CH_318N_Lecture3-08_Spring_08

CH_318N_Lecture3-08_Spring_08 - Lecture 3 NMR Spectroscopy...

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1 Chemistry 318N Lecture 3 NMR Spectroscopy January 22, 2008 Chemistry 318N Heinrich Rudolph Hertz c hertz (Hz) – the SI unit of frequency, equal to one cycle per second. The hertz is used to measure the rates of events that happen periodically in a fixed and definite cycle. Multiples of the hertz are common: the frequencies of radio and television waves are measured in kilohertz (kHz), megahertz (MHz), or even gigahertz (GHz), and the frequencies of light waves in terahertz (THz). The unit is named for the German physicist Heinrich Rudolf Hertz (1857-1894), who proved in 1887 that energy is transmitted through a vacuum by electromagnetic waves. Born: 22 February 1857 in Hamburg Died: 1 January 1894 in Bonn
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2 Chemistry 318N Spin States c Electrons have a spin quantum number of 1/2 with allowed values of +1/2 and -1/2 – One can consider this as spinning charge that creates an associated magnetic field – Electrons therefore behave like tiny bar magnets – Remember the Pauli exclusion principle? Spin “up” and spin “down” Chemistry 318N Nuclear Spin States c Nuclei with an odd mass, an odd atomic number, or both also have a net spin and a resulting nuclear magnetic moment. c The allowed nuclear spin states are determined by the spin quantum number, I , of the nucleus. c For each I there are 2 I + 1 spin states c If I = 1/2, there are two allowed spin states
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3 Chemistry 318N Nuclear Spins in a Magnetic Field E=h ν or ν = E/h Chemistry 318N Nuclear Spins in a Magnetic Field c Within a collection of 1 H or 13 C atoms, nuclear spins are random in orientation c When placed in a strong external magnetic field the interaction between nuclear spins and the applied magnetic field is quantized , with the result that only certain orientations of the nuclear magnetic moments are allowed
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4 Chemistry 318N Nuclear Magnetic Resonance c If the nucleus is irradiated with radiation having energy (E=h υ ) that is exactly the same as the difference between the nuclear spin states, – energy is absorbed, and – the nuclear spin is flipped from spin state +1/2 (with the applied field) to -1/2 (against the
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This note was uploaded on 04/07/2008 for the course CH 318N taught by Professor Willson during the Spring '08 term at University of Texas.

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CH_318N_Lecture3-08_Spring_08 - Lecture 3 NMR Spectroscopy...

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