B Breit D.A. Evans Introduction to Photochemistry Chem 206 Background Reading Knowing the absorption wavelength in nm, you can calculate the the energ Carey, and Sundberg Advanced Organic Chemistry, Parts A Third Edition, Chepter 13, "Photochemistry, pp 729-765 E( kcal/mol)=286×10 for 1= 200 nm:E=143 kcal Wo a( in nm) forλ New insights into an old mechanism: [2+2 photocycloaddition of enones to alkenes ,I Schuster, D L; Lem, G. Kaprinidis, N. A Chem. Rev. 1993, 93, 3. Stereoselective intermolecular[2+2H-photocycloaddition reactions and their application in synthesis., Bach, T. Synthesis 1998, 683-703 Consider a simple diatomic molecule A-B 2+2 photocycloaddition/fragmentation strategies for the synthesis of natural and unnatural products. Winkler, J D; Bowen, C. M: Liotta, F. Chem. Rev. 1995, 95, 2003- ·A-B A-B Synthetic Applications of Intramolecular Enone-olefin Photocycloadditions Crimmins, M T.chem.Rev198888,1453 The meta photocycloaddition of arenes to alkenes Cornelisse, J. Chem. Rev. 1993, 93, internuclear distance B A electronic ■ Morse curve a Important Regions of the Electromagnetic Spectrum gA-B Basic Types Information Energy Range excited state Ultraviolet-Visible Electronic States 40-140 kcal/mol Infrared Functional Groups 2-12 kcal/mol NMR H&c Connectivity 1010a Light-induced electron excitation ground state Electrons are excited to higher energy levels when a molecule absorbs 二 E vibration Time scale: electron excitation: 10-15s a photon of energy equal to the energy difference between the ground- state electronic level and the excited state electronic level Time scale: nuclei movement: 10-12s E= h for 2= 200 nm E= 143 kcal a Franck-Condon Principle: Upon light-induced electronic excitation, only the electrons are reorganized; the heavier nuclei stay in their ground-state for 1=700 nm: E =40.9 kcal geometry. (Vertical Transitions)B. Breit, D. A. Evans Introduction to Photochemistry Chem 206 Background Reading Carey, and Sundberg, Advanced Organic Chemistry, Parts A Third Edition, Chepter 13, "Photochemistry", pp 729-765 "New insights into an old mechanism: [2 + 2] photocycloaddition of enones to alkenes.", Schuster, D. I.; Lem, G.; Kaprinidis, N. A. Chem. Rev. 1993, 93, 3. "Stereoselective intermolecular [2+2]-photocycloaddition reactions and their application in synthesis.", Bach, T. Synthesis 1998, 683-703. "[2+2] photocycloaddition/fragmentation strategies for the synthesis of natural and unnatural products.", Winkler, J. D.; Bowen, C. M.; Liotta, F. Chem. Rev. 1995, 95, 2003- 2020. "Synthetic Applications of Intramolecular Enone-Olefin Photocycloadditions.", Crimmins, M. T. Chem. Rev. 1988, 88, 1453. "The meta photocycloaddition of arenes to alkenes.", Cornelisse, J. Chem. Rev. 1993, 93, 615. Worthwhile General Reviews 10-5–10-6 kcal/mol 2-12 kcal/mol Electronic States 40-140 kcal/mol Functional Groups NMR H & C Connectivity Infrared Ultraviolet-Visible Basic Types Information Energy Range ■ Important Regions of the Electromagnetic Spectrum Electrons are excited to higher energy levels when a molecule absorbs a photon of energy equal to the energy difference between the ground￾state electronic level and the excited state electronic level. E = hn = h c l ■ Light-induced electron excitation E (kcal/mol) = 2.86 x 10+4 Knowing the absorption wavelength in nm, you can calculate the the energy l( in nm) for l = 200 nm: E = 143 kcal for l = 700 nm: E = 40.9 kcal for l = 200 nm: E = 143 kcal for l = 700 nm: E = 40.9 kcal DE electronic s * A–B s A–B r 0 internuclear distance Consider a simple diatomic molecule A–B A B ■ Morse Curve Potential Energy r 0 (internuclear distance) E electronic DE vibration excited state ground state ■ Franck-Condon Principle: Upon light-induced electronic excitation, only the electrons are reorganized; the heavier nuclei stay in their ground-state geometry. (Vertical Transitions) Time scale: electron excitation: 10-15 s Time scale: nuclei movement: 10-12 s B A