Ring-Chain Tautomerism and Crystal Structure of Some 1,3-Oxazacyclanes, and the Electrophilic Substitutent Constants for Some Heteroaryl Groups in Solution and in the Gas-Phase

Abstract

In principle, the ring-chain tautomeric ratios of a number of 2-heteroaryl-substituted oxazolidines and tetrahydro-1,3-oxazines are well suited for determination of the Hammett-Brown σ + constants of heteroaryl substituents such as 2-furyl, 3-furyl, 3-thienyl and 2-pyrrolyl in CDCl 3 solution and in the gas phase. However, a number of factors, and especially hydrogen-bonding, can change the monomeric character of either the ring or the chain form (or both), leading to deviations from the ideal σ + values. X-Ray analysis has demonstrated the chain structures of the products of the reactions of L-(-)-norpseudoephedrine and (±)-trans-2-aminomethylcyclohexanol with pyrrole-2-carboxaldehyde