Open a new Spartan work space by clicking the new page icon . In the build menu click on the tab labeled Exp., this will switch the build tool bar on the right to the experimental atom set. The build tool kit on right should look like this:Click the boxes highlighted in the picture above to draw a carbon atom with only one bond, click in the work space to draw the carbon atom. Then select nitrogen and the box that indicates two bonds and click on the empty valence of the carbon atom you just drew. Now make sure you have the box selected that indicates you want to draw a triple bond and double click on the bond between the carbon atom and the nitrogen atom. Now select the hydrogen atom and the single bond square and add the hydrogen to the nitrogen atom. Now we have our product CNN.
Now set up the calculations to do a equilibrium geometry calculation just as we did before, try the calculation with semi-empirical and density functional and compare the results. Be sure to select that you would like the program to find the frequencies and calculate the thermodynamic quantities so we can finish up our overall calculations for the reaction.The semi-empirical calculation output should look like this:
Spartan '02 Mechanics Program: (PC/x86) Release 116
Heat of Formation: 48.838 kcal/molZero-point vibrational energy is 10.757 kcal/molStandard Thermodynamic quantities at 298.15 K and 1.00 atmTranslational Enthalpy: 0.889 kcal/mol
Rotational Enthalpy: 0.592 kcal/mol
Vibrational Enthalpy: 10.859 kcal/mol
....Total Enthalpy: 12.340 kcal/molTranslational Entropy: 35.816 cal/mol.K
Rotational Entropy: 11.772 cal/mol.K
Vibrational Entropy: 0.430 cal/mol.K
....Total Entropy: 48.018 cal/mol.KFree Energy (H-TS): -1.977 kcal/mol
And the density functional calculation should look like this:
Spartan '02 Mechanics Program: (PC/x86) Release 116
Optimization:
Step Energy Max Grad. Max Dist.
1 -93.3919573 0.061235 0.082852
2 -93.3960684 0.005086 0.007920
3 -93.3961139 0.001064 0.001920
4 -93.3961155 0.000051 0.000070Molecule is linear
Zero-point vibrational energy is 9.806 kcal/molStandard Thermodynamic quantities at 298.15 K and 1.00 atmTranslational Enthalpy: 0.889 kcal/mol
Rotational Enthalpy: 0.592 kcal/mol
Vibrational Enthalpy: 10.124 kcal/mol
....Total Enthalpy: 11.605 kcal/molTranslational Entropy: 35.816 cal/mol.K
Rotational Entropy: 11.784 cal/mol.K
Vibrational Entropy: 1.520 cal/mol.K
....Total Entropy: 49.121 cal/mol.KFree Energy (H-TS): -3.040 kcal/mol
Notice that again there are slight differences in the values returned by the calculations:
Method
|
Enthalpy
|
Entropy
|
Heat of Formation |
Ground State Energy |
Semi-empirical
|
12.340 kcal/mol
|
48.018 cal/mol
|
48.838 kcal/mol
|
-----
|
Density functional
|
11.605 kcal/mol
|
49.121 cal/mol
|
-----
|
-93.396 au
-58605.990 kcal/mol |
Take a look at the vibrations for the product molecule.They look very similar the the reactant vibrations, as they should.Finally, let's look at what kind of parameters that we can calculate for these three data sets.