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Discussionsessans1 - Bocknack CH 310N Discussion Session...

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Bocknack CH 310N Discussion Session Problems – Answer Key Thursday, January 25, 2007 1. Explain why the S–H stretching absorption in the IR spectrum of a thiol is less intense and occurs at a lower frequency (2250 cm –1 ) than the O–H stretching absorption of an alcohol (3200–3400 cm –1 ). Your answer must account for both of these facts! The S-H bond is weaker than the O-H bond because S is larger than O. The bigger size of S leads to a longer, and therefore weaker bond to H. As for intensity, thiols exhibit weak absorptions due to their very low polarity. Sulfur is a less electronegative atom than oxygen and therefore, the stretching vibrations of the S-H bond produce less of a change in the molecular dipole moment of that bond. 2. Two unlabeled bottles, A and B , contain liquids. Sloppy lab notes found on a nearby desk suggest that one compound is (HSCH 2 CH 2 ) 2 O and the other is (HOCH 2 CH 2 ) 2 S. Unfortunately, the only instrument available to analyze these samples is the IR spectrometer. The IR spectra of Compounds
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This note was uploaded on 05/02/2011 for the course CH 310 N taught by Professor Blocknack during the Spring '08 term at University of Texas.

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Discussionsessans1 - Bocknack CH 310N Discussion Session...

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