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Ethylene.
    The three theories of geometry optimization are shown below. Each theory is shown with the bond angles and lengths for ethylene.




6-21G was the lowest theory of optimization meaning it used the least amount of basis sets.



6-31G was the second best theory of optimization that was used. With the larger basis set the bond angles and lengths are closer to the theoretical value than in the 6-21G.




Table 1: Theoretical bond lengths in ethylene.

Bond
Length (nm)
C double bound C
0.1339
CH
0.1086

Table 2: Theoretical bond angles in ethylene.

Bond
Angle
HCH
117.6
HCC
121.2


DZV was the highest theory of optimization that was used. The bonding angles and lengths that was calculated should be the closest of the theories to the theoretical values.



DZV theory gave the best optimizations so this was the theory that was used for the molecular orbitals. The HOMO was found by adding all the electrons in all the atoms together and dividing by two, which was 8.



The LUMO orbital was found by taking the HOMO and adding one electron. This orbital happens when the atom is excited with enough energy that the electron can move into the next orbital.


The electrostatic potential shows where the most electron density is in the molecule. The blue area shows where the electrons are most likely to be, and the red shows where they are least likely. The intermediate colors represent the intermediate potentials.



When molecules have a asymmetric distribution of electrons the molecule has a partial atomic charge. The positive value shows that the molecule has more electrons near it's nucleus.

    Using the highest level of theory the vibrational frequencies could be calculated. Using an IR Spectrum for ethylene the major peaks could be found. Using the vibrational calculations the peaks could then be matched to the correct vibrations.

IR Spectrum
Figure 1: Theoretical IR spectrum for Ethylene found on NIST.

Table 3: The expected vibration frequencies from the IR Spectrum in Figure 1. The values in the table might not be exact compared to the vibrational frequencies that the DZV calculations provided.

Type of Bond
Frequency (cm-1)
CH2 Rock
826
CH2 Wag
949
CH2 Twist
1023
CH2 Scissor
1342
C-C stretch
1494
C-H stretch asymmetrical
3103
C-H stretch symmetrical
2989

    The graphics show the vibrational frequencies and how the molecule moves at each of the frequencies calculated using the DZV theory.

At 916 cm^-1
At 1110 cm^-1
At 1139 cm^-1
At 1356 cm^-1
At 1494 cm^-1
At 3337 cm^-1
At 3364 cm^-1

    The vibrational frequencies that was calculated using the DZV theory were quite off from the theoretical in some cases. This could have happened because the theory uses mathematics to calculate the vibrational frequencies where as the IR uses light and a detector.

     The theoretical dipole for ethylene is zero since it is a non-polar hydrocarbon. The 6-21G and the 6-31G theories gave a dipole of zero, but the DZV theory gave a dipole of 0.000003 Debyes which could have been cause by the large amount of basis sets in the calculation.

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