Absolute Configuration Assignment of Chiral Resorcin[4]arenes from ECD Spectra

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of Organic Chemistry, 82, 202–210 (DOI: 10.1021/acs.joc.6b02349), © 2016 American Chemical Society, after peer review and technical editing by the publisher. To access the final edited and published work, see http://pubs.acs.org/articlesonrequest/AOR-qqdQ8QSnr8M5MmPPRw2V
This Manuscript version is made available under the CC-BY-NC-ND 4.0 license. https://creativecommons.org/licenses/by-nc-nd/4.0/

ABSTRACT

Racemates of 5 chiral resorcin[4]arenes, 4 tetra O substituted and 1 hepta O
substituted, have been resolved by enantioselective HPLC and their ECD spectra have been recorded on line by stopped flow measurements. The absolute configuration has been assigned by comparison of the experimental ECD spectra with DFT and semiempirical calculations. For the 4 tetra O substituted resorcin[4]arenes, the ECD exciton couplet at longer wavelength depends on the chirality induced in the arene scaffold by the substituents, rather than on the precise nature of the substituents themselves. Accordingly, the exciton chirality model with excitons localized on the arene scaffold, here generalized to Cn symmetry, accurately describes the relationship between stereochemistry and chiroptical properties for this couplet, while its application at shorter wavelengths is unsafe. For the significantly larger hepta O substituted system the assignment has particularly benefit from the use of the semiempirical ZINDO method.