In the April, 1954 issue of Analytical Chemistry, Varian launched a unique series of advertisements, entitled' "This Is NMR at Work," with the publication of a high resolution 30-MHz 2H spectrum of a simple organic molecule. Many of these ads represented original contributions to science and served to educate a whole generation of chemists in, what was then, an obscure but promising field of spectroscopic analysis. In the intervening years, there have been a large number of technological advances in nuclear magnetic reso nance spectroscopy (many of them pioneered by Varian) and NMR has now become an indispensable tool for qualitative and quantita tive investigations in all modern chemical laboratories.
NMR at Work No. 100
With NMR at Work No. 100, we proudly bring this series to a con clusion. To exemplify our technological progress in NMR, we have chosen an application at 300 MHz obtained on the new HR-300 superconducting NMR spectrometer which operates at a magnetic field of 70.5 kG. Today, as in 1954, Varian offers you the most power ful research capabilities available in NMR.
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H NMR Studies at 300 MHz
Example: Conformational Analysis The ( - )-proto-stereoisomer of q u e r c i t o l ( c y c l o h e x a n e p e n t o l ) * is k n o w n from c h e m i c a l c o r r e l a t i o n s to have the absolute t (134/25) c o n f i g u r a t i o n , and is assumed to have the (AAEEE) c o n f o r m a t i o n as s h o w n . In the NMR s p e c t r u m at 300 MHz in d e u t e r i u m o x i d e , the axial methylene proton appears at 1.81 ppm as an 8-peak multiplet. T w o peaks of this multiplet are o v e r l a p p e d in the center of the pattern due to c o u p l i n g (large, large, small) with a d j a c e n t protons ( g e m i n a l . axial, equatorial). The equatorial methylene proton pattern (1.97 ppm) is similarly
p r o d u c e d by c o u p l i n g (large, small, small) with adjacent protons. Signals for the two O-C-H equatorial protons (H-4. H-5) appear d o w n f i e l d (3.88. 4.06 p p m ) ; and for the three axial protons ( H - 1 , H-2 and H-3) upfield (3.75, 3.56 and 3.71 ppm). The H-1 and H-5 patterns are a p p r o p r i a t e for c o u p ling with three n e i g h b o r i n g p r o t o n s ; the H-2, H-3 and H-4 patterns, for c o u p l i n g with two. * G . E. M c C a s l a n d , M. O. N a u m a n n . and L. J. D u r h a m , J. Org. C h e m . 33, 4220 (1968). See t h i s reference for c o r r e s p o n d i n g NMR spectra at 60, 100 and 220 MHz.
H, 12Hz J,,2;
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II
I
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H z
J,*.= 5Hz
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