Quantumchemistry, NWI-MOL406, Computer exercises, week 4
Hartree-Fock calculation of an enediyne and para-benzyne biradical using NWCHEM
Bergman cyclization
See P. M. Warner and G. B. Jones, J. Am. Chem. Soc., 123, 10322 (2001)
(or local copy)
- Do a geometry optimization of the enediyne at the Hartree-Fock level in a 3-21G basis.
- Follow the steps of the methane calculation with your preferred pre-processing tool.
- The geometry may be constructed either using the MOPAC2016 tool or MOLDEN.
If you choose to use the simpler MOPAC2016 tool, take care to add a line to the NWCHEM input file making NWCHEM write the data that the MOLDEN analyzer needs:
ecce_print ecce.out
- Run the geometry optimization
- Find the bond length of the single (C-C), double (C=C), and triple CC bonds in Angstrom
- Assign all occupied orbitals (core/sigma valence/pi/in-plane pi)
- Assign the unoccupied orbitals up to the highest Hückel and in-plane anti-bonding pi.
para-benzyne biradical
- Do a HF/3-12G geometry optimation in D2h symmetry (a useful link), i.e.
make an input geometry that has this symmetry.
- Do geometry optimization (and force the symmetry to be kept)
- View/assign orbitals up to highest unoccupied Hückel orbital
- Repeat calculation for the triplet state: in a biradical one
expects only a small energy difference between the singlet and triplet states.
Correlation diagram for Bergman cyclization
Along the reaction path the symmetry of the system is C2V. In a correlation diagram
we sort the MOs of reactants and products by energy, and connect them, such
that MOs of the same symmetry do not cross. If an occupied MO of the reactant
correlates with an unoccupied MO of the product the reaction is expected to
have a high barrier.
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Last updated: 22-Nov-2022.