Mass Spectra of Ethyl N-Phenylcarbamate and Ethyl N-Ethylcarbamate CARL P. LEWIS' Olin Research Center, Olin Mathieson Chemical Corp., 275 Winchester Ave., New Haven 4, Conn.
b The mass spectrometric fragmentation of ethyl N-phenylcarbamate and ethyl N-ethylcarbarnate have been investigated. With the aid of the spectra of various deuterated analogs of these compounds, it is possible to identify many of the fragments formed by electron bombardment. Rearrangement ions are plentiful, and a skeletal rearrangement with the elimination of carbon dioxide appears to be responsible for some of the observed ions. This information may be used to describe the general mass spectrometric behavior of aromatic and aliphatic N-substituted carbamates.
For example, the present study characterizes a mode of skeletal rearrangement, compares the relative influence of nitrogen and oxygen upon certain types of fragmentations, follows proton migration during rearrangement processes, and shows that an obvious cleavage does not necessarily account for an observed ion. These results are not limited to ethyl N-phenylcarbamate, ethyl ATethylcarbamate, or t o calbamates in general; they are of such a nature that they must be borne in mind during the interpretation of the spectra of many types of unknown compounds. EXPERIMENTAL
Undeuterated ethyl Ar-phenylcarthe mass spectrobamate and ethyl N-ethylcarbamate were metric behavior of various subprepared by reacting anhydrous ethyl stituted carbamates, a number of alcohol with phenyl- or ethyl isocyanate in ether which had been previously intense, characteristic peaks were obsaturated with gaseous hydrochloric served. To verify the assignment of acid. The majority of the impurities these peaks, and in some cases t o were subsequently removed by extracidentify them in the first place, it betion with dilute aqueous hydrochloric came necessary to examine selected acid and the organic layer containing compounds in some detail. For this the carbamates was separated and purpose, ethyl N-phenylcarbamate and warmed to evaporate the ether. Ethyl ethyl N-ethylcarbamate were chosen as N-phenylcarbamate was purified by typical aromatic and aliphatic N-subrepeated recrystallization from hexane; ethyl N-ethylcarbamate was purified by stituted ethylcarbamates. To elucidate vacuum distillation. The ds-carbathe fragmentation of these two commates, Ph NHCOOC2Ds and CzHbpounds, their spectra were compared NHCOOC2D5, were similarly prepared with those of the following deuterated from C2DsOH,. The four corresponding analogs: Ph NDCOOCzHs (Ph = carbamates w t h deuterium substituted phenyl); Ph NHCOOCtDs; Ph NDCOonto the nitrogen were not prepared as OCaDa; CeHaNDCOOC,Hs; GHs such, but rather, the inlet system of the NHCOOC2Ds; and CZHKNDCOOC~DK.mass spectrometer was saturated with The results presented in this report D20, and they then were formed when the "-carbamates were introduced specifically describe the fragmentation into the instrument. of ethyl N-phenylcarbamate and ethyl Saturation of the entire inlet system N-ethylcarbamate. with DzO was carried out just prior to Very few detailed mam spectrometric the admission of each carbamate. studies of specific compounds have apDuring the saturation procedure, the peared in the literature. However, sample reservoir was allowed to remain there is information to be gained from a t room temperature, but the rest of the such studies, for the significance of the system was heated to the temperatures results may go well beyond elucidating which were to be utilized during the subsequent determination. A small drop the behavior of the compounds under of D 2 0 was placed into the sample consideration. Not only is a knowlreservoir and allowed t o volatilize edge about a particular compound useslowly into the evacuated expansion ful in describing the spectra of volume until the peak monitor indicated structurally similar materials, but this that a significant pressure had been knowledge may reveal basic principles achieved. The intensities of the peaks of mass spectrometric fragmentation. a t m/e 18 and m/e 20 were compared, and, if their relative ratio indicated that a significant amount of HzO was present, 1 Present address, School of Medicine, the expansion volume was evacuated, The Johns Hopkins University, 725 N. D 2 0 was readmitted, and the relative Wolfe St., Baltimore 5, Md.
D
176
URINO A STUDY of
ANALYTICAL CHEMISTRY
ratio was again examined to determine residual H2O. Three or four such flushes were usually sufficient for the virtual elimination of H20. At the conclusion of deuteration experiments, D20 was similarly removed by repeatedly (10 or 12 times) flushing H2O through the system. Once saturation with DzO was considered to be complete, the sample reservoir mas dried and the carbamate was introduced in the usual way. Exchange of deuterium for active hydrogen appeared to arrive a t an equilibrium value very rapidly, and the extent of deuteration rcrnaiiied unchanged over long periods of time. In this m y , an 80 to 95% exchange could be effected. The per cent deuteration was calculated from the molecular ion regions, verified a t other locations in the spectrum, and the spectrum of the pure N-deuterated carbamate was derived by deducting the small contribution of the remaining "-carbamate from the total record. The spectra were obtained with a Consolidated 21-103C mass spectrometer equipped with a glass-gallium heated inlet system. The heated inlet (13) was a modification of the system devised by Lumpkin and Taylor (14). Unless otherwise noted, instrumental conditions were as follows: ionizing voltage of 70 volts, ionizing current of 10 pa., ion source temperature of 270' C., heated inlet temperature of 100'
c.
RESULTS
The spectra of the various X-phenylcarbamates are shown in Figure 1. Phenylisocyanate is formed from these compounds by a slow thermal decomposition; thus, its spectrum is presented in Figure 1E. The spectra of the ethyl N-ethylcarbamates and the corresponding ethylisocyanate are shon-n in Figure 2. The rate of phenylisocyanate formation from ethyl iYphenylcarbamate increases markedly with increasing temperature. At 100' C. this rate is rapid enough to have an effect on the sizes of the carbamate peaks to which the isocyanate and the accompanying ethyl alcohol contribute. Ethyl S-ethylcarbamates are more stable a t 100' C , and a significant increase in peaks resulting from ethyl isocyanate and ethyl alcohol generally is observed only at higher temperatures or after the sample has been a t 100' C. for
15 to 30 minutes. Isocyanate and alcohol appear to be the only products of thermal decomposition. A number of inteise rearrangement peaks are present n the carbamate spectra. In fact, rearrangement accounts for almost all of the high mass peaks, including the base peak, in the spectra of the aromatic compounds. For clarity of pres3ntation and discussion, the fragmer ts believed t o be responsible for the iinportant peaks in the two undeuteratcd compounds are schematically summarized in Tables I and 11. In those cases where there is some indication thal one fragment is produced from another of higher mass, the prewmed sequence is so indicated. However, the lack of metastable peaks or other evidence dsually prevented such a correlation, and most of the fragments are simp y represented as originating from the molecular ion.
93
29
A : PhNHCOOC,H, M W 165
'p"
60-
k
lM
xl 0 137
119
120: 0
I
J
I~I,J,
.I~L
111111
l.l/ll.
I
I
I
1
107
I
I
DISCUSI,ION
Molecular Ion Regions. All of the carbamates described in this report produce a n obvious molecular ion. ')1 01 Recombination peaks a t (M elsewhere cannot be detected, and the intensities of the (-11 1)+and ( N 2)+ peaks in the spectra of the undeuterated compounds agree with those to be expected from theoretical isotopic ratios. Thus, the extent of deuteration of the other carbamaies readily may be calculated from th: molecular ion regions. The essential absence of a (11- 1)+peak in the spectrum of Ph XHCOOCzH5 probatily indicates that the corresponding peaks shown in the spectra of Ph NHC'OOC2Db and P h h-DCOOC2D5 are du3 to a slight contamination (3%) by I'h NHCOOCZHD4 and Ph NDCOOCJIDl, respectively. Such a contamination, also reflected in the 107-109 regions in the spectra of these same compounds as well as in the 106-108 regions in spectra of their N ethyl analogs, would s s m to be due to a small amount of CJIDaOH originally present in the C2D&H used for the preparation of the deuterated carbamates. Ethyl Ions. The low m/e region of the spectra of the ethyl N-phenylcarbamates and ethyl N-ethylcarbamates generally agrees withexpectations based upon the spectra of structurally similar compounds. The ethyl ion a t mass 29 in the undeuterated materials is a frequent fragment of ethyl esters ( 1 , 8, 16). The fact that most of this peak moves up to 34 in the d6- and d6-c%rbamatesreveals that most of it is arising from the ethyl group originally bound to oxygen. It is interesting to note that the 27 peak, particularly in ethyl N-phenylcarbamate, is a130 derived from this ethyl group as is indicated by its displacement to 30 in the dg- and d6.compounds.
+
+
+
E : PhNCO MW 119 60.
9.1
Figure 1 . Mass spectra of ethyl N-phenylcarbamate, deuterated analogs, and thermal decomposition product, phenylisocyanate All peaks above m/e 25 which a r e
> 1%
Amine-Like Ions. Fragments of mass 92 and 93 from ethyl N-phenyl carbamate and 30 and 44 from ethyl N-ethylcarbamate are comparable to fragments derived from amides (IO), amines (1, 6) and ethyl esters of amino acids ( 5 ) . The deuterated analogs of ethyl AT-phenylcarbamate reveal that most of the 92 peak from the undeuterated material is formed independently rather than by a proton loss from the rearrangement ion of mass 93. If the latter had been the case, the spectra of Ph NDCOOCzHs and Ph NHCOOCzDa would have been quite similar in this region. It may be seen that the base peak a t 93 moves up by one mass unit when either the nitrogen or the ethyl
of intensity of largest peak are shown
group is deuterated. It moves up by two mass units when both groups are deuterated simultaneously (Figure 1). This ion then possesses the nitrogen's proton as well as one proton from the ethyl group and is thus consistent with the schematic structure of Ph-NH2+. By similar reasoning, the 30 and 44 peaks in the spectrum of ethyl N ethylcarbamate may be shown to be compatible with a rearrangement of a proton from the ethyl group bound to oxygen to give CH2NH9+ (mass 30) and a direct fragmentation to yield CHsCHzNH+ (mass 44). Loss of 15 M a s s Units. Loss of methyl from the ethyl group bound t o the oxygen with retention of the VOL. 36, NO. 1, JANUARY 1964
177
charge on the remaining portion of the molecule is not a significant mode of fragmentation. There is an intense (M-15) + peak in the spectrum of ethyl N-ethylcarbamate, but the deuterated analogs show that this is arising almost exclusively from fragmentation of the ethyl group bound to the nitrogen. The relative importance of the two possible modes of methyl loss may be estimated directly from the spectrum of CH3CH2NHCOOCD&D3. Here, the loss of CH, from the nitrogen side of the molecule would produce an ion of mass 107 while the ion produced by fragmentation 0 to the oxygen atom would give a fragment of mass 104. The peak a t 104 mass units is too weak to appear in Figure 2C, however, in the original record the ratio of 107 to 104 is about 80 to 1. Since the carboncarbon bond in CD2-CD2 is somewhat easier to rupture than the same bond in CH2-CHz (Y),the p-cleavage and charge stabilization by -NHmay be concluded t o be somewhat more than 80 times as frequent as comparable pcleavage and charge stabilization by -0during the hagmentation of undeuterated ethyl N-ethylcarbarnate. Biemann (3) has similarly shown that cleavage to nitrogen is more favored than the comparable cleavage 0 to oxygen. Loss of 28 Mass Units. The loss of C2H4, 28 mass units, is a common occurrence with ethyl esters (8, 16), and this loss, or the analogous loss of 32 mass units from the dr or de-carbamates, may be seen in Figures 1 and 2. An informative comparison may again be found in the spectrum of CsH5NHCOOGDs. By completely comparable rearrangements, the elements of ethylene may be lost from either side of the carbonyl group. The relative effects of -NHand -0may be compared directly from the intensities of the peaks at 94 and 90 as is indicated by the following representation:
OD / CH3CH2THC
+
B
178
ANALYTICAL CHEMISTRY
(mass 90)
l o o - 29
60
-
i3~
A : CZHSNHCOOCZHS MW 1 1 7
44
72 20
-
I
Figure 2. Mass spectra of ethyl N-ethylcarbamate, deuterated analogs, and thermal d eco m p o s i t i o n product, ethylisocyanate
aa
'
58 I'
II
60:
'
' I '
102
I,
M
45
134
(111
!
4f
72 I.
2ol
I...l.
I
M
63
All peaks m/e 25 which are > I % of intensity of largest peak a r e shown
107
. I .
I
73
100
While the methyl loss described above was found to occur almost exclusively from the nitrogen side of the molecule, this ethylene loss occurs almost exclusively from the oxygen side of the molecule. The ratio of 90 to 94 in the spectrum of C ~ H ~ N H C O O C is ~ Dabout E 75 to 1; again, the peak corresponding to the less favored fragmentation-Le., 94-is not of sufficient intensity to have appeared in Figure 2C, but it is distinctly present in the original record. Since the C-D bond is somewhat stronger than the C-H bond (9, 17), deuterium should rearrange with a little more difficulty than a proton. Thus it may be concluded that, during fragmentation of undeuterated ethyl N ethylcarbamate, charge retention and ethylene elimination from the ester-like oxygen atom is somewhat more than 75
E : CZHsNCO MW 71
times as frequent as charge retention and ethylene elimination from the amide-like -NHgroup. Biemann (4) has drawn similar conclusions about this type of fragmentation. It may be mentioned in passing that the only significant metastable peaks in the spectra of ethyl N-phenylcarbamate and ethyl N-ethylcarbarnate correspond to this elimination of the elements of ethylene from the molecular ion. Loss of 29 Mass Units. An examination of Figures 1 A and IC reveals a rather surprising fact. Although ethyl ions produce an intense peak, the loss of 29 mass units from P h NHCOOC2H6is not due t o the simple loss of the terminal ethyl group. Such a direct cleavage would produce a peak at 136 from both P h NHCOOCzHs and P h NHCOOC2Ds, b u t
136 is completely absent in the spectrum of the d5-compound. Instead, the 136 peak is clearly moved up by one mass unit signifying that this fragment retains one deuterium atom from the departing ethyl group. The spectrum of Ph NDCOOCzH5poinis out this same fact. I n this case, some of the deuterium is lost as is shown by the persistence of the 136 peak. The spectrum of Ph NDCC1OC2D6is further illuminating for peaks are now found a t both 137 and 138. The 137 peak corresponds to the loss of CzD4 plus the deuterium on the nit rogen; however, the presence of a pe,tk at mass 138 necessitates the loss of a ring proton. From those data, it seems reasonable to conclude that the normal loss of 29 mass units from undeuterated ethyl N phenylcarbamate is du? t o the elimination of ethylene followed by either the elimination of a proton from the ring or the nitrogen. Beynon (2) has suggested a mechanism fo- the elimination of a ring proton in somewhat similar compounds, but in view of the lack of revealing data, such :t loss is simply represented by "Cg+Hd" in this presentation (see Table I). The spectra of the ethyl N-ethylcarbamates shows a rather similar pattern except that in these cornpounds it is the nitrogen proton or deLterium which is not lost (compare Figures 2A and B or 2C and D). As is revezled by the presence of a peak a t 90 in Figure 2 0 , there is some loss of a proton from the nitrogen side of the mcdecule; this is presumably by cleavage 6 t o the nitrogen atom. The spectrum of C2H5NHCOOC2D6 shows a peak a t 88 which demonstrates that the complete ethyl group bound to the oxygen may be lost. In this same spectmm the absence of a peak a t 93, (M--29)+, indicates that a comparable ethyl loss by cleavage CY to the nitrogen atom does not take place. These various ,*elationships are shown in Table 11. Loss of 45 and 4(5 Mass Units. Elimination of the elements of ethyl alcohol, 46 mass units in the case of an undeuterated ethyl cai bamate, results in the formation of an ion or molecule corresponding to an isocyanate. Thus, a peak appears a t 119 in the spectra of the four ethyl N-phenylcarbamates, and a small peak a t 71 may be seen in the spectra of the ethyl N-ethylcarbamates. As mentioned earlier, the isocyanates and correi,pondingly deuterated alcohols may be idowly formed by thermal decomposition n the glass inlet system. However, even when the temperature is minimized, the fragments assciated with the isocyanates (see Figures 1E and 2E) are still present, and it would appear that they are produced by electron bombardment as well as by thermal degradation. A similar duality
Table 1.
Schematic Fragmentation of Ethyl N-Phenylcarbamate.
PhNHCOOCH,CH;
t
(165)b PhN'COOH
(13 6)
( 13 7 )
P h N H C OOH'
(1 3 6 )
--CC6+IH$lHCOOH
( P h NH C H 2 CH 3) -$3?hNHCHtCH,
(1 20)
PhNHCH? (1 0 6) PhNHCO' PhNCO' PhNH:
1-b
PhNH'
(120) (1 1 9 )
(93) (9 2 )
Ring f r a g m e n t s around 39, 5 1 , 65 and 77 'CH2CH3 (29) See Figure 1. * Value in parentheses refers t o mass of ion. a
in the formation of an ion has been reported by other authors (5, 11). Cleavage next to the carbonyl with a loss of the ethoxy group of 45 mass units is indicated by fragments of mass 120 from Ph NHCOOCzH5 and 72 from C ~ H ~ N H C O O C Z HThese ~. peaks may be seen t o move to 121 and 73 when the proton on the nitrogen is replaced by deuterium, but they remain at 120 and 72 in the d6-carbamates. The spectrum of Ph NHCOOCzD5 reveals that there is another mode of fragmentation contributing to the peak a t 120, and per-
haps to the one a t 119, in the spectrum of Ph NHCOOCzH5. Peaks a t 124 and 125 (Figure IC) represent the loss of 46 and 45 mass units from the dr-compound, thus, there must be some way of expelling this number of mass units without the loss of the terminal ethyl group. Although the 125 peak is small, it must be produced by a fragment possessing all five deuterium atoms, for it is much too intense to have been derived from any peak in the spectrum of Ph NHCOOCzH5 other than 120. The 125 fragment may also be stated to
'CHZNHCH,CH3 (5 8) __*
b
'CHzNHCOOCHZCH3 (1OZ)-< C H 3 ~ H Z N H(m)--< ~ ~ \~ ~ t
'CH~NHCOOH (74)
CH3CH'NHCOOH (88)
CH3CH,NHCOOt (88)4"
+ cH ~ H,NHC C '0 ( 7 z + CH3CH,NCOt (71)
+tCHZNCO
(56)
CH3CHzNHf (44) 'CH,NH,
(30)
'CH2CH3 (29)' See Figure 2.
Value h parentheses refers to mass of ion. Mostly from oxygen side of molecule. VOL 36, NO. 1, JANUARY 1964
179
have lost a ring proton for a proton must necessarily be lost to give a n ion of odd mass, but the spectrum of Ph NDCOOCzD6reveals that the proton bound to the nitrogen atom is still present. Effusion, temperature and pressure dependence studies, and the unaltered appearance of 124 and 125 after recrystallization of Ph KHCOOC2Ds from hexane indicate that these peaks result from fragmentation of the carbamate and are not due to decomposition, recombination, or an impurity. Close examination of the spectra of the ethyl .V-ethylcarbamates reveals that a comparable situation also appears to exist in the case of these compounds. The small peak a t 77 from the dscarbamate (Figure 2C) would be analogous t o the 125 peak described above. The mechanism by which these ions are formed is believed t o be related to the skeletal rearrangements described in the following section. This relationship is shown in Tables I and 11, but, if this is the correct interpretation, it is difficult to understand why a peak corresponding to Ph NHCH2CH3( 1 ) is not observed a t mass 121 in Figure lA, or a t corresponding masses in the spectra of the other carbamates. Loss of 59 Mass Units. The loss of 59 mass units produces a n intense peak at 106 in the spectrum of ethyl N-phenylcarbamate and a detectable peak a t 58 in the spectrum of ethyl N-ethylcarbarnate. An explanation of these peaks is not obvious, for they cannot be formed by simple cleavage or by cleavage with proton rearrangement from either compound without rupture of the C=O bond accompanied by further fragmentation and extensive proton migration. The available evidence points toward more direct skeletal rearrangements which may be represented as follows: CO-
I-
Ph
\
N-COOCzH,
/
CHa-CHs Ph-NH-CHZ
Ph
\
-+
+
+
(mass 106) CO, CH3
+
co-0
H2-C” +CH2--NH-CH-CHa
+
+
(mass 58) COa CHI
CHz-CHa -+ +CHz--SH-CHz-CH3
+ COn
+
or,
I-
‘CHz-XH
N-C2H6
/
+ COS(m* at 101)
-1
Here, it definitely is t o be implied that 0-cleavage within the group originally attached to the nitrogen is preferable (when possible) to p-cleavage within the group which migrates to the nitrogen. The spectra of the deuterated analogs of ethyl AT-phenplcarbamate and ethyl N-ethylcarbamate suggest this mechANALYTICAL CHEMISTRY
The mass spectrometric fragmentation of two simple carbamates, ethyl N-phenylcarbamate and ethyl N-ethylcarbamate, have been examined. By comparing the spectra of these compounds with those of their deuterated analogs, it is possible to schematically describe their behavior upon electron bombardment. Intense peaks in the spectrum of Ph NHCOOC2H5arise from the molecular ion (m/e 165), a direct fragmentation to yield CzHaf (m/e 29), fragmentation with proton rearrangement to give Ph KHzf, and an unusual elimination of 59 mass units. The latter is believed to be due to the following skeletal rearrangement :
I-
Ph-NH
’
co-0
’-
CH3-CHr-XH -~Hz-CH~+CH~--SH--CHTCH~ ( m / e 58). The molecular ion minus the elements of CH,, CZH,, CgHS, C2HS0, and CzHsOCO may also be observed. In this case, the loss of the elements of C2H6 apparently represents both the cleavage of the oxygen-terminal C2H5 group in its entirety and the elimination of CzH4 from this same group plus a proton from the ethyl group bound to the nitrogen. The spectra of CH3CH&HCOOCH2CHI and its deuterated analogs also provide a semiquantitative measure of the relative influence of -YHand -0during certain fragmentation processes. (1) Am. Petroleum In$.,
Analogous metastable peaks are absent in the spectra of the ethyl X-phenylcarbamates and ethyl N-ethylcarbamates, but the fact that this type of internal elimination can be verified in the above case lends support to the suggested mode of fragmentation.
co-
Less intense peaks correspond to the molecular ion minus the elements of CX“, CZHS, CZH~O,CZH~OH,and GHsOCO. The loss of the elements of CzHs demonstrates that an obvious cleavage does not, necessarily, account for an observed peak for it is not the terminal C2Hs group which is lost from this compound. Instead, this peak results from the elimination of C2HA plus a proton from either the nitrogen or the ring. Ethyl il’-ethylcarbarnate displays a somewhat similar fragmentation pattern with peaks corresponding to the molecular ion (mle 117), CZHS+(m/e 29). +CH2NH2 (m/e 30) and an unusual skeletal rearrangement which may be represented as:
LITERATURE CITED
+CHz
CONCLUSIONS
5 l--h CHrCHz-XH co-0
(mass 178) -L
+CHz
-1 O T
Ph-SH
180
anism, and they may be seen t o be quite compatible with it. Although skeletal rearrangements are not common, they are known to take place (15, 16). Furthermore, the general mechanism presented above receives some confirmation from the other N-substituted carbamates which have been studied (12). In particular, the following two specific examples may be mentioned. First, the deuterated analogs reveal that ethyl N-phenylcarbamate and ethyl N-ethylcarbamate do not lose 59 mass units by an identical mechanism; this is demonstrated by the loss of 59 mass units from C2HSSHCOOCzD6 but 62 mass units from Ph NHCOOC2Dj. Consequently. the compound ethyl N-2, 6-dimethylphenylcarbamate was prepared and examined to find out if a Fries or Claisen type of rearrangement could be taking place by way of the ring. Since the spectrum of this compound reveals that the loss of 59 mass units is not hindered by the ortho methyl groups, ring participation appears doubtful. Second, a metastable peak in the spectrum of ethyl N-butyl, N-phenylcarbamate may be attributed t o the loss of 44 mass units from an ion of mass 1 7 8 i . e . :
-I O T
CH?--CH3 -+ Ph-YH--CHz+
( m / e 106)
“Catalog of Mass SDectral Data, API Research Project 24. (2) Beynon, J. H., “Lfass Spectrometry and Its Applications to Organic Chemistry,” p. 378, ElseIier, Xew York, 1960. (3) Biemann, K., Mass Spectrometrv, Organic Chemical -4pplications,” p. 87, McGraw-Hill; K e w York, 1962. ( 4 ) Ibid., p. 124.
(5) Biemann, K., Seibl, J., Gapp, F., J . Am. Chem. SOC.83, 3795 (1961). (6) Collin, J., Bull. SOC.Roy. Sei., Liege 21,446 (1952). (7) Condon, F. E., J . Am. Chem. SOC.73,
4675 (1951).
( 8 ) Emerv, E. &I.? ANAL.CHEY.32. 1495
(1960).” (9) Evans, 11. W., Bauer, N., Beach, J. Y , J . Chem. Phys. 14,701 (1946). (10) Gilpin, J. A., AXAL CHEV.31, 935 (1959). (11) Junk, G. il ,Svec, H. J , ASTM E-14 Meeting on Mass Spectrometry, San Francisco, May 1963 (12) Lewis, C. P., Olin Vathieson Chem Coru.. Sew Haven. Conn. unuublished dat& ’1963. (13) Lewis, C. P.. Hoberecht, H. n., ANAL.CHEM.35, 1991 (1963). (14) Lumpkin, H. E., Taylor, G. R., Zbid., 33,476 (1961). (15) McLafferty, F. W , Zbid., 31, 8‘3 (1959). (16) McLafferty, F. W., Gohlke, R S., ( I i d i . ~2076. . I erg, W., Chem. Revs. 5 5 , 713 (1955). RECEIVED July 19, 1963. Accepted October 16, 1963.
