Thermodynamic rearrangements of larger polycyclic hydrocarbons derived from the 38.5 and 41.5.degree.C melting dimers of cyclooctatetraene. Crystal and molecular structures of 5-bromoheptacyclo[8.6.0.02,8.03,13.04,11.05,9.012,16]hexadecane (5-bromo-(C2)-bisethanobisnordiamantane), 6,12-dibromoheptacyclo[7.7.0.02,6.03,15.04,12.05,10.011,16]hexadecane, and nonacyclo[11.7.1.12,28.03,16,04,13.05,10.06,14.07,11.015,20]docosane (bastardane)