Molecule

  • now that you have been introduced to a few more basic features of computational chemistry, the association energy and potential energy surface scans, it is time to study another small molecule (actually an IL ion-pair!) more independently
  • your ionic liquid ion pair is 1-methyl-imidazolium chloride (HMim-Cl). Ionic liquids, are made up of many ions, however we can understand the relevant interactions by studying a single ion pair. The insights gained this way have been backed up by spectroscopic studies (NMR, IR, PES and EXAFS).
    • Screenshot
  • in terms of the *process* you are essentially repeating the activities carried out in the earlier sections but now applying these to this novel ionic liquid.
  • the following instructions are very brief because you know what is entailed. However if you have any doubts do ask the demonstrator or Prof Hunt.
  • 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.
  • in any study it is standard to provide key information for EVERY molecule (ion, cluster etc) examined. In your case you need: an opt-freq log file, method information, and convergence proof. To reduce work-load and to allow us to focus on the *interesting* material you do not need to provide the jmol, static mage, IR or population analysis data in your report
  • don't forget to upload all of your job .log files!
  • activities to complete:
    • optimisation of ion-pairs a-c above at the b3lyp/3-21G level
    • tabulate and compare all the H---Cl distances for all ion-pairs.
      • how do the H-bonds of Me3NH and HMim compare?
      • how do the H-bonds of the N-H and C-H H-bonds compare?
      • are these distances representative of a H-bond? Hint compare your distances to the sum of the van der waals radii of H and Cl.
      • will the ionic nature of the ions effect a distance based assessment of H-bonding?
    • provide a table and comparison of the association energy for a-c
      • make this explicit, so give the energy of each component in atomic units, compute the deltaE in au and then convert to kJ/mol
      • provide the relative energy of the two isomers (a) and (b), ask if you are not sure what this is.
      • rationalise why one conformer is less stable than the other.
      • discuss the dissociation energy of (c) relative to (a) and (b). What does the comparison tell us about the H-bonding?
    • scan the N-H coordinate towards Cl of (a)
      • take your optimised (a)structure, swap atoms to make N=1 and H=2, set the N-H distance to 0.8 and the N-Cl distance to 3.2, run the scan. This will take some time, start it early!
      • provide a snapshot from gaussview of the "raw" HMim-Cl PES plot
      • provide a chemical diagram of the two protonation states for HMim-Cl
      • graph the MeNH-Cl and HMim-Cl scans on a single PES plot
      • discuss your HMim-Cl PES plot, compare and contrast your results for the MeNH-Cl and HMim-Cl PES.
  • discuss means we are asking for some interpretation of your results. Students have a tendency to simply describe the data (do not do this!), we can see the data in the tables, make sure you are interpreting the data or adding new information. For example if the association a A is more stabilising than B, evaluate the difference and give the energy, provide a potential rationalisation of why this might occur, even better if you can suggest a way of testing your hypothesis!
  • do double check you have all the components and your links work!

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

  • your feedback is important to us, things like are the instructions clear? did you like the research aspect? and more, please take a few minutes to fill out a short online feedback form
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