NOTES
3196
Acknowledgment. We gratefully acknowledge financia1 support by the National Institutes of Health under Grant No. GM-10695.
High Resolution Mass Spectrum of Piperidine
by L. W. Daasch
c h a R ~ ~ ~ X ZandT CDevelopment ~ Labwatarisa, Edoeroaod Arsenal, Edgewood, Mawland (Received March 88,1986) Budsikiewicz, Djerassi, and Willirr.mR’ refer to their cleavage mechanisms for piperidine as tentative and in need of verification by isotope labeling or high resolution mass spectrometry, Such a spectrum2 under a resolution oiabout 1 in 2500 [Ah/H & 0.011 is presented in Table I.a Mass determinations for the fraglpents which produce the single peaks at m/q 42,43,44, 56, 57, and 70 Table I: Maea Spectrum of Piperidine m/n
26 27
Empirical formula
CaHz CzHs CHN
28
cza
29
NZ(background) CzHs
30
C“
CHzN CHsN
Intensity, arbitrary unitsa
16 44 3 18 80 17 18 64 71 37 3 3 30 10 68 58 84
56 57 -. 70
CAN
3 7 21 4 100 100 26
a Since instrumental adjustments were necessary while these data were being obtained, the relative intensities from one grroup of p& to m t h e r (as indicated by the spacings in the table) should be considered aa only a p p r o h t e l y correct.
prove that the ion formulas proposed for these fragments by B, D, and W are correct. This is equally true for the major peak contributing to m/q 28 and 29 whose structures were apparently chosen by B, D, and W on the basis of the ease with which nitrogen assumes a positive charge in ionization reactions. Note, however, that both m/q 28 and 29 have contributions from hydrocarbon fragments. The fragments (CHr NHCH2)+, m/q 44 and (CHsNH)+, m/q 30 require transfer of hydrogen and the moderately intense hydrogen-deficient hydrocarbon fragments CB7, C&a, and C B a probably result from these abstracting reactions. The hydrocarbon ions could be formed concurrently, with the corresponding nitrogen-containing ion, in competing reactions, or from an initial fragmentation without rearrangement and then subse quent loss of hydrogen. CsHuN+ +CH*N+ C4H7
+
CHiN or Ca11N+ 4C H a
+
+ C&7+ + C4Hs+
CBa+ H CB7+ There is no evidence in these spectra of the hydrocarbon ion immediately above m/q 55 (or m/q 41) as might be expected from the second reaction mechanism. Some indication of the purity of this sample of piperidine was obtained from a gas chromatographic analysis in which only 0.01% impurity was d e t e ~ t e d . ~ (1) H.Budsikiewics, C. Djersssi, and D. Williams,“Interpretationof Mass Spectra of Organic Compounds,” Holden-Day, Inc., San Francisco, Calif., 1964, pp. 98-102. (2) J. Beynon, “Msss Spectrometry and Its Application to Organic Chemistry,” Elsevier Publishing Go., New York, N. Y., pp. 52, 53. (3) Peaks in parent range and several very weak peaks are not included in the data. The low resolution spectrum is in agreement with that given in “Catalog of Mass Spectra,” American Petroleum Institute Ramarch Project 44, Agricultural and Mechanical College of Texas, College Station, Texas, Spectrum No. 618. Spectrometer used here is a Model 21-110 double focusing instrument, manufactured by Consolidated Electrodynamics Corp. (4) Results obtained by Mr. Robert Grula, CRDL, are much appreciated.
The Behavior of Alkali Metal Cations in the Pores of Silica Gel by Russell W. Maatman Department of Ch-, Dordt College, Swux Center, Iowa (Received April 1,1966)
Tien interpreted the interaction of alkali metal cations with silica gel in terms of ion exchange, physical
NOTES
sorption, and ion exclusion from small pores.’ This conclusion was based on his experimental results along with those of Dalton, et a1.,2 and Dugger, et aLa It i8 the purpose of this note to show that there has been some misinterpretation of the results of Dalton, et al., and that there is therefore no need to postulate physical sorption and ion exclusion for these systems. Tien found that the gel preference for cation is in the order Cs > Rb > K > Na > Li. This order, determined by a very accurate tracer method, is in agreement with the results for K, Na, and Li of Dugger, et al. (who did not work with Rb and Cs), taking into account their reported experimental error. Tien, however, bases much of his interpretation on a seemingly contradictory order deduced from pH measurements reported by Dalton, et al. There is actually no contradiction among the results reported in ref. 1-3. The pH values reported by Dalton, et al., were given to indicate that the amount of exchanged metal cation was orders of magnitude less than the amount of unexchanged metal cation in the pores. This gel and other commercial silica gels must be acid-treated before pH differences as small as those found by Dalton, et al., who did not acid-treat, can be used to deduce differences in the amount of exchange. To show that the gel which has not been acid-treated does not give the desired reproducible results, compare the equilibrium pH values obtained by Dalton, et al., with those of Daniel, et u Z . , ~ who used the same materials in very similar experiments and who measured pH values for the same reason. The difference between the two sets of experiments is that the former equilibrium was attained at 22” and the latter at go”, although in both cases the measurements were made at room temperature. The pH values are, respectively: Cs, 2.7, 2.4; K, 3.1, 2.8; Na, 2.6, 2.5; Li, 2.2, 2.7. The order is thus radically different. It does not seem likely that the temperature of equilibration is the important variable. Rather, there is an impurity problem: the necessity of acid-treating such gels to eliminate such surface reaction problems has been shown.96 There then remains no experimental result indicating that some experimental conditions can alter the order Cs > Rb > K > Na > Li found by Tien. Since Dugger, et al., determined affinities by H+ release from the surface, their results (and, by inference, those of Tien, who observed metal-metal exchange) can be interpreted in terms of ion exchange with surface H+, without invoking physical sorption. It seems diacult to visualize H + release from the surface connected with physical sorption. Furthermore, while Dalton, et al., did suggest that large, hydrated ions are excluded from the smallest pores, this effect has been shown not to
3197
exist? (Reference 7 had, however, not appeared when ref. 1 was submitted.) By considering a geometric effect found at any solution-solid interface it was shown that even hydrated AI3+of radius 5-7 much larger than any alkali metal ion, can enter the smallest pores in all the gels used by this group. There thus seems to be no need to postulate either physical sorption or ion exclusion from small pores in alkali metal cation-silica gel systems. Dugger, et al., in considering the silica gel reactions of 22 very different cations, found reasonable correlation with the tendency of the cation to hydrolyze. On the other hand, with ions as similar as the alkali metal cations only s m d differences in reactivity are expected and found. To make a correct prediction of affinity order, one would obviously need detailed knowledge concerning several factors; an “order of hydrolysis” is not enough. Rosseinskp showed that the matter is very complicated: cation hydration, the nature of the anion, and other factors must be considered.
fi.,
Acknowledgment. This work has been supported by A.E.C. Contract At (11-1)-1354. (1) H.T.Tien, J. Phga. C h . ,69,360 (1966). (2) R. W. Dalton, J. L. McClanahan,andR. W. Maatman, J . Colloid Sci., 17, 207 (1962). (3) D. L. Dugger, J. H. Stanton, B. N. Irby, B. L. McConnell, W. W. Cummings, and R. W. Maatman, J. Phga. C h . , 68, 757 (1964). (4) J. L. Daniel, J. N e t t e d e , and R. W. Maatman, J . MksisSippi A d . Sci., 8, 193 (1962). (6) S. Ahrland, I. Grenthe, and B. Noren, Ada C h . Scud., 14, 1059 (1960). (6) J. Stanton and R. W. Maatman, J. Colloid Sci., 18, 132 (1963). (7) B. L. McConnell, IC. C. Williams. J. L. Daniel. J. H. Stanton. B; N. Irby, D. L. Dugger, and R. W. Maatman, J . Phya. C h . ,68; 2941 (1964). (8) D.R.Rosseinsky, J . C h . SOC.,786 (1902).
Observations Concerning Directly and Nondirectly Bonded W-H Couplings with Respect to Symmetry Considerations by T. Vladimiroff Department of C h m k t w and Chemical Enginwing, Steoens Instilzlte of Technobm~,Hoboken, New Jmaey (Rm’ved April 6, 1966)
The Fermi’ contact contribution to n.m.r. spinspin coupling for nuclei N and N’ was first given by Ramsey2to be
