17O NMR study of substituent effects in 4-substituted N-chlorobenzamides and comparison with 4-substituted benzamides: Sensitivity to ring substituents (ρ) reflects electronic and steric effects

Michael De Rosa, David W. Boykin, Alfons L. Baumstark

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Abstract

Natural abundance 17O NMR spectra of 4-substituted N-chlorobenzamides were obtained in acetonitrile at 75°C and compared with those for similarly substituted benzamides. An excellent correlation (δ = 5.43σ+ + 350.1, r = 0.998) was obtained when the 17O chemical shifts of N-chlorobenzamides were plotted against σ+ and using σ- for the 4-nitro derivative. Based on the greater electronegativity of the N-chloro group the value of ρ observed for N-chlorobenzamides (5.4) would have been expected to be greater compared to that of benzamides (7.3). It is concluded that the 17O chemical shift in N-chlorobenzamides is very sensitive to torsion angle and that is why a low value of ρ is obtained. Sensitivity (ρ) of the chemical shift to ring substituents cannot be used as an unambiguous measure of electronic effects in systems where the torsion angle is greater than zero.

Original languageEnglish (US)
Pages (from-to)1547-1549
Number of pages3
JournalJournal of the Chemical Society. Perkin Transactions 2
Issue number8
StatePublished - Aug 1 1997

All Science Journal Classification (ASJC) codes

  • Chemistry(all)

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