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Substituent effects in heterocyclic systems. 1 H‐NMR Study of methyl 3,5‐diarylisoxazolium iodides
Author(s) -
Baumstark Alfons L.,
Dunams Tambra
Publication year - 1981
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570180611
Subject(s) - chemistry , substituent , chemical shift , series (stratigraphy) , chalcone , stereochemistry , isoxazole , pyridinium , aryl , methyl group , medicinal chemistry , group (periodic table) , organic chemistry , alkyl , paleontology , biology
Methyl 3‐aryl‐5‐phenylisoxazolium iodides (I) and methyl 3‐phenyl‐5‐arylisoxazolium iodides (II) were synthesized from the corresponding isoxazoles in moderate yields. The 1 H‐nmr chemical shifts for H‐4, series I and II, and the quaternary methyl group series II were found to correlate with values. The rho value observed for H‐4 series II was 3.3 times that observed in series I. The correlation observed in series I contrasts with the lack of (poor) correlations reported in the corresponding isoxazole and chalcone systems. The rho value observed in the correlation of the quaternary methyl group series II correlates well with an estimate based on methyl pyridinium salt data. The chemical shifts of the quaternary methyl group series I showed little or no variation. Swain‐Lupton and DSP treatments did not show improved correlations over the single parameter results. However, interpretation of these treatments reveals that similar processes are occuring in all three cases. The results for H‐4 series I showed that the reduction of transmission of the substituent effect in series I compared to that in series II was essentially due to equal reduction of both inductive and resonance effects. The mechanism of transmission seems to differ only in degree and not type.