The tautomerism of 3-hydroxyisoquinolines

Evans, David A. C.; Smith, G. F.; Wahid, M. A.

doi:10.1039/j29670000590

Cited by 26 publications

(24 citation statements)

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“…In contrast, from the solvent dependence of the UV spectra of 3-hydroxyisoquinoline a gase phase energy difference of 22.8 kcal mol-' in favor of the lactim tautomer 20a might be estimated. 34 The results of both AM1 and MNDO- PM3 calculations are in good agreement with these experimental estimates ( Table VI). The previously mentioned overestimation of the stability of compounds with pyridine-like lone pairs is further demonstrated by the calculated tautomerization energies for 3-hydroxycinnoline: UV spectra in aqueous solution indicate 21b as the predominant t a~t o m e r .~~ Although one can expect a shift of the tautomeric equilibrium towards the lactam form in aqueous solution the calculated energy differences in favor of the hydroxy form seem to be unrealistically high.…”

Section: Am1supporting

confidence: 84%

Tautomeric equilibria of heterocyclic molecules. A test of the semiempirical AM1 and MNDO‐PM3 methods

Fabian

1991

J Comput Chem

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Tautomeric equilibria (mainly of the lactam-lactim type) for a rather large number of six-membered heterocyclic molecules are calculated by the semiempirical AM1, MNDO-PM3, and MNDO methods. Except for compounds with adjacent pyridine-like lone pairs both AM1 as well as MNDO-PM3 give rather reliable predictions for relative stabilities of the various tautomeric species-comparable to quite high level ab initio calculations. The known errors associated with MNDO in the treatment of heterocyclic tautomerism are thus largely corrected in AM1 as well as MNDO-PM3. For 2-hydroxypyridine-pyrid-2(lH)-one the effect of self-association is less satisfactorily described by MNDO-PM3 than by AM1. MNDO-PM3 calculated relative stabilities of methylated derivatives are, however, in considerably closer agreement with experimental values than those obtained by AM1. Ionization potentials, especially those for lone-pair orbitals, are overestimated by all three semiempirical methods. MNDO-PM3 results for nitrogen lone-pair orbital energies are slightly better than those obtained by the AM1 or MNDO method.

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Section: Am1supporting

confidence: 84%

Tautomeric equilibria of heterocyclic molecules. A test of the semiempirical AM1 and MNDO‐PM3 methods

Fabian

1991

J Comput Chem

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“…Compounds 96 and 97 are all minor tautomers of the pyrazolone or indazolone, and their pK a values have been corrected [30]. Smith and coworkers [44] studied the tautomerism of 98 in a number of solvents, and log K T 1.69, rounded off here to 1.7, was obtained by linear solvation energy relationships (LSERs, see Chapter 11) from an extrapolation to water of their results [3]. Those for 82, 99, and 100 employ ''corrected'' pK a values throughout in our usual manner [3].…”

Section: Benzofusion To Give Quinonoid Structures In a Variety Of Commentioning

confidence: 99%

The “Basicity Method” for Estimating Tautomer Ratio: A Radical Re‐Appraisal

Taylor

2013

Tautomerism

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“…Isoquinolin-3-ol (124) remains in an intermediate situation since 125 (3-isoquinolone, 2H-isoquinolin-3-one) is of comparable stability. The less polar tautomer 124 (colorless) predominates in low polarity solvents such as diethyl ether, whereas the more polar 125 (yellow) dominates in water or ethanol [463,464]. The similar stability of these two systems is due to two opposite factors.…”

Section: Electrocyclic and Photochemical Reactionsmentioning

confidence: 99%