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PS 1 - UV-IR W12 Key

PS 1 - UV-IR W12 Key - Chem 112B W12 Problem Set 1 Problem...

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Chem 112B W12 Problem Set 1 Problem Set 1 Answer Key Infrared and Ultraviolet Spectroscopy Question 1. Describe how you would use IR spectroscopy to distinguish the following pairs of molecules: NOTE all the molecules will have C-H stretches ~2950 cm -1 , so you can t use that to distinguish them. a) Explanation: Look for the N-H vs O-H stretch O-H absorbs ~3400 cm -1 , N-H~3200 cm -1 . Also, the NH 2 will give TWO peaks from the symmetric and antisymmetric stretch, O-H only one. b) Explanation: One is an alcohol and has an O-H stretch (~3400 cm -1 ), one has none. c) Explanation: The keto-alcohol will have stretches at ~3400 cm -1 for the OH and ~1725 cm -1 for the ketone, whereas the ester will have a stretch at 1740 cm -1 and no other d) Explanation: Ester vs ketone the ester (left molecule) will have a higher absorbance (although not by much). e) Explanation: The terminal alkyne will show a C-H stretch at 3300 cm -1 , the internal alkyne will only show C-H stretches (as it is symmetrical, no C C stretch will be observed) f) Explanation: tert-butane is symmetrical, and so there will be no C-C stretches (although you should see weak C-H stretches). n-Pentane will have C-C and C-H stetches
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