212Lec4Sp09NMR3

212Lec4Sp09NMR3 - Todays agenda Proton Equivalency (13.8)...

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Today’s agenda… Proton Equivalency (13.8) Splitting (13.11) J Values (13.11) Group Question #2 Last time… Chemical Shift (13.3, 13.9) Proton Equivalency (13.8) Today’s Office Hours: 3 to 4 pm!!! Lecture 4
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Not all protons on sp 3 carbons (e.g. some -CH 2 - groups) are equivalent as in the molecule below. First, determine the following: • any planes of symmetry? • any prochiral centers? • does a chiral center already exist? O H 3 C CH 3 H 3 C Cl H H How many signals will be in this compound’s 1 H NMR spectrum?
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Determine the # of signals that would be seen in the 1 H NMR spectrum… 1. Let’s do a substitution test to help determine what type of protons the -CH 2 - protons are: homotopic, enantiotopic , or diastereotopic protons for the -CH 2 - protons. (Look at next slide.) Show work and indicate what type of protons they are. O H 3 C CH 3 H 3 C Cl H H 3. Now, how many signals will be in this compound’s 1 H NMR spectrum? 2. Are the -CH 2 - protons equivalent? Yes No
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Substitution tests are easy to perform. Just follow these steps… 1. Change one of the questionable Hs to a different group like D (deuterium); one at a time. 2. Step 1 will result in two new molecules. 3. Compare these two new molecules:
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212Lec4Sp09NMR3 - Todays agenda Proton Equivalency (13.8)...

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