Saturated heterocycles. 251 . Determination of σ+ values of heteroaryl-substituted phenyl groups via ring-chain tautomerism |
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Authors: | Ferenc Fü l p,Enik Forr ,G bor Bern th,Istv n Miskolczi,Pirjo Vainiotalo,Aarne Martinsen |
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Affiliation: | Ferenc Fülöp,Enikö Forró,Gábor Bernáth,István Miskolczi,Pirjo Vainiotalo,Aarne Martinsen |
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Abstract: | The Hammett-Brown electrophilic substituent constants σ+ for five heteroaryl-substituted phenyl groups were estimated via the ring-chain tautomeric equilibria of three sets of oxazolidines and 1,3-oxazines in deuteriochloroform solution. For oxazolidines derived from norephedrine and norpseudoephedrine, the σ+ values were also determined via the gas-phase ring-chain equilibria, by means of mass spectrometry. The results show that the heteroaromatic substituents studied have a slight electron-withdrawing character, with σ+ in the range -0.03 to 0.59. The gas-phase σ+ values are significantly higher than the solution values. |
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