if you are using infra-red N-M-R SPECTROSCOPY PROBABLY BELONGS IN YOUR LABORATORY TOO!
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(Nuclear Magnetic Resonance)
N - M - R at w o r k
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.
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of a s e r i e s
EFFECT OF MOLECULAR 1
INTERPRETATION. It has been pointed out by Professor J. D. Roberts' ' that in certain cases the chemical shift between like nuclei attached to the same carbon atom is not necessarily averaged out by rapid rotation. In molecules of the type Ό r c'R ' n w n ' c n R'< fo* a n t ^ ^3 a r e different there may be a chemical H R3 shift between the two protons if the resi dence times of the molecule in the three rotational conformations are not
ASYMMETRY equal. An example of such a molecule 1 2 ' is shown below. Its proton spec trum exhibits 12 lines which are assigned in the coupling diagram as aris ing from 3 non-equivalent protons with coupled spins. The spectrum is in dependent of temperature over a considerable range which suggests that this model more correctly describes the molecule than one involving a large potential barrier constraining the molecule to one conformation.
VARIAN associates Write for our latest Radio Frequency Spectroscopy Bulletin (Vol. 2 - * I ) . 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.
INSTRUMENT DIVISION P A L O
A L T O
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C A L I F O R N I A
For further information, circle number 23 A on Readers' Service Card, page 73 A
VOL.
29, NO. 8, AUGUST 1957
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23 A
