Small Molecule

  • now that you have been introduced to the basics of computational chemistry it is time to study another small molecule more independently
  • your small molecule is is cis-dinitrogen difluoride, N2F2 which has C2v symmetry.
    • If you need a reminder on symmetry point groups take a look at workshop4: Symmetry from last year
  • in terms of the *process* you are essentially repeating the activities carried out on NH3 molecule but now applying this to your small molecule. There are a few extra questions to answer as well.
  • the following instructions are very brief because you know what is entailed. However if you have any doubts do ask the demonstrators!
  • treat your wiki like a "report" or a presentation about your work. Think about which information is important and how it can be clearly communicated.
  • experience with previous groups has indicated a problem with people just taking a snap-shot of the screen, this is not appropriate for a report. When I say tabulate, I mean transcribe the data and produce a table. No table, 0 marks.
  • summary of activities to complete:
    • structure optimisation/frequency analysis, submit final file
    • report key information on the method
    • provide relevant information confirming optimisation
    • provide a 3d jmol and key bond distances, angles.
    • provide a spectrum image, vibrations table and answer the questions below
    • colour image and tabulate charges for symmetry unique atoms
    • generate all the occupied MOs (and discuss them with a demonstrator) then answer the questions below
  • the molecule from the log file does not have bonds between the F and N atoms, what is going on here?
  • for your IR analysis answer the following questions:
    • how many vibrations are expected from the 3N-6 rule?
    • why are there only 4 peaks in the IR spectrum?
    • which vibration is the asymmetric N-F stretch?
    • what is the nature of the highest energy vibration?
  • in your MO analysis answer the following questions:
    • which MOs are core orbital MOs?
    • provide a picture of MO 9 and beside it draw the LCAO diagram
      if you need a reminder of LCAO diagrams take a look at workshop5: Molecular Orbital Diagrams from last year
  • finally
    • check that you have all the items required
    • check against the marking criteria given in the outline
    • check that your log files are load properly
    • check that your jmol files animate properly
  • extra for experts, or just to have fun (not assessed, voluntary)
    • optimise trans-N2F2
    • what is the point group?
    • do the geometric parameters change?
    • the spectrum is quite different! Why is this?
    • contrast the MOs of both conformers

  • Now you are done! We do hope you have enjoyed the lab.

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