厦门大学化学化工学院：《有机化学》课程教学资源（课件讲稿，双语版）Chapter 13 Conjugated Unsaturated Systems（13.9-13.11）Ultraviolet-Visible Spectroscopy

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

ORGANIC CHEMISTRY Chapter 13 The greater the number of conjugated multiple bonds a compound contains, the longer will be the wavelengt at which the compound absorbs light max nm 217219 254 256 258 290 497 β Carotene(胡萝卜素) Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 13 The greater the number of conjugated multiple bonds a compound contains, the longer will be the wavelength at which the compound absorbs light. 497 β-Carotene (β-胡萝卜素) 217 258 290 256 O λ 219 254 max (nm)

ORGANIC CHEMISTRY Chapter 13 13.9C Analytical Uses of UV-vis Spectroscopy o Structure elucidation of organic molecules-to indicate whether conjugation is present in a given sample g Determining the concentration of an unknown sample o Used in biochemical studies to measure the rates of enzymatic reactions o Used in environmental chemistry to determine the concentration of various metal ions Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 13 13.9C Analytical Uses of UV-Vis Spectroscopy Structure elucidation of organic molecules — to indicate whether conjugation is present in a given sample. Determining the concentration of an unknown sample. Used in biochemical studies to measure the rates of enzymatic reactions Used in environmental chemistry to determine the concentration of various metal ions

ORGANIC CHEMISTRY Chapter 13 13.10 Electrophilic Attack on Conjugated Dienes: 1, 4-Addition Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 13 13.10 Electrophilic Attack on Conjugated Dienes: 1,4-Addition

ORGANIC CHEMISTRY Chapter 13 2-addition CH=CH-CH-CH HCI CH2=CH-CH=CH, 25C 78% CI H CH-CH=CH-CH 4-addition 22% Mechanism H-CI CH,=CH-CH=CH, + CH2=CH—CH-CH3-CH2CH=CH—CH2 CH2=CH-CH--CH3 CICH2-CH=CH一CH3 Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 13 CH2 CH CH CH2 CH2 CH CH CH2 Cl CH2 CH CH CH2 Cl 1,2-addition 1,4-addition HCl H H 25°C 78% 22% 4 3 2 1 CH2 CH CH CH2 H Cl Mechanism Mechanism CH2 CH CH CH3 CH2 CH CH CH3 Cl CH2 CH CH CH3 Cl Cl ClCH2 CH CH CH3

ORGANIC CHEMISTRY Chapter 13 HBr CH,=CH-CH=CH2 40 C CH,=CH-CH-CH2+ CH2-CH=CH-CH2 Br H H 20% 80% B 2 CH2=CH-CH=CH215°C CH=CH-CH-CH,+ CH,-CH=CH-CH 54% BrBr Bi B1 46% BI B CHCI 68 Br Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 13 CH2 CH CH CH2 HBr 40°C CH2 CH CH CH2 Br H CH2 CH CH CH2 Br H + 20% 80% CH2 CH CH CH2 Br2 -15°C CH2 CH CH CH2 Br Br CH2 CH CH CH2 Br Br + 54% 46% Br2 CHCl3 Br Br > 68%