Collect. Czech. Chem. Commun. 1999, 64, 1696-1708

Multivariate Regression with Substituent Shift Increments. III. 2,5-Disubstituted Furans

Miroslav Holíka,*, Zdeněk Friedlb and Štefan Marchalínc

a Department of Theoretical and Physical Chemistry, Masaryk University, CZ-611 37 Brno, Czech Republic
b Faculty of Chemistry, Technical University Brno, CZ-612 00 Brno, Czech Republic
c Department of Organic Chemistry, Slovak Technical University, SK-812 37 Bratislava, Slovak Republic


Six series of 2-X-5-Y-substituted furans were used for multivariate regression of 13C NMR chemical shifts with four substituent shift increments (SSI). Some of these series were measured in CDCl3 and DMSO-d6 on different spectrometers to exclude possible sources of deviation from the general trends. Program ASSIGN was written for visual and numerical estimation of correct assignment of 13C NMR spectra in the series of derivatives. Multivariate regression proved that the corresponding position in benzenes and furans are not affected by the substituents in the same way: in 2-X-5-Y-substituted furans, the "ortho" position requires correction for the different bond order, the "meta" 13C chemical shift is probably affected by change in diamagnetic contribution of the Y group, and "para" position behaves like another "ortho" position in the molecule.

Keywords: Substituent shift increments; 13C NMR substituent chemical shifts; Assignment of 13C NMR signals; Linear regression; Furans; NMR spectroscopy; Substituent effects.