1. T. I. Temnikova, Course in Theoretical Foundations of Organic Chemistry [in Russian], Khimiya (1968), p. 469.
2. Ya. A. Éidus, A. Ya. Ékmane, K. K. Venter, and S. A. Giller, Atlas of Electronic Spectra of 5-Nitrofuran Compounds [in Russian], Zinatne, Riga (1968), p. 19.
3. J. W. Breitenbach and J. Derkosch, Monatsh., 31, 530 (1950).
4. C. N. R. Rao, Electronic Spectra in Chemistry [Russian translation], Mir, Moscow (1964), p. 70.
5. Yu. A. Zhdanov and V. I. Minkin, Correlation Analysis in Organic Chemistry [in Russian], Izd. RGU, Rostov-on-Don (1966), p. 257.