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Remarkably Slow Rotation about a Single Bond between an sp 3 ‐Hybridised Carbon Atom and an Aromatic Ring without ortho Substituents
Author(s) -
Murrison Sarah,
Glowacki David,
Einzinger Christian,
Titchmarsh James,
Bartlett Stephen,
McKeeverAbbas Ben,
Warriner Stuart,
Nelson Adam
Publication year - 2009
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200802127
Subject(s) - conformational isomerism , ring (chemistry) , chemistry , single bond , rotation (mathematics) , crystallography , atom (system on chip) , bond length , stereochemistry , molecule , crystal structure , organic chemistry , group (periodic table) , geometry , mathematics , computer science , embedded system
Look, no ortho substituents! A series of polycycles were prepared by using a three‐component Joullié–Ugi reaction. The rate of rotation about the bond between a highly hindered bridgehead and a phenyl ring with no ortho substituents was measured, and was highly dependent on the substitution. Rotamer half‐lives of up to 21 h at 298 K were observed (see figure). Rotamers resulting from this restricted rotation were isolated for the first time.A series of polycycles was prepared by using a three‐component Joullié–Ugi reaction. The rate of rotation about the bond between a highly hindered bridgehead and a phenyl ring with no ortho substituents was measured by using, in general, variable‐temperature HPLC. The rate of rotation was highly dependent on substitution and rotamer half‐lives of up to 21 h at 298 K were observed. Insights into the effect of substitution on the rate of rotation were gleaned through electronic structure calculations on closely related derivatives. Rotamers resulting from restricted rotation about a bond between an sp 3 ‐hybridised carbon atom and a phenyl ring with no ortho substituents were isolated for the first time, and the equilibration of the separated rotamers was followed by using analytical HPLC. It was demonstrated, for the first time, that a highly hindered environment for the sp 3 ‐hybridised atom is sufficient for slow bond rotation about a single bond between sp 3 ‐ and sp 2 ‐hybridised carbon atoms.