Azulene And HOMO Explanations Analysis

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While azulene and naphthalene have the same formula of C10H8, their differing arrangement of carbon atoms in rings causes disparities in their molecular orbitals. As shown in the energy difference calculations below Table 1, naphthalene has an energy difference of -10.184 between its HOMO and LUMO orbitals while azulene has one of +6.904. The low energy difference of naphthalene FMOs would suggest that its HOMO and LUMO orbitals have relatively similar distributions of electron density among odd and even numbered carbons. Conversely, the high energy difference of azulene FMOs imply that there are disparate regions of electron density in the HOMO and LUMO orbitals of azulene. This is represented by Figure 2, in which odd-numbered carbons in …show more content…
The placement of an EDG on an odd-numbered carbon would increase the energy of the HOMO orbital, decreasing the energy gap and causing a red shift. The placement of an EWG on an even-numbered carbon would cause a decrease in the energy of the LUMO orbital, decreasing the energy gap between HOMO and LUMO and causing a red shift. The placement of an EWG on an odd-numbered carbon would decrease the energy of the HOMO orbital, increasing the energy gap and causing a blue …show more content…
This prediction was based on the presence of an EDG, amino, on an even carbon which would cause the LUMO energy to increase. The presence of 2 phenyl EDG groups on odd carbons was predicted to cause an increase in HOMO energy, while 1 phenyl EDG group on an even carbon would slightly decrease the energy of the HOMO orbital in order to produce a blue shift overall. When tested experimentally, the compound exhibited a maximum wavelength at 577.3 nm as shown in Table 4, lower than the maximum wavelength of 691 nm for azulene. This higher-energy peak in 6-amino-1,2,3-triphenylazulene shows that the prediction of a blue shift was correct, and it can be assumed from this that the increase in LUMO energy by the amino group was greater than the increase in HOMO energy by the phenyl groups on carbons 1 and

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