COMMUNICATIONS TO THE EDITOR
238
reported compounds. No evidence of sodium retention was obtained for this series of compounds. FUNDAMENTAL RESEARCH MERCKSHARP& DOHME RESEARCH LABORATORIES DIVISIOXOF MERCK& Co., INC. RAHWAY, NEW JERSEY
J. H. FRIED H. MROZIK G. E. ARTH T. S. BRY N. G. STEINBERG M. TISHLER RALPHHIRSCHMANN
MERCKINSTITUTE FOR THERAPEUTIC RESEARCH S. L. STEELMAN RECEIVED NOVEMBER 30, 19G2 RELATIVE SIGNS OF FLUORINE-19-FLUORINE-1 9 AND HYDROGEN-1-FLUORINE-19 N.M.R. COUPLING CONSTANTS
TABLE I RELATIVE SIGNS OF
F19-F18COUPLING CONSTANTS
kz
( X = H, CF3,C1, Br, I )
85
substituted lJ1,2-trifluoroethanes, which due to asymmetry show ABX n.m.r. spin s y ~ t e m s were , ~ studied. It was determined that the vicinal and geminal coupling constants have different signs in the three ethane derivatives studied a t room temperature and the one which was frozen into its separate conforiner~.~From the four halogen substituted fluoropropanes studied i t was found that the vicinal coupling has a sign different from the geminal and 1,3-couplings. From the data presented above the relative sign relationships between the most commonly encountered F19-F19n .m.r. coupling constants can he tabulated F
F
\c-c
F\C-C/
F\C-C-C
/F
F'
=i
f
Sir: The importance of the relative signs of n.m.r. coupling constants has only recently been realized in the analyses of high resolution n.m.r. spectra. The use of double resonance techniques for the determination of the relative signs of coupling constants is rather more attractive than the previously exploited long and tedious iterative high-resolution approach. I n this communication we wish to give the results of some double resonance studies which have given the relative signs of several important types of FI9-FI9and HI-FI9 coupling constants. I n Table I are summarized results from FI9-F19 double resonance studies on a number of fluorocarbon
L'OI.
f
=k
F-C
i
F-C
)c=c
F
T
\c=c/
F F-C
*
f
T
\c= c
\F
The one assumption involved in this correlation is that the F F>C-C coupling constant has the same sign as that of the :>C=C coupling. This may be a reasonable assumption on grounds that these coupling constants are all fairly large in magnitude (ranging from about 28-224 c.P.s.) and that the contributions to these two types of geminal couplings may be similar. The fact that the F-C-C-F coupling has the same sign as that of the F-C-CF=C coupling with this assumption is interesting and suggests that the contributions to these two types of vicinal coupling may also be similar. Appropriate compounds to test this assumption are in preparation. Table I1 summarizes some results for HI-FI9 couplings obtained either by "-HI or F19-F19decoupling. TABLE I1 RELATIVE SIGNSOF H1-F19 COUPLING CONSTANTS CH8CH2Fa CHsCHFz CF~CFHZ CFpCFzH CFaCFzCFzH CFzBrCFBrH CF2HCFzCFH2
CF,jCF2CF2Br J12 ?= J?3 'F J i 3 f ( 3 ) ( 2 ) (1) CFaCFzCF21 2 1 2 7 J23 p Jl3 f ( 3 ) ( 2 ) (1) CFjCFClCFClr Jl? =F , J 2 3 3=,J 1 3 ( 3 ) ( 2 ) (1) CFjCClICFsCl J13 f, J1'3 h,J 1 1 ' f (3) ( L l ' ) D. F. Evans, Mol. Phys., 5, 183 (1962). * D. D. Elleman and S. L. Manatt, J . Chem. Phys., 36, 1945 (1962). D. D. Elleman and S. L. Manatt, presented a t Third Conference on Experimental Aspects of N.M.R. Spectroscopy, Mellon Institute, Pittsburgh, Penna., March 2, 1962. S. L. Manatt and D. D. Elleman, J . A m . Chem. Soc., 84, 1305 (1962). p
j
I
1
cc !
F\
c-c/
H f
J
(1) F F (3Ibtc 1 1 4 f> J24 F r J 3 1 f (2) F>.=< 'H (4) A similar assignment of the relative signs of the Hl-F'g couplings in this molecule also has been obtained from highresolution analyses at two frequencies by s. L. Stafford and J. D. Baldeschwieler, J . Am. Chem. SOC.,83, 4473 (1961). D. F. Evans, Afol. Phys., 5, 183 (1962). D. D. Elleman and S. L. Manatt, presented a t Third Conference on Es-
perimental Aspects of N.M.R. Spectroscopy, Mellori I n stitute, Pittsburgh, Penn., March 2, 1962.
I t was found that the C
