124 XCLAFFERTY A N D BURSEY
The Journal of Organic Chemistry
Substituent Effects in Unimolecular Ion Decompositions. VIII. Rearrangement Ions in the Mass Spectra of Substituted Phenyl Methyl Ethers F. W. MCLAFFERTY Department of Chemistry, Purdue University, Lafayette, Indiana 47907 AND h f A U R I C E
M. BURSEY
Venable Chemical Laboratory, The University of North Carolina, Chapel Hill, North Carolina 67614 Received June 16, 1967 The effect, of a variety of substituents on the mass spectral behavior of anisoles has been compared to previous studies on phenetoles and nitrobenzenes. The rearrangement loss of CHzO in anisoles is not analogous to the corresponding loss of C2H& in phenetoles; there are substantial differences in ring position effects. Formation of the major product ions YCSH40 + and YCF,HI+parallel closely their formation in the spectra of nitrobenzenes. Mechanisms are proposed to account for these data.
A surprising loss of ring position identity appears to occur in the formation of the abundant, rearranged (R1 - C2H4) + ions in the mass spectra of many substituted phenyl ethyl ethers (reaction l).' Although loss of ring position identity is observed for ions from alkylben~enes,2,~ this does not occur in the formation of the rearranged (M - NO)+ ions in nitrobenzenes (reaction 2).4 In an effort to elucidat,e the factors causing loss of ring position identity, this study of substituent effects5 on the formation of the rearranged (XI - CH20) + ions (reaction 3) and other major ions in the spectra of substituted phenyl methyl ethers was undertaken. Previous reports*n7 showed substantial differences between some isomeric compounds employing ionization by higher (70 ev) energy electrons; direct comparisons of reaction rates are difficult owing to further decomposit'ions of the primary products at this en erg^.^,^ Harrison and coworkers1° report normal substituent effects on the appearance potentials for the formation of (&,I- CHB)+ions from such compounds (reaction 4), indicating no loss of ring position identity for this reaction at low energy.
+
YCcH40CzH5.' +YCaHaO*+ CZHI YCaHrNOz*+--+ (YC&HaONO* +) +YCeHlO' NO.
+
+ CH2O YCeH4OCHj.' +YCeHlO' + CH$* YCcH4OCH3*++YCe,Hr+
(1) (2) (3) (4)
Substituent Effects on Ion Intensities.-YCBH40+, YCsH5.+, and YC5H4+are major possible fragment ions in the mass spectra of phenyl methyl ethers; Table I summarizes the ratios of their ion intensities, relative to the intensities of their precursors, for a series of substituted anisoles. 'The data for anisole (Y = H) itself are taken as standards. In order to relate intensity (1) F. W. McLsfferty, M. M . Bursey, and S. M. Kimball, J . Am. Chem. Soc., 88, 5022 (1966). (2) F. -Meyer and A. G. Harrison, ibid., 86, 4757 (1964). (3) Some data for the (R.1 C o d . ion of particular aryl carbonates are consistent with this: P. Brown and C. Djerassi, i b X , 89, 2711 (1967), footnote 7. (4) M. M.Bursey and I?. W.McLafferty, ibid., 88, 5023 (1966). ( 5 ) M. M . Bursey and I?. W. McLafferty, ibid., 88, 529 (1966). (6) (a) C. S. Barnes and J. L. Occolowitz, Australian J . Chem., 16, 219 (1963); (b) C. 8. Barnes, D . J. Collins, J. J. Hobbs, P. I. Mortimer, and W . H. F. Sasse, ibid., 10,699 ( 1967). (7) H. Budzikiewicr, C. Djerassi, and D. H. Williams, "Interpretation of Mass Spectra of Organic Compounds," Holden-Day, Inc., San Francisco, Calif., 1964, p 174. ( 8 ) M. hl. Bursey and F. W. McLafferty, J . Am. Chem. Sac., 88, 4484 (1966). (9) M. M. Burnsey, and F. W. McLafferty, ibid., 89, 1 (1967). (10) J. M. S. Tait, T.. W. Shannon, and A. G. Harrison, ibid., 84, 4 (1962).
-
+
TABLEI ON THE ABUNDANCES OF YCsH5.+, SUBSTITUENT EFFECTS AT 5.0 V ABOVE I0NIZ64TIONPOTENTIAL YCEH~O',AND YC~HI+
Y
z-
Z-
[YCsHa. c ] [YCoHe OCHr +I
[YCsHtO [YCsHc OCHa. c ]
z -
H
0.00 0.00 0.00 0.00 -1.50 0.95 0.78 -2.16 m-NHt -0.01 -0.76 -0.84 -0.36 -1.54 0.81 0.65 -2.36 P-OH m-OH 0.42 -0.41 -0.49 -0.36 -2.02 p-OCHp 0.58 0.42 - 1.96 -0.92 m-OCHp -1.25 -1.27 0.04 -0.70 0.73 0.58 -1.08 P-F m-F 0.18 -0.57 0.04 -0.59 -1.13 p-c1 0.63 0.50 -0.88 m-C1 0.00 -0.54 -0.50 0.12 -1.40 p-Br 0.38 0.47 -1.03 -0.13 m-Br -0.23 -0.40 0.41 -1.71 0.51 -1.18 0.34 PI -1.40 m-I -1.70 0.34 -1.54 -2.74 0.21 0.05 -1.66 p-CeH5 -0.65 m-CaH5 -0.61 -0.56 0.12 -0.82 0.30 0.18 -0.64 p-CHa -0.38 m-CHa 0.06 0.02 -0.18 p-CHO -2.3 -1.7 -1.8 0.3 m-CHO -1.8 -1.2 -1.64 1.0 -1.55 p-COOH -1.6 -1.6 0.0 -0.88 m-COOH -0.84 -0.98 -0.90
