if you are using infra-red N-M-R SPECTROSCOPY PROBABLY BELONGS IN YOUR LABORATORY TOO!
41
(Nuclear Magnetic Resonance)
Ν - M - R at work
These two forms of spectroscopy have a number of areas of application in common . . . such as determination of molecular structure, identification of functional groups, measurements of amounts of impurities and study of molecular interactions. Often they solve the same problem and both techniques are widely applicable by themselves. So why have both? In gray areas where no conclusion is a certainty, infra-red and high resolution N-M-R can be a perfect check on each other. Toward the same end deductions, they measure totally different properties of molecules. Hence there is slim chance of a coincidence of error, and in addition each spectrum may expand the knowledge gained by the other. Also, because of this difference in approach, a chemical environment that causes a serious interference and ambiguity in infra-red may create no difficulties at all for N-M-R. With both spectroscopic techniques available in your laboratory, you can solve a much greater range of problems, more conveniently and with greater certainty than with either alone.
4 1 ofasenies
C13 C H E M I C A L S H I F T S - N A T U R A L
INTERPRETATION: Chemical shifts involving the C ' 3 nucleus have been reported recently for a number of compounds.'' 2 Due to the extremely long relaxation times, a rapid-passage, dispersion-mode display of the signals results in the best signal-to-noise ratio. In the trace below, the doublet on the left results from the resonance of the C nuclei in ordinary benzene, each nucleus coupling its spin to the spin of the attached proton. The equilibrium populations of the energy levels are such that the two components ought to be of equal
ABUNDANCE
amplitude, but the observation of the first signal with high r.f. power disturbs the equilibrium, and during the time required to reach the second signal (6 seconds) the protons reorient their spins (Τι ~ 3 sec onds) which disturbs the populations of the levels which give rise to the second signal. On the right the C' 3 resonance from CH,I is shown split into a quartet by the attached proton spins (total I = 3 / 2 ) . A chemical shift of about 1.7 gauss is observed for these compounds. J) P. C. Lauterbur.J.
Chem. Phys. 26,
217(1957)
2) C. H. Holm, J. Chem. Phys. 26, 707fJ057>
VARIAN associates INSTRUMENT DIVISION
W r i t e for our latest Radio Frequency Spectroscopy Bulletin (Vol. 2 - # J j. Full technical information on both N-M-R and E-P-R Spectroscopy and the complete " N - M - R at Work" series will be included.
PALO
ALTO
4,
CALIFORNIA
For further information, circle number 101 A on Readers' Service Card, page 99 A VOL.
2 9 , N O . 9 , SEPTEMBER 1 9 5 7
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101
A
