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Hydrogenation of cyclopentadiene dimers

This calculation involves investigating why the endo cyclopentadiene molecule is the major product.

Cyclopentadiene dimers
	1	2
Total bond stretching energy kcal/mol	4.54399	3.46791
Total angle bending energy kcal/mol	30.77260	33.18934
Total torsional energy kcal/mol	-2.73095	-2.94947
Total Van der Waals energy kcal/mol	12.80161	12.35873
Total electrostatic energy kcal/mol	13.01367	14.18451
Total energy kcal/mol	55.37342	58.19067

The table above shows the total energies for Molecule 1 and Molecule 2, the exo and endo cylopentadiene dimers respectively.

The energies of the transition states can also be inspected.

Transition states
Dimer	Transition state energy hartrees ^[1]	Transition state energy kcal/mol
1	-385.5131284	-241913.1920929
2	-385.5169885	-241915.6143428

The energy of the transition states are not as expected. The transition state for molecule 1 is higher in energy than for molecule 2. This does not follow the trend for the energy of the products, however, the energy difference between the molecules is very small so this does not have much effect, and the kinetic factors dominate the reaction.

The energy of the exo dimer is lower, showing it is the thermodynamic product. However, the endo dimer is the major product, indicating that this reaction is under kinetic control. explain, find literature - p orbital overlap, look at transition states http://www.enc.edu/~timothy.t.wooster/courses/CH322/Lab/3-21%20The%20Diels%20Alder%20reaction.pdf.

Cyclopentadiene dimers
	3	4
Total bond stretching energy kcal/mol	3.31162	2.82313
Total angle bending energy kcal/mol	31.94312	24.68533
Total torsional energy kcal/mol	-1.47870	-0.37841
Total Van der Waals energy kcal/mol	12.80161	10.63733
Total electrostatic energy kcal/mol	5.11948	5.14702
Total energy kcal/mol	50.44567	41.25749

These calculations show that Molecule 4 is more stable than Molecule 3 by 9.18818 kcal/mol, and hence 4 is the thermodynamic product and 3 is the kinetic product. Talk about relative contributions.

Atropisomerim

Cyclopentadiene dimers
	9	10
Total bond stretching energy kcal/mol	8.01644	7.74848
Total angle bending energy kcal/mol	30.38823	19.02575
Total torsional energy kcal/mol	2.58293	3.85601
Total Van der Waals energy kcal/mol	35.76228	34.94542
Total electrostatic energy kcal/mol	0.30547	-0.05749
Total energy kcal/mol	77.96334	66.34722

Molecule 10 is more stable than Molecule 4 by 11.61612 kcal/mol, which indicates that 10 is the more stable conformer. These types of bridged alkenes are known as hyperstable alkenes. A bridged alkene is very stable to reaction as it has addition strain energy (olefinic energy) due to the double bond and residual strain due to the carbon skeleton ^[2] !! .

References

↑ W. L. Jorgensen, D. Lim, and J. F. Blake, "Ab Initio Study of Diels-Alder Reaction of Cyclopentadiene with Ethylene, Isopropene, Cyclopentadiene, Acrylonitrile, and Methyl Vinyl Ketone", J. Am. Chem. Soc., 1993, 115, 2936-2942.DOI:10.1021/ja00060a048 10.1021/ja00060a048
↑ W. F. Maier and P. Von Rague Schleyer, "Evaluation and Prediction of the Stability of Bridgehead Olefins", J. Am. Chem. Soc., 1981, 103, 1891.DOI:10.1021/ja00398a003

[ja00060a048-1] W. L. Jorgensen, D. Lim, and J. F. Blake, "Ab Initio Study of Diels-Alder Reaction of Cyclopentadiene with Ethylene, Isopropene, Cyclopentadiene, Acrylonitrile, and Methyl Vinyl Ketone", J. Am. Chem. Soc., 1993, 115, 2936-2942.DOI:10.1021/ja00060a048 10.1021/ja00060a048

[ja00398a003-2] W. F. Maier and P. Von Rague Schleyer, "Evaluation and Prediction of the Stability of Bridgehead Olefins", J. Am. Chem. Soc., 1981, 103, 1891.DOI:10.1021/ja00398a003

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