10 Questions
What type of electronic transition is associated with oxygen, nitrogen, sulfur, and halogen compounds?
η το σ*
What is the typical energy requirement for σ → σ* and σ → π* transitions?
High-energy, accessible in vacuum UV
What type of compounds exhibit η το π* electronic transitions?
Alkanes and carbonyl compounds
How many types of electronic transitions are mentioned in the context of UV/Vis spectroscopy?
Four
What is the ground state of a molecule in the context of UV/Vis spectroscopy?
Ground state
What type of electronic transition is denoted by σ το σ∗?
Transition from a sigma bonding orbital to a sigma antibonding orbital
Which of the following types of electronic transitions is NOT mentioned in the outline?
η то η∗
What do the symbols σ and π represent in the context of UV/Vis spectroscopy?
Types of molecular orbitals
What is the general purpose of classifying electronic transitions in UV/Vis spectroscopy?
To understand the energy absorption patterns of molecules
Which type of electronic transition would be most likely to occur in a molecule with a non-bonding orbital?
n το π∗
Study Notes
Electronic Transitions in Ultraviolet/Visible Spectroscopy
- Electronic transitions occur when a molecule absorbs energy from the electromagnetic spectrum, resulting in the promotion of an electron from a lower energy level to a higher energy level.
Types of Electronic Transitions
- σ to σ* transition: involves the promotion of an electron from a sigma bonding molecular orbital to a sigma antibonding molecular orbital
- π to π* transition: involves the promotion of an electron from a pi bonding molecular orbital to a pi antibonding molecular orbital
- η to σ* transition: involves the promotion of an electron from a non-bonding molecular orbital to a sigma antibonding molecular orbital, typically found in oxygen, nitrogen, sulfur, and halogen compounds
- η to π* transition: involves the promotion of an electron from a non-bonding molecular orbital to a pi antibonding molecular orbital, typically found in alkanes and carbonyl compounds
Energy and Frequency of Electromagnetic Radiation
- Energy (E) is directly proportional to frequency (ν) and inversely proportional to wavelength (λ) of electromagnetic radiation, as described by the equation E = hν = hc/λ
- The shorter the wavelength of light or radiation, the higher the energy and vice versa
Absorption and Emission of UV-Vis Photons
- Absorption: the transition from a lower energy level to a higher energy level, resulting in the transfer of energy from the radiation field to the molecule
- Emission: the transition from a higher energy level to a lower energy level, resulting in the transfer of energy from the molecule to the radiation field
- Nonradiative decay: the transition from a higher energy level to a lower energy level without the emission of radiation
Chromophores
- A chromophore is a group of atoms that absorbs light, whether or not a color is produced
- Chromophores are responsible for the absorption of UV-vis photons, leading to electronic excitation of the molecule
Test your knowledge of light and its properties with this quiz. Learn about the relationship between energy and frequency, and how chromophores absorb light. Get ready to shine with your understanding of these fundamental concepts!
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