Compounds Equally Suited to Experiment or Computation Azapentalenes

If an experimental investigation is decided on, fixed tautomers for which R = alkyl, preferably Me, will be required to preserve tautomeric integrity and it will be necessary to use pK correction factors [9]. For triazoles these are A(NMe) 0.3 for an isolated nitrogen atom and 0.55 when two are contiguous, with A(OMe) 1.0 in all cases. However, we have indications [40] that isoxazoles behave abnormally and the same will probably be true for 53 and 54. Note that no model is needed for 54b unless it is the minor tautomer since annular tautomerism in 54a is improbable. 

Compounds Equally Suited to Experiment or Computation Azapentalenes  

An azapentalene may be defined as a 5,5-ring fused aromatic molecule containing bridgehead nitrogen many allow annular tautomerism and this is frequently present. In 1978, Elguero [41] reviewed this subject and set out to elucidate its underlying rules. Four were Identified (1) the avoidance of dipolar repulsion, 

Tautomerism in the 4-quinazolone 74 (R = H) has been studied quantitatively in water [4], resulting in logiC 1.6 in favor of 74b. Identical UV spectra resulted on protonation of each tautomer, showing (74 h, R = H or Me) to represent a common 

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