The particle in a box (PiB) model can be applied to electrons which move freely in a molecule such as π electrons. 1,3-butadiene CH2=CH-CH=CH2 has an absorption peak in the UV-Vis spectrum at 290 nm. This peaks is assigned to the π → π* transition of the lowest energy. This transition is also called the HOMO → LUMO transition. As a simple approximation, let’s consider molecule of butadiene as being potential 1D box of length 3 * 1.4 Å = 4.2 Å, when counting three carbon-carbon bonds each 1.4 Å long. Also let’s consider the four π electrons occupy molecular orbitals MOs and energy of MOs is calculated according to the PiB model. a)
The particle in a box (PiB) model can be applied to electrons which move freely in a molecule such as π electrons. 1,3-butadiene CH2=CH-CH=CH2 has an absorption peak in the UV-Vis spectrum at 290 nm. This peaks is assigned to the π → π* transition of the lowest energy. This transition is also called the HOMO → LUMO transition. As a simple approximation, let’s consider molecule of butadiene as being potential 1D box of length 3 * 1.4 Å = 4.2 Å, when counting three carbon-carbon bonds each 1.4 Å long. Also let’s consider the four π electrons occupy molecular orbitals MOs and energy of MOs is calculated according to the PiB model. a)
Principles of Modern Chemistry
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The particle in a box (PiB) model can be applied to electrons which move freely in a molecule such as π electrons.
1,3-butadiene CH2=CH-CH=CH2 has an absorption peak in the UV-Vis spectrum at 290 nm. This peaks is assigned to the π → π* transition of the lowest energy.
This transition is also called the HOMO → LUMO transition.
As a simple approximation, let’s consider molecule of butadiene as being potential 1D box of length 3 * 1.4 Å = 4.2 Å, when counting three carbon-carbon bonds each 1.4 Å long.
Also let’s consider the four π electrons occupy molecular orbitals MOs and energy of MOs is calculated according to the PiB model.
a) Sketch the scheme of MOs of butadiene molecule and populate them with electrons.
b) Calculate the wavelength of light λcalc which corresponds to absorption of light and excitation of π electron from the HOMO to the LUMO in the molecule of butadiene.
c) Compare this calculated λcalc with experimental value of λexp = 290 nm provided above, and explain the difference (at least two reasons).
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G butadiene absorption spectrum - Go... XNIST 1,3-Butadiene
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