Houben-Weyl Guide

General chart (X=Hal, O, S, Se, Te, N, P)

Number of Heteroatoms on 1-C-Atoms				Number of Heteroatoms on 2- or more C-Atoms
4	3	2	1	4	3	2	1	0
								Cyclopropenes Cyclobutenes Cyclobutadienes
							Arene-X Hetarene-X	Arenes, Arynes   Hetarenes E6-9
								Carbocyclic π-electron systems   Saturated hydrocarbons Cyclopropanes Cyclobutanes