7648
J. Am. Chem. SOC.1987, 109, 7648-7653
Ion-Neutral Complexes as Intermediates in the Decompositions of C5Hlo02'+Isomers David J. McAdoo,*+Charles E. Hudson,? Mark Skyiepa1,t Ellen Broido,+and Lawrence L. Griffin$ Contribution from the Marine Biomedical Institute and Department of Human Biological Chemistry and Genetics, University of Texas Medical Branch, Galveston, Texas 77550, and Department of Marine Sciences, Texas A&M University at Galveston, Galveston, Texas 77553. Received January 7 , 1987
Abstract: Ionized pentanoic acid, 3-methylbutanoic acid, and the enol isomer of ionized isopropyl acetate are shown to pass in part through common intermediates before decomposing to CH3CHC(OH)2+(7)and the "McLafferty + 1" ion CH3C(OH)2+ (10). The H transfer to form the methyl of CH$(OH),+ and the joining of two CH2 groups to form the C-C bond in the ethylene eliminated to produce CH3CHC(OH)2+are both attributed to reactions of the ion-neutral complex [CH3CH=CH2 CH2C(OH),+]. The McLafferty + 1 ion is also formed, especially from ionized esters, by another pathway in which complexes may or may not be intermediates. The intermediacy of the ion-neutral complexes is supported by energetic considerations, isotope effects, and the decomposition patterns of labeled ions. The latter correlate with a preference for hydrogen transfer from the end carbons of the C3 partner in other reactions proposed to be complex-mediated. Unification of the McLafferty rearrangement, the McLafferty 1 rearrangement, and the McLafferty rearrangement with charge reversal by a common initial y-hydrogen rearrangement followed by dissociation or isomerization in ion-neutral complexes is proposed. Group migration by 1,2-shifts, possibly by dissociation to form a double bond in one partner in an ion-neutral complex followed by addition at the opposite end of the double bond, is shown to be a general reaction of ions in the gas phase.
+
+
"McLafferty 1" ions are formed in the mass spectrometer by double hydrogen transfers accompanied by @-cleavagein ionized esters,] acids,2 ketone^,^ and other ions.4 These ions are formed ' 0H RCH2CH=CH2
+
II
kH2CR'
McLafferty rearrangement
1
/,.+II
-
RCH~CHZCH~CH~CR'
*OH RCHzCHtHCHz
+
II
CHaCR' McLafferty 1 rearrangement
\
II
RCH=CHCHi+
CHaCR'
+
charge reversal
CH2C(OH),+] that could be tested by characterizing the parallel formation of C3H,O2'+ (see Scheme I). This mechanism would also have to apply to CH3C(0H),+ and CH3CHC(OH),'+ formation from ionized pentanoic acid ( l ) ,as 1 and 2 reach those products through common intermediate^.^ W e will conclude that ion-neutral complexes are intermediates in the formation of McLafferty + 1 ions and then show that a variety of ionic decompositions can be rationalized by related mechanisms. A similar mechanism has been recently proposed to account for formation of acetic acid plus ionized 2-butene from ionized hexanoic acid.1° ( I ) (a) Sharkey, A. G.; Schultz, J. L.; Friedel, R. A. Anal. Chem. 1959, 31, 87-94. (b) Beynon, J. H.; Saunders, R. A,; Williams, A. E. Ibid. 1961, 33, 221-225. (c) Godbole, E. W . ;Kebarle, P. Trans. Faraday Sot. 1962, 58, 1897-1904. (d) Djerassi, C.; Fenselau, C. J . Am. Chem. Sot. 1965, 87, 5756-5762. (e) McFadden, W. H.; Boggs, L. E.; Buttery, R. G. J . Phys. Chem. 1966, 70, 3516-3523. (f) Benoit, F. M.; Harrison, A. G.; Lossing, F. P. Orp. Mass Sbectrorn. - r - ~ - 1977. 12. 78-82. (e) Borchers. F.: Levsen. K. Inr. j..M a s s Spectrom. Ion Phys. '1979, 31, 24jTi56. (2) (a) Weber, R.; Levsen, K.; Wesdemiotis, C.; Weiske, T.; Schwarz, H. Int. J. Mass Spectrom. Ion Phys. 1982,43, 131-155. (b) Halim, H.; Schwarz, H.; Terlouw. J. K.; Levsen, K . Ora. Mass Spectrom. 1983, 18, 147-149. .(3) (a) Carpenter, W.; Duffield,-A. M.; Djerassi, C. J . Am. Chem. Sot. 1968, 90, 160-164. (b) Bente, P. F.; McLafferty, F. W.; McAdoo, D. J.; Lifshitz, C. J . Phys. Chem. 1975, 79, 713-721. (4) McLafferty, F. W. Chem. Ind. (London) 1958, 1366-1367. ( 5 ) (a) Wendelboe, J. F.; Bowen, R. D.; Williams, D. H . J . Am. Chem. Sot. 1981, 103,2333-2339. (b) Hudson, C. E.; McAdoo, D. J. Int. J . Muss Spectrorn. Ion Processes 1984, 59, 325-332. (c) Traeger, J. C.; Hudson, C. E.; McAdoo, D. J. J . Phys. Chem., in press. (d) McAdoo, D. J.: Traeger, J. C.; Hudson, C. E.; Griffin, L. L. J . Phys. Chem., in press. (6) (a) Bowen, R. D.; Stapleton, B. J.; Williams, D. H. Chem. Commun. 1978, 24-26. (b) Bowen, R. D.; Williams, D. H . Int. J . Mass Spectrom. Ion Phys. 1979, 29, 47-55. (c) Morton, T. H . J . Am. Chem. Soc. 1980, 102, 1596-1602. (d) Hall, D. G.; Morton, T. H. Ibid. 1980, 102, 5688-5691. (e) Longevialle, P. Chem. Commun. 1980, 823-825. (0Schwarz, H.; Stahl, D. Int. J . Muss Spectrom. Ion Phys. 1980, 36, 285-289. (9) Biermann, H . W.; Freeman, W. P.; Morton, T. H . J . Am. Chem. Soc. 1982, 104, 2307-2308. (h) Morton, T. H . Tetrahedron 1982, 38, 3195-3243. (i) Longevialle, P.; Botter, R. Inr. J . Mass Spectrorn. Ion Phys. 1983, 47, 179-182. ti) Tumas, W.; Foster, R. F.; Brauman, J. I . J . A m . Chem. Soc. 1984, 106, 4053-4054. (k) Holmes, J. L.; Mommers, A. A,; Szulejko, J. E.; Terlouw, J . K . Chem. Commun.1984, 165-167. (I) Longevialle, P.Org. Muss Specfrom. 1985, 20, 644-645. (m) Bather, W.; Grutzmacher, H . Int. J . Mass Spectrom. Ion Processes 1985, 64, 193-212. (7) Audier, H . E.; Sozzi, G. Org. Mass Specfrom. 1984, 19, 150-151. (8) (a) McAdoo, D. J.; Hudson, C. E. A h . Muss Specfrom. 1985, 823. ( b ) Hudson, C. E., Griffin, L. L.; Broido, E.; Skyiepal, M. D.; McAdoo, D. J. Proc. 34th Annu. Conf: Mass Spectrom. Allied Top. 1986, 983-984. (9) (a) Audier, H.; Milliet, A.; Sozzi, G. Bull. Sot. Chim. Fr. 1985, 833. (b) Audier, H.; Sozzi, G. N o w . J . Chim., in press. (10) van Baar, B. L. M.; Terlouw, J . K.; Akkok, S.; Zummack, K. W.; Schwarz, H. Int. J . Mass Specfrom. Ion Processes, in press. 0
in parallel with the McLafferty rearrangement and the McLafferty rearrangement with charge reversal. Despite much study,'-4 satisfactory mechanisms for formation of many McLafferty 1 ions have never been proposed. Issues have included whether the two hydrogen transfers are stepwise or simultaneous,'C*dand, if stepwise, which hydrogen is transferred first.2a However, the most significant question is: how do bonds to itinerant hydrogens from alkyl chains replace the C-C bonds cleaved in the decompositions? Alkane eliminations from ions in the gas phase, which also involve replacement of a C-C by a C-H bond, probably achieve this by cleavage to ion-neutral complexes followed by hydrogen abstraction?
+
O'+
II R C H p '
-
O+
111
CRCH2C R ' l
-
RCH=C=O'+
+
R'H
Similar steps have been suggested for formation of McLafferty 1 ions.sb Passage through electrostatically bound complexes has been proposed6 to rationalize products of many other ionic decompositions in the gas phase. Audier and Sozzi' have shown that ionized 3-methylbutanoic acid (2) produces the McLafferty 1 ion C H 3 C ( 0 H ) , + containing C1 and C2, and C3H602" containing C1, C3, and a C4. This suggested* a mechanism for CH3C(0H),+ formation involving the complex [CH3CH=CH2
+ +
'Marine Biomedical Institute. 'Texas A&M University.
0002-7863/87/1509-7648$01.50/0
~
~
0 1987 American Chemical Society
J . Am. Chem. SOC.,Vol. 109, No. 25, 1987 1649
Ion- Neutral Complexes in the Decomposition of C5Hlo02'+ Scheme I
CH3CH2CH2CH2C
1 -
O' H
I
CH
1 2 /
CHCH,OC
/
5
i HO + OH
&,! C C H , CI H C H , ~ H ~
1;;'
6 -
-
t~"
CH,=CH,
C H ~ C
+
iCH2
.jcx ;I
~
,I:CH2
10 b'H
H-0
\CH3
/-1-
)cH3
'CH,
,OH /OH+
CH3EHiH2
+
CH3C
Yo \OH
16 -
Table I. Decomposition Patterns of Metastable C5Hl,0,'+ Ions product ion
CH,C(OH),+
CH,CH2CH2CH2C02H'+ CH,CH~CH~CHC(OH)~+ (CH3),CHCH2C02H'+ (CH,)2CHCHC(OH)2+ CH,CH,CH(CH,)CO,H'+ CH,CH,C(CH3)C(0H),+ CH3C0,'+CH(CH,)2 CH,C(OH)OCH(CH,)+ CH3C02'+CH2CH3CH3 CH2C(OH)OCH2CH2CH3+
CH,C(OH),' 94 0.6
3
CH2=CHC(OH)2+
50
100
0.3 63
51
2 9
2
49
100 100 100
0.3
0.4
2 8
100
1
2
1
100 3
C4H702+
39
100
2
CH3CHC(OH),+
100
100
5
100
4
Table 11. Decomposition Patterns of 13CC,Hlo02'+Ions product' ion
CH3CH2'3CH2CH2C02H'C CH,'3CH,CH,CH2COzH'+ 13CH,CH,CHzCH2C0,'+H CHzC(+OH)O'3CH(CH3)2
CH3C(OH),+
13CH,C(OH),+
100
100 100 100
m/z 73 42 47
2 2
37
m/z 74 81
51 68 0.6
13CC2H,02'+ 15'(17) 31 (32)
C4H702+
13CC,H,0,+
1
25 51
36
31
32'(18)
12
Values in Darentheses were obtained from decomuositions in the first field-free region of a DuPont 21-491 mass spectrometer. bFirst field-free region = 9. 'First field-free region = 10. Table 111. C2(H,D)S02+* Patterns from Metastable C5(H,D)loOz'+Ions
Derived from Acids product' ion CzH502' CzHdD02' C2H3D202' CzHzD30' CH3CH2CH,CH2C02D'+ 88 56 CH3CH2CHzCDzCOzH'+ 8 10 69 CH3CHzCD2CH2CO2H'+ 33 31 4 CH3CDzCH2CH2C02H'+ 100 70 3 CD3CH2CH2CH2C02H'+ 31 92 39 I (CH3)zCHCHzCOzD'+ 100 7s CH3CH(CD,)CHzCOzH'+ 26 100 41 (CH3)2CHCD2C02H'+ 5 100 'Each value is normalized to the most intense peak in the spectrum = 100. This intensity may appear in Table IV, or may be due to C4(H,D),02+formation.
Results and Discussion Similarity of the Decompositions of CH3CH2CH2CH2CO2H+, (CH3)2CHCH2C02H+, and &2C(+OH)OCH(CH,)2. Metastable decomposition patterns of assorted C 5 H l o 0 2 ' +isomers and labeled
+
Table IV. C3(H,D)502+ C3(H,D)602'+Patterns from Metastable C5(H,D),002'+Ions Derived from Acids product m/za ion
CH$H2CH,CH2CO,D" CH3CHzCH,CD2C02H'+ CH3CH2CD2CH2C02H'+ CHjCD2CH2CH2C02H" CD,CH,CH2CHZC02H'* (CH3)2CHCH2CO2D'+ CH3CH(CD3)CH2C02H'+ (CH3)2CHCD2C02H'+
73 4
56 31 79 54
3
74 100 56
75 96 100
16
16 3
100 100 51
25
68 25
11
2 62 59
64
43
47
11
21 60
''Values normalized as in Table 111.
forms thereof are given in Tables I-VI. The C5HI0O2'+spectra divide roughly into those dominated by CH,C(OH),+ and C 3 H 6 0 2 ' +formation and those dominated by C3H502' and/or
1650 J . Am. Chem. SOC., Vol. 109, No. 25, 1987
McAdoo et al.
Table V. C2(H,D)502' Products of Metastable CI(H,D)lnO,'+
Ester Ions Droductb
ion
C2HSO2"
CD,C('OH)OCH(CH,), CD3C02"CH(CH3), CH,C('OH)OCD(CH,), CH3C02'+CD(CH3)2 CH2C(+OH)OCH(CD3), CH,C( *OH)OCH(CD3)CH3 CH3C02"CH(CD3)2 CH3CO,"CH(CD3)CH3 CD3C02"CH,CH,CH3 CH3CO2'+CD2CH,CH, CH3CO2'+CH2CD,CH3 CH3CO;'CH,CH2CD3 CH~C(+OH)OCD,CH,CH, CH2C('OH)OCH2CD2CH3 CH2C('OH)OCH2CH2CD3
C2H4D02' 10
C2HD402'
C2H3D202+
C2H3D202'
100 100
100 100 9" 3 1.5a 2
3.1 3 14 100 1.5 100
100 2 1 100 1
19 100 100 11 100' 1OOd
100
22
100 3 4
3
0.7
100
2
2
bValues normalized similarly to those in Table 111. c,dWaterlosses in the CAD spectra of products of metastable decomposition demonstrate near exclusive formation of 'CH2DC(OH),+ and dCH3C(OD)OH'. "C,H,DO,".
Table VI. C3(H,D)602'+Products of Metastable C,(H,D),,O;'
Ester Ions product"
ion
C3H602'+
CD2C('OH)OCH(CH3)2 CD,CO,"CH(CH,), CH,C(+OH)OCD(CH,), CH,CO,"CD(CH3)2 CH2C('OH)OCH(CD3), CH,C('OH)OCH(CD3)CH3 CH3CO,'+CH(CD3), CH3C02"CH(CD3)CH3 ~~
C3HSD02'+
C3H4D202"
16
1.1
1.8
50.2 1.2
2.4 0.5
0.5 1
C3H3D302"
C3H2D402'+
54
