NMR spectra of the porphyrins. 38—Conformational analysis of azacycloheptane and azacyclooctane using a novel cobalt(III) porphyrin shift reagent

✍ Scribed by Raymond J. Abraham; Craig J. Medforth

• Publisher: John Wiley and Sons
• Year: 1990
• Tongue: English
• Weight: 501 KB
• Volume: 28
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1260280412

✦ Synopsis

Abstract

A novel NMR shift reagent, cobalt(III) meso‐tetraphenylporphyrin (CoTPP) was used to determine the conformations of azacycloheptane and azacyclooctane ligands complexed to the metalloporphyrin. Using the observed ring current shifts and a previously calibrated ring current model, the best agreement between the observed and calculated ring current shifts for azacycloheptane was obtained for a chair conformation, in agreement with previous theoretical and experimental studies on the conformational stability of seven‐membered rings. The ring current shifts for azacyclooctane are best interpreted in terms of a mixture of many conformations. These results suggest that CoTPP may be useful as a probe of other conformationally mobile ligands.