ORGANIC CHEMISTRY Chapter 13 13.9 Ultraviolet-Visible Spectroscopy Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 13 13.9 Ultraviolet-Visible Spectroscopy
ORGANIC CHEMISTRY Chapter 13 13.9A Ultraviolet-Visible Spectroscopy o a uV-Vis spectrophotometer measures the amount of light absorbed at each wavelength of the uv and visible regions of the electromagnetic spectrum o nmaxthe wavelength of maximum absorption o- molar absorptivity C×l Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 13 13.9A Ultraviolet-Visible Spectroscopy A UV-Vis spectrophotometer measures the amount of light absorbed at each wavelength of the UV and visible regions of the electromagnetic spectrum. λmax— the wavelength of maximum absorption. ε — molar absorptivity ε = A C × l
ORGANIC CHEMISTRY Chapter 13 3.9B Absorption Maxima for Nonconjugated and Conjugated dienes o alkenes and nonconjugated dienes usually have absorption maxima below 200 nm o Compounds whose molecules contain conjugated multiple bonds have absorption maxima at wavelengths longer than 200 nm o When a molecule absorbs light at its longest wavelength, an electron is excited from its HOMO to the Lumo Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 13 13.9B Absorption Maxima for Nonconjugated and Conjugated Dienes Alkenes and nonconjugated dienes usually have absorption maxima below 200 nm. Compounds whose molecules contain conjugated multiple bonds have absorption maxima at wavelengths longer than 200 nm. When a molecule absorbs light at its longest wavelength, an electron is excited from its HOMO to the LUMO
ORGANIC CHEMISTRY Chapter 13 不π(LUMO 平73*(LUMO excitation excitation 丌2(HOMO) 丌(HOMO) CH2-CH2 CH2=CH一CH=CH max 171 nm 217nm Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 13 excitation excitation π*(LUMO) π3*(LUMO) π(HOMO) π1 π2(HOMO) π4* CH2 CH2 CH2 CH CH CH2 λmax 171 nm 217 nm
ORGANIC CHEMISTRY Chapter 13 CH2-CH2 入max(nm)17 177 178 182 184 185 max(nm)217 223 223.5 228 274 239 256 Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 13 CH2 CH2 171 184 177 182 185 λmax (nm) 178 217 223 228 274 239 256 λmax (nm) 223.5