformational Study of N-Alkyl 5,6-Dihydro-7h,12h-Dibenz[C,F]Azocines by Nuclear Magnetic Resonance Spectroscopy

Canadian Journal of Chemistry ◽

10.1139/v75-023 ◽

1975 ◽

Vol 53 (2) ◽

pp. 167-176 ◽

Cited By ~ 14

Author(s):

Robert R. Fraser ◽

Mohammad A. Raza ◽

Roger N. Renaud ◽

Robert B. Layton

Keyword(s):

Nuclear Magnetic Resonance ◽

Magnetic Resonance ◽

Magnetic Resonance Spectroscopy ◽

Resonance Spectroscopy ◽

Boat Conformation ◽

Conformational Study ◽

Conformational Properties ◽

Boat Form ◽

Twist Boat ◽

Influence Of Substituents

The influence of substituents on the conformational properties of N-substituted 5,6-dihydro-7H,12H-dibenz[c,f]azocines and their conjugate acids was studied by n.m.r. spectroscopy. The position of the equilibrium between a rigid boat-chair and a flexible twist-boat conformation has been measured. The twist-boat conformation in deuterochloroform increased as the size of the substituent increased. However, the effect was opposite for the series of conjugate acids in trifluoroacetic acid.A number of inversion barriers for the [Formula: see text] and the [Formula: see text] equilibria in CDCl3 and TFA were determined. It was found that all barriers to interconversion were raised on protonation. The barrier to racemization for the twist-boat form of the quaternary methiodide of 1 was found to be >18 kcal/mol.

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Conformational Study of N-Methyl-5,6-dihydro-7H,12H-dibenz[c,f]-azocine by Nuclear Magnetic Resonance Spectroscopy

Canadian Journal of Chemistry ◽

10.1139/v73-504 ◽

1973 ◽

Vol 51 (20) ◽

pp. 3380-3385 ◽

Cited By ~ 8

Author(s):

Roger N. Renaud ◽

Robert B. Layton ◽

Robert R. Fraser

Keyword(s):

Experimental Data ◽

Nuclear Magnetic Resonance ◽

Magnetic Resonance ◽

Resonance Spectroscopy ◽

Conformational Study ◽

Conjugate Acid ◽

Trifluoracetic Acid ◽

Deuterated Derivative ◽

Conformational Properties ◽

Crown Form

A study of the n.m.r. spectra of N-methyl-5,6-dihydro-7H,12H-dibenz[c,f]azocine, its deuterated derivative, and its conjugate acid in deuteriochloroform and in trifluoracetic acid at 27 and at −62° has shown that the molecule prefers the rigid "crown" conformation. From the equilibrium constant for the equilibrium flexible [Formula: see text] crown at 27 and at −62°, ΔH and ΔS values of −3.2 ± 0.5 kcal/mol and −7 ± 3 e.u. respectively were determined, indicating the preference for the crown conformer. A barrier to interconversion of the flexible to crown form at −62° was determined to be 15.3 ± 0.3 kcal/mol.These parameters provide the first experimental data pertinent to the conformational properties of the 1,4-cyclooctadiene system.

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Nuclear magnetic resonance characterization of the ring conformations of monosubstituted derivatives of 1,3-dioxa-5,6-benzocycloheptene

Canadian Journal of Chemistry ◽

10.1139/v83-019 ◽

1983 ◽

Vol 61 (1) ◽

pp. 109-115 ◽

Cited By ~ 13

Author(s):

R. St-Amour ◽

M. St-Jacques

Keyword(s):

Nuclear Magnetic Resonance ◽

Magnetic Resonance ◽

Substituent Effects ◽

Steric Effects ◽

Slow Exchange ◽

Conformational Properties ◽

Derivatives Of ◽

Ring Conformations ◽

Twist Boat

The conformational properties of 2-alkyl (Me, Et, i-Pr, and t-Bu) and 2-phenyl derivatives of 1,3-dioxa-5,6-benzocycloheptene (1) were studied by 13C dnmr. Analysis of slow exchange spectra at 100.6 MHz indicates that all derivatives except tert-butyl exist in an equilibrium of chair (major) and twist-boat (minor) conformations. Substituent effects on the position of the equilibrium are rationalized in terms of steric effects.

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