Lecture 8 - Spectroscopy The study of the interaction of...

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Spectroscopy The study of the interaction of molecules with electromagnetic radiation Electromagnetic spectrum: (recall E = h ν = hc/ λ ) High Energy ( λ in μ m) Low Energy 10 -6 to 10 -4 10 -4 to 0.1 0.1 to 0.4 0.4 to 0.8 0.8 to 10 2 10 2 to 10 6 10 6 to 10 10 γ -Rays X-Rays Ultra violet Visible Infrared Microwave Radiowave UV IR NMR UV, IR and NMR are key spectroscopic tools for the organic chemist. We will focus on IR and NMR. How do these rays interact with matter? γ -Rays (gamma rays) - emitted by the nuclei of certain radioactive elements - extremely high energy – cause ionization - penetrate tissues and kill cells therefore used in cancer treatment X-Rays - not as high in energy as γ -Rays and therefore not as destructive to tissues and do not penetrate as deep as γ -Rays - since they are absorbed by tissues, when an X-ray is taken, the regions of high and low density can be differentiated - also ionize molecules so they are still dangerous Ultraviolet/Visible light - sunlight (causes burns!) - interacts with electrons in π bonds by exciting them to higher energy levels (recall π * antibonding orbitals) - sunscreens are full of unsaturated organics that absorb the UV light! oxybenzone Infrared radiation - sometimes referred to as heat radiation - 50% of sun’s heating effect due to IR radiation in sunlight - often used in remote controls - interacts with stretching and bending motions in bonds
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This note was uploaded on 11/13/2011 for the course CHEM 281 taught by Professor Williams during the Spring '11 term at Simon Fraser.

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Lecture 8 - Spectroscopy The study of the interaction of...

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