1. : Die Lagerung der Atome im Raum, 2. Aufl., Braunschweig 1894, S. 36.
2. Hindered Rotation of the Methyl Groups in Ethane
3. THE NATURE OF BOND ORBITALS AND THE ORIGIN OF POTENTIAL BARRIERS TO INTERNAL ROTATION IN MOLECULES
4. : Structure and Mechanism in Organic Chemistry, Cornell Univ. Press, Ithaca 1953, Chapter II.