Establishing linear-free-energy relationships for the quadricyclane-to-norbornadiene reaction
Journal article, 2020

The kinetics of the thermal quadricyclane-to-norbornadiene (QC-to-NBD) isomerization reaction was studied for a large selection of derivatives where the one NBD double bond contains a cyano and aryl substituent of either electron-withdrawing or -donating character. While the kinetics data did not satisfy a linear-free-energy-relationship for all the derivatives based on Hammett sigma values, we found individual linear relationships for derivatives containing either electron-withdrawing or electron-donating para substituents on the aryl group; with the most electron-witdrawing substituent in the one series and with the most electron-donating substituent in the other providing the fastest reaction (corresponding to opposite slopes of the Hammett plots). All data were well described, however, by a linear relationship when using Creary radical values; the correlation could be slightly improved by using a combination of sigma and values (used in ratio of 0.104 : 1). The results imply a combination of polar and free radical effects for the isomerization reaction of this specific class of derivatives, with the latter playing the most significant role. The NBD derivatives were prepared by Diels-Alder cycloaddition reactions between cyclopentadiene and 3-arylpropiolonitriles, and in the case of bromophenyl derivatives further cyanation and Sonogashira coupling reactions were performed.

AB-Initio

Substituent

Storage

Resonance

Constants

Kinetic Stability

Thermal-isomerization

Author

Mads Manso

University of Copenhagen

Chalmers, Chemistry and Chemical Engineering, Applied Chemistry, Kasper Moth-Poulsen Group

Anne Ugleholdt Petersen

University of Copenhagen

Kasper Moth-Poulsen

Chalmers, Chemistry and Chemical Engineering, Applied Chemistry, Kasper Moth-Poulsen Group

Mogens Brondsted Nielsen

University of Copenhagen

Organic and Biomolecular Chemistry

1477-0520 (ISSN) 1477-0539 (eISSN)

Vol. 18 11 2113-2119

Subject Categories

Inorganic Chemistry

Theoretical Chemistry

Organic Chemistry

DOI

10.1039/d0ob00147c

PubMed

32119025

More information

Latest update

8/31/2020