02032010 - CH 310N MWF 8:00 Lecture 7 W 2/3/2010 Reading...

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CH 310N – MWF 8:00 – Lecture 7 – W 2/3/2010 Graded Homework : HW#04 deadline = 2:00 p.m. on F 2/5 HW#05 deadline = 4:00 p.m. on Tu 2/9 (this assignment will be available later today!!!) Reading Assignment : No new reading… Textbook Problems : Keep working assigned Chapter 13 problems!!! Last Time : Coupling constants Multiplicative splitting 13 C NMR If you have an excusable conflict for ANY of the three midterm exams, the deadline to sign up to take a conflict exam is 5:00 p.m. on Friday, February 5 . Today : 13 C NMR (continued…) Solving spectroscopy problems If you have an iClicker remote, you can use it to “sign in” at the Friday afternoon seminars. Instructions for registering your clicker will be posted on Blackboard…
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So what does a 13 C NMR spectrum look like? Let’s look at the 13 C NMR spectrum of butyl acetate: H 3 C C O CH 2 CH 2 CH 2 CH 3 O butyl acetate Most 13 C nuclei resonate between 0–220 ppm downfield from TMS (which is still d e c b a f CDCl 3 b c d a e f Most d 0–220 ppm downfield from TMS (which is still used as the zero point reference compound) A single, sharp signal is typically observed for each chemically nonequivalent carbon atom in the molecule. Why are there 7 signals in the spectrum above? Only 6 of the signals are “real.” The other signal (triplet centered at d 77.0 ppm) is due to the solvent, CDCl 3 (a very common solvent for NMR). D has magnetic spin = +1, 0, or –1. 13 C NMR is very useful for “counting” the number of chemically nonequivalent kinds of carbon atoms in a molecule If we assign the peaks in the spectrum above, we can make some generalizations about the relationship of chemical shift to structure…
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1) Just as in 1 H NMR, there is an electronegativity effect. Carbons attached to electronegative elements tend to absorb downfield. As we have seen, a nearby electronegative group withdraws electron density, leading to deshielding. More electronegative = further downfield (Appendix 5 in the text) Effect of electronegativity decreases with distance 2 sp 3 hybridized C atoms typically absorb 2) sp hybridized C atoms typically absorb between d 0–90 ppm. sp 2 hybridized C atoms typically absorb between
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This note was uploaded on 04/07/2010 for the course CH 310n taught by Professor Iverson during the Spring '08 term at University of Texas.

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02032010 - CH 310N MWF 8:00 Lecture 7 W 2/3/2010 Reading...

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