COMMUNICATIONS TO THE EDITOR
308
characteristic (+ or -) amount Axl which we assume to be independent of the other substituents. In CHXYZ, the resulting difference in the 2s electron content a t the bottom of the wells is Ax Ay Az, which must be accommodated by a change in the common level a t the top of each of the four wells. This, by means of Eq. (7), leads to
1701. 83
THE REACTIONS OF ATOMIC CARBON WITH ETHYLENE
Sir: The reactions of atomic carbon with ethylene have been studied. Recoil Cll from a nuclear reaction was introduced into the gaseous reagent, and analysis made for the Cll-labeled radioactive products by techniques outlined previously. Kesults are summarized in Table I. Column I shows AX Ay + A9 = 4 [ a ~ ' ( C H x y Z )- (1/4)] (8) products obtained with pure ethylene, column I1 For monosubstituted derivatives, Eq. (8) re- with oxygen added as a radical scavenger, and duces to column 111 is representative of runs containing a large excess of neon to thermalize (;.e., remove AX 4[aH2(CH&) - (1/4)] (9) excess kinetic energy from) the carbon atom before which enables us to eliminate Axl Ay, and Az from reaction. Eq. (8) and obtain As with the alkanes previously reported,? the CXH'(CHXYZ)= [aa2(CHaX) - ( ~ / ~ ) ( Y H * ( C H-k' ) ] main products are highly unsaturated hydro[ ~ H * ( C & Y) (2/3)a~~((CHd)] carbons. The high yield of acetylene, in particular, probably results largely from the C-H [ ~ H Y C H J Z-) (2/3)a~*(CHd1 (10) And, finally, the relation between JCHand C Y H ~ , bond insertion process as postulated for the alkanes. in Eq. (6)) converts this to H&=CHz .-,CHZ + HCl1=CH
+
+
+
3
+
JcH(CHXYZ) = Tx
+ by + Sz
+
(1)
(11)
However, there are two significant differences between ethylenic hydrocarbons in general and saturated systems: (1) in the presence of 0 2 the CO yield is appreciably less with alkenes than with alkanes. This indicates the alkenes are more reactive. (2) The yields of products containing yields essentially the same equation as Eq. (6)) one more carbon atom than the reacting hydroafter which the analysis is identical. The formalism introduced above enables one to carbon are considerably higher with alkenes than alkanes. Thus about twice as much allene use experimental values of JCHto obtain not only with and methylacetylene form from ethylene, as do C Y Hbut ~ also a x 2 . The relation of these quantities propane and propylene from ethane. to parameters such as bund angles and lengths is The most obvious and satisfactory explanation under investigation and will be reported laterlo is that C atom can react of these observations along with details of the present work. I n addi- directly with the double bondthe to form a n-bonded tion, i t appears that substituent parameters obtained from the monosubstituted methanes can species. This intermediate then can rearrange to allenea be applied to J C H in substituted ethylenes. The Si2"H coupling has been observed in SiH4 and in a number of derivatives." However, our :C" 3. HzC=CHz +HzC-CHz +HzC=C"=CHz inspection of the results shows that the substituent y 1 1 (11) effects are nQt additive. Nonetheless, the deviations from additivity are systematic in that for the (In the case of higher alkenes, the corresponding halosilanes, the deviations follow the sequences : substituted allene largely isomerizes to a conSiHXa > SiHzXz; and F > C1 > Br > I. Several jugated diene.) We are presently attempting to factors can contribute to these effects, of which the confirm this mechanism by showing that C" most likely appears to be the use by Si of 3d appears in the central position of allene.4 orbitals, the importance of which is suggested also The intermediate formed by this double bond by the dependence of JHHupon the H S i - H addition also has sufficient energy to decompose angle.11912The inclusion of 3d orbitals in Eq. (5) with bond rupture. It may thus contribute to the may prevent Eq. (6) from applying to J S i H , yield of acetylene-Cl1 from ethylene. and also it could affect Eq. (7). This presents The cyclopropane observed is consistent with the the attractive possibility of learning something previous hypothesis that a few per cent of the C about the d hybridization from the deviations, atoms react by H atom pick-up from hydrocarbons2 to compensate for the more difficult nature of to form C11H2. This will react in a characteristic the analysis. (1) Contribution No. 1685 from Sterling Chemistry Laboratory, which is exactly the form of additivity observed by M a l i n ~ w s k i . ~A two-center molecular orbital of the form fi cl(lsH) f ce(2sC) f C'd2p0,) (12)
hTOYES CHEMICAL LABORATORY UNIVERSITY OF ILLINOIS
Yale University.
We are indebted to the operating staff of the Yale
H. S. GUTOWSKY University Heavy Ion Accelerator for their assistance. Invaluable URBANA,ILLISOIS CYNTHIA S. JUAN discussions with Professor William Doering of Yale University, are gratefully acknowledged. This work was sponsored by the Atomic RECEIVED DECEMBER 15, 1961 (IO) C. S. Juan and H. S. Gutowsky, to be submitted to J . Chcm.
Phys. (11) E. A. V. Ebsworth and J. J. Turner, J . Chem. Phrs.. in press; we are indebted to the authors for making their results available t o us before publication. (12) J. C. &hug and H . S. Gutowsky, unpublished results.
Energy Commisssion. (2) C. MacKay and R. Wolfgang, J . Am. Chcm. Soc., 83, 2399
(1961). (3) W.R. M o a e and H. R . Ward, J . Org. Chem., 26, 2073 (1960). (4) Note that a certain amount of allene with terminal C11, resulting from the C-H bond insertion mechanism (see ref. Z ) , also may be expected.
TABLE I ATOMICc" WITH ETHYLEXE YIELDS AS 7 0 O F TOTAL GASEOUSACTIVITY Each yield represents the average of at least three runs. Errors indicated are a measure of reproducibility. C, or lighter hydrocarbons not mentioned c" LABELEDPRODUCTS O F REACTION OF
C" Product
309
COMMUNICATIONS TO THE EDITOR
Jan. 20, 1962
Composition of reacting gas (Total press. 1 atm) CrH4 (4.5%) 0 1 (0.2%) CtHl (98.5%) Ne C1H6 Oz (1.5%) (95.3%)
Carbon monoxide' 0 . 9 0.3 9.8 i 2 . 0 24 5 2 . 0 f 1.0 ... 1.5 f 0.5 Ethylene Acetylene 38.0 f 3 . 5 36.6 f 1 . 5 31 f 5 3 . 2 f 0.7
