Cycloundecane (1) was shown to exist at -183.1 degrees C as a mixture of the [12323] (approximately 59%) and [335] (approximately 41%) conformations. Populations were determined from the (13)C NMR spectrum, and assignments were based on the (13)C spectra, calculated free energies and chemical shifts, and information from the literature, including X-ray studies of solid derivatives and calculated barriers.
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Conformations of cycloundecane.
J Org Chem
August 2006
Department of Chemistry, Jackson State University, Jackson, Mississippi 39217-0510, USA.
Cycloundecane (1) was shown to exist at -183.1 degrees C as a mixture of the [12323] (approximately 59%) and [335] (approximately 41%) conformations. Populations were determined from the (13)C NMR spectrum, and assignments were based on the (13)C spectra, calculated free energies and chemical shifts, and information from the literature, including X-ray studies of solid derivatives and calculated barriers.
View Article and Find Full Text PDFPreferred conformation of peptides based on cycloaliphatic C(alpha,alpha)-disubstituted glycines: 1-amino-cycloundecane-1-carboxylic acid (Ac11c).
J Pept Sci
November 2000
Biocrystallography Research Centre, CNR, Department of Chemistry, University of Naples Federico II, Napoli, Italy.
Two complete series of N-protected oligopeptide esters to the pentamer level from 1-amino-cycloundecane-1-carboxylic acid (Ac11c), an alpha-amino acid conformationally constrained through a medium-ring C(i)alpha<-->C(i)alpha cyclization, and either the L-Ala or Aib residue, along with the N-protected Ac11c monomer and homo-dimer alkylamides, have been synthesized by solution methods and fully characterized. The preferred conformation of these model peptides has been assessed in deuterochloroform solution by FT-IR absorption and 1H-NMR techniques. Furthermore, the molecular structures of one derivative (Z-Ac11c-OH) and two peptides (the tripeptide ester Z-Aib-Ac11c-Aib-OtBu and the pentapeptide ester Z-Ac11c-(Aib)2-Ac11c-Aib-OtBu) have been determined in the crystal state by X-ray diffraction.
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