Theoretical study of tetracyclo[3.3.3.13,10.17,10]tridecane (bowlane) and its methylene spacer edge and lip expanded (−CH2−)n(n = 1–4) homologs

Gas phase geometries and strain energies (ES) at 298.15 K and 1 atm were calculated using the G4MP2 composite method and various density functional model chemistries for tetracyclo[3.3.3.13,10 .17,10]tridecane (bowlane) and its methylene spacer edge and lip expanded (−CH2−)n(n = 1–4) homologs. Enthalpies of formation were also estimated using the atomization method for bowlane and its single methylene edge spacer homolog. Calculated ES are strongly dependent on the choice of functional, varying up to 62 kJ/mol for a particular compound with different theoretical methods. Lip spacers have a significantly lower absolute effect on ES than edge spacers. Sequential additions of methylene lip spacers progressively decreases the strain energy of bowlane derivatives, whereas edge spacing results in a more complex ES relationship that depends on the number and geometrical arrangement of the spacers.