Difference Between Azulene And Naphthalene

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Introduction Molecular orbital theory allows for the relation between the nature of chemical bonds and the properties of molecules.1 Many times, the frontier molecular orbitals, named HOMO and LUMO, are analyzed in order to predict these properties. In this lab, each double bond corresponds to a molecular orbital. The HOMO, or highest occupied molecular orbital is the most energetic (highest n-value) orbital that contains an electron. The n-value is equal to the number of double bonds present. The orbital that corresponds to the first excited state is referred to as the LUMO, or lowest unoccupied molecular orbital. The transition of an electron from the HOMO orbital to the LUMO orbital is the transition that requires the least amount of energy. …show more content…
Namely, Azulene absorbed a much higher wavelength, 576.0nm, compared to naphthalene’s absorbance of 309.3nm. This was due to differences in molecular orbitals. Naphthalene, being a benzenoid compound, had identical electron densities for its HOMO and LUMO. Azulene instead had different HOMO and LUMO. Because the orbitals in Azulene did not occupy the same location, electron-electron repulsion decreased when an electron transitions to the LUMO. As a result, there was a lower energy gap between the HOMO and LUMO of Azulene, and it absorbed a longer wavelength than Naphthalene.4 These molecular orbitals were estimated by the Hückel calculation, so they may not have been exactly accurate. This may have either increased or decreased the energies associated with the HOMO and …show more content…
Seven azulene derivatives were analyzed. 6-amino-1,2,3-triphenyl azulene had two phenyl groups (EDG) on odd carbons, which increased the energy of the HOMO orbital. It also had a phenyl group (EDG) and an amino group (EDG) on even carbons. These increased the energy of the LUMO orbital. The absorbance shift of the compound depended on the effectiveness of the amino group in comparison to the effectiveness of a phenyl group. Evidenced by the blue-shifted spectrum, the prediction that an amino group was a better electron donor than a phenyl group was supported. Next, 6-formamido-1,2,3-triphenyl azulene was tested, this molecule also had two phenyl groups (EDG) on odd carbons, which increased the energy of the HOMO. The molecule had one phenyl group (EDG) and one formamido group (EDG) on different even-carbons. The spectrum was red-shifted because the formamido group was not as effective at donating electrons as a phenyl group. The HOMO and LUMO energies became closer together. 6-isocyano-1,2,3-triphenyl azulene was the next solution tested. It had a phenyl group (EDG) on two of its odd carbons; the HOMO energy was increased. A phenyl group (EDG) and an isocyano group (EWG) were present on odd carbons; these worked

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