1.3: Generating an Electrostatic Potential Map of a Molecule
An electrostatic potential (ESP) surface or map of a molecule shows the partial distribution of change along the molecule’s surface. These map are very useful to help determine molecular polarity and allow for the placement of the dipole arrow.
To generate the map, first the molecular surface must be created. Go to Extensions on the menu bar and select Create Surfaces… at the bottom of the menu.
The Create Surfaces pop-up menu then appears. Using the dropdown arrow on Color By: select Electrostatic Potential and then press the Calculate button.
The ESP surface will be generated, with red areas being negative and blue areas being positive .
Here is the ESP map for the water molecule. The two lone pairs on the water molecule are slightly negative and the hydrogens are slightly positive. The computer generated dipole arrow is also shown.
The calculated dipole moment is 1.176 D.
Here are the ESP maps of two dichlorobenzene isomers, which are planar molecules. Are they polar or nonpolar molecules? If polar, draw the dipole arrow. You may want to build these two molecules and generate the ESP maps.
Build and produce the ESP maps for ethane (C2H6), ethene (C2H4), and ethyne (C2H2). You may want to do Lewis dot structures for the molecules. How do the three compare to each other?