11-09 - 11/10/2009 The Interaction of Light with Matter The...

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Unformatted text preview: 11/10/2009 The Interaction of Light with Matter The Interaction of Light with Matter Spectroscopy and Molecular Structure Determination electronic short wavelength long wavelength short wavelength ir long wavelength electromagnetic spectrum electromagnetic spectrum Choose the true statements about electromagnetic absorptions. 2. Ultraviolet absorptions (uv) cause the transition between two electronic states. Typical Typical electromagnetic absorptions. infrared: electronic nuclear nuclear magnetic resonance: 1. Infrared absorptions (ir) cause the transition between two vibrational states. 3000 cm-1 300 nm 300 MHz energy 3. UV absorptions are higher energy than IR absorptions. A. 1+2+3 B. 1+2 C. 1+3 D. 1 E. 2 F. 3 300 nm = 400 kJ/mol 3000 cm-1 = 36 kJ/mol 300 MHz = 0.00012 kJ/mol electronic short wavelength ir long wavelength short short wavelength electronic ir nmr long wavelength electromagnetic spectrum electromagnetic spectrum ultraviolet visible x-rays infrared radio 1 11/10/2009 infrared: infrared: electronic nuclear magnetic resonance: antibonding antibonding 3000 cm-1 300 nm 300 MHz infrared: electronic nuclear magnetic resonance magnetic magnetic moment of a hydrogen nucleus magnetic field field energy bonding electronic ir nmr long wavelength short wavelength electromagnetic spectrum ultraviolet visible electromagnetic radiation 8 x-rays infrared radio Nuclear Magnetic Resonance Resonance Spectroscopy Spectroscopy HO O H H H H H H H H H H H How many absorptions would be predicted in the 13C nmr spectrum of the cyclopentadienyl cation? A1 B2 C3 D4 E5 F6 H Both Both 13C and 1H have magnetic magnetic moments and can give nuclear magnetic resonance absorptions. Natural abundance of 1H = 100% Natural abundance of 13C N O OH O O O O O OH O H H H H Review: Review: Each carbon atom in a different chemical environment environment gives a different 13C absorption absorption O O H H = 1.1% H H H H H 9 220 200 180 160 140 rapamycin C51H79NO13 H H 120 100 PPM 80 60 40 20 0 11 H H H H H H H H H H H H H H H H H H H H H H H How many absorptions would be predicted in the 13C nmr spectrum of the cyclopentadienyl cation? A1 B2 C3 D4 E5 F6 Choose the answer that has correctly predicted the number of 13C absorptions for compounds I and II. H H Br Br Br Br or or Br Br H H Review: Review: Each carbon atom in a different chemical environment environment gives a different 13C absorption absorption I II 13C absorptions I II 7 7 1 5 7 4 14 A B 7 5 1 7 4 7 H H H H H H C D E 12 F 2 11/10/2009 Nuclear Magnetic Resonance. Mass Spectroscopy. Rapamycin is an important immunosuppressant drug. Nuclear Magnetic Resonance. Mass Spectroscopy. Spectroscopic methods of structure determination! separation rapamycin Streptomyces hygroscopicus Rapamycin only constitutes a small part of Streptomyces hygroscopicus 15 separation rapamycin What is the structure of a molecule in this stuff? 17 Streptomyces hygroscopicus Once the structure is known synthetic chemistry can prepare both rapamycin and unknown derivatives from petroleum. This This is what we know about person X (beginning). rapamycinal Spectroscopic methods of structure determination! 1. 1. What can be wrong? 2. 2. What tests can narrow the possibilities? possibilities? HOUSE organic synthesis rapamycin What is the structure rapamycinic of a molecule in this acid stuff? 18 19 What What is the structure of an unknown compound X? O Possibilities Possibilities for compound X compound OH What What test could we perform on compound X to eliminate other possibilities? possibilities? OH molecular molecular formula formula (C6H10O) 1 2 3 O OH 5 OH 6 OH 4 molecular molecular formula formula (C6H10O) 2 3 O OH 5 OH 6 OH 4 infrared infrared spectroscopy spectroscopy Which Which compounds cannot be cannot be X? Which Which compounds cannot be cannot be X? A. 1 B. B. 2 C. C. 3 D. D. 4 E. 5 F. F. 6 20 A. 2 + 5 B. B. 2 C. C. 3 D. D. 4 E. E. 5 F. F. 6 21 3 11/10/2009 What chemical test What chemical test could we perform on compound X to eliminate eliminate other possibilities? OH What What spectroscopic test could we perform on compound X to eliminate eliminate either 2 or 6? OH molecular molecular formula formula (C6H10O) 2 3 OH 5 OH 6 OH molecular formula formula (C6H10O) 2 3 OH 5 OH 6 OH infrared infrared spectroscopy spectroscopy catalytic catalytic hydrogenation hydrogenation infrared infrared spectroscopy spectroscopy chemical reactions reactions Which Which compounds cannot be cannot be X? C6H10O A. A. 2 + 3 B. B. 2 + 5 C. C. 3 + 5 H H catalyst (Pd/C) Which Which compounds cannot be cannot be X? C6H12O E. E. 2 + 6 F. 2 F. 22 + 6 C6H10O C6H14O - C6H10O = H4 (2 rings, 2 double bonds or one of each) H H catalyst (Pd/C) C6H12O C6H14O - C6H12O = H2 (one ring) 23 D. D. 3 + 6 What What spectroscopic test could we perform on compound X to eliminate eliminate either 2 or 6? OH OH Nuclear Magnetic Resonance. Review: 13C 1H molecular molecular formula formula (C6H10O) 13C H H H H OH NMR NMR O HO HO spectrum spectrum of the reduced product. product. 2 catalyst (Pd/C) 6 OH catalyst (Pd/C) OH or OH N O OH OH O O O O O OH OH O O Which Which compound is X. A. 2 B. B. 6 24 O H H H H rapamycin C51H79NO13 25 Nuclear Magnetic Resonance. N In In a magnetic field how do most of the hydrogen nuclei how hydrogen These orient magnetic moments have no orient their magnetic moments? orientation. A. parallel to the magnetic field. B. B. antiparallel to the magnetic to field. field. C. perpendicular to the magnetic C. field. D. D. their magnetic moments show no organization in a magnetic field. field. Nuclear Magnetic Resonance. N In In a magnetic field how do most of the hydrogen nuclei how hydrogen orient orient their magnetic moments? A. parallel to the magnetic field. B. B. antiparallel to the magnetic to field. field. C. perpendicular to the magnetic C. field. D. D. their magnetic moments show no organization in a magnetic field. field. S 27 S 4 11/10/2009 Nuclear Magnetic Resonance. N If E = 0.12 J/mol, will the wave length of electromagnetic for a nuclear spin transitions be longer or shorter than that used to break bonds? N A. A. longer, i.e. B. B. shorter, i.e. = 1 meter. = 10-8 meters. E the the molecules absorb light of an energy equal to the energy difference between the two spin states. energy E energy ~ frequency = =  energy S 29 E = 300 MHz = 300,000,000 S E = 0.12 J/mol E(H-H bond) = 436,000 J/mol 30 Magnetic Resonance Imaging (MRI) N Magnetic Resonance Imaging (MRI) N E frequency = =  energy S 31 31 energy S 32 What molecule is everywhere in our bodies? H H O N water in different tissues has a different relaxation rates (T1). N MRI measures differences in relaxation rates. (images) NMR (MRS) spectroscopy measures differences in nuclear spin transition energies. (molecular structure) N N E S S 33 S S 34 5 11/10/2009 MRI measures differences in relaxation rates. (images) When When we think the brain requires glucose and oxygen. The oxygen is attached to Fe (hemoglobin) which can dramatically affect the relaxation rate of water. fMRI glucose + OO Fe N diamagnetic paramagnetic S 35 6 ...
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