Nuclear Magnetic Resonance Spectroscopy

Over the past fifty years nuclear magnetic resonance spectroscopy, commonly referred to as nmr, has become the preeminent technique for determining the structure of organic compounds. Of all the spectroscopic methods, it is the only one for which a complete analysis and interpretation of the entire spectrum is normally expected. Although larger amounts of sample are needed than for mass spectroscopy, nmr is non-destructive, and with modern instruments good data may be obtained from samples weighing less than a milligram. To be successful in using nmr as an analytical tool, it is necessary to understand the physical principles on which the methods are based.

The nuclei of many elemental isotopes have a characteristic spin (I). Some nuclei have integral spins (e.g. I = 1, 2, 3 ....), some have fractional spins (e.g. I = 1/2, 3/2, 5/2 ....), and a few have no spin, I = 0 (e.g. ¹²C, ¹⁶O, ³²S, ....). Isotopes of particular interest and use to organic chemists are ¹H, ¹³C, ¹⁹F and ³¹P, all of which have I = 1/2. Since the analysis of this spin state is fairly straightforward, our discussion of nmr will be limited to these and other I = 1/2 nuclei.

مواضيع ذات صلة

Spectroscopic Properties of Alkynes

Spectroscopic Properties of Alkenes

Application of Chemical Shifts to Structure Determination

Correlations Between Structure and Chemical Shifts

Electronegativity and Chemical Shifts

Effects of Carbon Bond Type

Mass Spectroscopy

Hydrogen Bonding

Chemical Exchange

Proton-Proton Splittings and Conformational Analysis

Spin-Spin Splitting - What We Observe

Proton-Proton Splittings and Chemical Exchange