Stability of heteroazulene-substituted tropylium ions: synthesis and properties of the (2-oxo-2H-cyclohepta[b]thiophen-3-yl)tropylium ion, and its oxygen and nitrogen analogues
Stability of heteroazulene-substituted tropylium ions: synthesis and properties of the (2-oxo-2H-cyclohepta[b]thiophen-3-yl)tropylium ion, and its oxygen and nitrogen analogues