Table 3.

The prevailing tautomers for the OH derivatives in solution with relative free energy of at least 4.184 kJ/mol ^a.

	CH2Cl2	Water	Exp b,c
2OH
oxazole	2-one, NH	2-one, NH	2-one, NH
thiazole	2-one, NH	2-one, NH	2-one, NH
3OH
isoxazole	3-one, NH/3OH cis	3-one, NH	Mainly 3OH in all media
isothiazole	3-one, NH	3-one, NH	3OH
4OH
oxazole	4-one, C5H	4-one, C5H	4-one, C5H
thiazole	4-one, C5H	4-one, C5H	4OH and 4-one, C5H no ratio provided
isoxazole	4OH, trans/4OH, cis	4OH, trans/4OH, cis	4OH
isothiazole	4OH, trans/4OH, cis	4OH, trans/4OH, cis	4OH
5OH d
oxazole	5-one, C4H	5-one, C4H	5-one, C4H (in crystal)
thiazole	5-one, C4H	5-one, C4H
isoxazole	5-one, C4H/5-one, NH	5-one, C4H/5-one, NH	5-one, C4H in CH3Cl3, NH/CH 55:45 in water e
isothiazole	5-one, NH	5-one, NH	5-one, NH f
3CH3,5OH isoxazole		5-one, C4H	C4H/NH 70:30 in water
4CH3,5OH isoxazole		5-one, NH	5-one, NH

^a If the difference between the most stable and the second-most stable species is less than 4.184 kJ/mol, the code of the second-most stable form appears after the slash; ^b,c [49,50]. For the original references see “e” and “f” specifically; Theoretical results from ^d [19], ^e [51], ^f [52].