Experiment 4: Applying DFT to Organic Chemistry – Part B

Diels–Alder, alkane isomers and dispersion-bound dimers

Four more textbook reactions, where dispersion and changes in bonding start to matter.

At a glance. 10 molecules × 16 methods = 160 jobs with def2-TZVP. Most take seconds; the two hexanes with hybrid functionals take up to about 5 minutes each. You will learn when error cancellation stops helping, and what dispersion corrections (-D4) and nonlocal correlation (VV10) actually fix.

Warm-up

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Background

Reactions studied in Experiment 4: Diels–Alder reaction of ethene and butadiene (4a), isomerization of n-hexane to neohexane (4b), and formation of the ethane (4c) and methanol (4d) dimers. Carbon is black, oxygen red, hydrogen white; the dotted line is a hydrogen bond.

In this experiment you will deal with four more organic reactions commonly found in textbooks:

• 4a: the Diels–Alder reaction between ethene and butadiene to give cyclohexene, ΔE_ref = –45.40 kcal/mol.
• 4b: the isomerization of n-hexane to neohexane (2,2-dimethylbutane), ΔE_ref = –2.49 kcal/mol.
• 4c: the formation of the ethane dimer, held together only by van der Waals (dispersion) interactions, ΔE_ref = –1.34 kcal/mol.
• 4d: the formation of the methanol dimer, held together by a hydrogen bond, ΔE_ref = –5.81 kcal/mol.

These structures come from the DARC  [1–3] and ADIM6  [1,4] subsets of the GMTKN55 database  [1], and from the AlkIsomer11  [5,6] and S66  [7,8] subsets of the MGCDB84 database  [9].

As in Experiment 3, use SPW92, BP86, BLYP, PBE, PBE-D4, SCAN, B97M-V, B3LYP, B3LYP-D4, B3PW91, PBE0, M06-2X, M11, MN15, ωB97M-V and Hartree–Fock (references in Experiment 3), all with the def2-TZVP basis set  [10]. For each functional, compute the reaction energies and the errors with respect to the reference.

Note

For the dimers (4c, 4d) the reaction is monomers → dimer, so a negative ΔE means the dimer is bound. In 4d the two methanol monomers have slightly different geometries (they are cut from the dimer), so compute both.

The molecules

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Predict first

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Run the calculations

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Enter your results

For every job, record the total energy, the number of SCF cycles and the wall time (where to find them), then enter your reaction energies in the last tab. Reactions 4a and 4d involve three species each, and in 4c the ethane monomer counts twice (ν = −2): mind the coefficients.

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Explore your data

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Questions

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Submit

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References

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L. Goerigk, A. Hansen, C. Bauer, S. Ehrlich, A. Najibi, and S. Grimme, Phys. Chem. Chem. Phys. 19, 32184 (2017).

[2]

L. Goerigk and S. Grimme, J. Chem. Theory Comput. 6, 107 (2010).

[3]

E. R. Johnson, P. Mori-Sánchez, A. J. Cohen, and W. Yang, J. Chem. Phys. 129, 204112 (2008).

[4]

S. Grimme, J. Antony, S. Ehrlich, and H. Krieg, J. Chem. Phys. 132, 154104 (2010).

[5]

L. A. Curtiss, K. Raghavachari, P. C. Redfern, and J. A. Pople, J. Chem. Phys. 106, 1063 (1997).

[6]

A. Karton, D. Gruzman, and J. M. L. Martin, J. Phys. Chem. A 113, 8434 (2009).

[7]

J. Řezáč, K. E. Riley, and P. Hobza, J. Chem. Theory Comput. 7, 2427 (2011).

[8]

J. Řezáč, K. E. Riley, and P. Hobza, J. Chem. Theory Comput. 7, 3466 (2011).

[9]

N. Mardirossian and M. Head-Gordon, Mol. Phys. 115, 2315 (2017).

[10]

F. Weigend and R. Ahlrichs, Phys. Chem. Chem. Phys. 7, 3297 (2005).