Quantum Calculations

Quantum Calculations for Fluoride, H2CS, and Benzoic Acid
Kaitlyn Harsla and Ross Denholm

Introduction
Quantum mechanics is a powerful tool for gaining insight into particular forces that govern molecular interactions and atomic relationships. The immensely complex calculations made in these computer programs would take a team of chemists months to decipher, allowing one to make assertions about molecular phenomena with confidence. Wavefunctions for electrons are represented in these visual aids by colorful, bulbous molecular orbitals. This enables an onlooker the ability to visualize what these calculations are outlining. The wavefunctions created using different levels of theory provide a variety of perspectives on the particular behavior on an atomic scale. The larger the data set, more factors taken into account offer a clearer the picture of what is happening in molecules.

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	Depiction of the highest occupied molecular orbitals (HOMO) of fluoride.

In order to find the HOMO of F2, Gamess quantum calculator determined that fluoride's ninth orbital domain, which was determined to be the highest energy orbital occupied by
at least one electron due to valence considerations.

Valence energy level diagram for F2. The highest occupied molecular orbital is 2p pi antibonding. The lowest unoccupied is the 2p sigma antibonding orbital.

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	The lowest unoccupied molecular orbital of the F2 molecule, orbital ten, pictured above.

Pictured is a model of the lowest unoccupied molecular orbital of the fluoride molecule. It is one energy level higher than that of the highest energy orbital occupied by electrons.

Electronic Potential vs. Bond Length

As atoms approach one another potential energy drops due to the stabilizing effect chemical bonding has on molecules. 8+ angstroms essentially demonstrates two atoms at infinite distance, where around -200 Hartrees represents the zero energy of nonbonded atoms.

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	The highest occupied molecular orbital of H2CS; orbital 12.

This disjointed array of orbitals represents the grouping containing the highest energy electrons of H2CS.

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	H2CS model of the lowest unoccupied molecular orbitals.

The picture illustrates the shape of the 13th orbital shell of H2CS, its lowest unoccupied shell.

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	Charge separation of H2CS

Molecular model of H2CS, including separation of charges between the individual atoms. Due to the existence of partial charges, this molecule is considered polar.

Dipole Moments of H2CS and Benzoic Acid

                           H2CS

Level of Theory              Dipole Moment (in Debeyes)

AMI                                            2.119675
DZV                                            2.154723
PM3                                            2.074266
621-G                                          2.447574
631-G                                          2.572209

                       Benzoic Acid

Level of Theory              Dipole Moment (in Debeyes)

AMI                                            2.417831
DZV                                            2.492621
PM3                                            2.252452
621-G                                          1.998134
631-G                                          2.446429

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	Benzoic acid highest occupied molecular orbital- orbital 61.

HOMO of benzoic acid. Its 61st orbital shell, containing the electrons of highest energy.

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	Depiction of the lowest unoccupied orbital shell of benzoic acid.

Layout of the lowest energy orbital pattern for benzoic acid that is unoccupied by electrons.

Infrared Spectrum of Benzoic Acid

Spectrum website: http://sdbs.db.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi

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Bond length comparison between literature and experimental values for benzoic acid.
Bond     Literature Value (Angsr) Experimental Value (Angst)
O=C            1.22                                1.22
O-C             1.36                                1.36
C-C             1.48                                1.40
C-C(arom.) 1.39                                1.39
O-H            0.95                                0.96
C-H            1.09                                1.07

Bond Angle    Literature (Deg)    Experimental (Deg)_______
C-C=C                119.9                        120.6
C-O-H                85.0                           85.0
C-C-H                121.2                         119.5

Based on template by A. Herráez as modified by J. Gutow

Page skeleton and JavaScript generated by export to web function using Jmol 14.2.15_2015.07.09 2015-07-09 22:22 on Feb 29, 2016.The bond length between carbon bonds varies slightly due to the high electronegativity of chlorine present

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