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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Chem 112B W12 Problem Set 1 Question 2. Four reactions that you studied in CHEM 112A are shown below. Which reactions can be monitored by IR spectroscopy, and why? Which reactions CANNOT be easily monitored by IR spectroscopy and why? Assume you don’t have comparison spectra (i.e. ignore the fingerprint region).
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This note was uploaded on 02/02/2012 for the course CHEM 112b taught by Professor Marsella during the Spring '11 term at UC Irvine.

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

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