Hueckel; Wagner Chemische Berichte, 1941 , vol. 74, p. 657,660 Full Text Show Details Hueckel et al. Justus Liebigs Annalen der Chemie, 1959 , vol. 624, p. 142,202 Full Text Show Details Dewar; Read Journal of the Chemical Society, 1936 , p. 1781,1782 Full Text Show Details Nerdel; Doll Ber. Schimmel, 1939 , p. 116 Full Text Show Details Hueckel; Niggemeyer Chemische Berichte, 1939 , vol. 72, p. 1354,1357