Chapter13-6 - Chapter 13 Spectroscopy Nuclear magnetic...

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Chem 212 B. R. Kaafarani 1 Chapter 13 Spectroscopy Nuclear magnetic resonance spectroscopy (NMR) Infrared spectroscopy (IR) Ultraviolet-Visible spectroscopy (UV-vis) Mass Spectrometry (MS) Carey, F. A.; Giuliano, R. M. In Organic Chemistry, 8 th Ed., 2011.
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Chem 212 B. R. Kaafarani 2 NMR: Carbon skeleton & environment of the hydrogens attached to it. IR: Presence or absence of key functional groups. UV-vis: Electron distribution specially in molecules with -conjugated systems. MS: Molecular weight and formula of the compound & its fragments. Structure Determination
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Chem 212 B. R. Kaafarani 3 13.1. Principles of Molecular Spectroscopy: Electromagnetic Radiation Is propagated at the speed of light. Has properties of particles and waves. The energy of a photon is proportional to its frequency (E = h ).
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Chem 212 B. R. Kaafarani 4 400 nm 750 nm Visible Light Longer Wavelength ( ) Shorter Wavelength ( ) Higher Frequency ( ) Lower Frequency ( ) Higher Energy (E) Lower Energy (E) Figure 13.1: The Electromagnetic Spectrum 400 nm 750 nm 7.5 10 14 s -1 4.0 10 14 s -1
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Chem 212 B. R. Kaafarani 5 Ultraviolet Infrared Longer Wavelength ( ) Shorter Wavelength ( ) Higher Frequency ( ) Lower Frequency ( ) Higher Energy (E) Lower Energy (E) Figure 13.1: The Electromagnetic Spectrum
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Chem 212 B. R. Kaafarani 6 Energy Figure 13.1: The Electromagnetic Spectrum Cosmic rays -Rays X-rays Ultraviolet light Visible light Infrared radiation Microwaves Radio waves
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Chem 212 B. R. Kaafarani 7 E = h Electromagnetic radiation is absorbed when the energy of photon corresponds to difference in energy between two states. 13.2. Principles of Molecular Spectroscopy: Quantized Energy States E 1 E 2
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Chem 212 B. R. Kaafarani 8 sample compartment M E 1 E 2 Source of radiation M* 1x10 6 1x10 6 1x10 6 9x10 5 8x10 5 0.0 0.2 0.4 0.6 0.8 1.0 Absorbance (a.u.) Frequency More molecules exist in the lower energy state E 1 than in the higher energy state E 2 . Source scans through a range of frequencies, the sample absorbs when frequency equals E thereby decreasing the intensity of light from the source. Absorbance and frequency are plotted as a spectrum. Spectrometers Probe Quantized Energy States detector
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Chem 212 B. R. Kaafarani 9 Electronic Vibrational Rotational Nuclear spin UV-Vis infrared microwave radiofrequency What Kind of States?
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Chem 212 B. R. Kaafarani 10 1 H and 13 C. Both have spin = ±1/2. 1 H is 99% at natural abundance. 13 C is 1.1% at natural abundance. The nuclei that are most useful to organic chemists are: 13.3. Introduction to 1 H NMR Spectroscopy
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Chem 212 B. R. Kaafarani 11 + + Nuclear Spin A spinning charge, such as the nucleus of 1 Ho r 13 C, generates a magnetic field . The magnetic field generated by a nucleus of spin +1/2 is opposite in direction from that generated by a nucleus of spin –1/2.
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Chem 212 B. R. Kaafarani 12 The distribution of nuclear spins is random in the absence of an external magnetic field.
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This note was uploaded on 01/06/2012 for the course CHEM 212 taught by Professor Bilalkaafarani during the Fall '10 term at American University of Beirut.

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Chapter13-6 - Chapter 13 Spectroscopy Nuclear magnetic...

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