spectro - Nuclear Magnetic Resonance Spectroscopy What can...

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Nuclear Magnetic Resonance Spectroscopy What can NMR tell us about ethanol? -There are two types of carbons in a 1:1 ratio. -There are three types of hydrogen in a 3:2:1 ratio. -The methyl and methylene groups are bonded together. NMR Overview NMR only works for nuclei that have the quantum mechanical property of SPIN! The spin properties of nuclei characterize each nucleus according to a physical parameter called the chemical shift. For a given molecule, coupling constants and relaxation times give information about the connectivity between atoms. NMR can be used to follow chemical reactions. NMR samples can be solid, liquid, or gas. NMR can be used to analyze mixtures. Sample quantities should be in the micro- to milligram range. Proton NMR What information can you obtain from a proton NMR spectrum of a compound? -How many different kinds of hydrogen are present (-CH, -CH 2 , -CH 3 ). -Environment of the hydrogen atoms. -Relative number of hydrogen atoms. -Which hydrogen atoms are 2- or 3-bond neighbors. What to get from today’s lecture: -An electron may be in a position of spin up or spin down. -In General chemistry, you constructed spectrometers to view the quantum steps of electrons from one energy level to another. This was observed, as light of a given frequency that resulted in a characteristic observed color for the transition. -Protons, like electrons, can also be in a position of spin up or spin down for certain nuclei. -In Organic spectroscopy, you view the quantum jumps of protons, that possess the property of spin, as they switch from spin up to spin down. -What we are able to observe is the absorption of energy that results from a proton switching from a spin of + ½ to a spin of – ½. -What follows are the details of this phenomenon! Details Synonymous with Theory Magnetic Moment ( ) -The magnetic field generated by a spinning nucleus with a positive charge. Spin Quantum Number ( I )
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-The value assigned to spinning nuclei. -Nuclei that possess spin must have either: a.) Odd mass – I = ½ These nuclei have a spherical shape. Can you think of any? 1 H, 13 C, 15 N, 19 F, 29 S, and 31 P b.) Odd atomic number – I = 1, 3/2, 2, 5/2, …(increments of ½) 2 H, 11 B, 14 N, 17 O, 33 S, and 35 Cl These nuclei have non-spherical or elliptical shape they are referred to as quadrupolar. Quadrupolar nuclei have a spin of one or more. c.) What type of nuclei have no spin? I = 0 12 C and 18 O For Nuclei with a Spin of ½ The RIGHT-HAND-RULE gives the direction of the spin of the nucleus. If the nucleus is aligned with the magnetic field, what direction will the nucleus spin? I = ____? If the nucleus is oriented opposite the magnetic field, what direction will it spin? I = ____? How does the magnetic moment ( ) of a nucleus relate to the spin (
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This note was uploaded on 04/27/2008 for the course CHEM 3410 taught by Professor Wilson during the Spring '07 term at Dallas Baptist.

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spectro - Nuclear Magnetic Resonance Spectroscopy What can...

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