1. Modelling using Molecular Mechanics

1.1: The Hydrogenation of Cyclopentadiene Dimer

Via Diels Alder reacion, cyclopentadiene acts as diene and dienophile to form dicyclopentadiene at room temperature which will result in two isomers: the exo and the endo dimers as shown above. The highly favoured endo dimer proceeds to form two dihydro dervatives via hydrogenation and the tetrahydro derivative can be formed only by prolonged hydrogenation.

Cyclodimerisation and hydrogenation can be due to either thermodynamics (product stability) or kinetics (transition state stability) factors. On the basis of the results obtained from molecular mechanics technique, conclusion can be drawn that whether cyclodimerisation of cyclopentadiene and the hydroenation of the dimer is kinetically or thermodynamically controlled.

Using Chembio3D, exo dimer 1 and endo dimer 2 were drawn and their geometries were optimised using the MM2 force field option which gave the minimum energy of the drawn molecules.

Comparison Of Dihydro Derivatives

	Dihydro 3	Dihydro 4
Images
Jmol
Stretch	1.2859	1.2439
Bend	20.5871	20.8701
Stretch-Bend	-0.8379	-0.8344
Torsion	7.6717	9.5092
Non-1,4 VDW	-1.4353	-1.5636
1,4 VDW	4.2335	4.3273
Dipole/Dipole	0.3778	0.4488
Total Energy	31.8829 kcal/mol	34.0013 kcal/mol