between the heats of formation of Si+, SiH+, SiH(CH3)2+ and SiH(CH)3+, which are established by other evidence in this work. m/e %-The heat of formation of Si(CH&+ is calculated to be 201 kcal./mole, in good agreement with the value of 193 kcal./mole calculated from the tetramethylsilicon study.3 r n / e 73.-The heat of formation for trhis ion is calculated to be 146 kcal./mole, assuming the neutral fragment to be a hydrogen atom. This can be the only process for formation of this ion, but the vaIue of 146 kcal./moIe for AHff(SiMe3) appears low compared to the heat of formation of Si(CH3)3 = 165 kcal./mole calculated from the tetramethylsilicon study. m/e 74.-The small abundance of the parent molecule-ion in the mass spectrum of trimethyl-
silane undoubtedly contains significant contributions made by SiZ9(CHa)s+ and SiZ8(ClaH3) (CH3),+. Several determinations of the ionization potential, using m/e 74, and in one case m/e 75, gave good agreement. The ionization potential for trimethylsilane has not been reported previously. The ionization potential of 9.8 i 0.3 e.v. is essentially the same as that of tetramethylsilicon, as might be expected, and is in good agreement with the calculated value of 10.1 e.v. (see Table IV). The ionization potentials of the series of rnethyl-substituted silanes is expected on the basis of the equivalent-orbital treatment to fall into a series, where I S i H a > ISiHaMe > ISiHzMez > I s ~ H > ISiMec. M~~ Acknowledgments.-We wish to acknowledge valuable discussions of porticns of this work with Professor F. W, Lampe.
ELECTRIC MOMENTS OF METRAZOLE AND SOME RELATED TETRAZOLES BY ALEXANDER I. POPOV~ AKD ROGER D. HOLM Department of Chemistry, State University of Iowa,Iowa City, Iowa Received August SO, 1961
As part of a general investigation of the physical properties of certain central nervous system stimulants, the electric moments of metrazole, 8-t-butylmetrazole, 8-sec-butylmetrazole and 1-cyclohexyl-5-methyltetraxole have been mettsured in benzene solution, values of 6.14, 6.20, 6.18 and 6.00 D, respectively, being obtained.
Introduction In the process of screening various tetrazoles for convulsant activity, it was observed2 that those substituted tetrazoles possessing aromatic substituents generally tended to exhibit depressant activity upon the central nervous system, while aliphatic substituents generally conferred convulsant activity to the compound. One of these aliphatically substituted tetrazoles, 1,5-pentamethylenetetrazole, hereafter referred to as rnetrazole, has found clinical application as a stimulant, and much information has been published on its physiological
Since it has been shown by Featherstone, et a1.,2 that the presence of substituents can greatly affect the convulsant strength of the metrazole derivative, an investigation of certain physical-chemical properties of metrazole and related compounds was begun as part of a broader study of the relations between physiological activity and physical properties. Since convulsant activity seems to be related to those tetrazoles in which the central ring is “electron-rich” it was felt desirable to initiate a study of the dipole moments of a series of metrazoles which vary considerably in convulsant activity but which exhibit relatively minor structural differences. A few dipole moment investigations of various tetrazoles have been carried out. Jeiisen and Friediger16 in 1943, measured the moments of tetrazole, 5-aminotetrazole and 1-methyltetrazole, attributing the fairly Iarge moments of 5.11 and 5.71 D in dioxane and 5.38 D in benzene, respectively, to the contributions of various charge3 effects. Relatively little attention has been paid, separated structures. I n 1956, Kaufman, Ernshowever, t o the characterization of the physical- berger and McEwan6 published the electric mochemical properties of metrazole, and even less in- ments of 12 substituted tetrazoles and discussed the formation exists concerning the physical-chemical origins of these moments in terms of the resonance properties of various metrazole derivatives. Only contributions of a number of charge-separated the halogen3 and silver4 complexes of metrazole structures to the meso-ionic ring. A more analytical have been investigated with any degree of thorough- treatment of tetrazole moments was made by Kaufman and Woodman17who applied the method ness. of Hill and Sutton8 to a discussion of l-phenyl-5(1) Department of Chemistry, Northern Illinois University, DeKalb, Illinois. (2) F. W. Schueler, S. C. Wang, R. M. Featherstone and E. G. Gross, J . Pharmacol. Ezptl. Therap., 97, 266 (1949), and references listed therein. (3) A. I. Popov, C. Castellani-Bisi and hI. Craft, J . A m . Cham. Sac., 80, 6513 (1958). (4) A. I. Popov and R. D. Holm, ibid., 81,3250 (1959).
(5) K. A. Jensen and A. Friediger, K g l . Danake Videnskab. Selskab iWat.-fus. Medd., 20, No. 20, 1 (1943); Chem. Zentr., I , 416 (1944). (6) M. H. Kanfrnan, F. M. Ernsberger and W.S. M c E w m J . Am. Chem. SOC. 7 8 , 4197 (1956). (7) M. H. Kaufman and A. L. Woodman. J . Phys. Chem., 62, 508 (1958). ( 8 ) R. $. Hill and L. S. Button, J . Chem. Sac., 746 (1949).
inethyItetra~ole aiid 1-mcthyld-phenyl~rtra~ole,tric const:inr, data furnished by the heterodyne Yet the origin a n d nature of the tetmzolc ring mo- instrument, a war surplus radio frcqiienry cahbrumeut atill is incompl ly itnderstood, and this t,or, thus was felt to be sufiiciciit~lyacwiratr for Rtudy xvvrzs begiia IU order t o providr more informa- iurtlicr work. The results of the dielcctric constant, specific tion conccrning the dipole momeiits of scvcral tctvolume and refractive index measurements for razole derivatives. beiizeiie solutions of metrazolc, 8-t-butylmetrazok:, Experimental Part 8-sec-butylmetrazole and 1-cyclohrxyl-3-methylReagents.--Thr piirifivhtion arid physical constants of t h c tetrazolc arc summarized in Table I. Distortion e\ clohcxanc rcfereiicc liquid a d beiimno solvent have hccn polarizations wnrc calculated by extrapolation of clchcribcd previoiialy Metrazolo (Knoll l'li~irnmnc~t~lltlc~al Co.) \\'as purificd by the molar refraction to infinite wavc length (PD= filterha a yaturatrd snlutiorr 111 \varm, distilled ether, and 1 .Ob@ which differed from the sodium-n line polarithen stirring in an icr-bath to ol>taiii the roduct in small zation by only 1. I 1 cc. In view of' the fact that, the r.rjstallina form. The mrtrmole then IVS h e r e d und dried orientatiori polarization is about 763 cc., this diSi r i LUCUO over PL05 for a wcck; m p. 60 3-60 9", literature3 fcrence is negligible, and 1he molar refraction was value. 61 . A d . C:ilcd. for CbHllJY4:C, 58.16; 11, 7.30. Found: henceforth measnrcd for the sodium-u line. It) is C, 62.02; 11, 7.08. likely that the atomic polarization is reasonably T h e S-t-butylmotruzole was prepared according to the pro- constant in view of the similarities between the ccdure of Harvill, Roberts und Hcrbst.'o The nietmzolv tirrivative w:ts recrystallized five times from isopropyl ulco- molccular structures studied. In addition to thc three metrazoles, the momcnt hol and, aftrr drying in vacuo over 1'206 for t w o days, cxhihited a iiieltiriR measured _. -point of 129.6-130.4° (lineor.); lit.lo of 1-cyclohexyl-5-mcthyltctrazole WTS 13'2.5- I :1Y . bccausc this dialkyl tetrazole should not be subject A w l . Calctl. lor CIJI,,S~: C, 61.82; H, 9.34; N, 28.S4. to any tetrazole ring deformation which might be Found: 0, 01.71; 11, 9.11; X, 37.89. Tho X-scc-i)iitSlmr?t,razole (I
