The enthalpies of formation of lithium, sodium, potassium and thallium cycl
opentadienyls were determined by reaction-solution calorimetry as Delta H-f
degrees [LiCp] = -76.5 +/- 2.9 kJ/mol, Delta H-f degrees [NaCp] = -39.7 +/
- 2.5 kJ/mol, Delta H-f degrees [KCp] = -83.2 +/- 3.2 kJ/mol, and Delta H-f
degrees [TlCp] = +117.7 +/- 1.9 kJ/mol. Using a previously developed model
, the enthalpies of formation of RbCp and CsCp were estimated.