Jan., l96Z
SPECTROSCOPY OF TETRAMETHYLGERMANIU~, TRIMETHYLSILANE, DIMETHYLYERCURY 155
ELECTRON IMPACT SPECTROSCOPY OF TETRAMETI-kYLGERMANIUM, TRIYIETIIYZSILAXE AND DIhlETHYLMERCURY1 BYBRICEG. HOBROCK AND ROBERT W. KISER Kansas State University, Department of Chemistry, Manhattan, Kansas REceiWd August 86, 1961
Electron impact data determined with a mass spectrometer are reported for tetramethylgerinanium and two related organometallics, trimethylsilane and dimethylmercury. Probable ionization and dissociation processes are given and the heals of formation of the principal ions, consistent with the proposed processes, are calculated. Ionization potentials for the series of methyl-substituted silanes are calculated using the equivalent orbital treatment. The calculated values for the ionization potential of tetramethylgermanium and trimethylsilane are compared to the experimentally determined values of 9.2 i O.;! and 9.8 i 0.3 e.v., respectively, and 8.90 f 0.2 e.v. for dimethylmercury.
Introduction Lampe and Field2 have studied the electron impact spectroscopy of neopentane, and we have recently reported data for tetramethyl-silicon, -tin and -1ead.3 Electron impact data for the remaining member of the group I V tetramethyl compounds, tetramethylgermanium, is reported in this work. A study of two other related organometallics, trimethylsilane and dimethylmercury, also is included. From the previously reported data for tetramethylsilicon, and the present data for trimethylsilane, one may compare heats of formation for the ions and the dissociation processes in the two methyl-substitu ted silicon compounds. Molecular ionization potentials for the series of methyl-substituted silanes are calculated using the equivalent orbital treatment. Experimental valuea for the ionization potentials of trimethysilane and tetramethylgermanium are compared to calculated values. Experimental The mass spectra and appearance potentials reported here were obtained with a Bendix Model 12-100 time-of-flight mass spectrometer with an analog output system consisting of B monitor and scanner. This instrument has previously been descrik~ed.~ Mass spectm for each of the compounds were obtained at nominal electron energies of 70 e.v. Appearance potentials were calculated using the method of extrapolated voltage differences, described by Warren.6 Krypton or xenon, mixed with the compound being investigated, was used to calibrate the ioniEing voltage. Known spectroscopic values for the ionization potentials of krypton and xenon were used.6 Tetramethylgermanium was obtained from Chemicals Procurement Laboratories. No impurities were noted in the mass spectrum; hence, the sample pias used as received. Gas chromatographic analysis was not attempted. The sample of trimethylsilane was obtained from Peninsular Chem-research, Inc. The gaseous sample of trimethylsilane was received in compressed form and was transferred directly t o sample bulbs on a vacuum line without the samples being exposed to air. KO attempt was made to determine the purity of the sample by gas chromatography, although a small impurity was indicated by the presence of (1) This work was supported in part by the U. 8. Atomic Energy Commission under Contract No. AT(ll-1)-751 with Kansas State University. Taken in part from a thesis submitted by B. G. Hobrock to the Graduate School of Kansas State University in partial fulfillment of the requirements for the M.S. degree, August, 1961. (2) F. W. Lampe and F. R. Field, J . Am. Chem. Soc., 81, 3235 (1959). (3) B. G. Hobrock and R. W.Kiser, J . Phyis. Chsm., 65,2186 (1961). (4) E. J. Gallsgos and R. W . Kiser, J . A7a. Cham. Soe., 83, 773 (1961); J. Phy8. Chem., 65, 1177 (1961); ibid., 66, 136 (1962). ( 5 ) J. W. Warren, Natura, 165, 811 (1950). (6) C. E. Moore, “Atomic Energy Levels,” Natl. Bur. Standards Circ. 467, Val. 111, U. S. Government Printing Office, Washington, D. C., 1958.
m/e 77, which was not identified further. This impurity was present in quantities of less than 1.0%. Dimethylmercury was obtained from K and K Laboratories. Gas chromatographic analysis using a Fisher-Gulf model 160 Partitioner with a 14 foot column of tri-n-tolyl phosphate on Celite3 revealed no impurities.
Results The appearance potentials for the principal ions in the mass spectra of tetramethylgermanium, trimethylsilane and dimethylmercury are summarized in Tables I, I1 and 113. The probable processes by which the various ions were formed are given, consistent with measured and extrapolated energetics. The calculated heats of formation are given in the last column. The following heats of formation were used in the calculations with the measured appearance potentials: GeMe4, -35 kcal./mole (see below); SiHMe3, -54 kcal./mole7; HgMen, -47.5 kcal./ mole8; CH3, 32.0 kcal./moleg; CH4, -17.8 kca1.l moleg; C2Ha,-20.2 kcal./moleg; CtH4, 12.5 kca1.l moleg; H, 52.1 kcal./moleg; and GHs, 24.5 kcal./ mole.1° Mass Spectra.-The mass spectra of tetramethylgermanium and dimethylmercury axe in essential agreement with those reported by Dibeler, et al. W2 To the best of our knowledge, the mass spectrum of trimethylsilane has not been reported previously. Molecular Ionization Potentials.-Calculated and observed ionization potentialb for the series of methyl-substituted silanes are listed in Table IV. An equivaleiit orbital treatment similar to that employed for the calculation of the ionization potentials of the group I V tetramethyl compounds was used. The parameter for methyl group-silicon atom interaction was calculated using the experimentally determined ionization potential of tetramethyl~ilicon.~The calculated value of 10.1 e.v. for the ionization potential of trimethylsilane compares favorably with the experimental value of 9.8 f 0.3 e.v. The calculated ionization potential of tetramethylgermanium reported previously, 9.1 (7) S. Tannenbaum, S. Kaye and G. F. Lewenz, J . Am. Chem. Soe., 15, 3753 (1953). (8) L. H. Long and R. G. W. Norrish, Trans. Rou. SOC.(London),
A241, 587 (1949). (9) R. D Rossini, D. D. Wagman, W. H. Evans, S. Levine and I. Jafie, “Selected Values of Chemical Thermodynamic Properties,” Natl. Bur. Standards Circ. 500, U. 8. Government Printing Office, Washington, D. C., 1952. (IO) P Gray and A. Williams, Chem. Revs.,59, 239 (1959). (11) V. H. Dibeler and F. L. Mohler, J . Research Nail. Bur. Stand. ards, 47, 337 (1951). (12) V H. Dibeler, zbzd., 49 235 (1952).
150 TAB1.E
I
I\PPl3AMNC'U P O T E N T I A L S ANI) 1IEATS OF I'ORhlATION OP l3lUP I t I N C i P A L I O N S OF ~~ISTBAhIBTIIYLCEI(MhNIUM Li'o Appearance Abundanco potontial Allr Ion (~nonois~ito~ic) (e.7.) Process (kca~./nlole)
CHI + Ge CleCIT1+ GdCHJr' Ge( C€Ta)a Ch(CI13)4+
16.7 3.3
20.1 f 0 . 5 19.2 i . d 16.8 f .4 14.1 f . 2
74.8 1.4
10.2 f . 1 9.2 f .2
3.8
+
+
+ + + + + +
Ge(CII8), --+ClL+ Go 3CH1 --+ Go+ 4CH, *GtCII,+ 3CHs --+ Cre(Cl-IJ.+ 2CHs ---t Ge(CHa)l+ C€Is +Ge(C€Jj)c+
254 279
245 226 168
177
TABLE I1 APPEARANCE POTENTIALS A N D HEATSO F FORMATION OF THE PRINCIPAL IONSOF TRIMETHYLSILANE Relative abundance
d e
Appearnnce potential (c1.v.)
Process
ANI+
+ + + + + + + + + + + + + + + + + + + + + + + + + + + +
(kcal./niole)
SiH(CHJ, -+ CI-IO+ SiII(CII& ( 25) -* CzIIt+ SiCHs 2H2 ( 73)= --+C2HI+ SiHCHa I-11 I% (21)" 28 59.8 13.7 f . 3 +Si+ cE14 c2I-1~ 300 29 17.2 14.2 f . 2 -3 SiII+ C2He CHI 262 --+ SiH+ G H , CH, 267 31 10.4 14.3 f . 5 --+ SiH8+ CI& CdI, 231 41 11.4 11.7 f .6 --+ SiCII+ k1 C2He H, 186 --+ SiCH+ CzH6 2112 194 42 12.1 10.6 f . 3 +SiCHn+ C P H ~ IIs 21 1 --3 8IcEIl+ 2CH4 226 43 42.8 12.4 f . 3 --+ Si(CH3)+ CH4 CHI 218 44 11.0 11.0 f .R +SiHCHa+ C2IIb 220 45 14.7 12.8f .5 & I ~ z C I I ~ +CIH, 21 6 58 27.9 10.3 f . 2 --+Si(CHJ2+ CH. 201 59 100 11.9 .3b --j SiH(CIi8)2+ 3. CFIo 188 73 53.8 10.9f . 2 b -+ Si(C1131a+ H 146 7.1 !j.S f .3 --+ SiH(CHJI+ 172 74 Heat of forination of the radical. b Values of 11.82 e.v. for A.F. (5!)+)arid 11.02 e.v. for A.P. (73+) have bcon deterniinod by F.14'. l m n p e and G . HCSR,privut.e colrimunic:stion. 15 27
14.8 f 0 . 5 1 5 . 3 f .5
31.1 7.6
-
*
TARm!
I11
A N D H E A T S OF F O R M A T I O N OF TITI? 1"TLlNCIPAL IONS O B nIMETHYLMERCURY Arwnrance % Abundmw I~lltt.JItild
AIJI~EARANCE 1'OTENTIALS Ion
ITg
(IllOnOJ8OtOplC)
22.4 54.2 23 4
+
IIgC€Id+
Hd CIL) 2 11
+
V.)
10 4 f 0 . 2
8.00
* 0.2
See rcf. 9. TABLE I\'
C'ALCULATED A N D OBSERVED ~ o i m A T l O NP O T E N T I A L S
OF T H E
~ I F . T I I Y I . - ~ U B S T I T U T E ISILANES ) b,
Ciimnoiind
parnmetero
Si{C1IJ), SIH(CHs)a SiH2(CII,)* a
SiHaCWa Src ref. 3.
*
1. 5 1 5 1 5 1 5 This work.
Cnlrd. 11'
Obsd. I P
(ev)
(0.Y.)
(9 8)
9.8"
10 1 10 5 11 1
9
c . v . , ~is in good agreement with the experimental
value of 9.2
f 0.2 C.V.
Discussion Tetramelhy1germanium.-The heat of formation for tetramethylgermanium has not, to our knowledge, been reported in the literature. The calculations of the heats of formation for the ions produced from tetramethylgermanium are based upon an estimated value of -35 lical./mole. This estimation was made on the basis of interpolation between the experimentally determined heats of
formation for tetramethylsilicon, -tin and -lcnd, and by calculations using the method due to Franklin.lS Calculations of heats of formation of ions based upon the estimated value of AIIr(GeMeJ are found to bc rcasonable. Appearancc potent in1 measurements were made using the germanium isotope of mass 70 in order to minimize the effect of hydride formation. Hydride formation is quite apparent in the mass spectrum but no significant effects were noted in the measurement of appearance potentials of any ion using either the isotopes of m/e 70 or 74. The appearance potential of the parent molecule-ion was determined using the isotope of mass 74, exclusively, in order to obtain greater detection sensitivity. m/e lS.-The heat of formation calculated for CI18+,with the accompanying fragments of Ge and 3CI-13,is 254 kcal./mole, only slightly lower than the value of AHff (CHJ = 202 kcnl./mole, given by Field and Fmnklin.14 (13) J.
L Frnnklin.
Ind. Ene. Ckem. 41, 1070 (1949).
Jan., 1962
SPECTROSCOPY OF TETRAMETHYLGERMANIUM, TRIMETHYLSILANE, DINETHYLMERCURY 157
m/e 7O.-This ion can be only Ge*. The calculation of its heat of formation gave a value of 279 kcal./mole considering the ncutra,l fragments formed to be four CH, groups. This is in fair agreement with the literature value for AhHf+(Ge) = 267 kcal./m~le.~ m/e 85.-The heat of formation for this ion, GeCH3+, is 245 kcal./mole considering the formation of three C€L groups as neutral fragments. If the neutral fragments were C&Ie 4- CHB, AHt+ (GeCHJ = 328 kcal./mole, a value considered to be unreasonably large. m/e 100.-This ion is Ge(CH&+. The process is believed to involve the formation of two CH3 groups as neutral fragments. The heat of formation of the ion then is 226 kcal./mole. Considerations of approximate energies needed to remove subsequent methyl groups and interpolation between the heats of formation of the other ions also lead to the conclusion that two CH3 groups are the neutral fragments. Hydrides were apparent in the mass spectrum in this region, but it is believed they did not interfere with the determination of the appearance potential of this ion. m/e 134.-Good reproducibility (for repetitive determinalions) was obtained for the ionization potential of tetramethylgermanium in spite of the low abundance of the ion. The experimentally determined ionization potential, 9.2 i 0.2 e.v., is in good agreement with the value of 9.1 e.v. calculated using the modified equivalent orbital treatment. s Dimethylmercury.-The heat of formation for dimethylmercury has been reported as -47.5 kcal./mole by Long and Norrisks The heats of formation for the ions Hg(CH&+ and HgCH3+ are based upon this value. All determinations were made on ions containing the mercury isotope of mass 200; hydride formation is not considered significant. The ionization potential for this molecule, 8.90 =t0.2 e.v., is similar to the ionization potentials of the other molecules reported here and agrees with the vdue of 9.02 f 0.2 e.v. determined by Reese and Dibeler. l 6 Trimethysi1ane.-The heat of formation for trimethylsilane, -54 kcal./mole, as determined by Tannenbaum, Kaye and Lewenz,’ was utilized in the calculation of the heats of fiormation for the principal ions in its mass spectrum. Heats of formation for various ions calculated using A H f (SiHMeJ =: -54 kcal./mole compare very favorably with literature valued4 that are available, and with the heats of formation for the ions from tetramethyl~ilicon.~The values for the heats of forma-. tion for the series of silanes reported by Tannenbaum, et al., 7, -36, -54 and -63 kcal./mole for SiHzMez, SiHMe3 and SiMe4, respectively, appear to fall into a regular series corresponding to relative stabilities of these compounds and are believed to be quite reliable. Appearance potentials were measured for a number of hydrides that are formed as well as for the (14) F. H. Field and J. L. Franklin, “Electron Impact Phenomena and the Properties of Gaseous Ions,” Academic Prees, Inc., New York, N. Y., 1957. (16) R M. Rews and V. H. Dibeler, privato communication.
principal ions that appeared in the tetramethylsilicon spectrum, I n several cases, the precision was not a8 good as was desired; the ionization efficiency curves for some of the hydrides tailed off as if two or more processes were occurring. This made it difficult to obtain accurate determinations. m/e 15.-This ion can be only CHa*, and is probably formed by a process involving the formation of SiE[Mezas the neutral fragment. The heat of formation for the SiHMezradical is not available, thus the heat of formation of CHI+ cannot be calfor the culated. ‘Using a value of 262 k~al./mole’~ heat of formation of CHI+, however, the heat of formation of the SiHMe2 radical is calculated to be approximrttcly 25 kcal./mole. m/e 27.-The absence of heats of formation for neutral fragments containing silicon again prevents the calculation of the heat of formation of this ion, which is C2H3+. A possible process for the formation of this ion involves the formation of SiCH3 2Hz as neutral fragments. Also possible is the formation of SiHCH, Hz H. Taking the heat of formation of C2H3+as 280 kcal./mole,14 either the heat of formation for the SiCH3 radical would be 73 kcal./mole or the heat of formation of the SiHCH3 radical would be 21 kcal./mole. We cannot differentiate between these two values, although we believe the latter is more reasonable. m/e 28.-The energetics indicate the process to be that given in Table 11; the calculated heat of formation of Si+, 300 kcal./mole, compares fairly well with the literature value of 278 kcal./m0le.~4 Any other process is incompatible with the energetics. m / e 29.-The process in which CHI and CzHO are the neutral fragments leads to a heat of formation of SiH+ = 262 kcal./mole, which compares favorably with the value of 267 kcal./mole for AHr+(SiH) as determined in a study of SiH4.’4 However, the reaction SiMesH --+. SiH+ CH4 C2H5 leads to AHf+ (SiH) = 267 kcal./mole. m/s 31.-The heat of formation of SiH,+ is calculated from the energetics to be 231 kcal./mole, in fair agreement with the value 214 kcal./m0le.~4 m/e 42.-This ion could be only SiCH2+ and has a heat of formation of 210 kcal./mole, if its formation is accompanied by the formation of Cdi6 Hz as neutral fragments. The process for the formation of two methane molecules also is possible, giving a heat of formation for SiCH2+ = 226 kcal./mole. m/e 43.-The shapes of the ionization efficiency curves obtained in the determinations of the appearance potential of this ion indicate that two or more processes are occurring. We did not, however, separate the processes. The appearance potential determided was 12.4 rt 0.3 e.v. Since this ion can be only &CHI+, it is believed that the formation of this ion involves the production of neutral fragCHa. A H f + (SiCH3) then is calments of CH, culated to be 218 kcal./mole, in fair agreement with the value of 234 k~al./mole.~ m / e 44.-The heat of formation calculated for SiHCH3+,considering the accompanying formation of the neutral fragment C2H6,is 220 kcaI./mole. This process is selected on the basis of interpolation
+
+ +
+
+
+
+
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
3
effects. Relatively little attention has been paid, however, to the characterization of the physicalchemical properties of metrazole, and even less information exists concerning the physical-chemical properties of various metrazole derivatives. Only the halogen3 and silver4 complexes of metrazole have been investigated with any degree of thoroughness. (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).
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 chargeseparated structures. In 1956, Kaufman, Ernsberger and McEwan6 published the electric moments of 12 substituted tetrazoles and discussed the origins of these moments in terms of the resonance contributions of a number of charge-separated structures to the meso-ionic ring. A more analytical treatment of tetrazole moments was made by Kaufman and Woodman17who applied the method of Hill and Sutton8 to a discussion of l-phenyl-5(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. McEwm 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).
