LITERATURE CITED
(1) Am. Petrol. Inst. Project 44, Catalog of Mass Spectral Data, Carnegie Institute of Technology, Pittsburgh, Pa. (2) Ausloos, P., J . Am. Chem. SOC.80, 1310 (1958). (3) Beynon, J. H., ASTM E-14 Meeting on Mass Spectrometry, Kern York, X . Y., May 1957. (4) Beynon, J. H., Imperial Chemical Ind., Ltd., Hexagon House, Blackley, Manchester 9.. England,, private com. munication. (5) Bryce, W. A,, Kebarle, Paul, Can. J . Chem. 34. 1249 (1956). (6) Burr, J. G., Jr., J : Phys. Chem. 61, 1483 (1957). (7) Caldecourt, V. J., ANAL.CHEM.27, 1670 (1955). (8) Caldecourt, V. J., ASTM E-14 Conference on Mass Spectrometry, X e x Orleans. La.. Mav 1954. (9) Collin, J., kull.“soc. roy. sci. Likge 23, 377 (1954). - -,. (10) Collin, J., Lossing, F. P.,J . i l m . Chem. SOC.79, 5848 (1957); 80, 1568 (1958). (11) Cummings, C. S., Bleakney, Walker, Phys. Rev. 58, 787 (1940). (12) Eliel, E. L., Prosser, T. J., J . ’4m. Chem. SOC.78, 4045 (1956). (13) Farmer, J. B., Lossing, F. P., Can. J . Chem. 33, 861 (1955). (14) Field, F. H., Franklin, J. L., “Electron Impact Phenomena,” p. 186, .4cademic Press. New York. 1957. ~ - (15) Ihid., 193. (16) Field, $. H., Franklin, J. L., J . Chem. Phys. 22, 1895 (1954). (17) Florin, R. E., Wall, L. A., Mohler, F. L., Quinn. Edith. J . Am. Chem. SOC. 76, 3343 (1954). ’ (18) Friedman, Lewis, Long, F. -Ibid., I., 75, 2832 (1953). (19) Friedman, Lewis, Turkevich, John, Ibid., 74, 1666 (1952). (20) Gilpin, J. A , , J . Chem. Phys. 28, 521 (1958). (21) Gilpin, J. A,, L‘RIass Spectrometric I
\--
I
Analysis, Aliphatic Amides.” submitted to ANAL:CnEM. (22) Gilpin, J. A., McLafferty, F. W., Zbid., 29, 990 (1957). (23) Gohlke, R. S., McLafferty, F. W., ASTM E-14 Meeting on Mass Spectrometry, San Francisco, Calif., May 1955. (24) Gohlke, R. S., hlclafferty, F. W., Division of Gas and Fuel Chemistry, 127th Meeting, ACS, Cincinnati, Ohio, 195.5
(25) Happ, G. P., Stewart, D. W., J . Am. Chem. SOC.74, 4404 (1952). (26) Johnson, C. P., Langer, Alois, J . Phys. Chem. 61, 891, 1010 (1957). (27) Judson, C. M., Francel, R. J., Weichsel, J. A., J . Chem. Phys. 22, 1258 (1954). (28) Kraus, J. W.,Calvert, J. G., J . Bm. Chem. SOC.79, 5921 (1957). (29) Krauss, Morris, Wahrhaftig, A. L., Eyring, Henry, Ann. Rev. -Vuclear Sci. 5 , 241 (1955). (30) Langer, Aloia, J . Phys. & Colloid Chem. 54, 618 (1950). (31) Lan-, R . W., Margrave, J. C., J . Chem. Phys. 25, 1086 (1956). 132) Levv, E. J.. Stahl, W. H., ASTM E14 Meeting on M a s s Spectrometry, Xew York, N. Y., May 1957. (33) McDonnell, William, Newton, A. S., J . Am. Chem. SOC.76, 4651 (1954). (34) McFadden, W. ‘H., Wahrhaftig, A. L., Zbid., 78, 1572 (1956). (35) McLafferty, F. W., ANAL.CHEM.28, 306 11956). (36) Zdid., 29, 1782 (1957). (37) McLafferty, F. W.,Appl. Spectroscopy 11, 148 (1957). (38). h!cLafferty, F. W , “Mass Spectra of Nitriles,” ASTN E-14 Meeting on Mass Spectrometry, Cincinnati, Ohio, Rlay 1956. (39) McLafferty, F. W.,Peard, W. J., ASTRl E-14 Meeting on Mass Spectrometry, Kew York, May 1957. (40) Meyerson, Seymour, Rylander, P. N., J . A m . Chem. Soc. 79, 1058 (1957).
(41) Meyerson, Seymour, Rylander, P. S . ,J . Chem. Phys. 27, 901, 1116 (1957). (42) Momigny, J., Bull. SOC. roy. sei. Likge 22, 541 (1953). (43) Kewton, A. S., Strom, P. D., J . Phys. Chem. 62,24 (1958). (44) Peard, W. J., McLafferty, F. W., ASTM E-14 Meeting on Mass Spectrometry, Xew York, N. Y., May 1957. (45) Repka, Benjamin, Dissertation Abstr. 17, 1667 (1957). (46) Rosenstock, H. SI.,Wallenstein, R l . B., Wahrhaftig, A. L., Eyring, Henry, Proc. h’atl. Acad. Sei. U.S. 38, 667-78 (1952). (47) Rylander, P. N., hfeyerson, Seymour, J . .4m. Chem. SOC. 78, 5799 (1956). (48) Rylander, P. K., Meyerson, Sevmour, Grubb, Henry, Zbid., 79, 842 (1957). (49) Schissler, D. O., Thompson, S. O., Turkevich. John. Discussions Faradaii SOC.,No. io, 46 (1951). (50) Sharkep, A. G., Jr., Friedel, R. A., Langer, S. H., ANAL. CHEM.29, 770 (1957). (51) Sharkey, A. G., Hickam, W. hl., Friedel, R. A., -4STll E-14 Meeting on Mass Spectrometry, Xew York, K. Y., Mal. 19.57
(52) Sharkey, A. G., Jr., Shultz, J. L., Friedel, R. A., ANAL.CHEW 28, 934 (1956). (53) Sharkey, A. G., Jr., Shultz, J. L., Friedel, R. 8., ASTM E-14 Meeting on Mass Spectrometry, Cincinnati, Ohio, May 1956. (54) Stevenson, D. P., Trans. Faiaday SOC.49, 867 (1953). (55) Stevenson, D. P., Wagner, C. TI., J . Chem. Phys. 19, 11, 17 (1951). (56) Whiteway, S. G., Masson, C. R., J . A m . Chem. SOC.77, 1508 (1955). RECEIVED for review February 24, 1958. Accepted September 15, 1958. ASThl E-14 Conference on Mass Spectrometry, New York, N. Y., May 1957.
Mass Spectra of Esters Formation of Rearrangement Ions A. G. SHARKEY, Jr., JANET L. SHULTZ, and Bureau o f Mines, Region V,
U. S.
Important fragmentation peaks in the mass spectra of 31 aliphatic esters have been correlated with molecular structures. Each type of ester produced a characteristic major rearrangement peak. A possible process for the formation of these rearrangement ions is discussed. Examples are given of the use of both rearrangement and fragmentation peaks for the identification of esters.
M
spectral correlation studies have been carried out on several classes of hydrocarbons (2, 16). The mass spectra of various oxygen-containing compounds have been investiASS
R. A. FRIEDEL
Department o f the Inferior, Pittsburgh, Pa.
gated, including aliphatic acids b y Happ and Stewart ( l d ) , ethers b y McLafferty (20), and aldehydes b y Gilpin and McLafferty (11). Correlation studies at this laboratory on alcohols, ketones, acetals, trimethylsilyl derivatives, and esters have been described (7, 8, 23, 25, 26). Previous investigations of the mass spectra of esters have been limited primarily to methyl ( 1 , l S ) and aromatic esters (12). Newton and Strom have compared the spectra of isopropyl and isopropenyl acetate (28). Several investigations of the formation of rearrangement ions In mass spectra have been reported (I, 6,9,lo, 16, li’, 21, 27).
Rearrangement and normal fragmentation ions have been studied in the mass spectra of 31 esters, ranging from methyl formate (mass 60) to decyl acetate (mass 200). EXPERIMENTAL
Spectra were obtained on a Consolidated Model 21-103 mass spectrometer equipped with a mercury orifice system for introducing samples. The ionizing voltage was 70 volts and the temperature of the ion source was controlled a t
250°
c.
Compounds were used as obtained without further purification. The source for each compound is given in Table I. VOL. 31, NO. 1, JANUARY 1959
87
Table 1.
Methyl Source. Carbone Molecular weight Mass 27 28 29 30 31rd 32 33 40 41 42 43 45 46 47rj 55 56 57 58 59 60r 61r 69 70 71 72 73 74r 75r 83 84 85 86 87 88r 89r 97 98 99 100 101 1021103r 111
E 2 60
E 3 74
...
556* 813 906c 72.0 1140 15.9 2.2 2.0 9.4 31.8 108 33.4 372 60.0 73.8 0.9 18.5 1.3 0.3 10.2 1.4
499 172 592c 58.2 1430 29.0 8.6 55.2 316 990 165 19.7 86.7 8.7 107 6.8 14.0 77.3 14.8 73.5 15.9 4.8
... ...
...
176 119oc
119 15200 508 8.9 0.7 0.7 1.6 1.7 35.0 18.3 1.0
44
... ...
... ...
...
8.99 P 480h 11.5
...
... ...
...
...
... 4.4 9.60 P 89.4 4.3
...
...
...
... ...
... ...
... ...
...
... ... ... ..
... ...
... ...
...
... ... ...
4
88
... 0.8 0.8 19.0 0.9
0.5
...
... ...
...
1.9Q P 5.8
Ethyl
E 3 74
E 4
0 5 102
E 6 116
333 114 606 40.5 44.6
359
378 166 338 19.1 139 3.4 7.6 30.5 395 132 2150c 65.5 28.5 1.0
25.7 72.7 322 38.0 85.5 11.4 4.4 7.0 37.4 253 230OC 71.3 40.4 1.3
0.6
1.1
2.1
1.8
7.7 1560 6.0 2.0
...
...
... 2.1 3.5 P 368 13.7 ... ... , . .
... ... ,..
...
...
...
... ...
...
88
1.8
...
3.3 21.1 157 229OC 68.2 307 7.2 2.2
...
7.9 0.7 1.7 9.7
15.1
241
...
113 5.1 0.5 81 . O g 3.6 1.0 ... ... . .
... 4.6 P 90.3 4.6 , . .
... ... ... ... ...
, . .
...
...
, . .
, . .
...
...
...
...
...
... ... ...
...
.. ... ...
...
...
0
... ...
...
... ...
... ...
t . .
... ...
...
..
...
...
...
. . I
... ...
109
... ... ...
... , . .
...
... ...
, . .
...
...
... ... ...
... ... ... ... ... ... ... ... ...
... ...
111
200 31.4 140 3.6 1.0 27.4 212 264 249OC 65.5 29.8 0.8
...
6.1 16.9 32.4 9.4 104 16.0 507 0.5
...
1.1
26.6 263 9.5 1.1 ... ... ...
...
15.40 0.7
...
... .. ... ...
3.8 P 1.7 0.4
...
... ... ...
...
... ... ... ...
... ... ...
... ...
...
132 744 91.5 29.1 2.5 5.2 231 0.6 1.0 25.4 5.6 269 11.4 2.6 ... ... ...
13.3 25.0 3.2 0.3
...
&Butyl
Octyl
Decyl
K 6 116
K 10 172
K 12 200
168 66.4 292 7.6 39.4
142 45.4
22.6 12.4 29.6 1.2 2.0 1.3 ... 2.4 34.5 17.7 102c 3.8 1.4 .., ... 26.4 26.2 22.6 2.5 0.7 0.6 li.4 17.9 22.8 7.0 0.6 4.0 0.6 3.9 14.2 12.8
E
32.9 25.5 0.3
...
40.0 351 675 34.9 413 19.7 23.8
...
... 0.7 0.8 2.7 0.5 ...
... ... ... ... ... ... ...
...
...
... ... ... 16.40 9.2 1.0
...
...
1.2 ... ...
3.3n 0.4
...
...
...
... ... ...
... 0.9 P 1.5 ... ... ... ...
5.5 12.0 1.6
...
15.5 225 146 813c 24.4 6.1 0.3
-
...
179 198 90.9 18.5 3.8 1.3 145 129 180 37.7 3.7 35.5 2.3 5.3 103 126 9.8 1.6 6.8 1.2 1.7 11.9 11.3 3.2 3.1 9.8 2.5
...
4.5 54.8 4.5 0.5 0.9 13.1 0.9 0.8 0.5
P . ..
, . .
... ... ...
1.1
...
-
2.5
0.3 1.3 0.2 1.0 6.6 6.4 ...
... ... 1.2
0.1 3.4 7.6 0.8 0.2 0.3 2.1 0.4 0.2 0.1 0.2 ...
... ...
...
0.8 ...
...
...
... ...
,..
... ...
, . .
...
, . .
...
...
...
...
..
...
... ...
178
236
285
358
327
243
... ...
171
2.4
0.5 32.4 471 73.8
... ... ... ...
...
...
... ...
...
...
... ... ...
124
... ...
...
...
... ...
...
Acetates %-Propyl n-Butyl
Methyl
... ... ...
...
112 113 114 115 1161117r 127 128 120 130 143 144 158 172 186 200 Sensitivity of base peak, div. per pmole
Formates Ethyl n-Propyl
Mass Spectra of Esters
... ...
P
... ...
...
306
...
...
P ... 175
E = Eastman Kodak Co., K = Paul Kletzke, Lacrosse, Wis., 0 = purified by Organic Chemistry Section, Bureau of Mines, Bruceton, Pa. * Peak heights in division per liquid volume (0.00068 cc.), based on n-heptane mass 27 = 493 div./liquid volume. c Parent mass minu8 ORn. Rearrangement peak except for methyl esters. e Base peaks are underlined-. See Table I1 for correlation. f Rearrangement peaks where over isotope unless indicated as parent peak (P).
88
ANALYTICAL CHEMISTRY
Table 1.
Mass Spectra of Esters (Continued)
Butanoates Normal iinsecMethyl Ethyl Propyl Butyl Hexyl Heptyl Ethyl Propyl Butyl Hexyl Allyl Propanoates
Source. Carbons Molecular weight Mass 27 28 29 30 31d 32 33 40 41 42 43 44 45 46 47rf 55 56 57
58 59 60r 61r 69 70 71 72 i3 i4r c v
1
ar
E
4 88
O 6 116
510 729 639 219 313 199 139Oevi 1760' 907' 55.5 7 3 . 5 45.0 100 65.8 97.2 4.4 2.1 2.9 15.6 , . . 0.3 2.2 3 . 1 18.7 14 7 23 7 242 42 7 57 3 146 25 9 156 354 7 . 9 13.0 18.6 69.6 186 33.7 1.8 6.2 1.6 .. 3.2 0.7 47.1 36.9 29.3 33.6 47.8 94.2 105OC 126OC E O c 37.0 44.7 62.1 342" 1 0 . 3 65.4 13.2 1.7 3.2 3.6 8.3 0.3 ... ... 0.5 ... 0.9 0.2 1.0 6.2 3.1 ... 3.2 1.8 1 . 8 74.00 26.4 2 . 2 107 43.0 ... 144 460
- -
K
7
130
K 9 158
495 380 183 161 972' 644' 25.6 22.0 26.5 37.6 1.9 3.1
...
K 10 172 230 85.5 452' 12.5 21.0 2.3
1 4 . 3 ii:o i 5 : 6 291 241 212 42 3 176 109 103 379 155 21.8 21.1 9 . 9 94.5 26.4 5 . 5 2.3 1.6 0.3 0.6 1.1 0.3 54 0 193 152 297 328 247 2100c 855c 656c 76.8 2 9 . 5 2 4 . 4 14.5 5 . 7 3 . 0 1 . 5 5.8 0 . 6 0.4 3.0 1.3 0 . 5 104 106 1 . 0 10.0 182 3 . 6 13.8 15.7 1 . 8 13.6 9 . 4 62.5 16.7 4 . 2 34.9 30.2 11.9 156 296 231 ... ... ... ... 26.6 21.0 ... 11.8 . . . . . . 229 3.6 .. 1.o . . . ... 32.4 5 . 0 , . . ... 11.3 13.0 3 . 6 1.1 22.1 21.5 90.30 9 . 0 42.5 22.1 P 296 2.6 4.2 0 . 6 5.9 1.4 14.3 1.Q 1.4 0 . 5 1.7 1.3 ... ... ... ... 0 . 3 14.9 ... ... ... ... 1 . 5 117 ... ... 15.3 1 1 . 0 ... ... ... ... 4 . 5 2.9 ... 1 . 9 37.0 1520 11.3 7 . 3 . , , P 146 2.3 8.0 1.9 1.6 ... 0.8 0 . 2 . . . ... ... 2.0 . . . ... ... 1 . 0 3.5 ... ... 0.6 7.0 ... ... 1.0 1.8 6 . 6 27.2 6 . 0 6 . 7 P 0.7 1.5 1 . 2 1.8 0.2 . . . 0.4 0.4 ... ... ... ... ... ... ... ... ' 0 : 7 '0:3 ... ... 0 . 6 11.40 0 . 3 ... ... ... P 2 . 2 1.3 5.1 ... ... ... . . . . . . 3.79
83 81 85 86 87 88r 89r 97 98 99 100 101 102r 103r 111 112 113 114 115 116, ll7r 127 128 129 130 143 144 158 172 186 ... 200 ... Sensitivity of base peak, div. per micromole 175 0 Parent mass minus Rl. * P = parent peak. 1
0 5 102
... ...
...
...
...
...
251
294
-
... P... ... . . . . . . P... . . . . . . . . . . . . . . . . . .
362
-
Is0 niMethyl Propyl Propyl
'
226
266
E 6 116
K 7 130
K 8 144
K 10 172
K 7 128
K 5 102
K 7 130
K 7 130
442 298 475 451 642 429 658 518 106 81.6 117 110 140 84.6 158 100 141 271 203 137 169 57.9 780 110 22.3 27.6 1.4 2 . 7 12.9 6 . 8 9.3 35.2 34.2 62.4 21.0 33.5 23.1 45.1 22.3 26.8 2.4 2.4 1.9 2.1 2.0 3.0 2.3 2.0 17.2 0.5 0.6 7.0 ... 43.9 43.9 35.3 29.2 3 7 . 5 35.3 22.9 63.2 476 527 433 428 309 897 -. .. - . -__ 300 434 229 171 180 171 155 195 217 236 669' 679' 1080' 1320' 1850' 2090' 915i 1690' 45.5 63.4 81.0 42.2 62.5 26.0 2 9 . 1 4 3 . 2 36.7 3 0 . 3 132 175 61.6 66.7 16.9 53.0 1.0 1.0 3.0 4.7 1.5 2.1 0 . 5 1.1 0.3 2.3 1 . 0 1.7 1.5 0.6 8.1 2.4 74.6 29.1 15.9 40.1 22.8 61.5 155 58.0 13.6 18.3 13.2 17.0 8.7 5 . 7 370 247 12.0 52.3 61.7 96.0 9.3 17.6 7 . 6 222 6.6 2.7 1.5 2.0 3 . 1 11.0 6 0 19.2 3220 67.2 8 1 . 3 5.1 4.0 3.2 3 . 4 167 255 37.5 11.2 11.8 5.2 4.0 171 185 1.3 1.0 46.5 1.6 75.9 7 . 1 11.2 20.3 4.6 2.8 6 . 6 8 6 . 7 17.0 9.2 7.6 5.5 11.9 10.8 6.1 55.1 9 . 0 18.8 17.7 16.3 817c 413" 81gC 533c 93lC 1010" 503c 1070c 36.4 3 9 . 7 4 5 . 2 23.1 49.8 18.3 36.6 23.1 13.7 61.0 30.7 9.6 80.7 124 25.6 149g 6.2 1.6 2.0 7.8 2.0 6.2 36.9 3.2 1.9 1.2 0.4 5.3 3.0 1.2 3.0 1.7 0.7 3.0 ... ... ... 18.2 ... ... ... ... . . . . . 211 0.7 ... 2 . 1 37.0 1 . 8 ... ... 8.90 1.3 0.3 1.2 9.2 0.7 . . . 1.2 2.0 ... 2.0 8.89 5.20 9.4 6.9 5.7 196 6.19 7.3 36.8 29.2 9 . 4 25.6 2 6 . 9 383 129 0.8 179 1 . 3 566 107 309 140 295 25.7 ... 0.4 . . . ... ... ... ... ... ... ... ... 4.0 0.4 ... ... ... 0 . 8 11.7 1.3 . 5.2 .. ... 4.3 . 1 . 0 3 . 9 23.4 ... ... ... 4.1 8.3 44.0 1.6 51.8 1 . 3 55.30 21.2 4.4 2.2 i.0 pi46 3.1 ... 3 . 6 31.7 1.2 0.6 ... 1.1 8 2 1.0 . . . 1.7 ... ... 0.8 ... ... ... 0.2 ... ... ... 0.3 1.4 ... ... 15.0 1 . 6 . . . ... ... ... ... ... 2.0 3.9 . . . 1 . 0 64.0 ... 2.9 44.4 9 . 3 0.7 . . . P 37.4 ... ... 2.2 3.7 3.0 . . . 0.7 0.8 . . . ... ... ... . . . . .. ... ... . . . . . . ... ... ... 1.0 P 6 . 7 ... 1 . 8 9.50 0.6 ... 0.6 1.1 . . . ... $0.8 P 2 . 9 P 4.3 . . . . . . 2 . 0 . . . . .. ... ... ... P 2 . 6 2.1 , , . ... ... ... ... ... ... 0.5 . . ... ... ... ... ... ... . . . PO.3 . . . ... ... ... .. ... . . . . .. ... ... .. ... ... ... . ,.. ..
- -
~
.
143
296
198
235
204
194
334
.
I
423
/OR** Parent mass minus C \O
(Continued on page 90)
VOL. 31, NO. 1, JANUARY 1959
0
89
CORRELATION OF MASS SPECTRA WITH MOLECULAR STRUCTURES
RI-C-0-Rz /I
d
All important peaks in the spectra are given in Table I. For this investigation, alkyl groups (R) have been designated as follows:
Table I.
FRAGMENT IONS
The ions from normal fragmentation and from rearrangement are discussed separately.
Mass Spectra of Esters (Continued)
8
Kormal Is0 Methyl n-Propyl' Methyl n-Propyl K I< K I< 6 8 6 8 116 144 116 144 377 171 492 26.9 54.8 3.2 6.6 27.0 370 118 364 28.0 40.7
27
44 45
46 47rJ --
1.1
...
139 87.9 391' 19.2 264 10.5 4.8 17.2 1.3 3.7 0.7 17.5 8436 30.6 6.7 3.7 30O0 16.3 214 84.0 4.4
30
56 57 58 59 60r
61r 69 70 71 T2
73 74r
--or i
83 84 85 86 87 88r 89r 97 98
1 1
9 9 6 0 98 1 35 2 21 4 7 4 4 5 6930 40 1
54 50 3 0 4 2
. . . . .
100 101 102r 103r 111 112 113 114 115 11Gr 117r 127 128 129 130 143 144 158 172 186 200 Sensitivity of base
4b:8
3.5 . .
4 0 9 2 82 8 455
. . ... ...
... 2.6 P 6.7 0.9
295 86.0 416 24.5 46.6 2.5 5.6 38.8 441 137 402 25.8 29.4 0.7 0.8 67.7 95.6 441' 21.5 3589 12.8 5.9 53.7 3.2 4.8 1.2 26.4 674 25.9 6.7 2.1 246c 13.8 17.7 194 8.8 ... ...
2 0
99
3 1 28 1 12 8
1 3
...
, . .
...
143 9.7
0.8
0
16.4 42. 2 2.1
n- . 2 33. 1 429 197 498 18.5 34. 8 0 .8
2 .5 41, 1 66. 9 514' 27. 1 71. 4 187 165 15.6 2 .4 33. 0 4.8 10.2 49. 5 5 .7 3 .2 2 .6 525c__ 31. 7 l08Q 5 8 3 ... 1. 3
-
i
70.
340
. .
. . .
0 :3
2 .4 16.4 "2. 4
2.9
P 9.5
1.0
. .
1
6
...
. .
1 9
...
3 1
...
. .
P1 L
.. . .
1' 1
..
...
145'
micro mole
ANALYTICAL CHEMISTRY
...
143
106'
Hexanoate
iGth\ I i-Propyl i-Butyl K 7 130
K 9 158
K 10 172
390
360 84.0 213 5.3 15.6
279 84.3 324 11.1 28.7 1.9 2.3 27.0 352 145 438 16.9 16.4
118
342 18.8 51.0 3.9 1.8 6.9 0.3 38.0 32.1 330 344 238 238 720 1040 38.1 35.7 48 9 43.0 1.0 1.3 ,.. 1.0 197 102 32.4 49.8 53.3 34.0 4.0 5.1 149 2980 12.0 358 5.1 50.8 37.5 43.4 43.3 51.3 104' 164' 8.8 6.1 18.0 122 17.8 1100 __ 53.0 7.2 6.5 5.5 0.3 0.8 2.0 2.3 ... 0 5 52 40 346 47.3 11 4 3.4 14 4 8 5 5.2 4 8 6.5 210" 403" 14.5 28 4 8 0 84.6 17.1 117 1. 0 7 1
-
0 5
..
peak div. per
90 *
511 174 452 22 3 56 5 2 2 0 5 30 5 455 219 462 19 2 33 8 0 8 2 2 82 2 79 2 517' 28 3 67 0 244 193 8 0
i1
0
I'
Pentanoates
28 29 30 3lrd 38 33 40 41 42 43
II
CI
K i t h only two exceptions among the examples studied (isopropyl isobutanoate and methyl hexanoate), massions corresponding to the structure R1-Chave intensities at least 30%
R1--C-O-R2
Name Source. Carbons Molecular weight Mass
Major mass peaks in Table I can be correlated with the structural fragmerits R ~ R , ~ - ~ - , and -c-o-R2.
... 1.9 0.3 0.5 .. . . 1 . :?I
P 6.5 . . . .. ...
1 2 49 76 1 197 0 2 3 9 0 3 19 0 1 7 1' 2 9
. . I
.. 105 464 313 14.9 6 0 114 26.9 24.4 25.9 177' 11.5 82.5 10.9 5.8 4.6 2.0 2.7 6 9 34 6 8 3 72 4 8 5 1 586~ 42 6 10 00 2 8 0 6 0 3 0 9 3 2 39 0 172 12 0
1 3 8 3
...
207
I1
0 rearrangement ion, are characteristic of the higher methyl esters. Parent and base peaks can be summarized as follom. Parent peak intensities, with few exceptions, decrease sharply n i t h increased length of the alkyl radical Rz that is attached to the oxygen atom. As an example, the intensity of the parent mass peakof methyl formate is 480 divisions and of ethyl formate only 89 divisions. For the acetates through the butanoates. base peaks (most intense in spectrum) are produced by either the fragment (R1-C-)+ or the alkyl group RI+,
II
0 as shown in Table 11. The base peak for formates is mass 31, a rearrangement ion except for methyl formate. Olefin-type ions forming the mass series 27, 41, etc., are 30% of the base peak intensity in many instances. Ions corresponding in mass to olefin niolecular ions (not rearrangement ions) are discussed below under rearrangement ion correlations. Using ester spectra given in Table I and also literature spectra ( l a ) , only five comparisons could be made to show the effect of branching in the alkyl group R2. The same major fragmentation peaks (>20% of base peak) appear in the spectra of normal and is0 compounds of the same carbon number. Five long chain methyl esters, investigated by Asselineau, Ryhage, and Stenhagen ( I ) , shorn definite spectral changes with various R1 alkyl groups.
PO 6
, . .
125
0 of the base peak intensity. These ions form a mass series analogous to the paraffin mass series 29, 43, 57, etc. Peaks corresponding in mass to the remaining structural fragment, -0-RZ (masses 31, 45, etc.), are distinctive where the alkyl group Rz is saturated, even though their intensities are only a few per cent of the base peak intensity. Mass 87, corresponding to the structure, -C-C-C-0-C, and mass i l , a
REARRANGEMENT IONS
264
186
Empirical rules have been found which relate rearrangement peaks to various ester types. Two series of rearrange-
ment peaks were found in the mass spectra of esters. Peaks resulting from the fragment, RI-C-0-, are small;
I1
0 however, there are peaks equivalent in mass to this fragment plus two hydrogen atoms. They form a series of rearrangement peaks including masses 47, 61, 75, 89, 103, and 117. One or more of these peaks were found in the mass spectrum of each ethyl and higher ester investigated (much less intense for allyl butanoate and tertiary butyl acetate). Leak-rate determinations on mass 61 from n-propyl acetate and mass 75 in the spectrum of n-propyl propanoate eliminate the possibility that impurities are the source of these peaks ( 5 ) . The most intense rearrangement peak in each instance is characteristic of a particular type of ester-mass 47 for formates, 61 for acetates, etc. I n a few instances, a major contribution is made to mass 61 b y esters higher than acetates (most intense exceptions are n-propyl n-propanoate, and n-propyl isopropanoate). For the other peaks in this series, masses 75, 89, etc., only esters of a particular type make major contributions to the characteristic rearrangement peak. This correlation is summarized in Table 111. These characteristic peaks are found only when the alkyl group attached to the oxygen atom has two or more carbon atoms. Further limitations are described below. A second series of rearrangement peaks includes masses 60, 74, 88, and 102. Mass 74 is the only intense rearrangement peak associated with methyl esters n-butanoates and higher, but not isobutanoate). This mass-ion can be formed by the transfer of only one +. hydrogen atom, R -C-C-0-C
-lr
3
II
Mass 60 is not in the mass spectra of the methyl esters. Structure a is therefore consistent with the first series of rearrangements (masses 47, 61, etc.) that appear to involve the transfer of two hydrogens from R2. For ethyl esters and higher types the spectra indicate formation of an olefintype ion corresponding to the alkyl group RZ,minus one hydrogen. This type of fragmentation becomes very evident for butyl and higher homologs. I n several instances a typical olefin pattern is produced as shown in Figure 1, where the patterns for heptyl propanoate and 1-heptene are compared. Both have intense peaks at masses 98 and 70 with insignificant peaks in the CF Table II. Mass Spectra of Esters Origin of base peaks from Rl--CO-R*
/I
0 Ester Formates Acetates
Base Peak,
Fragment Ion 31 Rearrangement ion, except methyl + 43 Ri-C-
mle
ii
h-
Propanoates Methyland ethyl 29 Propyl and higher 57
Rl-+ RL-C-'
Butanoates
Ri-A
43
A
region. On the basis of the correlation shown in Table 111, the hydrogen atoms appear to have migrated from the hydrocarbon chain R2 to a n oxygen atom(s). Alcohol and olefin spectra are similarly related (8). For esters having small RZ groups, olefinic parent ions are of lower intensity and also less evident because of more intense general fragmentation a t the lower masses. Olefin parent peaks are intense only for esters having intense rearrangement peaks. Keither the characteristic intense rearrangement peak nor the corresponding olefin parent appears for a compound having an R, group deficient in hydrogen, such as allyl butanoate, or an Rz group with no hydrogen on particular carbon atoms, such as tert butyl acetate. The characteristic acetate rearrangement peak is very weak (
