Integral intensities of the absorption bands of the skeletal vibrations of the heteroaromatic ring in the IR spectra of the furanoquinoline alkaloids

Summary

1. The integral intensities of the bands of the skeletal vibrations of the heteroaromatic ring in the 1480–1630-cm⁻¹ region of eight furanoquinoline alkaloids have been measured.

2. A connection has been found between the values of ΣA and the structures of the furanoquinoline alkaloids and their derivatives which enables such a series of heteroaromatic compounds to be identified: It has been shown that the introduction of an -OCH₃ group into the γ position of the pyridine nucleus leads to a marked rise (almost twofold) in the value of ΣA;

In derivatives of dictamnine (VII-XII), the value of ΣA depends on the position of the methoxy group and on the nature of the substituent in position 7 of the benzene ring;

With an increase in the delocalization of the unshared pair of electrons of the oxygen atom of the furan ring, the value of ΣA of the series of alkaloids investigated (VI-XIV) decreases; and

Compounds (V-XIV) have the very high values of ΣA of 5.0–7.0 practical units and they exceed the value of the intensities of the carbonyl bandsv(C=0).