Hayden- GAMESS Project

MacMolPlt / GAMESS Problem Set

CHEM 502- Summer 2007
Dr. Dailey

Introduction

The purpose of the problem set was to calculate the ground states of structural isomers HCOH and H₂CO and the transition structure that connects them at the HF/3-21G level of theory. First, each molecule was created in Chem3D and made into an input file. The "input builder" function in MacMolPlt was then used to set the parameters needed for creating the output file with GAMESS. Once the output file was created, it could be re-opened with MacMolPlt where the energy was displayed in Hartrees. Finally, Excel was used to organize the energy values, convert them to kcal/mol, and create an energy profile.

Results

Figure 1.4: Carbene in MacMolPlt as GAMESS Output

Figure 1.5: Transition State in MacMolPlt as GAMESS Output
formaldehyde

Figure 1.6: Formaldehyde in MacMolPlt as GAMESS Output

Table 1.1: Calculated Energy Values
Molecule	Energy (Hartrees)	Energy (kcal/mol)
carbene (A)	-113.1463	-71000.43471
transition state (B)	-113.0501	-70940.06825
formaldehyde (C)	-113.2218	-71047.81172
energy difference (D)	-0.0755	-47.37701
activation energy (E)	0.0962	60.36646

Figure 1.7: Energy Profile (Drawn to scale)

Conclusions

Carbenes are very unstable. A significant reason for this is that carbon is lacking an octet as shown in both 1 and 2 in Figure 1.1. The ground state for the analyzed carbene was found to be -71000.43471 kcal/mol (-113.143 Hartress) and is pictured above in Figure 1.4. Formaldehyde, a more stable molecule, satisfies the octet rule for all atoms and contains no formal charges. It's ground state energy was lower at -71047.81172 kcal/mol (-113.2218 Hartrees) and is pictured above in Figure 1.6. The calculated difference in energy for the change between the carbene and formaldehyde was -47.37701 kcal/mol (-0.0755). This indicates that the process is exothermic going from A to C as pictured in Figure 1.7.

The transition structure that connects HCOH and H₂CO is pictured in Figure 1.2. The carbon is lacking an octet. Both the carbon and hydrogen have a formal charge as the hydrogen is partially bonded to both the carbon and the oxygen. This makes its energy higher than each of the structural isomers. The output had an energy of -70940.06825 kcal/mol (-113.0501 Hartrees) and was identical to Figure 1.5. The energy barrier was determined to be 60.36646 kcal/mol (0.0962 Hartrees) when going from A to C in the energy profile.