Computational Chemistry

The energies of the diradical and cyclopentane can be compared:

1,5-Pentanediyl

(Energy before frequency calculation (i.e. without ZPE)"195.0603078)

Zero-point correction 0.140164

Thermal correction to energy 0.147459

Thermal correction to enthalpy 0.148403

Thermal correction to Gibbs free energy 0.109777

Sum of electronic and zero-point energies "194.920144

Sum of electronic and thermal energies "194.912849

Sum of electronic and thermal enthalpies "194.911905

Sum of electronic and thermal free energies "194.950531

Cyclopentane

(Energy before frequency calculation (i.e. without ZPE)"195.1797025)

Zero-point correction 0.150327

Thermal correction to energy 0.155259

Thermal correction to enthalpy 0.156203

Thermal correction to Gibbs free energy 0.121800

Sum of electronic and zero-point energies "195.029375

Sum of electronic and thermal energies "195.024444

Sum of electronic and thermal enthalpies "195.023500

Sum of electronic and thermal free energies "195.057902

Cyclopentane Bond Energy

1. The crudest value for this is based on the energies from the optimization step, i.e.
   without ZPE

" 195 : 0603078 "ð" 195 : 1797025 Þ¼ 0 : 119395 ¼ 313 :5 kJ mol"^1

2. Using ZPE-corrected energies, i.e. 0 K enthalpies

" 194 : 920144 "ð" 195 : 029375 Þ¼ 0 : 109231 ¼ 286 :8 kJ mol"^1

3. Using sum of electronic and thermal enthalpies, i.e. room-temperature (298 K)
   enthalpies
   " 194 : 911905 "ð" 195 : 023500 Þ¼ 0 : 111595 ¼ 293 :0 kJ mol"^1

To improve the relative energies, a single-point perturbational calculation was
done on both species to correct for dynamical electron correlation. CASPT2N was
not available, and the CAS-MP2 method used here, with the 6-31G* basis, can lead
to suspect results [ 67 ]. Nevertheless, the values obtained for these two species seem
reasonable:

8.2 Singlet Diradicals 545