NMR Spectroscopy and Theoretical Calculations in the Conformational Analysis of 1-Methylpyrrolidin-2-one 3-Halo-derivatives

Author(s)

de Melo, Ulisses Zonta ^[1] ; Silva, Rai G. M. ^[1] ; Yamazaki, Diego A. S. ^[1] ; Pontes, Rodrigo M. ^[1] ; Gauze, Gisele F. ^[1] ; Rosa, Fernanda A. ^[1] ; Rittner, Roberto ^[2] ; Basso, Ernani A. ^[1]

Affiliation

^[1] Univ Estadual Maringa, Dept Chem, BR-87020900 Maringa, Parana - Brazil

^[2] Univ Estadual Campinas, Inst Chem, Phys Organ Chem Lab, BR-13083970 Sao Paulo - Brazil

• Document type: Journal article
• Source: Journal of Physical Chemistry A; v. 119, n. 10, p. 2111-2121, MAR 12 2015.
• Web of Science Citations: 2

Abstract

This study reports the results of ab initio and density functional theory (DFT) electronic structure calculations as well as (3)J(HH) experimental and calculated coupling constant data obtained in the investigation of the conformational equilibrium of 3-halo-derivatives of 1-methylpyrrolidin-2-one. The five-membered ring assumes an envelope conformation owing to the plane of formation of the O-C-N-R bond, with C4 forming the envelope lid. When the conformation changes, the lid alternates between positions above and below the amide plane. The a-carbonyl halogen assumes two positions: a pseudo-axial and a pseudo-equatorial. In the gaseous phase, the calculations indicate that the pseudo-axial conformer is more stable and preferable going down the halogen family. Natural bond orbital analysis showed that electronic delocalization is significant only for the iodo derivative. In the other derivatives, the electrostatic repulsion between oxygen and the halogen determines the conformational equilibrium. When the solvated molecule was taken into account, the pseudo-equatorial conformer population increased with the relative permittivity of the solvent. This variation was strong in the fluoro derivative, and the preference was inverted. In the chlorine derivative, the two populations became closer in methanol and acetonitrile. In the bromine and iodine derivatives, the percentage of pseudo-equatorial conformer increased only slightly owing to the dipole moment of the conformation: the pseudo-equatorial conformation has a greater dipole moment and thus is stable in media with high relative permittivity. (AU)

• FAPESP's process: 12/03933-5 - Conformational equilibria and intramolecular interactions for a series of amino-acids: theoretical and experimental approaches
• Grantee: Roberto Rittner Neto
• Support Opportunities: Regular Research Grants