1237
NOTES
tions (0.5%) diminish the radiolytic yield of exchange from Gcxeh= 9.,5 to 6.0 and 7.Fj2 for 0 2 and Hz, respectively. The sodium mirror experiment shows that traces of oxygen present in the nitrogen do not affect Grxch a t all. The effect of oxygen and hydrogen may be explained by their action as scavengers of nitrogen atoms. The possibility of reaction between O2 or H2 and Kz*is excluded by their low concentration and the limited lifetime of Nz*.
+ +NOz N + Hz +NH2 N
0 2
(8) (9)
Reactions 8 and 9 compete with reaction 6, the bimolecular recombination of nitrogen atoms. From their effects on (3,,,1, the specific rate of reaction 8 seems to be about twice that of reaction 9, in other words, oxygen is a superior scavenger for N atoms. Preliminary experiments with NO as scavenger showed this gas to be about twice as effective as oxygen. The radiation-induced isotope exchange in nitrogen is the only known example of a gas phase radiolytic isotope exchange reaction which proceeds without any chemical change by a nonchain, mechanism. Hydrogen-deuterium exchange is a chain process, so are also the oxygen-oxygen and the CO2-CO2 reactions. The latter two reactions are accompanied by the formation of radiolytic products, O3 and CO 02, respectively. Other exchange reactions like C@CO and NHrNH3 are even more complex as far as the mechanism and radiolytic products are concerned. As the behavior of this system is predictable up to complete isotopic equilibration, it may be suitable for the dosimetry of radiation over a wide range of doses. As nitrogen-15 has a very low cross section for neutrons, mixtures of N216*16 with N214,14may be used for y-dosimetry in the presence of neutron fluxes.
+
Specific Rearrangements in the Mass Spectra of Short Chain Esters
by D. R. Black, W. H. McFadden, and J. W. Corse Western Regional Research hboratory, Western Utilization Research and Development Division, Agricultural Research Service, U . S. Department of Agriculture, Albany, California (Received October 1 1 , 1963)
Previous studies of the mass spectral rearrangement processes of aliphatic esters have utilized both
series of esters and deuterium-labeled compounds. Information concerning the proton-transfer processes has been obtained by Sharkey, et aL,l and Colomb, et a1.,2from the study of tho mass spectra of series of , ~ the high short chain esters and Beynon, et ~ l . from resolution spectra of series of esters. M ~ l a f f e r t y , ~ Colomb,2 and Godbole arid Kebarle5 have used deuterated compounds to indicate the availability of the protons along the carbon chain in the transfer processes. An interesting rearrangement involving a cyclic intermediate with the resultant loss of a hydrocarbon fragment from the center of the molecular ion was detected by Ityhage and StenhagenGP8and Guriev and T i k h o r n i r o ~in~ their ~ ~ ~ studies of a series of long chain methyl esters. Subsequently Dinh-Nguyen, et uZ.,’~ using deuterated esters established that the group most frequently lost in this process originated next to the carbonyl group. However, these rearrangements are still not fully understood, and this study on selectively deuterated butyl acetates and propionates was carried out to clarify these processes.
Experimental Sample Preparation. Synthesis and nuclear magnetic resonance (n.m.r.) analysis of 4-deuterio-lbutanol and 3-deuterio-1-butanol have been described. l 2 Synthesis of 3-deuterio-l-butanol yielded 4-deuterio-2-butanol as a by-product. To obtain 1,1-dideuterio-1-butanol,the acid chloride was reduced with LiA1D4.l3 To synthesize l,l,l-trideuterio2-butanol, CD31 was added to magnesium and the CD3MgI treated with propionaldehyde.’4,*5 (1) A. G. Sharkey, Jr., J . L. Shults, and R. A. Friedel, Anal. Chem.,
31, 87 (1959).
(2) H. 0. Colomh, R. D . Fulks, and V. A. Yarborough, 10th Annual Meeting, ASTM Committee E-14, New Orleans, La., June, 1Y62. (3) J. H. Reynon. R. A. Saunders. and A. E. Williams, Anal. Chem., 33, 221 (1961). (4) F. W. McLafferty, ibid., 31, 82 (1959). (5) E. W. Godbole and 1’. Kebarle, Trans. Faraday S o c . , 58, 1897 (1962). (6) R. Ryhage and E. Stenhagen, Arkiv Kemi, 15, 332 (1060). (7) R. Ryhage and E. Stenhagen, ibid., 15, 291 (1960). (8) It. Ityhage and E. Stenhagen, ibid., 13, 523 (1959). (9) M. V. Guriev and M. V . Tikhomirov. Zh. Fiz. Khim., 32, 2731 (1957). (10) M . V. Guriev, M. V. Tikhornirov, and N . N. Tunitxky, Dokl. Akad. Nauk SSSR, 123, 120 (1958). (1 1) N. Dinh-Nguyen, R. Ityhage, S. StallberK-steiihageri, and E. Stenhagen, Arkiv Kemi, 18, 393 (1962). (12) W. 1%. McFadden. D. It . Black, and J . W . Corse. .I. Phys. Chem., 67, 1517 (1963). (13) R. F. Nystrom and W. G . Brown, J . A m . Chem. Soc., 69, 1197 (1947). (14) N. L. Drake and G. B. Cooke, “Organic: Syntheses,” Coll. Voi, 11, John Wiley and Sons, Inc., New York. N. Y.. 1943, pp. 4 0 6 407.
NOTES
1238
Acetic anhydride was obtained commercially, and the acetyl and propionyl acid chlorides were made by refluxing the desired acid in phthaloyl chloride and distilling over the acid ch1oride.l6 High purity commercial CD3COODwas used to prepare CD3COC1. All esterifications were carried out by adding an excess of either anhydride or acid chloride to the desired alcohol. The excess was subsequently hydrolyzed to the acid and then neutralized with carbonate. The ester was taken up in ether, dried, and then purified using a Carbowax 20M g.1.c. preparatory column. Mass Spectrometry. A Bendix Time-of-Flight mass spectrometer (T.O.F.) using continuous ionization produced the mass spectra. The electron accelerating voltage was 70 e.v. Temperature was not measured in the ionization chamber but the source end of the mass spectrometer was 100 f 5'. The mass spectra obtained are presented in partial form pertaining to the rearrangement processes discussed. The complete mass spectra will be submitted to the ASTM File of Uncertified Mass Spectra. Isotopic Purity. The isotopic purity of compounds was checked by n.m.r. and, where feasible, by mass spectra of the deuterated alcohol or ester. Only compounds whose isotopic purity was better than 95% in the labeled position are reported. No corrections were made for the isotopic impurities detected by n.m.r., and no corrections were made for natural isotopic species. In all cases the conclusions are based on observed effects that exceed any contributions from isotopic impurities.
Table I : Partial Mass Spectra of Deuterated 1-Butyl Acetate and 1-Butyl Propionate
c
8 8 116
m/e
86 87 88 89 90 100 101 102 103
_-0.31 0.47 0.05
0.34 0.02 0.02 0.44
+
The Journal of Physical Chemistry
117
ID 117
I
! 119
! 130
132
---.
Total ionization, yo------
0.76 0.08 0.04
0.79 0.07 0.03
0.33 0.47 0.21 0.44 0.05
0.19 0.04 0 03 0.42
Table I1 : Partial Mass Spectra of Deuterated 2-Butyl Acetates
d
c c c c CDo I I I =o c=o c=o c=o c=o c=o
A-c
Results and Discussion The principal features of the mass spectra of the deuterated esters are, for the most part, those that would be predicted from previous studies of the undeuterated esters. l f 3 However, certain peaks in the former spectra, in spite of their low intensities, give new information on the rearrangement processes of these esters. One of these rearrangements is the wellknown transfer of two protons from the butyl group 2H)+ ion. Anin the formation of the (CH,COO other rearrangement is the apparent loss of a CHzO fragment from the center of the molecule with retention of the two end groups by the ion. A third rearrangement, observed with 2-butyl acetate, seems to involve an unexpected rearrangement in the formation of the apparently simple C&H,O+ion. The partial spectra of the deuterated 1-butyl acetates and 1-propionates in the mass range 86-90 and 100-103 (Table I) and the partial spectra of the deuterated
p"
118
c
A
116
d
d
L c A-c
d
d
hD-ch-cDoC-c
& D L A D A 117 117
A A 117
119
oI
h A119
-_ Total ionization, Yo-----m/e
Iona
72 73 74 75 76
C4H80+ C4H90+
MagMagT.O.F.b T.O.F.b netiocrd netiocBd T.O.F.b T.O.F.b
0,46 2.55 0.18
0.43 2.30 0.14
0.34 1.94 0.15
0.34 0.16 1.23
0.48 1.60 0.12 0.12 1.75
0.77 0.60 0.47 1.00
5 See ref. 1. b T.O.F. = Bendix Time-of-Flight mass spectrometer. c Magnetic = Consolidated Electrodynamics Corporation Type 21-103C. d F. W. McLafferty and M. C. Harnming, Chem. Ind. (London), 42,1366 (1958).
(15) J. D. Roberts, W. Bennett, R. E. McMahon, and E. W. Holroyd, Jr., J . Am. Chem. SOL, 74, 4283 (1952). (16) J. D. Cox and H. S. Turner, J . Chem. Soc., 3176 (1950).
NOTES
2-butyl acetatef, (Table 11) give evidence of these rearrangements. Both the T.O.F. data and that obtained with the magnetic instrument (Table 11) give evidence for the second rearrangement mentioned above. The ions of interest are those that result from loss of 30 m.u. from the molecular ions of the undeuterated 1-butyl esters a t mass 86 and mass 100 (Table I) and the one that results from loss of 44 m.u. from the holecular ion of undeuterated 2-butyl acetate a t mass 72 (Table 11). The mass spectra of those compounds deuterated in the 3 or 4 positions of the butyl groups show that the ionization normally observed at, masses 72 or 86 is absent, indicating retention of the terminal ethyl group. However, in the spectra of esters with deuterium on the C-1 of the 1-butyl group or on either the C-1 or C-2 of the 2-butyl groupl no shift of the ionization is evident a t masses 86 or 100 (Table I) or a t inass 7%(Table 11) thus indicating loss of those carbons. Furthermore, if the acetyl group is completely deuterated, a corresponding mass shift of 3 m.u. in the spectra occurs, although this is somewhat speculative in the spectrum of 2-butyl acetate. Evidently this mode of ionization results from cyclization of the molecular ion followed in each case by loss of the group immediately adjacent to the carbonyl group: CHzO from the 1-butyl esters and CH3CH0 from the 2-butyl acetate. This is contrary to the usual suggestion that loss of 30 or 44 m.u. is due to loss of C2Hs or C3Hs. One possible mechanism for this rearrangement would be !;Ha+
CHS
\
CHs
Other cyclic int,ermediates are also possible. Guriev, l o Ryhage and Stenhagenlegand Dinh-Sguyen, et al.," detecteid similar rearrangements in the mass spectra of long chain esters. The possibility of cyclical intermediates h,as been suggested as an explanation of observations in the mass spectra of many other compounds. 2,12, 17,18 The ionizations observed a t mass 87 in the spectrum of undeuterated 1-butyl acetate and a t mass 101 in the et al. ,9,
1239
-
spectrum of 1-butyl propionate are known to be due to loss of CzH6. from their high resolution ~ p e c t r a . ~ The data in Table I confirm this and indicate that reactions occur with very little hydrogen-deuterium exchange. In addition to the above rearrangement, the spectra of the deuterated 2-butyl acetates (Table 11) indicate that an unexpected exchange process occurs prior to the formation of the mass 73 ion in the deuterated compound. From high resolution mass spectra3 this ion is known to have the formula C4H90+. The mass spectral data of the esters in which the 2, 3, or 4 position of the 2-butanol has been deuterated would seem to confirm the expectation that this ion occurs by a simple bond break. However, data obtained from the ester deuterated on C-1 of the 2-butanol show the ionization due to this mode in two places: approximately one-half the ions retain the deuterium (mass 76) and one-half lose the deuterium (mass 73). Since very little ionization is observed a t masses 74 and 75, H-D exchange cannot explain this observation. Apparently an exchange of the methyl groups is occurring, by some mechanism. The mass spectra of CH3COOCH(CD3)CD2CH3 and CHsCOOCD (CD3)CD2CH3 also confirm this observation but the data for these compounds are not presented because of uncertain chemical purity. As shown in the last column of Table 11, deuteration on the acetyl moiety is also only partly lost to give the mass 73 ion and partly retained to give the mass 76 (C4HeD30+) ion. (In this case there appears to be some H-D exchange leading to the m/e 74 ion and, in addition, the ion formed by loss of CH3CH0 presumably occurs a t m/e 75 as previously discussed.) Thus, the formation of the CdH90+ ion apparently involves a complex intermediate in which the acetyl methyl and the 2-butanol methyl (1 position) become indistinguishable. The C4H90+ ions could be formed by a variety of processes including formation of part of the ions by a simple mechanism; cyclization followed by relatively simple H--D rearrangements, or even rearrangement of an entire CH3 group onto an adjacent oxygen. Further study seems to be indicated. I n the rearrangement process resulting in the formation of the ( c H 3 c o 0 2H)+ ion, the origin of the two protons of 1-butyl acetate is of interest and is indicated in the mass spectra of the deuterated esters (Table 111). The ionization resulting from transfer of the protons is seen at mass 61 in the spectrum of the
+
~
~~~~~~~
(17) W. H. McFadden, 11. Lounsbury, and A . L. Wahrhaftig, Can. J . C h r m . , 36, 990 (1958). (1s) J. H . Beynon, I t . A. Saunders, A . Topharn, and A. E. Williams, J . Phy8. Chem., 6 5 , 114 (1961).
Volume 68, Number .5
Maw, 196k
NOTES
1240
undeuterated ester, and that ionization resulting from transfer of the deuterium is seen a t mass 62 in the other spectra. The mass 62 peak in the second spectrum represents only 8% of the total ionization due to this process and shows that the availability of the protons on the terminal methyl group is less than staJistical. In the third spectrum the mass 62 peak is more intense; it makes up 37% of the total ionization due to the rearrangement process, indicating that the protons on the carbon 6 to the carbonyl group are favored. The mass 62 peak in the last spectrum represents only 16% of the total intensity of the mass 61 and mass 62 peaks. This result indicates that direct transfer of a, proton to the adjacent oxygen is not highly favored, a, result also indicated by the data of hlcLafferty4 on deuterated 2-butyl acetate.
In addition, data exist for deuterated ethyl acetates which indicate that deuteration on the C-1 of the ethanol5or the C-219leads to a nearly statistical selection of deuterium in formation of this rearranged ion. Thus, it is possible that for some molecules the twoproton transfer process proceeds by a mechanism different from that proposed by M ~ L a f f e r t y . ~The present data suggest a selective transfer of one proton from C-3 followed by a random selection of the second proton from the other protons in the alcohol moiety. Such a random selection will always occur if the second transfer proceeds a t a rate significantly less than the rate of H-D exchange within the alcohol group. Acknowledgment. The authors20 thank Dr. R. E. Lundin for n.m.r. analyses of the deuterated esters. (19) Unpublished data of authors.
(20) Reference to a company or product name does not imply approval or recommendation of the product by the U. S. Department of Agriculture to the exclusion of others t h a t may be suitable.
Table 111: Effect of Deuteration on the Acetate Rearrangement Peaks of 1-Butyl Acetate C
L
I
O
C I b=O I
C
C
c-0
A==0
I
I
I I
0
c:
(3 I
C
t:I
62 63
X"
CD
r2 A I
C
Ionization. %
m/e
59 60 61
c:I
0.08 0.16 5.42 0.16 0.05
0.14 5.09 0.48 0.08
0.15 3.45 2.03 0.07
0.10 5.14 1.01 0.10
The 2-monodeuterio-I-butyl acetate was not synthesized but the availability of this hydrogen for the rearrangement can be surmised. As shown above, the deuterium on the dideuterated C-1 and the monodeuterated C-3 and C-4 are available for transfer 16, 37, and 8% of the time, respectively, for a total of 61%. The second two values would be considerably greater if each position were fully deuterated (approximately 37y0 x 2 and 8% X 3); consequently the transfer of a proton (deuteron) from the C-1 would not seem to be significant. These results indicate that in this rearrangement of the 1-butyl acetate the protons on C-3 of the butyl group participate to a greater extent than do those on the C-1 or C-2, contrary to the observation of Colomb, et al., from the mass spectra of deuterated hexyl butyrate and valerate. The Journal of Physical Chemistry
Long-Range Metal-Proton Coupling Constants i n Vinyl Metallic Compounds
by S. Cawley and S. S. Danyluk Department of Chemistry, University of Toronto, Toronto 6 , Canada (October l d , 1963)
Metal-proton spin-spin coupling constants for metals with spin l/z have shown several interesting features in compounds of the type (C2H6),X.' In all cases, except the fluoro compound, vicinal coupling constants are of greater magnitude than geminal couplings and are of opposite sign. For ethyl fluoride the absolute magnitudes are reversed with J c H ~ - -> F JcH~--F and the relative signs are identical. Several mechanisms, including contributions arising from electron-orbital interaction2 and involvement of d-electrons in the C-X bond1 in addition to Fermi contact interaction, have been proposed to account for these coupling constants. Recently Maher and Evans3 interpreted long-range thallium(TlZ06)-protoncoupling constants qualitatively in terms of a Fermi contact interaction arising from a large effective nuclear charge on the thallium atom. A similar coupling mechanism was suggested for other metal alkyls.a (1) S. L. Stafford and J. D. Baldeschwieler [ J . Am. Chem. Soc., 83, 4473 (196l)l gave a summary of metal-proton J values for ethyl
derivatives. (2) P. T. Narasimhan and M. T. Rogers, J . Chem. Phys., 34, 1049 (1961).
