It is dcnionstratcd in mass spcctromctry that alkylamincs substitutcd at C2 and containing weak internal cncrgy isorncrizc in thc gas phasc into intermediary ions composcd of ionizcd cyclopropanes co~nplexcd with an ammonia niolcculc. This process is induced by a C3 hydrogen shift on thc nitrogen atom.. Aftcr opening of thc cyclopropanc, thc dissociation of thcsc complcxcs lcads to rn/z 44, 58. and 72 ions having [CH3(CH2),,CH NHZ] structures. Thc nicclianisni of thcir formation is dcmonstratcd by thc MlKE spectra of I3C and deutcriurn labcllcd compounds. Thc cxpcrirncntal rcsults arc in good agrccment with thosc described by Gross e! ell.. who studied thc fragmcntation of thc complcxcs fornicd during thc reaction bctwccn substitutcd ionizcd cyclopropancs and ammonia in thc gas phasc.
Radical cations derived from the ethers ROCH,CH,OR (R, R = H, CH, , C,HJ were studied, since Bdistonic oxonium ions are often prepared from ionized ethers of glycol. The first step in the fragmentation is a 1,Stransfer of an a-hydrogen to oxygen of a terminal alkoxy group leading to a Wistonic oxonium ion. This step is thermoneutral and reversible in the ROCH,CH,OH radical cations and exothermic and irreversible in the dialkyl ether radical cations. Depending on R and R', these Sdistonic oxonium ions fragment by three reactions: the loss of an alcohol or a water molecule, the formation of a /Idistonic oxonium ion 'CH2CH20(H)+R and a 1,QH migration between carbon atoms. Competition between these processes is discussed.
The reactions of propyl ether radical cations close to threshold are initiated by (reversible) formation of ydistonic isomers, R6(H)CH,CH,CH,'. The three methylene groups in these ions lose their positional identity by ring closurelring opening via [ cyclopropane + alcohol] + ' intermediates. Extensive hydrogen exchange occurs within the C,-chain. When R is not methyl the y-distonic isomer undergoes further intramolecular hydrogen atom transfer reactions that lead to formation of a-and /l-distonic ions. The a-distonic isomers expel ethyl and propyl radicals by C -0 bond cleavage.
LElTERS TO THE EDITORThe n(T) curves of the m/z 56 ions are identical, and likewise for the mlz 73 ions.The three CA spectra are also identical.These results lead to the conclusion that all the m/z 74 ions studied have an enolic structure [CH,CH==C-(OH),]+..The formation of this mlz 74 ion by decomposition of 1 cannot be explained by rearrangement mechanisms through cyclopropane or cyclobutane diol intermediates (Scheme 1): the transposition a would lead to a permutation of the carbons of the chain without modification of the structure of the molecular ion. Moreover, the labelled derivatives indicate unambiguously that such a permutation does not occur (Table 2). The pathway 0 would lead to the tert-pentanoic form which cannot be a precursor of the [M-C2HJ ion.On the other hand, the isomerization process y (Scheme 1) explains ethylene elimination and is in full agreement with the MIKE spectra of labelled derivatives (Table 2): the H(2) hydrogens are eliminated (lb) but the H(3) hydrogen remains in the ion (lc). H exchanges between y-hydrogens and the hydroxylic hydrogen occur prior to the loss of ethylene.In the spectrum of l a m/z 74 is shifted to the extent 74% to mlz 75 but 25% remains at m/z, 74 (statistical distribution would lead to 28.5171.5). Similarly, the peak is shifted to m/z 78 (73%) and m/z 79 (26%) on the spectrum of Id and only to mfz 79 for le.Further work is in progress to determine the origin of the m/z 61 and m/z 87 ions generated from the different pentanoic acids.
De*ar SirThe MIKE spectra of cyclohexylamine (1) and 2-methylcyclopentyIamine (2) are identical (Table 1) and differ from the spectrum In contrast with la, lb, 2a and 26, hydrogen scrambling of amino and C(1) hydrogens occurs prior to fragmentation of 4a and 4b (Table 2).The first step in the decay of 4 is the protonation of the nitrogen by 1-4 hyd- LETTERS TO THE EDITOR cyclopentylmethylamine described in this study is very similar to the process observed for 2-or 3-substituted alkylamines.' Yours
A Fourier transform ion cyclotron resonance study of the gas-phase reaction of W+ with allene is reported. W+ successively dehydrogenates at least nine allene molecules, leading to the formation of a series of WC,,H:, ions, with WC,,H:8 as the largest product observed after a reaction delay of 40 s. Starting from the third reaction, there is a competition between elimination of H, and C,H, at each step. The activation of propyne was also investigated and found to lead to essentially the same sequence as with allene. The reaction of W+ with 1,l-d,-allene and collision-induced dissociation spectra of product ions are used to discuss a plausible mechanism for the formation and structures of some of the species observed.
The MIKE spectra of amines RCH,NH, containing more than five carbon atoms exhibit m/z 44 and m/z 58 peaks. 'Ihe structures of these [C&NI' and [-I+ ions have been established by collisional activation spert~ The results are in agreement with the fragmentation mechumspreviously proposed.
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