310NSp0801232008 - CH 310N MWF 8am Lecture 4 W 1/23/2008...

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Unformatted text preview: CH 310N MWF 8am Lecture 4 W 1/23/2008 Reading Assignment : Sections 13.813.11 Textbook Problems : No new problemswell need to discuss most of the material in Chapter 13 before youll be able to tackle the problems!!! Graded Homework : HW#01 deadline = 3:00 p.m. on Mon 1/28 HW#02 deadline = 3:00 p.m. on Thu 1/31 Last Time : Introduction to nuclear magnetic resonance (NMR) spectroscopy (begin Chapter 13) Today : 1 H NMR (continued) NMR integration Relationship of chemical shift to structure Spinspin splitting and the (n+1) rule Answers for the Organic I review problems (online handout) have been posted on the course website So what does the 1 H NMR spectrum of allyl alcohol look like? C C H H H C O H H 5 signals, each corresponding to one of the 5 sets of chemically nonequivalent protons a b c d e c b a d e Some issues that we need to consider : What factors influence the chemical shift of a proton? Why are some of the absorptions split into more than one peak? c b a What do the squiggly lines represent? The integral of the absorption NMR Integration The integral of an NMR absorption is equal to the area under the peak, which in turn is proportional to the number of protons causing the absorption In modern NMR instrumentation, a computer measures the integral of each absorption. These integrals are then printed out as squiggly lines (or as numbers when the data is tabulated). By measuring the relative height of each integral, it is possible to determine the relative number of protons responsible for each different absorption in the spectrum. C C H H H C O H H a b c d e c b a d e All integrals have the same relative height, except the integral corresponding to absorption d, which is twice as big. 1H 1H 1H 2H 1H IMPORTANT!!! The integrals give relative numbers of protons. The actual number of protons present in the molecule may be some multiple of the total calculated from the integration. Relationship of Chemical Shift to Structure Earlier, we said that differences in chemical shift are caused by differences in the effective magnetic field experienced by each nucleus. Nuclei that are more strongly shielded by electrons require a larger applied field to bring them into resonance, and therefore absorb upfield (right side of chart). Nuclei that are deshielded require a smaller applied field to bring them into resonance, and therefore absorb downfield (left side of chart)....
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This note was uploaded on 08/20/2008 for the course CH 310n taught by Professor Iverson during the Spring '08 term at University of Texas at Austin.

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310NSp0801232008 - CH 310N MWF 8am Lecture 4 W 1/23/2008...

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