The mechanism of alkyl radical loss from ionised alkenyl methyl ethers containing two γ-alkyl substituents, R1R2C=CHCH2OCH3+•, has been studied by investigating the collision-induced dissociation spectra of the resultant CnH2n–1O+ oxonium ions (n = 5–7). Comparison of these spectra with one another and those of reference ions generated by dissociative ionisation of secondary allylic alkenyl methyl ethers indicates that expulsion of a γ-alkyl group occurs without isomerisation of the heavy atom skeleton via an allylic rearrangement. This finding is consistent with the occurrence of two consecutive 1,2-H shifts in R1R2C=CHCH2OCH3+•, followed by γ-cleavage of the ionised enol ether, R1R2CHCH=CHOCH3+•, to give R1CH=CHCH=OCH3+ or R2CH=CHCH=OCH3+. Thus, CH3CH2CH2(CH3CH2)C=CHCH2OCH3+• loses C2H5• and C3H7• to yield CH3CH2CH2CH=CHCH=OCH3+ and CH3CH2CH=CHCH=OCH3+, respectively.
Get full access to this article
View all access options for this article.
References
1.
For an overview, see: BouchouxG., Mass Spectrom. Rev.7, 1 (1988); BouchouxG., Mass Spectrom. Rev.7, 203 (1988).
2.
For reviews, see: KingstonD.G.I.BurseyJ.T.BurseyM.M., Chem. Rev.74, 215 (1974); SchwarzH., in Advances in Mass Spectrometry 1985, Ed by ToddJ.F.J., John Wiley & Sons, New York (1986); TurecekF., in The Chemistry of Enols, Ed by RappoportZ., John Wiley & Sons, Chichester (1990).
3.
McAdooD.J.HudsonC.E.WitiakD.N., Org. Mass Spectrom.14, 350 (1979); McAdooD.J.HudsonC.E., Org. Mass Spectrom.18, 466 (1983); BowenR.D.HarrisonA.G., J. Chem. Soc. Perkin 21483 (1989), and references therein; HudsonC.E.McAdooD.J., Tetrahedron46, 331 (1986), and references therein.
4.
TurecekF.McLaffertyF.W., J. Am. Chem. Soc.106, 2528 (1984); LifshitzC.PeresT.OhmichiN.Pri-BarI., Int. J. Mass Spectrom. Ion Processes72, 253 (1986); BouchouxG.HoppilliardY.JaudonP., Org. Mass Spectrom.22, 98 (1987); BouchouxG.DjaziF.HoppilliardY.JaudonP.NoutsN., Org. Mass Spectrom.23, 33 (1988); for a review of earlier work, see: LifshitzC., J. Phys. Chem.87, 2304 (1983).
5.
YatesB.F.BoumaW.J.RadomL., J. Am. Chem. Soc.106, 5805 (1984).
6.
HammerumS., Mass Spectrom. Rev.7, 123 (1988).
7.
Reviews: MortonT.H., Tetrahedron38, 3195 (1982); McAdooD.J., Mass Spectrom. Rev.7, 363 (1988); MeyersonS., Org. Mass Spectrom.24, 267 (1989); HammerumS., in Fundamentals of Gas-Phase Ion Chemistry, Ed by JenningsK.R., Kluwer, Dordrecht, p. 379 (1990); BowenR.D., Acc. Chem. Res.24, 364 (1991); LongevialleP., Mass Spectrom. Rev.11, 157 (1992); McAdooD.J.MortonT.H., Acc. Chem. Res.26, 295 (1993).
8.
McLaffertyF.W., Anal. Chem.28, 306 (1956); GilpinJ.A.McLaffertyF.W., Anal. Chem.29, 990 (1957); McAdooD.J.WitiakD.N.McLaffertyF.W.DillJ.D., J. Am. Chem. Soc.100, 215 (1978); McAdooD.J.HudsonC.E.SkyiepalM.BroidoE.GriffinL.L., J. Am. Chem. Soc.109, 7648 (1987); see also Reference 2.
9.
van BaarB.L.M.TerlouwJ.K.AkkokS.ZummackW.SchwarzH., Int. J. Mass Spectrom. Ion Processes81, 217 (1987); HeinrichN.SchwarzH., in Ion and Cluster Ion Spectroscopy, Ed by MaierJ.P., Elsevier, Amsterdam, p. 329 (1988).
10.
BouchouxG.TortajadaJ.DagautJ.FillauxJ., Org. Mass Spectrom.22, 451 (1987); BouchouxG.BidaultF.DjaziF.NicodB.FillauxJ., Org. Mass Spectrom.22, 748 (1987).
11.
Molenaar-LangeveldT.A.FokkenR.H.NibberingN.M.M., Org. Mass Spectrom.23, 364 (1988).
12.
BowenR.D.WrightA.D.ThomasS.R.JenningsK.R.MaccollA., Org. Mass Spectrom.26, 421 (1991).
13.
McLaffertyF.W.BenteP.F.IIIKornfieldR.TsaiS.-C.HoweI., J. Am. Chem. Soc.95, 2120 (1973); LevsenK.SchwarzH., Angew. Chem. Int. Edn Eng.15, 509 (1976); CooksR.G., Collision Spectroscopy.Plenum Press, New York (1978); McLaffertyF.W., in High Performance Mass Spectrometry, Ed by GrossM.L., ACS Symposium Ser. 70, American Chemical Soc., Washington, DC (1978).
14.
BowenR.D.WrightA.D., J. Chem. Soc., Chem. Commun.1055 (1991); BowenR.D.WrightA.D., J. Chem. Soc., Chem. Commun.96 (1992); WrightA.D.BowenR.D., Can. J. Chem.71, 1073 (1993).
15.
NonhebelD.C.TedderJ.M.WaltonJ.C., Radicals.Cambridge University Press, Cambridge (1979); BeckwithA.J.L.IngoldK.U., in Rearrangements in Ground and Excited States, Ed by DeMayoP., Academic Press, Vol. 1, p. 162 (1980); BeckwithA.L.J., Tetrahedron37, 3073 (1981).
16.
CaoJ.R.GeorgeM.HolmesJ.L., J. Am. Soc. Mass Spectrom.3, 99 (1992).
17.
BowenR.D.WrightA.D.DerrickP.J., Org. Mass Spectrom.27, 905 (1992); BowenR.D.WrightA.D.ColburnA.W.DerrickP.J., Int. J. Mass Spectrom. Ion Processes116, 193 (1992).
