The molecular geometry was
optimized at three different levels of theory. The bond length as well
as the bond angle for each level of theory is shown below. Table 1
contains the literature
9 values for bond angles of fluorobenzene and Table 2 contains the literature
9
values for bond length. Since all of the levels of theory produced
almost the exact same values for bond length and bond angle no one
theory was considered the "best". The DZV level of theory was used for
further calculations simply because it contained the largest basis set.
6-31G was the second largest basis set used to calculate molecular geometry.
DZV was the largest basis set used to calculate molecular geometry.
Table 1: Literature values for bond angles in fluorobenzene.
Reference Atoms
|
Angle Between Atoms (o)
|
C-C
|
117.956
123.348
119.747
120.496
|
C-H
|
119.579
119.925
119.983
120.127
122.060
|
C-F
|
118.326
|
Table 2: Literature values for bond lengths in fluorobenzene.
Type of Bond
|
Bond Length in nm
|
C-C
|
0.13896
|
C-H
|
0.108185
|
C-F
|
0.13540
|
The highest occupied molecular
orbital (HOMO) is shown below. This is the orbital geometry that
represents the valence electrons in their ground state.
This was calculated by summing the total number of electrons for the
molecule and dividing by two.
The lowest unoccupied molecular
orbital (LUMO) is shown below. This is the orbital that the valence
electrons occupy once they have been excited by some form of energy.
This was calculated by selecting the molecular orbital that was adjacent
to the HOMO orbital but with a different sign associated with the
energy.
The electrostatic potential
graphic shown below, represents the probability density of where the
bonding electrons are located in a given molecule. Red colors represent
regions of greater probability density, while blue colors represent
regions of lower density. Colors between red and blue represent
intermediate probability densities.
The calculated partial atomic
charges for fluorobenzene are shown below. These values represent the
distribution of electrons between atoms.
Graphics representing the
vibrational frequencies of fluorobenzene are shown below. All of these
vibrational frequencies were calculated using the DZV level of theory
as it offered vibrational frequencies closest to that of the literature
9
values. Vibrational frequencies for molecules are most often observed
through Infrared spectrum. An IR spectra for fluorobenzene is shown below as
Figure 1.
Figure 1: A representative IR spectrum of fluorobenzene.
All of the vibrational graphics shown are representative of major peaks shown in Figure 1
.
The vibration at 553.25 cm
-1 represents a C-C bend.
The vibration at 686.95 cm
-1 represents a C-C bend.
The vibration at 887.84 cm
-1 represents a C-H bend.
The vibration at 1063.02 cm
-1 represents a C-H wiggle.
The vibration at 1297.18 cm
-1 represents a C-C stretch.
The vibration at 1481.83 cm
-1 represents a C-H wag.
The vibration at 1626.16 cm
-1 represents a C-C stretch.
The vibration at 3390.38 cm
-1 represents a C-H stretch.
The wavelengths of UV light that
fluorobenzene would absorb were calculated using the DZV level of
theory. A table of these values is given as Table 3. A UV-Vis spectrum
of fluorobenzene
9 is shown in Figure 2 to be used as a comparison.
Table 3: A list of calculated wavelengths of absorbance for fluorobenzene.
Calculated UV Absorbance Wavelength (nm)
|
187.64
|
126.67
|
122.00
|
118.06
|
116.19
|
Figure 2: A representative UV-Vis spectrum of fluorobenzene.
The dipole moment for
fluorobenzene was calculated at each level of theory with 6-21G
generating a dipole moment of 2.011737 debyes which was closest to the
literature value
9 of 1.600 debyes. This calculated value was in error by 25.73%. The
ab initio
calculations used in this work have a difficult time modeling molecules
with aromaticity, which is why the error in the dipole moment is so
great.
You may look at any of these intermediate views again by clicking on the appropriate button.
Based on template by A. Herráez as modified by J. Gutow
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