, which correspond to the expulsion of one of the substituents on the central carbon atom. These fragment ions further decompose into various ions following hydrogen or skeletal rearrangement in the metastable time window. In a review of the mass spectra of compounds of this type, Beynon et al. have emphasized that deuterium labeling would seem to offer the only means of elucidating the true fragmentation process. ) from 1,1-dimethoxyethane, (CH 3 CH(OCH 3 ) 2 , 2).6 Further, they have reported that the metastable ion at m/z 45 (CH 2 =O CH 3 ) from 1 Á decomposes into the m/z 29 ion (CH 4 loss) in preference to the m/z 19 ion (C 2 H 2 loss). 7 The structure of the m/z 59 ion) from 2 Á has been investigated by measuring the intensity ratio of m*(H 2 O) and m*(C 2 H 4 ), where m*(X) is the intensity of the metastable peak corresponding to the loss of X from the m/z 59 ion. 8 The suggestion of Beynon et al.3 prompted us to reinvestigate the fragmentation mechanims of RR'C (OCH 3 ) 2 ions by using mass-analyzed ion kinetic energy (MIKE) spectrometry and D-labeling. In a preliminary report, we have proposed that sequential transfers of a methyl group and a hydrogen atom occur during the fragmentations of [M À H] from 1 and 2. 9 In this paper, more detailed fragmentation pathways of 1 and 2 are reported. The relative abundances of the ions in the MIKE spectra are rationalized by considering the total heat of formation (AE DH f ) of the ion plus the neutral fragment.
EXPERIMENTALThe mass and unimolecular MIKE spectra were obtained using a JEOL JMS-HX100 tandem mass spectrometer. The electron energy was 70 eV, and the ion accelerating voltage was 5 kV. The CID spectrum of protonated ethanol was obtained using a JEOL JMS-DX303 tandem mass spectrometer equipped with a chemical ionization (CI) source. The electron energy was 200 eV, and the ion accelerating voltage was 3 kV. Samples were introduced via a heated (100°C) inlet system from which they were leaked into the ion source (180°C).Samples 1, 2 and ethanol were research grade products from Tokyo Kasei Co. Ltd, and were used without further purification. Ethanol was used as a reference compound. Isobutane was used as a reagent gas for CI. Samples 1-d 6 , (CH 2 (OCD 3 ) 2 ), and 2-d 6 , (CH 3 CH(OCD 3 ) 2 ), were prepared
Loss of CO from the molecular ions (I CH,OC,H,COF 1 ' *) of o-, m-and p-anisoyl fluorides has been investigated by mass-analysed ion kinetic energy (MIKE) spectrometry. Tbis reaction involves fluorine atom migration from the carbonyl group to the benzene ring. In the cases of o-and p-anisoyl fluorides, the fluorine atom migrates via a three-membered transition state to form the molecular ions (I CH,OC,H,FJ ' *) of o-and p-fluoroanisoles, respectively. On the other hand, in the case of m-aaisoyl fluoride, the fluorine atom migrates from the carbonyl group to the benzene ring via a three-or four-membered transition state.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.