Absorption spectra in the near ultraviolet of some α- and β-monosubstituted derivatives of thiophene

Abstract

The near ultraviolet absorption spectra in solution of some α-monosubstituted thiophenes have been discussed in relation to the analogous derivatives of furan and thiophene. An electron-acceptor substituent modifies the first excited level of the molecule more in furan than in benzene, thiophenes being intermediate, since the transition energy decreases in the series furan > thiophene > benzene. This order in the series is similar to that expected from the resonance energies. The absorption spectra of some β-substituted derivatives of thiophene have been described and compared with α-derivatives and with the analogous compounds of furan. In these compounds too the substituent is more conjugated when in the α-position.