The controversial dynamic stereochemistry of bifluorenylidenes

P. Ulrich Biedermann; Amalia Levy; Michal Rachel Suissa; John J. Stezowski; Israel Agranat

The controversial dynamic stereochemistry of bifluorenylidenes

P. Ulrich Biedermann
, Amalia Levy
, Michal Rachel Suissa
, John J. Stezowski
, Israel Agranat^*

^*Corresponding author for this work

Institute of Chemistry

Research output: Contribution to journal › Article › peer-review

16 Scopus citations

Abstract

Two distinct Gibbs free energies of activation (ΔG_c‡) have been determined by the dynamic NMR method for simple twisted homomerous overcrowded bistricyclic enes of the bifluorenylidene series: ΔG_c‡ = 44 kJ/mol for the conformational inversion (enantiomerization) of 2-i-propyl-bi-9H-fluoren-9-ylidene, and ΔG_c‡ = 104 kJ/mol for the E,Z-isomerization of 2,2′-dimethyl-bi-9H-fluorene-9-ylidene. These barriers are not biased by additional steric constraints and reflect the intrinsic dynamic properties of bifluorenylidenes. Mechanisms for the dynamic processes are proposed, based on the experimental evidence and semiempirical PM3 calculations.

Original language	English
Pages (from-to)	75-80
Number of pages	6
Journal	Enantiomer
Volume	1
Issue number	1
State	Published - 1996

Keywords

Bistricyclic enes
Chirality
Conformational behavior
Dynamic NMR
Overcrowding
Semiempirical calculations

Cite this

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title = "The controversial dynamic stereochemistry of bifluorenylidenes",

abstract = "Two distinct Gibbs free energies of activation (ΔGc‡) have been determined by the dynamic NMR method for simple twisted homomerous overcrowded bistricyclic enes of the bifluorenylidene series: ΔGc‡ = 44 kJ/mol for the conformational inversion (enantiomerization) of 2-i-propyl-bi-9H-fluoren-9-ylidene, and ΔGc‡ = 104 kJ/mol for the E,Z-isomerization of 2,2′-dimethyl-bi-9H-fluorene-9-ylidene. These barriers are not biased by additional steric constraints and reflect the intrinsic dynamic properties of bifluorenylidenes. Mechanisms for the dynamic processes are proposed, based on the experimental evidence and semiempirical PM3 calculations.",

keywords = "Bistricyclic enes, Chirality, Conformational behavior, Dynamic NMR, Overcrowding, Semiempirical calculations",

author = "Biedermann, \{P. Ulrich\} and Amalia Levy and Suissa, \{Michal Rachel\} and Stezowski, \{John J.\} and Israel Agranat",

year = "1996",

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T1 - The controversial dynamic stereochemistry of bifluorenylidenes

AU - Biedermann, P. Ulrich

AU - Levy, Amalia

AU - Suissa, Michal Rachel

AU - Stezowski, John J.

AU - Agranat, Israel

PY - 1996

Y1 - 1996

N2 - Two distinct Gibbs free energies of activation (ΔGc‡) have been determined by the dynamic NMR method for simple twisted homomerous overcrowded bistricyclic enes of the bifluorenylidene series: ΔGc‡ = 44 kJ/mol for the conformational inversion (enantiomerization) of 2-i-propyl-bi-9H-fluoren-9-ylidene, and ΔGc‡ = 104 kJ/mol for the E,Z-isomerization of 2,2′-dimethyl-bi-9H-fluorene-9-ylidene. These barriers are not biased by additional steric constraints and reflect the intrinsic dynamic properties of bifluorenylidenes. Mechanisms for the dynamic processes are proposed, based on the experimental evidence and semiempirical PM3 calculations.

AB - Two distinct Gibbs free energies of activation (ΔGc‡) have been determined by the dynamic NMR method for simple twisted homomerous overcrowded bistricyclic enes of the bifluorenylidene series: ΔGc‡ = 44 kJ/mol for the conformational inversion (enantiomerization) of 2-i-propyl-bi-9H-fluoren-9-ylidene, and ΔGc‡ = 104 kJ/mol for the E,Z-isomerization of 2,2′-dimethyl-bi-9H-fluorene-9-ylidene. These barriers are not biased by additional steric constraints and reflect the intrinsic dynamic properties of bifluorenylidenes. Mechanisms for the dynamic processes are proposed, based on the experimental evidence and semiempirical PM3 calculations.

KW - Bistricyclic enes

KW - Chirality

KW - Conformational behavior

KW - Dynamic NMR

KW - Overcrowding

KW - Semiempirical calculations

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EP - 80

JO - Enantiomer

JF - Enantiomer

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The controversial dynamic stereochemistry of bifluorenylidenes

Abstract

Keywords

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