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Frequently Asked Question
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Indicate the transition responsible for peak(s) in the UV-spectrum and explain
Accepted Answer
The peak(s) in a UV-Vis spectrum are due to electronic transitions within the molecule. When a molecule absorbs UV or visible light, an electron is excited from a lower energy level to a higher energy level. The specific energy difference between these levels determines the wavelength of light absorbed, which corresponds to the observed peak in the spectrum. Common types of transitions include:
π → π
: Transitions involving electrons in pi (π) bonding orbitals to pi antibonding (π
) orbitals. These transitions are typically observed in molecules containing double or triple bonds.
n → π
: Transitions involving electrons in non-bonding (n) orbitals to pi antibonding (π
) orbitals. These transitions are observed in molecules containing heteroatoms like oxygen or nitrogen.
σ → σ
: Transitions involving electrons in sigma (σ) bonding orbitals to sigma antibonding (σ
) orbitals. These transitions usually require higher energy and are observed in the far-UV region.
The intensity and location of the peaks in the spectrum can provide information about the structure and bonding of the molecule.
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