NMR Notes - Learning Guide for Chapter 5 - NMR Spectroscopy...

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Learning Guide for Chapter 5 - NMR Spectroscopy I. Introduction to NMR spectroscopy - p 1 II. Distinguishing equivalent H's - p 3 III. Chemical shift - p 4 IV. Integration - p 7 V. Spin-spin Splitting - p 9 VI. Practice with NMR spectra VI. Deuterium in NMR - p 12 VII. Carbon-13 NMR- p 13 I. Introduction to NMR spectroscopy To introduce you to NMR spectroscopy, we will first compare it to IR spectroscopy. I R s p e c t r o s c o p y N M R s p e c t r o s c o p y type of light: infrared type of light: radio waves what causes light to be absorbed: vibration of a bond with a dipole at the same frequency as the light what causes light to be absorbed: transistions in energy state of nuclei of atoms what bands represent: bonds what peaks represent: atoms what we learn about a compound: functional group what we learn about a compound: structure of the compound x-axis: frequency in cm -1 x-axis: ratio of magnetic field strength in ppm complicated - we won't worry about how it works O OH IR NMR OH OH Which kind of spectroscopy can distinguish each pair of compounds? yes no yes yes C=O vs O-H, C-O (different fingerprints) both have O-H, C-O functional group structure Which type of spectroscopy is more powerful? NMR - more powerful, more complication, more expensive!
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LG Ch 5 p 2 What characteristic allows an atom to be detected by NMR? atomic weight is an odd number What elements are commonly found in organic molecules? Which are suitable for NMR? hydrogen isotopes: element: NMR? 1 H yes - most common kind of NMR (also called carbon 12 C no 13 C yes - not as useful, only 1% of C's oxygen 16 O no nitrogen 14 N no A typical proton NMR spectrum looks like this: 0 5 10 Each cluster of spikes is called a: peak Where can you find each of the following, and what does it tell you about the peak? chemical shift: where it is on the x-axis what other atoms are nearby OH integration: 3 1 2 area under the peak how many H's are in that peak splitting: how many spikes how many neighbors H H H H H A B C B A C What should you be able to do? 1. Assign peaks on a compound to a spectrum. 2. Sketch the spectrum of a compound. 3. Deduce the structure of an unknown compound from its spectrum. proton NMR)
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LG Ch 5 p 3 II. Distinguishing Equivalent Hydrogens When do we say that two H's are equivalent? same nearby atoms, same # of neighbors What happens on a spectrum when two H's are equivalent? both part of the same peak, gets more area Draw in all H's for the following compounds. Circle those that are equivalent, and then count the number of sets. (5) (3) (6) (7) show how to write them all out, or my abbreviations Rules of thumb: 1 - H's on the same carbon are equivalent (except on C=C) 2 - H's on different carbons are not equivalent (except on identical groups) More exact rule: If you can separately replace two H's with a Cl, and the same compound results, they are equivalent.
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NMR Notes - Learning Guide for Chapter 5 - NMR Spectroscopy...

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