Levels of Theory Used
We used five different methods for calculating bond length. AM1 and PM3 were the simplest calculations. 6-21G, 6-31G , and Double Zeta Valence (DZV) used increasingly larger basis sets and were ab initio calculations making them computationally more difficult but theoretically more accurate.

AM1 was the simplest level of theory used.


PM3 was the second highest level of experimental geometry used to calculate bond length.

6-21G was the first ab initio calculation ran.

6-31G was another ab initio calculation with a larger basis set.


DZV was the most computationally intense level of theory used to calculate bond length. It was also slightly closer to the literature values than the other levels of theory.
Table 6. Experimental Literature Values for Bond Length in Styrene⁴

Bond Type	Length (Angstroms)
C-C	1.53
C-H	1.937

Bond angle is shown using DZV theory because all of the other models gave very similar results and DZV is the highest level of theory.

The literature showed a C-C bond length of 1.53 angstroms, C-H bond length of 1.084 angstroms and C-Br bond length of 1.937 angstroms⁴.

The highest occupied molecular orbital was orbital 28.

The lowest unoccupied molecular orbital was orbital 29.

The partial atomic charge of each atom in the molecule is due to differences in electronegativity of the atom.

The electrostatic potential represents the potential surface around the molecule. The red regions are low electrostatic potential while the blue regions are the highest electrostatic potential.

Table 7: Calculated dipole moments using different levels of theory.

Theory	Calculated Dipole Moment (Db)	Percent Error (%)
6-21G	0.039350	18.4
6-31G	0.125771	3.25
DZV	0.131452	0.145

The literature value was 0.13 debye⁴.

DZV, the highest level of theory, gave the dipole moment value that was closest to the literature value as expected.

Table 8: IR values obtained from literature with buttons for animations shown below

Type of Bond	Frequency (cm^-1)
C-H Stretch	3000
C-C Stretch	1700
Ring Stretch	1600
H-C-C Bend	1200-1000

Figure 2. IR spectrum of Styrene³

Table 8: Calculated values for peaks on a UV-vis spectra.  The oscillator strength shows the probability of that peak being on the graph. Values less than 0.1 were omitted from the data.

Oscillator Strength (unitless)	Wavelength (nm)
0.340946	208.93
0.807007	167.90
0.947094	156.24
0.101199	141.07
0.531012	137.93

Figure 3. Experimental UV-Vis spectrum³


The predicted peaks using the DZV level of theory do not agree well the observed experimental value. It may be necessary to use a basis set even larger than DZV to find a more accurate calculated value.


In general the estimated peaks do not align well with experimental peaks. The most likely peak using the calculations is 156 nm while the highest absorbing peak experimentally is at approximately 240 nm.

You may look at any of these intermediate views again by clicking on the appropriate button.