Mass Spectrometric Analysis Aliphatic Halogenated Compounds F. W. McLAFFERTY’ Chemical Physics Research laboratory, The Dow Chemical Co., Midland, Mich.
A correlation of the spectra o f 103 monohalogenated aliphatic compounds shows the unique usefulness o f the mass spectrometer in the identification and structure determination of such compounds. Major ion degradation paths are characteristic of the electronegativity of the halogen atom, although none of the rearrangement paths typical of the unsaturated electronattracting functional groups (as carbonyl) are found for the halogenated compounds. The molecular ion abundance i s in the order I Br CI F. Cleavage of the carbon-halogen bond in the lower molecular weight compounds i s very prominent, with the tendency to lose I and Br atoms but HF and HCI molecules. If the carbon-carbon bond adjacent to the halogen i s branched, cleavage i s increased in the order CI Br 1. In the higher molecular weight halides the hydrocarbon ions become very similar in relative abundance to the corresponding hydrocarbon. CdHgCI + and C4H8Br+ become very prominent, in contrast to the scarcity o f haloalkyl ions in the other spectra. Mechanisms are proposed for the several favored ions and cleavages.
>
>
T
>
>
>
mass spectra of a wide variety of organic compound types have now been correlated [for a recent summary of such publications see (21)]. The lack of a comprehensive discussion of the mass spectra of a major common and useful class of organic compounds, those containing halogen, prompts this review of monohalogenated aliphatic compounds and the accompanying paper (19) on the corresponding aromatic compounds. The spectra of a number of simple monohalogenated compounds have been discussed, as in the work of Stevenson and Hipple (99), Collin (6), Taylor et al. (SO), Irsa ( I S ) , Momigny ( d S ) , D’Or, Nyens, and Momigny ( 9 ) , and Dibeler and Reese (8). Rylander and hieyerson report and discuss the partial spectra of 3-chloro-3-ethylpentane and The 3-chloro-3-methylhexane (28). HE
Present address, Eastern Research Laboratory, The Dow Chemical Co., Framingham, Mass. 1
2
ANALYTICAL CHEMISTRY
spectra of some polychloroethanes have been reported b y Bernskin, Semeluk, and Arends (9), of perhalomethanes b y Craggs, McDowell, and Warren (7), and of perfluorocarbons b y Mohler, Dibeler, and Reese (29) and Natalis (94). The recent book by Beynon (3) contains a useful general discussion of halogenated spectra and reviews our preliminary report of this work (20). Halogenated compounds present particular advantages for mass spectrometric analysis. Vnlike polar compounds, they show little adsorption in the vacuum inlet system, and thus a minimum of pump-out or “memory” experimental difficulties. The characteristic 3 to 1 natural abundance ratio of the two stable isotopes of chlorine (masses 35 and 37) and the 1 to 1 ratio of those of bromine (masses 79 and 81) make for ready identification and empirical formula determination of ions containing these elements (21). Tables are available for the ratios exhibited by multiple combinations of the elements ( 3 ) . Additionally, in contrast to many compound types containing oxygen and nitrogen, the common ions of the halogen spectra are usually different in mass number from the common hydrocarbon ions. Only the monohalogenated compounds have been considered in these initial papers. With multiple substitution it is often difficult to identify the particular halogen atom in a fragment ion and thus to show individual effects on the molecular ion degradation. However, the correlations found for the monohalogenated compounds have proved very useful for structure elucidation of more highly hqlogenated materials. EXPERIMENTAL
The spectra were obtained on 90” sector-type instruments, whose inlet systems (4) were maintained at 200’ C. except where otherwise noted. The ionizing voltage was lis volts. I n most cases the compounds were used as obtained without further purification. RESULTS
Tables I to IT’ list the prominent and characteristic peaks of the mass spectra
of aliphatic fluorides, chlorides, bromides, and iodides, respectively. Prominent peaks whose intensity is mainly due to the isotopes chlorine-3i and bromine-81 are not necessarily included, although the reported peaks are not corrected for the abundances of these heavier isotopes. Only a very limited number of fluoride spectra were available, so that the generalizations here Rere of necessity narrow. Thus, in correlations postulated as applying to all halogens, there is a much greater chance that there may be exceptions in the fluorides. The spectra of 1-, 2-, and 3-bromopentane are markedly and inexplicably different from those reported by D’Or et a2. (9). As is found with aliphatic hydrocarbons, fragmentation of the molecular ion generally becomes greater as the molecular weight and chain branching increase. Collin has observed that the molecular ion abundance for ethyl chloride, bromide, and iodide increases as the electronegativity of the substituent halogen atom is decreased. This was found to be generally true for all the aliphatic halides studied here, including fluorides. Hydrogen does not fall exactly where this electronegativity classification would r e q u i r e 4 . e , replacement of onc of the hydrogen atoms of an alkane by an iodine atom generally increases the abundance of the molecular ions. Thus, the parent peak intensity (relative to the most abundant peak) for thP alkyl halides generally falls in the order iodine > bromine = hydrogen > chlorine > fluorine. Thus the degree of molecular ion degradation increases in the halogen series in the same order as the increase in the ionization potential of RX and the electronegativity of X. Similar regularities have been observed previously, such as the increased molecular ion abundance of sulfides as compared to ethers (14) I
ALKYL I O N S
With the exception of some halogenated alkanes containing six or more carbon atoms, the formation of the major fragment peaks in the spectra studied involves the loss of the halogen atom. This is generally through either (A) cleavage at the carbon-halogen bond
or (B) cleavage a t a nearby branched carbon-carbon bond. I n either case the hydrocarbon ions produced may have lost one or more hydrogen atoms. I n both these mechanisms, i t is not surprising t h a t the fragments containing the electronegative halogen atom tend to retain the extra electron from the bond cleavage, so that the hydrocarbon fragments are usually the predominant positive ions in the spectrum. Mechanism A can be pictured as withdrawal of electrons by the electronegative halogen atom from the carbon-halogen bond to favor rupture at this point. This is similar to the “a-cleavage” found in ethers a t the carbon-oxygen bond ( 1 7 ) . Tendency for this cleavage increases as the halogen is attached successivrly to primary, secondary, and tertiary carbon atoms, as would be expected from the analogous chen~ical lability of such bonds and from the stability of the corresponding carbonium ions formed (16). This cleavage is prominent for compounds of any of the halogen atoms (up to Cs compounds). Possibly the much stronger electron-attracting power of the rhlorine and fluorine atoms is offset b y the known (8) higher strengths of the carbon-chlorine and carbon-fluorine bonds. The kind of halogen atom does have a strong effect on whether the carbonhalogen bond cleavage involves the loss of X (mechanism A l ) or loss of the rearranged HX (mechanism A2). Al.
RCHzCHz--X
+
A2.
ItCH*CHZ-X
+
RCH?CH2+
RCH
R Sourcea Mol. Wt . m/ e 15 19 20 27 28 29 31 32 33 34 41 42 43 45 46 47 48 54 55 56 57 59 60 61 62 67 68 69 73 74 75 76
Table I.
Mass Spectra
Me G
Et G 48
n-Pr G 62
i-Pr A 62
0.6 0.1
1 0.4 0.4 34
2 7 0.1
0.8 0.3 0.4 9 0.8 0.2 0.8 0.2 3 0.1 7 2 1 3 28 100 2
0.1 0.5
0.1 0.2
34
12 0.3
18
8 4 89 100
7 2
1
2 27
0.5
0.1 7
10 100
11
of Aliphatic
46 100 2
1 9
0.1 12 27 2 3
3 8 1 3 3
1
2 0.5
15 1
Fluorides (R-F)
n-Bu G 76 1
0.1 43
47 41 1
2
8
0.1 89 7 100 3
7 15 1
0.7
13
83 5 11
2
3 0.1
0.2
0.4
0.6
0.4
0.9 0.07
81 82
83 84 85 88 89 97 98 99
+ X.
cychex H 102
Hept H 118
0.5
0.8
11
6 5 0.4 0.2 3
39 11
7
0.9 5 3
0.2 28 18 25 3 20 4
7t-
24
6 40 0.2 0.1 4
79 35
96 0.8 2 16 0.3 5 39
100 63 8 2
6
1
0.2 100 6 4 5
0.3
1 5 61 2 4
5 0.4
4 0.2 0.3
9 31
0.1 8 0.6 0.6 2 1
3 0.7 0.7
0.5
0.3
2 0.1
0.1
100 =
CHz+
+ HX
ALechanism -42 is most pronounced in fluoro and chloroalkanes and is of little significance in the iodo compounds The higher stability of the carbonium ion formed in A1 vs. the olefin ion of A2 is evidently offset in A2 by the increased stability of HX when X = C1 or F (28). However, A1 can be favored w e n in chloride. or fluorides when a secondary or tertiary carbonium ion can be formed, as hydrogen loss can destroy its stabilization of these ions by hyperconjugation. This is evidently more true for the simple secondary or tertiary carbonium ions-e.g., as formed from iso-CaH;X or tert-C4H9X-thnn the more complex one3 which can stabilize the olefin ion of A2 by further rearrange1-methyl-1-ethylpropyl ment -e g., chloride, Collin (6) establishes from appearance potential data that mechanism A2 is probably the main mode of formation of C,H4+ from C2H5Cl. Such HX elimination is analogous to the loss of HOH and ROH from alcohols (IO) and ethers ( 1 7 ) .
101
0.4
6
102 117
118 Mol. ion -Hb -CH3 -CH, -CzH6 -GHe -C3H7 -C&a -CIHO -CBio -F -HF -CHxF -CHsF -CH,F -C*H,F -CzHbF -CzHBF
0.1
100 89
0.3
12 3
11 100 27 2 0.1
2
7 0.6 0.6 0.2
3 3
7 2 9 1 0.4
2 27 100 46 34 1 0.5
0.1
1
15 100 28 3
0.2
0.3
1
2 0.2 0.8 9
0.8 0.3 0.1
0.07
0.9 3
2 15 7
8 2 0.1
5 83 100 7
89 41 47
43
1.16 Relative peak heights referred t o base peak of spectrum as 100.
S/STol ,c
a
0.1
6 0.4 0.5
0.1
1
5
2
2 20
4
4 6 2 0.1 2 0.6 0.6
0.3
0.9
0.4 3
31 4 6 100
18 28
6 0.67
8
7 47 61 0.35
A . API Project 44 ( 1 ) . C. Union Carbide. D. Dow (compounds listed are not necessarily commercially available). E. Eastman Kodak. G. W. I. Edgell, Purdue University. H. Halogen Chem. 11. Matheson. Ion formed by loss of hydrogen atom. Sensitivity of base peak, in scale divisions per mg., referred to m / e 92 of toluene.
VOL. 34, NO. 1 , JANUARY 1962
3
Table II. R Source0
Mol. wt. m/e 15 27 28 29 35 36 41 42 43 47 48 49 50 54 55 56 57 61 62 63 64 67 68 69 70 71 75 76 77 78 81 82 83 84 85 90 91 92 97 98 99 103 104 105 106 111 112 113 117 118 119 120 126 127 132 133 140 141 146 147 154 155 160 161 168 169 174 175 183 188 189 196 197 202 203
Me M 50
21
2 0.7
6 3 9 100
Et D
n-Pr
i-Pr
64
78
78
0.9 41 48 48 1 0.8
2 32 13 40 0.3 0.9 23 100 14 0.6 0.6
1 30 1 0.1 0.2 0.6 19 5 100 0.2 0.2 1 0.1
1 2 19 1
D
2 2 5 100 0.8
5 0.7
0.9
1 6 0.5
0.6 0.2 0.5 6 0.1
D
1 3 28 2
0.2 0.2 0.7 25 0.3
Mass Spectra of Aliphatic Chlorides (R-CI) n-Bu E 92
S-BU E 92
i-BU
0.9 25 14 16 0.2 0.3 52 4
1 34 11 34 0.2 0.6 54 3 0.5 0.2 0.3 3 2 0.6 7 100 88 1 15 47 6
1 18 2 7 0.1 0.3 51 57 100 0.3 0.3 4 1 0.2 4 7 4 0.5 0.3 1 0.1
0.8
0.1 0.2 0.7 0.6 1 5 0.5
31
0.2 0.2 3 1 0.4 7 100 7 0.7 2 6 0.8
0.6 0.1 0.4 0.1
0.2 0.7
E
92
1
6 0.6
0.1 0.4 0.6
2 11 3 20 0.3 1 62 3
0.9 0.1 0.1 3 2 0.3 4 6 100 1 0.3 0.9 0.1
0.5 4 48 3
0.01
pent
n-Am
104
106
106
106
-er
3-Me -bu E 106
0.5 7 2 2 0.1 0.4 34 38 2 0.1 0.1 2 1 0.4 6 0.4 0.3 0.8 3 2 1 29 100 31 2 0.2 4 7 1 2
1 28 9 36 0.1 0.3 66 88 43 0.1 0.2 5 1 1 88 7 19 1 2 6 0.7 0.7 0.6 4 100 9 1 2 4 0.8
1
1 23 6 20 0.3 1 84 35 56 0.3 0.2 5
0.9 19 3 16 0.1 0.2 34 36 100 0.1 0.1 2
1 1
1
0.1 0.2 0.3
0.1 0.1 0.1 0.1 4 0.2
c
0.2
0.3 0.1
Relative peak heights referred to base peak of spectrum as 100.
4
0.1 0.9 0.6
t-Bu E 92
ANALYTICAL CHEMISTRY
1,1-
1-Me -bu
cyc-
E
0.1 0.1 1
c
22 3 20 0.1 0.4 50 44 66 0.1 0.1 2 1 1
52 3 3 1 2 7 0.8 0.5 0.2 3 100 30 0.8 8 16 3 0.1 0.1
0.8 0.1 1 0.1 0.2 0.1 0.1 0.1 0.2 0.2
1-Et
35 18 5 1 2 4 0.7 0.5 0.1 3 100 57 1 22 38 8 0.1 0.1 0.2 0.6 0.4 0.1 0.7 0.2 0.1
0.1 0.1 0.5
0.9 48 5 8 0.6 1 5 0.6 0.4 0.2 4
Dime.
2 22 7 23 2 15 55 19 49
-E'
106
0.1
3 3 2 91 5 2 2 1 7 0.4
2 0.5 5
51 5 0.8 2 3 0.7 0.1 0.1 0.6 0.5 0.4 0.6 4 0.4 0.3 0.2 0.1
25 66 0.9. 61 100 23 0.2 0.4 0.6 0.3 0.2 2 17 2 0.5
0.2 0.1
0.2
Table It. R Sourcea
Mol. wt. m /e 15 27 28 29 35 36 41 42 43 47 48 49 50 54 55 56 57 61 62 63 64 67 68 69 70 71 75 76 77 78 81 82 83 84 85 90 91 92 97 98 99 103 104 105 106 111 112 113 117 118 119 120 126 127 132 133 140 141 146 147 154 155 160 161 168 169 174 175 183 188 189 196 197 202 203 211 216 217
Mass Spectra of Aliphatic Chlorides (R-CI)
cychex D 118
nHex E
nHiP
1Oct
120
1-Me -hex C
134
134
0.5 12 6 5 0.1 0.6 38 5 3 0.1 0.1 1 2 29 39 9 1 0.6 3 1 0.9 100 6 5 0.5 0.5 3 0.9 3 0.6 7 75 30 2
0.9 20 5 24
0.6 15 6 19
0.1 45 33 56 0.1 0.1 3 2 2 61 41 15 0.5 1 5 0.6 0.9 0.4 20 2 6 0.8 0.7 1 0.3 0.1 0.2 1 5 2 0.4 100 5 0.4 0.2 0.3 0.2 0.1 0.4 0.1 0.2 0.1 0.2 0.2 0.2 0.2 0.1
0.3 0.1 0.1
0.3 3 0.3 0.9
I-Ne
0.2 9 2 19
0.1 7 2 19
4 1 12
0.1 37 12 58
35 11 70
0.1 47 13 92
0.2 42 12 84
0.1 40 10 82
0.5 29 7 60
0.8 0.2
1 0.2 2 40 15 26 0.2 0.4 2 0.2 2 2 24 10 10 0.5 0.2 2 0.2 0.5 0.9 10 4 4 0.4 100 5 5 2 0.2 0.1 0.4 15 1 0.2 0.1 0.1
2 0.3
0.8 0.1
0.5 0.2
0.7 24 7 25
0.2 44 15 45
0.2 58 19 54 0.1
2 0.7 2 36 28 21 0.3 0.8 4 0.4 1 2 32 14 3 0.7 0.9
0.3 63 38 74 0.1 0.1
1 0.6 6 43 100 36 0.4 1 5 0.4 2 4 54 48 8 0.7
0.1 39 13 54 0.1 0.1 2 0.4 2 39 16 27 0.2 0.6 3 0.3 2 2 28 14 9 0.6 0.3 2 0.7 0.3 0.7 12 4 2 0.4 100 5 0.7 0.2 0.2 0.7 0.3 11 0.7
1
3 0.2 0.9 0.2 2 33 3 0.2 0.2 5 0.6
0.1
0.2 0.1 0.3 0.1 0.5 0.1 0.1 0.1
0.2 0.1 1 1
0.7 0.1
0.4
0.2 0.1
0.3 0.1 0.2 0.3 0.3
288
0.3 12 7 22
0.4 13 4 18
0.2 0.3 0.1 2 0.3 0.8 0.3 100 4 0.4 0.4 0.1 0.1 0.8 8 0.5
260
0.3 10 3 16
0.8 19 4 21
1
232
0.3 12 3 17
148
2 0.5 0.5 0.5 10
n-
Octadec C
0.2 7 2 10 0.1 0.4 21 4 22
148
1
n-
Hexadec E
176
148
1
n-
Tetrdec C
Dec E
-hex C
0.6 4 68 64 41 0.5 0.8 8 0.5 4 6 46 100 19 0.9 1 3 0.6 0.8 11 59 42 6 0.3 5 0.6 7 0.9 0.6 0.1 0.2 8 0.6 0.7 17 2 0.1 0.1 0.9 0.1 0.2 0.2
n-
Non C 162
-hep E
E
n-
Dodec E 204
2-Et
0.9
19 7 100 0.1 0.3 1
0.2 0.8 0.4 3 4 2 0.6 0.1 1
0.1 0.2 0.2 4 0.8 0.2 0.2 0.6 0.1 0.2 8 22 0.2 0.3 0.2 0.1
5 0.3
0.1 1 0.1 0.1 0.1 0.1
7t-
1 0.2 2
4i 15 46 0.2 0.3 2 0.2 2 2 32 11 15 0.8 0.3 2 0.2 0.7 1 12 5 9 0.5 100 5 7 2 0.5 0.1 0.9 20 1 2 1
0.2 0.1 0.3 2 0.2 0.1 0.1 0.2 0.5 0.1 0.1 0.1 0.3 0.1 0.1
0.1
4
3
3
4? 19 100 0.1 0.2 2 0.1 4 4 42 15 55 0.5 0.4 2 0.2 2 4 24 9 31 0.4 75 4 17 6 5 0.1 3 22 2 6 4 2 0.2 1 7 0.9 2
39 15 100 0.1 0.2
37 15 100 0.1 0.1 1 0.1 4 4 32 14 62 0.3 0.2 1 0.2 2 5 23
.?
51 19 92 0.1 0 3 2
0.1 4 3 44 14 42 0.5 0.4 3 0.7 1 3 2i 8 21 0.5 100 5 12 5 2 1 2 26 2 17 2 1 2 2 5 0.6 0.9 0.7 0.5 2 0.1 0.3 0.4 0.9 0.1 0.5 0.3 0.6 0.3 0.6 0.2 0.5 0.1 0.1 0.6 0.4
0.3
'
~~
1
0.7 4 1
0.9 0.5 2 0.5 0.4 0.6 2 0.6 0.3 0.6 1 0.1 0.4 0.9 0.4 0.3 0.4 0.7 0.1
0.1
1
0.1 3 3 31 12 55 0.3 0.2 2 0.2 1 3 18 7
33 0.4 44 2 12 5 7 0.2 2 14 2 5 3 4 0.3 0.9 6 0.8 2 2 0.5 4 1 2 0.8 3 0.8 1 0.5 2 0.4 0.7 0.6 2 0.3 0.6 1
0.3 0.2 0.6 1
R
41 0.3 32 2 18 7 10 0.2 2 13 1
8 5 6 0.3 1
6 0.8 3 4 0.7 5 2 3 0.5 4 2 2 0.7 3 1 1 0.7 2 1 0.7 2 0.4 0.6 0.8 1 0.3 0.6
0.1 0.4 0.9 1 (Continued)
VOL. 34, NO. 1, JANUARY 1962
5
Table II. R Source5 Mol. wt.
Me
Et
50
64
bl:
D
n-Pr D 78
i-Pr D 78
n-Bu E 92
s-Bu E 92
(Confinued) i-Bu E 92
t-Bu E 92
cycpent C 104
n--4rn E 106
1-Me
-bu C 106
1-Et -pr C 106
3-Me -bu E 106
1,l-
Dime -Pr E 106
mle
Mol. ion 100 100 6 25 0.7 1 0.2 0.6 0.6 0.01 0.3 0.5 0.1 -Hb 9 5 0.5 0.2 0.7 0.2 0.4 0.9 0.1 0.1 0.2 0.2 -CHs 2 19 6 0.4 0.4 6 5 4 1 28 0.7 4 48 17 2 1 -CHI 0.1 0.1 4 1 1 3 0.1 0.1 0.6 2 1 5 6 4 1 47 1 16 4 38 3 100 -C2Hs 0.9 0.6 2 2 0.2 0.1 8 2 22 15 0.3 0.1 61 -42He 0.3 7 3 0.2 3 4 6 0.8 3 4 5 7 -C3H7 2 2 0.2 0.2 1 2 0.3 0.3 0.1 1 -CaHs 0.2 0.1 2 5 2 0.2 0.1 5 0.3 3 -GHs 0.2 0.1 0.1 0.2 --C&o -c1 21 48 14 100 7 86 4 31 9 30 100 57 5 66 -HC1 5 100 100 7 100 100 1 48 100 100 100 51 6 25 0.9 40 -CH2C1 6 31 3 0.1 19 2 0 . 5 100 5 8 0.9 1 13 1 4 0.4 3 -CH3Cl 7 3 57 18 5 3 5 4 -CHIC1 0.4 32 52 30 54 51 88 52 91 62 35 48 2 66 -C2HdC1 43 1 34 7 16 20 56 100 34 49 11 2 44 6 -C,HbC1 0.5 0.4 14 35 36 88 3 19 0.1 50 -C2H&l 34 17 18 11 84 34 66 25 55 0.50 1.23 0.47 0.80 0.76 0.49 0.81 0.67 0.39 0.36 0.56 0.83 0.54 0.25 S/STol.= a A. API Project 44 (I). C . Union Carbide. D. Dow (com ounds listed are not necessarily commercially available). E. Eastman godak. El. Halogen Chem. M. Natheson.
With such two carbon compounds the mechanism should involve loss of the p-hydrogen atom with the halogen (or OH or OR with alcohols or ethers) through a four-membered ring intermediate ( I S , $1). Preference for @hydrogen loss has been found in the high energy irradiation of alkyl halides (5, I d ) . However, RfcFadden and coworkers have shown , using deuterated isomers, that only a small proportion of either the a- or 8-hydrogens are involved in the loss of water from n-butyl alcohol to form C4H, (15). Cleavage of the carbon-halogen bond with the positive charge remaining on the halogen fragment -Le., formation of X + and HX+-is not significant except for I+. I n the decomposition path (B) the strong electron-attracting power of
the halogen atom can evidently enhance cleavage a t polarizable bonds further removed in the molecule (16). As this would predict, the chlorine atom is much more effective than the bromine and iodine for this enhancement. This is illustrated in Table V, whose figures represent the abundances (relative to total ion yield) of C,H2,+ C,H2, where n = the number of carbon atoms in the alkyl fragment formed by cleavage of the bond indicated. Thus, cleavage of bond €3 of isobutyl chloride is shown as the sum of the relative intensities of GHs+ and
+
6
ANALYTICAL CHEMISTRY
CBH,+,although secondary reactions and intramolecular rearrangements could make this figure less indicative of the relative cleavage of the bond. Thus, for the n-butyl halides, bond cleavage is favored next to the halogen atom, while at the more distant bond, B, there appears t o be a real inductive effect only with chlorine. On introduction of a polarizable branched carbon atom on bond B, the cleavage becomes much more specific. I n the isobutyl halides the strongly electronegative chlorine atom cauies cleavage a t this chain branch to be dominant in the spectrum, while with bromine and iodine the effect falls off sharply. I n the isoamyl halides where the halogen is one more atom removed from the branching, the influence is difficult t o discern, although the chlorine still may have an effect. Loss of the largwt alkyl group a t such a branched carbon is favored, as had been pointed out b y Rylander and hleyerson (28). The tendency to lose an additional hydrogen accompanying cleavage by mechanism B is not striking, probably because the branched chain necessary for path B lowers such hydrogen loss, as found in mechanism h 2 . A third distinct mechanism, the “ion-pair” process (8),can be an important source of alkyl ions, especially a t low electron-accelerating potentials.
The energy required to produce R+ by route C is lower by the electron affinity of the halogen atom, and thus can even appear below the appearance potential of RX+ (3). For the monohalomethanes, Dibeler and Reese (8) find the ion-pair process significant only for the fluoride and chloride. For the bromide and iodide the electron capture process is predominant a t low electron energies (8). Irsa finds the ion-pair process unimportant even for the chloride ( I S ) . LARGER MOLECULES
-4s the size of the molecule increases, the effect of the single halogen atom becomes diluted and the spectrum tends to be similar to that of the corresponding hydrocarbon. Thus, $bromomethyl - 2,2,4,8,10,10 - hexamethylundecane shoms loss of C4H9- (1 %) and C8HI7-- (3%) as the only significant (although relatively small) peaks in the higher mass end of the spectrum, especially compared to the insignificant loss of Br or CH2Br. These cleavages a t the branching of the carbon skeleton correspond \\-ell to those expected from a large hydrocarbon (25). Table V I shows the striking similarity in the abundances of the small alkyl ions for C,H2,+lX when X = Cl, Br, or I. The similarities are even more surprising in comparison with the parent alkane (X = H), especially above n = 10. This similarity is un-
Table II. (Contimad) R source. Mol. wt.
2: D 118
nXp ;
Ha-x
E
-p
Oct
1-Me
I-Me
1-
-hep E
E
120
134
134
148
0.1
0.1 0.1
0.2
0.1
n-
n-
%Et hex
c
n-
Non
148
148
C 162
0.1 0.3 0.3
0.1
U.6
0.9
5
n-
I)ec
E
176
Dodec E 204
Tetrdrc C 232
-
n-
Hew dec
E
nChtS-
dec C
260
2%
2
2
w e
Mol. ion
-Hb
-CH( -C&
-GHr
-CiHs -GHI
-C,% -CA -C,Hic
-.
-I71
-HCI -CH&I -CHIC1 -CHdCI --CyH,CI -GHsCl -c*H aC1 S/STal.’
3 0.3 0.4 0.3 3 0,a
0.6 30 75 8
6 100 39 29
7 0.53
0.2 0.4 0.1 100 0,4 1 0.7 5
0.5 0.1
8 0.8
5 0.2 0.9 0.2 2
1 0 0.3 1
1
2 i;
6
2 20 15 41 61 0.37
1
0.9 0.1 0.4 0.8 0.3 2 3
3
33 3 1 10 8 48
14
32 0.43
0.7 1 11 0.3 0.4 0.1 0.2
8 0.2 5 0.8 2 17
0.2
0.6
0.2
0.9
100
I
0.7 2 4
54
12
0.44
0.I
0.47
0.2
0.6 0.2 0.1
0.2
22
a
0.2 0.2
0.1 0.1 1 0.1 5 0.4
0.1 0.1 0.1
42
0.8
59 0,37
4
0.2 0:2 2 5
1.05
0.&3
7
b
0.3 0.3 0.1
0.6 0.2 2 0.3 0.1 0.1 0.1 0.1
1
1
0.4
0.6 0.3 0.2 0.1
0.4 1 ‘0.8 0.6 0.4 0.1 0.1
0.2 0.3
0.1 0.3 0.1
0.39
0.36
0.5 0.2 0.6
0.7 0.4 0.9 1
A
0.4
0.6 0.3 0.4
0.3 0.9
0.4
0.1 1
0.3
0.6 0.3
0.52
0.27
0.44
2
0.2
0.2 0.1
0.6 0.3 0.5 0.1 0.1 0.3 0.7
0.2
0.1 0,.2
0.4 0.1
0.1
0.2 0.1 0.3
0.1 0.7 0.3 ‘0.9
0.2 0.1 0.7 0.3
1
“Ion formed by lose of hydrogen atom. Sansitivitv of baee mak, in scalc divisions par mg,, referred to m / e 92 of toluene.
doubtcdly helped by the generally low abundance of halogen-containing ions. CH< AND C~Ha5r+
A striking exception to thk scarcity of ions containing halogen is C&X+ found as a major or the base peak in the malkyl chlorides and bromides from hexyl through octadccyl. This is not found with the iodides nor apparently with Piuoridert, for example. Of the is homologous halide ione C&X+ much less abundant and CaHdi+ is neariy negligible. This evidence suggests a possible explanation.
Initial ionization of a nonbonding ialogcn electron would c ~ u s ea localized :barge a t this point of the molecule. 4ttrsction through space by lowering the electron density in thc delta carbon:arbon bond could cause the rupture ahown with formation of a new bond from $he delta carbon atom to the halogen. Such II fivc-memhred ring should be sterically favorable, with the divalent halogen ion-e.g;, btomonium analogous to trivalent oxonium and quaternary ammonium ions. The in-
-
donate electrons to form the second
bond, If C4HsF+ is also scarce despite the strong tendency of fluorine to form hydrogen bonds, this may be due to higher ionization potential and the resulting increased ion decompositions. In fact; initial ionization might.,occur at other than the fluorine atom (II), removing the postulated driving force for cyclization. However, there must be an extra driving force in the formation of the five-membered ring. From steric strain conditions alone, the six-membered ring, CsHI&+, should be more stable than the CaH&+, as is found, but should be roughly equivalent to the C4H++, which is not the case. In fact, it has been postulated (21) that rearrangements tend to proceed through four- or six-membered ring transition states instead of five-membered. However, in thew cases it is thought that a concerted effect is a significant part of the driving force of the reaction. Here, the five-mcmbercd ring is in the product ion, not the transition state, BO that just the opposite is desiredLe., stability rather than tendency to decompose.
The abundant resrranged ion HOCI&OHI+ found in the spectra of &hydroryethy1 ethers has also been postulated to gain stability through a fivemembered ring configuration (17)
The analogous C4H$H ion is unusually prominent in the spectra of the corand C,t thiols responding n-Gl Cg, GO, (14). Compounds other than n-1-halodkanes do not form the prominent Q&C1+ or C4€&Br ions, as would be expected from the postulated mechanism. However, the tendency to form the corresponding substituted cyclic halide ion is markedly reduced or absent. Thus, Zchloroheptme and Zchloro-octane show 5 and 8% CrH&l+, respectively, while l-chloroheptane and l-chIorooctane yield 8 and 11%, respectively, of the same ion. Inductive effecte of the alkyl substituentg could dccreaect the tendency for ring formations. Further investigations of this mechanism are in order. Stevenson and HippIe (%9) note the anomalous ions CHJGl+and GH,CI+ in n-CaH,Cl., Though appear in some of t here, none are of significant abundance. VOL S4, N6:’I, JANUARY 1962 e
7
3
3
3
0
3
3
.
.
c? ON-
?? 0
b
8
ANALYTICAL CHEMISTRY
4
.
"'.? ??-!
i
33.0330
0
r
.
(
3 N m
-
0
N.
3
3
3
N
a
0
0
,
W
. d i.
m,c?
o o M o o03 c o w m 3m u 35
N
3
303
1 00
N
0-
. .
300 33
?' 3
c:
"109 033
m. +. i .
033
.
c?
i
4
0
c
0
,
?@?
,
0 " r O O r n "m Nfi
E;
0 4
VOL. 34, NO. 1, JANUARY 1962
9
m
N
qw
m
tshMi01
e?
0 ~ N + ~ N + M 3 + 0 m N ~ 9 o O 0 1 o t . 0 0 0 00 0
r-
10
ANALYTICAL CHEMISTRY
h??lc?11". 0030000000
2
. 0 1.
?
?
3
0
0
0
0
m
9
1 N . *o 0
3
2 0
N
c?
0
. 0
c?
d
0
N. 3. m . I.
-3
. .
3 +
0 0 O C N 0 0
Tc? 00
c?
0
3
c? 0
W
m 0
": 0
N
??
1 1 1 ?1ct:
00
0
c
0
0co
"??c? 0000
n? 0
m 3
p'.
0
0
01
. .
i
3d
3
00
m
d
0
-0
N
n?
Y
0
0
3t.y . .
109
020
c?
000
3
N
N
O
W
c? 0
d
p ' 1 0
0
W
N
'?
c?
9
0
Y 0
0
0
?
c?
00
0
0
3
0
c?
+
3
0
0
0
d: -30
0
5
1:
0
Q,
0
L3
c ? ?
m o
m
Y
p' -30
0
CD. 0
+
0
'9
P-
0
O
3
09 0
N. 0
q 0
09 0
3
-33 00
d: 0
'9 0
*. 0 0
VOL 34, NO. 1, JANUARY 1962
s i u
0
11
~
Table IV.
R
Source" Mol. wt.
Me D
142
Et D
n. Pr E 170
156
Mass Spectra of Saturated Aliphatic Iodides
i-Pr D 170
n-Bu D
3 44 3 0.4 45 4 100
cyc-
184
S-BU E 184
i-Bu D 184
t-Bu E 184
Pent C
0.6 20 6 53 45 2 0.4 0.3 5 1 100
0.5 10 2 37 36 2 0.8 0.4 4 3 100
1 10 2 40 45 4 4 0.2 4 1 100
0.6 7 4 29 48 4 3 0.4 6 4 100 0.2
0.1 0.1 0.8
2 2 1 0.2 0.2 2 1 2 1 0.1 0.5 0.6 0.5
0.5 6 2 1 60 7 0.9 0.7 2 0.1 0.3 27 10 100
196
n-Am E 198
s-Am C 198
3-Me Bu D 198
0.7 18 5 21 30 8 100 0.3 11 4 3
0.4 12 1 18 25 6 78 0.4 11 0.9 1 0.3 0.1 0.8 0.6 100
0.6 17 3 13 26 4 100 0.5 18 2 0.8 0.2 0.1 1 1 73
t-Am E 198
cyc-
Hex D 210
mle
15 27 28 29 41 42 43 54 55 56 57 67 68 69 70 71 81 82 83 84 85 97 98 99 111 112 113 126 127 128 139 140 141 142 153 154 155 156 167 168 169 170 181 182 183 184 195 196 197 198 209 210 211 2 1.2 224 225 238 239 252 253 266 267 280 281 294 295 309
13
0.1 19 3 36
1 26 1 2 35 3 100
0.1 0.1 0.1 0.1
0.2 0.1 0.1 0.1 0.1
0.2 0.3
0.1
0.1 0.1
0.3 0.9 2 0.4 0.1
1 0.9 87
0.1
1
38 3 5 4 14 100
15 6 0.5 0.5 2 0.1 0.2 0.1 0.6 100
0.4 14 3 0.5 0.5 3 0.8 0.3 0.2 2
0.1 68
17
3
0.2 0.2 0.4 0.5 0.2 0.1 1 0.1
7 2 0.2 0.2 2 0.2 0.2 0.5 6 0.2
6 1 0.1 0.1 0.4 0.1 0.1 0.1 1
0.1
46
55
38
5 1
0.3 0.3 3 0.9 0.2 0.1 0.5
2 0.3 0.5 40
11 2 0.1
0.4
0.1
0.3 3 0.1
6 8 0.1 0.1 0.2 0.1 0.1 0.4 0.2 0.1 0.2 0.1 0.1
3 1 0.1 0.1 2 0.2 0.2 0.6 5 0.6
3 0.9
0.4 0.1 0.1 1 0.1 0.1 0.4
3
0.6 21 1 0.1
0.1 28
24
4 1 0.1 0.1 2 0.3 0.2 0.7 7 0.3 0.7
0.8 0.3
38
4
0.6 0.7 1 2 0.4 0.3 0.5 0.8 0.2 0.2 0.3 0.3 0.3 0.1 0.2 0.4 4 0.1 0.1 0.2 2
0.3 6 1 5 30 2 3 12 62 3 0.6 18 0.8 0.3 0.1 0.1 3 5 100 7
0.3
2 1 0.1 0.1 0.1 0.2 0.2
17 1
Relative peak heights referred to base peak of spectrum a8 100.
12
7
0.6 13 2 19 40 19 69 0.6 14 33 100 0.9 0.5 10 12 48 0.5 0.3 3 4 15 2 2 4 2 2 5 1
ANALYTICAL CHEMISTRY
Table IV,
R Source"
Mol. wt.
n-Hex E 212
n-Hep E 226
Mass Spectra of Saturated Aliphatic Iodides
2-Et
Hex C
s-Hep C
n-0ct E
226
240
s-Oct E 240
240
0.3 8 4 20 33
0.4 13 2 19 39 7 78 0.9 15 4 100 0 . 7. 0.2 4 1 81 0.1 0.1 0.6 0.3 1 0.1
0.7 16 2 28 62 22 86 4 46 25 100 3 2 15 20 78 1 2 8 4 4 1 0.2 0.3 0.2
0.3 12 3 21 44 5 75 1 28 7 100 1 0.3 5 3 77 0.4 0.1 2 0.8 1 0.3 0.1 0.3 0.4 0.6 43
nTetradec
nHexa dec E
Undec C
nDodec E
268
282
296
324
352
0.3 10 2 17 37 8 100 1 23 6 75
0.4 8 2 15 34 8 77 2 28 9 100 2 1 16 5 56 0.6 0.8 7 2 34 4
0.1 5 1 12 28 6 63 2 25 8 100 2 1 12 5 67 0.6 0.8 6 2 .
0.3 6 2 12 30 7 66 2 31 11 100 3 2 21
n-
n-Yon C 254
n-Dec E
0.3 13 2 20 42 9 100
c
nOctadec C 380
mle
15 27 28 29 41 42 43 54 55 56 57 67 68 69 70 71 81 82 83 84 85 97 98 99
0.5 14 3 13 25 Y
100 0 5 7 2 14 0.2 0 9 0.2 0.3 0.3 0.1 51 1
111
112 113 126 127 128 139 140 141 142 153 154 155 156 167 168 169 170 181 182 183 184 195 196 197 198 209 210 211 212 224 225 238 239 252 253 266 267 280 281 294 295 309
0 4 11 2 17 27 5 34 0 5 9 2 100 0 4 0 2 2 0 8 1
0 0 0 0 0 9
2 1 2 2 1
a 34 0.8 10 4 100 1 0.5 3 1 2 0.3 0.1 0.3 0.2 2 0.2 0.5 41 0.1
0.1
2 0.5
0 4
1 0.1 0.1 0 5 4
1 0 1 0 1 0 4
I
1
0.1 0.1
4 0 1 0 1
0.4
0 4
0.9 0.4
0.3
0 1
18
1
11
41
1
0.7 7 3 58 0.3 0.3 3 1 55 1 0.4 10 0.3 0.3 0.2 0.1 0.9 0.4
0.1 0.8 0.1 0.1 0.3 12 1 0.1
1
20 6 78
2 12 1
1
9
1
0.5 6 0.2 3 0.5 0.3 0.2 2
0.5
5 9 0.2
0.9 0.4 0.1
1 0.9 0.1 0.1 2 0.3 0.1
1
1
0.1 0.1 1
2 0.1 0.2 0.6 7 0.3 0.1
0.1 0.2 5 0.2 0.3
0.1 0.5 8 0.2 0.1
0.1 13 2 0.1 0.5 8 0.3 0.1
0.4
0.7
1
1
0.8
1
0.9
0.1
0.2
0.1
0.1
1 0.1
0.6
0.2 0.1
0.3
0 1 0.2
0.1 0.2 0.1 12
1
0.4 6 2 74 0.2 0.1 1 0.4 38 0.4 0.2 0.6 0.1
0.2 8 1 12 31 7 77 1 21 6 100 1 0.6 8 3 50 0.4 0.3 3 0.7 36 1 0.4 11 0.3 0.2 5 0.1 0.6 0.2
0.1
0.2
1 0.1 0.2 5 0.3 0.1 0.1 7
44
3 1 11 1 0.6 7 0.4 6 0.6 0.2 0.3 4 0.5 0.1 0.3 6 0.5 0.2 0.2 2
8
68 1 2 12 4 45 8 3 12 3 2 8 1
0.5 0.1 0.1 1 0.2
0.4 0.1 0.1 1 0.3
0.2 6 1
0.2 0.6 0.2 0.1 0.1
0.7 0.1
0.8 0.1
0.7
0.6
0.2
0.2
0.3
0.1 0.2 0.1
0.2
0.2
0.1
0.1
0.3
0.3
0.1
0.1
0.1
1
0.3 6
0.1
0.3
0.1
4 1 11 27
6 49 2 30 10 100 3 2 19 7 70 1 3 13 4 4% 9 3 15 4 2 9 1
7
5 0.8 0.5 0.7 4 0.6 0.4 0.6 5 0.5 0.2 0.3 3
0.1 1 0.1
0.1 0.1
0.1
2 0.7 0.7 5 0.6 0.4 0.5 6 0.5 0.3 0.4 4
0.5 0.1 0.2 3 0.4 0.1 0.2 2 0.3 0.1 0.1 0.8 0.1 0.3 1 0.1 0.1 0.6
0.1
7 0.2
0.1
0.2
(Continued) E-
VOL. 34, NO. l , JANUARY 1962
0
13
Table IV. (Continued) R Source* Mol. wt.
BIe
D 142
n-Pr E 170
Et D 156
i-Pr D 170
n-Bu D 184
i-Bu D 184
S-BU E 184
t-Bu E 184
cycPent C 196
n-Am E 198
s-Am
3-Ue
Bu D 198
c
198
t-Am E 198
cycHex D 210
mle 24 2 40 21 28 Mol.ion 100 100 68 46 55 38 3 38 17 0.1 0.2 0.6 0.1 0.5 -Hb 14 2 2 2 1 0.1 3 0.8 -CHs 38 0.4 0.3 0.2 0.2 -CHI 0.5 0.1 0.2 6 1 0.1 0.3 0.5 0.4 3 0.4 15 -CzHs 0.1 0.1 0.2 0.7 0.5 0.3 0.5 0.2 -CZH6 0.1 5 1 2 3 0.4 0.4 7 14 17 0.2 0.8 -C3H7 0.6 0.2 0.1 0.1 0 7 0.5 0.1 0.3 -C3Hs 2 2 0.1 2 0.1 5 6 11 0.4 7 -C4Hs 0.1 0.1 0.1 1 0.1 -CAo 100 100 100 100 100 87 i3 48 100 100 100 100 -1 13 36 0.6 1 4 12 4 1 1 10 0.9 5 3 3 3 -HI 0.9 2 1 4 3 3 0 . 8 100 0.3 0.8 0.1 2 0.4 0.4 -CHzI 4 2 2 2 4 4 33 0.8 0.7 0.9 1 3 -CHJ 0.1 11 11 6 14 44 45 36 45 48 18 18 26 -CH,I 100 62 60 100 78 68 40 3 53 37 29 1 -CzHJ 2 6 4 12 4 2 5 8 19 2 6 0.2 -CzHsI 10 30 25 26 40 4 7 16 0.6 10 20 -C~H~I 0.40 0.47 0.50 0.52 0.50 0.47 0.50 0.37 0.43 0.48 0.65 0.88 0.43 S/ST,I.C 0.65 a A. API Project 44 (1). C. Union Carbide. D. Dow (compounds listed are not necessarily commercially available). E. Eastman Kodak. H. Halogen Chem. M. Matheson. b Ion formed by loss of hydrogen atom. c Sensitivity of base peak, in scale divisions per mg., referred to m/e 92 of toluene.
Effect of Halogen on Cleavage of Polarizable Bonds C,HZ,+,+, C,H,,+, formed by cleavages of indicated bonds X-CH+~HZ~CZ& X-CHz-CH-( CHOz X-CH~-CHZ-CH-( CHII)2 Table V.
X
c1-
BrI-
h B
39 43 37
13 2 1
11 16 19
ACKNOWLEDGMENT
The author is indebted t o H. H. Freedman for stimulating discussions on the theoretical aspects of this work; t o R. S. Gohlke and V. J. Caldecourt for making their mass spectrometric files and facilities freely available; t o E. 0. Camehl for tabulation of data; and to W. F. Edgell of Purdue University for certain fluoride samples.
A A b
A H L
4 38 41
28 23
59 17 3
(1) Am. Petrol. Inst., Project 44, Catalog
of Mass Spectral Data, No. 1453,
14
0
ANALYTICAL CHEMISTRY
16
4 2 1
37 31 32
Carnegie Institute of Technology, Pittsburgh,-Pa. (2) Bernstein, R. B., Semeluk, G. P., Arends, C. B., ANAL. CHEM. 25, 139 (1953).’ (3) Beynon, J. H., “Mass Spectrometry and Its Applications to Organic Chemistry,” pp. 413ff, Elsevier, Amsterdam, 1win.
(4) Caldecourt, V. J., ANAL. CHEW 27, 1670 (1955). (5). Cochran, E. L., Hamill, W. H., Williams. R. R.. Jr.. J. Am. Chem. SOC. 76.2i45 ’ - - , - - -(1954). (6) Collin, Jacques, Bull. soe. roy. sci. Lidge 25, 426 (1956). (7) Craggs, J. D., McDowell, C. A., Warren, J. W., Trans. Faraday SOC. 48, 1093 (195:1 ) . \
LITERATURE CITED
0 1 0
Electronegativity (26) 3.0 2.8 2.5
(8) Dibeler, V. H., Reese, R . M., J. Research Natl. Bur. Standards, 54 9 127 (1955). (9) D’Or, L., Nyens, H., Momigny, J., Ann. soc. sci. Bruxelles, Ser. I, 71, 61 (1957). (10) Friedel, R. A., Schultz, J. 1.1 Sharkev. A. G.. Jr., ANAL. CHEM.28, 926 (1!%6). (11) Glockler, George, “Fluorine ChemI
.
,
Am. Chek SOC.79, 2429 (1957). (13) Irsa. A. P.. J. Chem. Phus. 26, 18 (i957).’ (14) Levy, E. J., Stahl, W. A., ANAL. CHEM.33,707 (1961). (15) McFadden, W. H., Lounsbury, M. ~
~~
~~
Table IV.
R Sourcea Mol. wt. mle l l o l . iori
-Hh
n-Hep E 226
s-Hep C 226
n-0ct E 240
s-Oct E 240
2-Et Hex C 240
6
2
6
0.2
2
0 2 0 4
0 1 0 3
0 1
0.2
4
0 4
0.4
0.6
9 0 1 0 2 0.1 0.2
41 0.5 2 0.2 0.3 2
12 0.1 0.1
n-Hex E 212 18
(Confinued)
nUndec C 282
Dodec E 296
nTetradec C 324
0.8
0.5
0.1
n-Yon C 254
n-Dec E 268
7
2
0.2
0.1
0.1
1 0.1
0.2
0.2
0.1
13 0.1 0.9 0.1
12 0.3 0.8 0.1
n-
nHexadec E 352
nOctadec C 380
6 0.3 0.3 0.1 0.1 0.6 0.2
7 0.6 0.1 0.1
-CH, -CH,
-C,OHL --C*HG --CaH7
-C3H8 --C4Hs -GHio -1 -HI -CH*I -CH?I -CHJ --CzH,I -C2HjI -C?HCI S/STUI.
0 5
51 0.1 0 3 0.2 0.9 14 2 7 0 62
1
0 8 2 0 4i
0.1
0.1 1
0.3 0.6 0.34
1
3 0.62
Table VI.
0.2 41 11
0.3 0.2 1
4 4
43 0.6 0.3 0.1 0.3 1 0.8
8
0.19
2 0.38
12 2 0.1 0.6 0.2
0.2 0.3 0.3 0.5i
0.4
0.36
Effect of Halogen Atom
C3H7
+
C4Hs+
CsHu 9 57
+
81
29 92 84 56 100
92 92 100 93
42 49 77 46 55 62 66 57
61 64 70 90
Wahrhaftig, A. L., Can. J . Chem. 36,990 (1958). (16) McLafferty, F. W.,“Advances in Mass Spectrometry,” p. 355, Pergamon Press, London, 1959. (17) llcLafferty, F. IT.,ASAL. CHEAT.
100 100 100
100
62 60 59 58
29, 1782 (1957).
0.1
0.6 0.1 0.1 0.45
7 0.1 5 0.2 0.1 2 0.2 0.3 0.28
6
0.2 1
0.1 0.1 2 0.2
0.2 0.47
0.18
1
0.3 0.1 0.29
(21) McLafferty, F. W., “Mass Spectrometry,” in “Determination of Organic Structures by Phvsical Methods,” suppl. ed., ed. by F. C. Nachod and W. D, Phillips, Academic Press, New York, 1961. (22) Mohler, F. L., Dibeler, V. €I., Reese, R . M., J . Research Y a t l . Bur. Standards, 49.343 i1952). (23) ‘Momigny, J., Bull. SOC. chim. Belges 64.144 (1955’1. (24) ‘Xatalis, Paul, Bull. SOC. roy. sci. Ldge 29, 94 (1960). (25) O’Neal, J. M., Wier, T. P., A x ~ L . CHEY.23, 830 (1951). (26) Pauling, Linus, “Sature of the Chemical Bond,” 3rd ed., p. 90, Cornel1 University Press, Ithaca, N. Y., 1960. (27) Peard, W. J., McLafferty, F. W., ASTM E-14 Meeting on Mass Spectrometry, Kew York, May 1957. (28) Rylander, P. N., bleyerson, Sevmow, J . A m . Chem. Soc., 77, 6683 (1955). (29) Stevenson, D. P., Hipple, J. il., Ibid., 64, 2766 (1942). (30) Taylor, R . C., Brown, R . A. Young, W. S., Headington, C. D., ANAL. CHEM.20, 396 (1948).
(18) Ibid., 31, 82 (1959).
(19) Ibid., 34,16 (1962). (20) McLafferty, F. \Ti., ASTM E-14 Meeting on Mass Spectrometry, San Francisco, May 1955.
RECEIVEDfor review May 23, 1961. Accepted October 16, 1961. .4STM E-14 Conference on Mass Spectrometry, San Francisco, Calif., June 1955.
VOL. 34,
NO. 1, JANUARY 1962
15
