COMMUNICATIONS TO THE EDITOR
Nov. 5, 1961
4473
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c
TTT
CH3
111
I11 (m.p. 284-285°)3. Three types of hydrogen absorption in an abundance of 4, 6, and 8 are present (cf. Fig. 2). The two tertiary hydrogen absorptions centered a t 230.5 and 185.5 cps. are still a doublet of doublets ( J = 10.5 cps.) but have additional splitting of each line into symmetrical triplets ( J = 3 cps.) by the new methylene groups. This confirms that these tertiary hydrogen atoms were CY to the double bond in the photodimer and further identifies this coupling in Fig. 1. The N-methyl line has shifted to lower field because of the removal of the double bond with its diamagnetic anisotropy. The new ring methylenes show an absorption a t 116 cps. which lacked the usual distinction between hydrogens in the axial and equatorial conformations. The formation of symmetrical triplets ( J = 3 cps.) is of interest because it indicates that the coupling to both methylene hydrogens which have different conformations is identical and that the dihedral angles are about 45'. The situation was clarified when a Dreiding Stereomodel was constructed and the molecule was observed to undergo very facile ring interconversion between two boat forms of the two six-membered rings. The third form, with the ring fusions in the flagstaff positions, is highly strained and is the transition state between the other two. I t is of interest to observe that the two forms (cf. Structure 111) are mirror images after rotation of one through 150'. During this process, the equatorial hydrogens become axial and vice versa (see III), the net effect averaging the methylene hydrogens (only one absorption frequency) and the dihedral angle to about 45' as required. This reaction has proved to be general. The products present interesting problems in magnetic anisotropy effects, rates of conformation mobility, and chemical synthesis which are presently under active investigation.
-THS
Fig. 1.-High field portion of proton n.m.r. spectrum of CHICHSF at 15.08 Mcps., with spectra calculated for like -. and opposite signs of J C H ~and
spectrum of CHaCHzF,an additional compound of this type. The relative signs and magnitudes of the proton-fluorine coupling constants in ethyl fluoride apparently are inconsistent with the trends suggested from previous measurements. TABLEI COUPLING CONSTANTS IN SOME (CHICHI).X COMPOUNDS Rel. signs of
Compound
JCHY-x Atomic J C E Y - C E X J ,C E ~ - X Jcnr-x, and number cps. cps. cps. J C I I Z - Kef. x
(CH:CHs)F'O 9 (CHKHt):P" 15 ( C H I C H Z ) S ~ ' ~50~ (CH:CHt)&llO 50 (CHsCHi)tHg'" 80 ( C H I C H ~ ) : T ~ 81 ~~ (CH:CHa)dPbm' 82
6.9 25.2 46.7 Same ... 7.6 13.7 0 . 5 Opp. 1 -8.2 -68.1 -30.8 Opp. 1 8.2 71.2 3 2 . 2 Opp. 1 7 . 0 115.2 87.6 Opp. 1 -7.7 396 198 Opp. 4 8 . 2 125.0 41.0 Opp. 1
The n.m.r. spectrum of ethyl fluoride a t 60 Mcps. is readily assigned from first order considerations. The coupling constants determined from this spectrum are given in the table. (Approximate THERESEARCH LABORATORIES OF G. SLOMP THEUPJOHN COMPANY F. A. MACKELLAR coupling constants of JCH-F 20 cps. and J C H ~ P 60 cps. have been reported.6) The chemical KALAMAZOO, MICHIGAN L. A. PAQUETTE shifts of the CHa and CHs protons are -1.24 and RECEIVED JULY 31, 1961 -4.36 ppm., respectively, relative to tetramethylsilane (these shifts have been reported previously6 THE RELATIVE SIGNS OF PROTON-FLUORINE as 6.07 and 2.89 pprn. relative to benzene). COUPLING CONSTANTS IN ETHYL FLUORIDE The Flg chemical shift relative to CClaF is 214 Sir: PPm. There has been considerable interest recently in (2) P.T.Narasimhan and M. T. Rogers, i b t d . , S1, 1430 (1959). the relative signs and magnitudes of CH3-X and (3) P. R. Narasimhan and M. T. Rogers, J . Am. Chrm. SOC.,82, CHz-X coupling constants in compounds of the 34 (lQ60). (4) I.P.Maher and D. F. Evana, PYOC. Chum. Soc., 208 (1961). type (CHICH&,X, where X is a nucleus of spin (5) H.S. Gutowsky, L. H. Meyer and D. W. McCall, J . Chem. l/2.1-4 We wish to report the analysis of the Phys., 83, 982 (1955). (1) P.T.Narasimhan and M. T. Rogers, J . Chcm. Phyr.. 34, 1049 (1961).
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(6) B. P. Dailey and J. N. Shoolery, J . Am. Chem. SOC.,77, 3977
(1955).
4474
COMMUNICATIONS TO THE EDITOR
Vol. 83
The relative signs of the proton-fluorine coupling for the A3BrX spectra were performed on the IBM constants can be found from the analysis of the 709 computer of the M.I.T. Computation Center. proton spectrum a t 15.08 Mcps. a t which the DEPARTMEST OF CHEMISTRY S. L. STAFFORD UKIYERSITY J. D. BALDESCHWIELER spectrum is a typical A ~ B z Xspectrum. The ob- HARVARD served spectrum of CH3CHzF a t 15.08 Mcps., C A X B R I D G E , I f ASSACIIUSETTS RECEIVED SEPTEMBER 15, 1961 and the spectra calculated for like and opposite and J C H ~ -are F shown in the figure. signs of JCH$-F The spectrum calculated for like signs of JCH~-F A CYCLOPENTADIENYL DERIVATIVE OF TECHNETIUM and J C H ~ -is F in good agreement with that obSir : served. The coupling constants for other molecules of the It was of interest to obtain a cyclopentadienyl type (CH3CHz)nX that have been reported pre- derivative of technetium for comparison with the viously are listed with those for ethyl fluoride in the known derivatives of manganese and rhenium. table. For the molecules other than CH3CH2F, These two differ from each other both in their IJcH~-xI will be seen to be larger than IJcH~xI composition and nature of ring-to-metal bonding; and opposite in sign. Furthermore, the values of while (C5H&Mn1 is ionic and possesses unpaired JCH-X seem to increase regularly with the atomic electrons, rhenium forms covalent, diamagnetic number of X. The coupling constants of ethyl (c5H5)~ReH.~&-e now wish to report the synfluoride are quite.inconsistent with these trends. thesis and properties of a corresponding derivative From theoretical and experimental considera- of technetium. tions, both JCH&-X and J C H ~ -would X be expected In a typical preparation, ammonium pertechne, X is a tate3 (1.50 g., 8.27 mmoles) was converted to the to be positive, with JCH?X> J c H ~ - xwhen pr~ton.~ The coupling constants observed for heptoxide4 in a Vycor tube (15 mm. diameter, 30 ethyl fluoride are consistent with the results of ml. capacity). After addition of carbon tetrathe tube was sealed and heated valence bond theory, if i t is assumed that when X chloride (9.2 d.), is F19contributions to the coupling constants from to 400' in an autoclave for five hours, to form terms other than the contact electron-spin inter- technetium tetrachloride after the method of K. action can be neglected, &ox, S. Y. Tyree, Jr., et a1.j The moisture It has been suggested that the unusual relative sensitive, blood-red tetrachloride was filtered in a and J C H ~ .in X dry atmosphere, washed with dry, redistilled signs and magnitudes of JCII~-X compounds other than CH3CH2Fmight arise from pentane, and added a t room temperature to a comcontributions to the coupling constants from terms pletely colorless6 solution of sodium cyclopentaother than the contact electron-spin interaction. dienide (from sodium, 1.15 g., 50.0 mmole and However, calculations have indicated that con- monocyclopentadiene, 3.64 g., 55.0 mmole) in 30 tributions from electron-orbital8 and dipolar elec- ml. of tetrahydrofuran. The reaction mixture, now purple-red, was stirred for four hours a t 50' tron-spin termsg are not often very important. Only s-type wave functions provide non-zero as in the preparation of (C5H&ReH.2 Sodium contributions to the Fermi contact term a t the borohydride (0.38 g., 10 mmole) was added, and nucleus. It has been shown that the contributions after stirring for four more hours a t 50', solvent of spin-polarized Is, Zs, and 3s orbitals to the Fermi was removed by vacuum distillation. Sublimation contact term can differ in sign.1°-12 Because of of the dry reaction mixture a t 55-60' (0.1 mm.), the competion between terms of differing sign, the yielded 60-80 mg. of extremely air sensitive golden value of the Fermi contact term is quite sensitive yellow crystals (I), m.p. 155' (corr.). More to the behavior of the d-electrons, for example, when product could be obtained from the reaction mixthe X atom is involved in chemical bonding." Thus ture only by redissolving the salts in a quantity the results for molecules other than CH3CH2Fin the of dried tetrahydrofuran, stirring for a few hours table indicate that the Jd electrons in Pb, T1, and a t 50°, followed by solvent removal and a new Hg; the 4d electrons iii S n ; and even the lone pair sublimation. It was possible to obtain from three in P(CH*CH3)3 may be involved in the chemical to five more crops of crystals each of about 30 mg., bonding of the ethyl group to atom X. The making total yield for a typical reaction from 150involvement of these additional electrons in the 200 xng. of I. The infrared spectrum for carbon disulfide ant1 chemical bonding not only could give rise to changes in magnitude and sign of the Fermi contact term, tetrachloroethylene solutions of I consisted mainly but also could provide an additional contribution (1) G . Wilkinson, F. A. Cotton a n d J. M. Birmingham, J . Inorg to the coupling, which of course could be opposite in & Nuclear Chent., 2, 95 (1956). (2) G. Wilkinson and J . hl. Birmingham, J . A m . Chem. Soc., 7 7 , sign to the contribution arising through the usual 3421 (1955). a-bond. (3) Consisting mainly of isotope PgTc, obtained from Oak Ridge The financial support of the National Science National Laboratories, Oak Ridge, Tennessee. (4) Cf.J. C. Hileman, D. K. Huggins a n d H. D. Kaesz, J . A m . Chem. Foundation, and the assistance of Professor F. G. A. 83, 2953 (1961). Stone in obtaining the sample of ethyl fluoride, Soc., ( 5 ) K. Knox, et al., i b i d . , 79, 3358 (1957), pentane (337 9 . ) was used are gratefully acknowledged. The computations a s pressure equalizing liquid in t h e autoclave (1300 ml. capacity) (7) M. Karplus, J. Chem. Phys., 30, 11 (1959). (8) J. A. Pople, dlolec. Phys., 1,216 (1958). (9) G. A. Williams a n d H. S. Gutowsky, J. Chem. P h y s . , 30, 717
(1959). (10) V. Heine, P h y s . Rev., 107, 1002 (1957). (11) R . E. Watson a n d A. J. Freeman, ibid., 120, 1125 (1960). (12) R E Watson and A . J. Freeman, ibid.. 120, 1134 (1960).
r a t h e r t h a n carbon tetrachloride which proved unsuitable for this purpose as i t reacted t o completion with steel a t 400' causing t h e Vycor reaction t u b e t o burst. (6) For this stage of t h e preparation, as well as for handling extremely air sensitive product d e s r r i t e d below, rigorously oxygen-free nitrugen, (obtained by scrubbing with a solution of tri-isobutylaluminun1 i n decane) i 9 recjiiirwl
