TY - JOUR
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
UR - http://www.scopus.com/inward/record.url?scp=0002476833&partnerID=8YFLogxK
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AN - SCOPUS:0002476833
SN - 1024-2430
VL - 1
SP - 75
EP - 80
JO - Enantiomer
JF - Enantiomer
IS - 1
ER -