WebMO Electrostatic Potential maps

(4/23/20, bes)

Exercise 5: Electrostatic Potential Maps

Electrostatic potential maps show the electron distribution (ie. the composite wavefunction for all electrons) within a molecular frame. Did you get that ? <--these pictures are a visual representation of the composite electron wavefunctions.

The figure below shows an example of the electrostatic potential maps for LiH, H₂, and HF.

• H₂, the electrons are evenly distributed among the two H-atoms (green = neutral),
• LiH, being an ionic compound, the 1s valence electron is transferred to the H-atom showing a Li⁺/positive charge (blue - on left) and an H^-/negative charge (red - on right),
• HF, being a covalent bond with the highly electronegative F-atom showing showing a H⁺/positive charge (blue - on left) and F^-/negative charge (red - on right).

reference

Note: these maps are "surface" maps...electrostatic potential surface maps...and represent what the electron distribution looks like from a external perspective.

Using WebMO/Gaussian please complete the following table by optimizing the geometry based the stated level of theory and basis set:

Activity 1: Generating an Electrostatic Potential Map for Benzene (C₆H₆)

Note: this calculation is a 2-step process:

1) Optimize Geometry, then,

2) Calculate Molecular Orbitals.

Step 1: Optimize Geometry for Benzene

- Click “New Job”, then “Create New Job”. The Build Molecule window opens,

- Build C₆H₆ using the "fragments:

... from the menu bar, select Build: Fragments, then

- Category: --> Rings

- Fragment: --> Benzene

- OK

...then a single click in the drawing area will generate a benzene ring.

- Choose Clean-Up > Comprehensive – Mechanics,

- Symmetrize the molecule...(click "red" D_6h^* <-- 10th item down in left side menu),

- Click the blue “continue” arrow in the lower right side of the Build Molecule window.

- Setup the job as

- Name: C6H6 (should be this already)

- Calculation: Geometry Optimization

- Theory: Hartree-Fock

- Basic Set: Routine: 6-31(G)d

- Charge: 1

- Multiplicity: Singlet

- Click the blue “continue” arrow to submit the job.

Step 2: Calculate Molecular Orbitals for Benzene

- Once the job is complete, click on the hyperlinked name, C6H6 to open the “View Job” window.

- Click the "New Job Using This Geometry" button at the bottom of the window, then click the blue “continue” arrow,

- Setup the job:

- Name: C6H6 (should be this already)

- Calculation: Molecular Geometry

- Theory: Hartree-Fock

- Basic Set: Routine: 6-31(G)d

- Charge: 1

- Multiplicity: Singlet

- Click the blue “continue” arrow to submit the job.

- Once the job is complete, click on the "molecular orbital" hyperlinked name to view the “View Job” window.

- Scroll down to the Molecular Orbitals table and look at the bottom:

...and click the magnifying glass across from the "Electrostatic Potential" label...this will bring your view back to the top and after a short calculation time, the window will display the electrostatic potential map. Note the positive (blue), negative (red), and neutral (yellow/green) areas.

Start your...Report on Electrostatic Potential Map Calculations (more below)

For this lab activity, i am requesting that you prepare a short report...due on Tuesday, April 28th, at 5 pm.

When viewing the electrostatic potential (EP) map, you can save this graphic as a PNG file that can be inserted into WORD.

- When the EP map is displayed, select File: Save Image --> PNG (portable network graphic)...

- Insert this image into a WORD file and save for later additions.

Activity 2: Generating an Electrostatic Potential Map for substituted Benzenes

As discussed previously, substitutions on the benzene ring can be activating or deactivating towards electrophilic aromatic substitution.

- Activating groups (electron donating) --> weakly (alkyl, -CH₃), moderately (alkoxyl, -OCH₃, hydroxy, -OH), and strongly (-O^-).

- Deactivating groups (electron withdrawing)--> weakly (halo, -F, -Cl), moderately (carbonyl, -COR), and strongly (nitro, -NO₂).

Please generate an electrostatic potential map for the following compounds:

1. benzene (done)
2. toluene/methylbenzene
3. anisole/methoxybenzene
4. phenol/hydroxybenzene
5. fluorobenzene
6. benzoic acid/carboxybenzene
7. nitrobenzene

Remember: these calculations are a 2-step process:

1) Optimize Geometry, then,

2) Calculate Molecular Orbitals.

Report on Electrostatic Potential Map Calculations

For this lab activity, i am requesting that you prepare a short report...due on Tuesday, April 28th, at 5 pm. (extensions allowed for good reasons)

When viewing the electrostatic potential (EP) map, you can save this graphic as a PNG file that can be inserted into WORD.

- When the EP map is displayed, select File: Save Image --> PNG (portable network graphic)...

- Insert this image into a WORD file.

Report requirements:

1. NAME/CLASS/DATE
2. INTRODUCTION: a short paragraph related to why we are doing these calculations.
3. METHODS: discuss the software used and the details (theory, basis sets,etc) of the calculations. (You do NOT need to do a step by step description of WebMO/Gaussian)
4. RESULTS: present electrostatic potential maps from calculations.
5. DISCUSSION: Interpret the results in terms of the above calculations.
6. CONCLUSION...if needed.