upon bond formation produces a charge on each atom of the sign which is circletl. Only one C'O group is shown. 1 is fornietl by puttinq the four C O groups tetrahedrally about the cobalt atom in its sp3 orbitals. The negative charge on the cobalt atom is reduced by the transfer of the d elcctrori to the hydrogen atom on the C3axis.
I
111
I1
Structure I1 may be obtained from I by removing an electron pair from one CO s bond and placing it in the p orbital of the oxygen followed by bond formation between the p orbital of the carbon and the s orbital of the hydrogen using the electron pair previously on the hydrogen. Of course there are three resonating structures like 11. Structure I11 enters into the resonance composite to counter-act the negative charge on the cobalt atom in structures I and 11. Comparison with Experiment.-The bonding found for the bridge model is in qualitative agreement with the substantiated experimental facts now known for CO(CO)~H. It predicts a diamagnetic molecule. The weak covalent bonding of the hydrogen atom agrees with the ease of decomposition t o form Hz and c o ~ ( C 0 ) ~T. h e large negative charge on the hydrogen atom calls for the large negative chemical shift found by Gutowsky and coworkers" in the proton magnetic resonance spectrum. And an interesting prediction may be made about the CO stretching vibration in C O ( C O ) ~ - , which may be described as having two electrons in $" and two in followcd by the delocali7ation of (11) H 3 ' Giltowsky, private report
the charge. This latter process will riot chniige the general c-hnractvr of tht: orbitals. Since, $1 1 is ; i i i tibonding will: rpg:tr(:s to the CO bond, cine exl'ccts the frequency oi the CO stretching vibration in Co(CO)1- to be less than those in C O ( C O ) ~ H .The exare6 2122, 2043 perimental values ior C O ( C O ) ~ H and 2062 em.-' while the value for C O ( C O ) ~is3 1S83 cm.-l, in striking agreement with theory. The question naturally arises as to how a 111olccule with a negative charged hytlrogen can tlissolvrin water to form a strong acid. This proccs.: in:iy he divided into the following steps Co(COj,H(gj +Co(CO),*--(g) Co(C0j;" -(g) -+ Co(cOl4-(g) H + ( g ) --+ I l + ( a q ) Co(COJ)-(gi --+Co(CO),-(ayj Co(CO)JI(g) --+ Co(C0j4-(,zqj
+ TWg)
f8.2 e . v . 11 )
-H
( 21 13)
-11.1 -1.7
(1)
- 4 . 9 -I
hy Crawfortl and Cross3 gives k ~ i . = . ~2.52 x 1 dynes/cm.). The difference between the first two
(257 aiid 22-4 kcal. ,'molej corresponding to the two controversial values for the heat of sublimation oi' carbon (172 and 1-10 kcal. ;mole, respectively), we give two sets of predicted bond energies. The CO bond energies niay be combined with the heat of at~tiii~,:~tioii of Fc(CYN5 and NiiCO), to give thc. Fe -c' a i i ( 1 Xi C blJl1d ciitrgies, r(::i]wctivc.ly. 'I'lic. rtsult:; :in' x.iveri iri 'L'ul,lc L r I I l . '1'11~~ (.' I ) o i i ( l t1ierg.y is Ii kcal. ' i i i o I ( ~largcr t l i : ~t ~l w ~ Ni C i)oii(i energy. Cable aiitl Sheline'6 lia\-e niatle ;L s i i i i i l ; ~ ~ calculation whereby they obtained bond energies of
( I O ) -1. \V. Cablc i i i i t l 1< K Slir,linc. " l j o r i i l Ilglxi~lizaliiiii ani1 h ( r u c t u r e in tlie h f c t a l C;irlx,n?Is," J ~ C I NI Z ~ F S5, 6 , I ( l ! J 5 l ~ ~
, l!J.5.i1
(17) I:
I< l . i ~ 1 1 1 i n ~ ~. n~i ,tIt I < . S c l i r ~ ~ e d e.Ir .
DIPOLEMOMENT MEASUREMENTS OF TETRAZOLE DERIVATIVES
Scpt. 5 , 1956
9s and S9 kcal./niole, respectively. Their calculation was based on the incorrect assumption that the CO bond energy is the same in Fe(C0)6 as in Ni(C0)4. The Raman spectrum of Fe(C0)5 indicates t h a t this assumption is not justified. Also, they had no effective means of estimating the %O bond energy from that of carbon monoxide. The Fe-C and Ni-C bond energies calculated here are of the same order of magnitude as bond energies calculated for Sn-C and Pb-C, indicating that the Fe-C and Ni-C bonds must have a bond order only slightly larger than 1.16 This result is consistent with the values for the Sn-C,Pb-C, Zn-C and
4197
Cd-C bond stretching force constants which have values of 2.37, 1.94, 2.39 and 2.05 X lo7 dynes,’ cm., respectively. l 8 hi^^^ ADDED I N PROOF.-L$”? have recently made detailed calculations of the valence force symmetry coordinates (VFSC) and valence force coordinates (VFC) for Fe(CO)s using the Wilson F G technique and the above assignment of frequencies. We calculate for the axial and equatorial Fe-C bond stretching VFC the values 3.06 X 105 and 3.29 X lo5 dynes/cm, respectively.
This work was supported in part by the U. S . Atomic Energy Commission. (18) R. K. Sheline, J. Chern. Phrs., 1 5 , 602 (1‘35‘3). COLLEGEPARK,MD.
u. s. NAVALORDNANCE TESTS T A T I O N ] Dipole Moment Measurements of Tetrazole Derivatives [COSTRIBETION FROM
13l’
h1,UXTIN 13. KAUFMAN, FRED31. ERNSBERGER ,4ND
II‘ILLIAM
s. MCEWAN
RECEIVEDDECEMBER 27, 1955 Uipolc rnoiiients have been measured for a variety of tetrazole derivatives. inents are not suitable for recognizing “meso-ionic” compounds.
It has been established that such nicdwrc-
Dielectric Constants.-These mere measnred with a Leeds Introduction and Worthrup Company capacitance and conductance bridge Henry, Finnegan and Lieber‘ recently reported using No. 1553 shielded ratio box. The dielectric constant the preparation of 1,3-dimethyl-5-i:ninotetrazole, a cell consisting of three concentric cylinders of brass tubing was similar in design to the measuring condenser of Smyth cyclic “meso-ionic“ compound. It was antici- and Morgan.6 The assembly was sealed into an annular pated2 that the reaction of 2-methyl-3-aminotetra- “Pyrex” glass cylindrical vessel. The annular space rezole with methyl benzenesulfonate, according to duced the quantity of solution required and aided in the the procedure of Herbst, Roberts and H a r ~ i l l , ~circulation of the thermostated kerosene. The apparatus calibrated with benzene, the dielectric constant of which would result in the formation of the 1,2-dimethyl was was taken to be 2.2750 a t 25O.6 derivative. However, a preliminary X-ray analySpecific volumes were determined with a 25-ml. “Weld” sis of the hydrobromide salt of the resultant com- specific gravity bottle with which specific gravities can be pound? and a modified three-dimensional Fourier determined t o within 0.001 7c. Refractive indices were measured with a “Spencer Abbe” synthesis by Bryden? demonstrated unambiguously refractometer. The pure benzene was taken to havc a that the compound was the cyclic “meso-ionic” standard refractive index of 1.5002.
1,5-dimethy1-5-iminotetrazole. A complete X-ray analysis will lead to an accu-
rate structure; however, it is not generally applicable t o all compounds. The purpose of this investigation was to see what information about the structure of tetrazoles could be obtained from dipole moment measurements and whether it was possible to recognize “meso-ionic” compounds by such measurements. Experimental Materials and Methods.-Mallinckrodt, analytical reagent grade benzene was purified by crystallizing twice and then fractiimally distilling after standing several days over freshly cut and ribboned sodium. All was rejected but the center cut which was redistilled in the same nianner before use. The spccific volume parameter for the solvent was obtained for each run from a least-squares examination of the specific volume, weight fraction data and was found to be cbnstant to rt0.02y~: Tetrazo1es.-These were obtained, fairly pure, from Drs. I
