COMMUNICATIONS TO THE EDITOR
H6
I
H3
2
2371
H5
3
7
Figure 1. The nmr spectrum of the ring protons of diethyl(4,4'-dimethyl 2,2'-dipyridyl)nickel in a dimethoxyethane solution at 60 mc/sec.
abstraction from fully halogenated compounds, in particular halogenated methanes, as well as C&&Cla, CBHJ, n-C&I, and sec-C3H71. Di-t-butyl peroxide was used as thermal source of methyl radicals. Attempts by us3 to obtain similar quantitative results for ethyl chloride, neopentyl chloride, ethyl bromide, n-propyl bromide, and sec-propyl bromide were largely unsuccessful owing to complicating reactions resulting from hydrogen abstraction. The presence of hydrogen halide among the products also led us to suspect that because of facile reactions of the types CH3
+ HC1+
CHd
+ C1
CH3
+ HBr
CHI
+ Br
and In the same 'way, we synthesized diethyl(4,4'-dimethoxy 2,2'-dipyridyl)nickeI and carried out the nmr measurements of it. The data in Table I support the assignments described above of 11. From the comparison of the spectrum of I with that of 11, the assignments of the ring protons of I follows naturally. The chemical shifts of Ht, and Hg of I are probably near those of I1 because of the similarity of the structures of I and 11, and hence the doublet a t T 0.93 is assigned to Ht, and the quartet a t 7 2.45 to Hs. Consequently, the doublet a t T 1.95 is assigned to H3 and H4. As was pointed out by Castellano and Gunther12the high-field shift of He signal observed in is lacking in the specthe spectra of [Fe(di~y)3]C12~ trum of I due to the absence of the shielding effect of the adjacent ligand. We conclude, therefore, contrary to our previous presumption,' that the shielding effect of the nickel atom upon Ht, is not predominant. The high-field shift of H3of I might be due to a deviation from a complete cis coplanar structure of the two aromatic rings. This is also suggested by Castellano and Gunther.2
halogen atoms were largely replacing methyl radicals as the attacking species. We believe it important also to report that in experiments with di-t-butyl peroxide and ethyl iodide, explosions occurred when mixtures were frozen under vacuum to liquid nitrogen temperature. The reactions were carried out in a conventional static system a t 120-200", and in most cases there was an excess of alkyl halide over di-t-butyl peroxide. With alkyl chlorides, methyl chloride was only formed in trace amounts, although with the corresponding bromides methyl bromide was formed somewhat more readily. I n both instances, however, the nature of the products indicated that hydrogen abstraction was the dominant process, as noted by Tomkinson and Pritchard12and also by Alcock and Whittle4 for the reaction of trifluoromethyl radicals with methyl chloride. Typical product analyses for the reaction of ethyl chloride with di-t-butyl peroxide are shown in Table I.5 It may be observed that methane and ethylene are (2) S. M. Castellano and H. Gtlnther, J. Phys. Chem., 71, 2368 the major products. Tomkinson and Pritchard2 noted (1967). that ethylene is a by-product (ca. 0.5-la/, yield) of the (3) S. Castellano, H. Gtlnther, and S. Ebersole, ibid., 69, 4166 thermal decomposition of di-t-butyl peroxide, and (1965). DEPARTMENT OF INDUSTRIAL CHEMISTRY T. SAITO that when the peroxide is decomposed in the presence OF TOKYO M. ARAKI of large amounts of carbon tetrachloride, the amount of UNIVERSITY Y. UCHIDA ethylene formed is comparable to the ethane. ,We also HONGO, TOKYO, JAPAN A. MISONO observed a similar increase in the ethylene: ethane ratio as the initial concentration ratio of ethyl chloride to RECEIVED APRIL3, 1967
Abstraction of Halogen Atoms by Methyl Radicals
Sir: Recent reports on the abstraction of halogen atoms by methyl radicals in the gas phase's2 refer to
(1) D. M. Tomkinson, J. P.Galvin, and H. 0. Pritchard, J. Phys. Chem.,68, 541 (1964). (2) D. M. Tomkinson and H. 0. Pritchard, ibid., 70, 1579 (1966). (3) A preliminary report was given in Australian J . Chem., 18, 121 (1965). (4) W. G. Alcock and E. Whittle, Trans. Faraday SOC.,61, 244 (1965). (5) A. M. H o g g and P. Kebarle, J. Am. Chem. Soc., 86,4558 (1964)
Volume 71, Number 7 June 1067
COMMUNICATIONS TO THE EDITOR
2372
C2H&1+
Table I : Product Distribution from the Reaction of Di-t-butyl Peroxide with Ethyl Chloride Run
TemDerature Reaction time C2H6C1,initial pressure Di-t-BP, initial pressure Products
CHaCl HCl
no. 1
Run no. 2
189°C 8 min 45.4 mm 23.6 mm
163°C 25 min 38.3 mm 15.7 mm
20.2 mm 1.Omm 2.9 mm 1.Omm Trace
11.7 mm 0 . 5 mm 2 . 1 mm 0 . 5 mm Trace
a
a
C3H7
+ HC1-
CzH,
+ C1 (7)
C3Hs
+ C1
(8)
The nature of the products with other alkyl chlorides and bromides indicated comdicated reaction svstems of a similar nature. These studies have therefore been discontinued because of the difficulty in obtaining useful quantitative information from such complicated systems.
Not measured quantitatively. Its presence was tested for by a procedure similar to that used by Hogg and Kebarle.6
SCHOOL OF CHEMISTRY THEUNIVERSITY OF NEW SOUTH WALES SYDNEY, AUSTRALIA
K. D. KING E. S. SWINBOURNE
RECEIVED MARCH 27. 1967
di-&butyl peroxide was increased (see Table 11). However, we feel that in our experiments the ethylene is also produced from decomposing chloroethyl radicals C2HdCl+
C2H4
+ C1
Comment on “Electron Spin Resonance of
01W17, 017-018, and 018-016” by L. K. Keys
Correspondinglyl propene was probably via bromopropyl radicals with similar experiments using n-propyl bromide.
Sir; We wish to call in question number of statements in s, recent communication by on the electron resonance spectrum of gaseous 02. First, it is not the case that lines below 5500 gauss
~~
Table 11: Effect of Ethyl Chloride Concentration upon the Relative Production of Ethylene and Ethane at 163” [(CxHsCl)/ (Di-t-RP)1initial
0.4 1.6 2.4
Isobutylene oxide is one of the major products resulting from chlorine atom attack on di-l-butyl peroxide,6 but was not detected among our products. Conditions in our experiments probably favored chlorine atom attack upon the hydrogen atoms in the alkyl halides in preference to those on the di-&butyl peroxide. The fully halogenated compounds used in the experiments of Tomkinson and Pritchard2 would be inert to chlorine atom attack. Likely reactions resulting from methyl radical attack on ethyl chIoride are
+ CzH&l----f CH4 + CZH4C1 CH3 + c~HsC1 CHaC1 + C2H6 CHs + CH3 +C2He CH3
The Journal of Physical Chmiatry
(1) (2)
(3)
(at X-band frequency) have not previously been reported. Tinkham and Strandberg,2 in their classic papers on 0 2 , list no fewer than 35 lines between 1400 and 5500 gauss and interpret all of them with high accuracy in terms of 0l6-Ol6alone. Second, the formula E = g j/3HMj is quite inapplicable to the 0 2 molecule, for a number of reasons. Even if there were no zero-field splitting of the spin triplet, this formula would be inadequate because of off -diagonal magnetic field matrix elements which give rise t o a nonlinear Zeeman effect. However, as shown originally by K r a m e r ~ ,and ~ in more detail by Van Vleck4 and by Tinkham and Strandberg, the spinspin and spin-orbit interactions are extremely important. They split the triplet components of each rotational level, the J = N & 1 components being separated from the J = N component by about 2 cm-l. The J = N f 1 components are themselves not degenerate and the splitting between them to l cm-’ for different rotational levels) is sufficient for the (1) L. K. Keys, J . Phys. Chem., 70,3760 (1966). (2) M. Tinkham and M. W. P. Strandberg, Phys. 951 (1955). (3) H. A. Kramers, Z . Physik, 53,422,429 (1929). (4) J. H. VanVleck, Phys. Rev., 71,413 (1947).
Rev.,97,
937,
