Structure of Five-membered Rings with One Heteroatom

Structure of Five-membered Rings with One Heteroatom 

Aromatic species include the neutral molecules pyrrole, furan and thiophene (1 Z = NH, O, S) and the pyrrole anion (2). The radicals derived from these rings are named pyrryl, furyl and thienyl. The 2-furylmethyl radical is called furfuryl. Compounds in which two pyrrole nuclei are joined by a CH2 group are called dipyrromethanes when the linkage is by a CH group, they are named dipyrromethenes . The 2- (3) and 3-pyrrolenines (4) are isomeric with the pyrroles, but are nonaromatic as the ring conjugation is broken by an. s/r -hybridized carbon atom. 

Three types of cationic species exist (5-7) all are non-aromatic. The 2-oxo derivative exists in two tautomeric forms (8 and 9) the 3-oxo derivatives have a unique structure (10). 

Neutral aromatic Pyrrole species anion v Isomers of aromatic pyrroles  

Three types of dihydropyrrole (11-13) and two types of dihydro-furan and -thiophene exist (12-13), but only a single class of tetrahydro compounds (14). 

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Structure of Five-membered Rings with One Heteroatom Table 12 Magnetic Properties of Heteronuclei... 

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