ISSN:
0030-493X
Keywords:
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The quadrupole ion-trap mass spectrometer is used to investigate aspects of the ion-molecule chemistry of the pyretic molecular radical cation (M+), the [M — H]+ ion and the [M — H2]+· ion. Cycloaddition and alkyl halide addition reactions with the reagents pyrene, methyl iodide, ethyl iodide, isopreue and 2-iodopropane are investigated. The pyrene molecular radical cation is remarkably unreactive while the closed shell [M — H]+ ion is highly reactive and the [M — H2]+· ion shows intermediate reactivity. Analogies are found between the behaviour of the pyrene molecular radical cation and the corresponding [M — H]+ ion on the one hand, and the benzene radical cation and the phenylium ion on the other. The total lack of reactivity of the M+· ion is attributed to π-delocalization of the radical and the cation over the large aromatic system. Addition of isoprene to the [M — H]+ and [M — H2]+· ions of pyrene occurs via cycloaddition reactions. A characteristic fragmentation of each adduct ion is methyl radical loss and evidence obtained using pyrene-d10 indicates that the product in the case of [M — H]+ is an ionized indene. Addition of methyl iodide, ethyl iodide and 2-iodopropane to the [M — H]+ ion of pyrene occurs to give an iodonium product (C16H9-I+-R) which fragments by loss of I· or CH3· to give the methylpyrene or iodopyreue product ions. Reactions of ethyl iodide and 2-iodopropane with the dehydropyrene ion, [M — H2]+·, give primarily an HI addition product, together with small contributions from the intact adducts. Evidence is provided suggesting that in this case the HI and alkyl halide molecules add across a C—C bond rather than forming an iodine-bound adduct. An experiment in which nine consecutive isolation and activation steps (MS10) are used to couvert the [2M — H]+ adduct, C32H19+, to C32H2+· exemplifies the intriguing ion chemistry and the stability of the carbon skeleton of the adduct ions.
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/oms.1210270417
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