Ion—molecule chemistry of pyrene in an ion‐trap mass spectrometer

Abstract

The quadrupole ion-trap mass spectrometer is used to investigate aspects of the ion-molecule chemistry of the pyrene molecular radical cation (M+9, the [M -HI + ion and the [M -H,] +' ion. Cycloaddition and alkyl halide addition reactions with the reagents pyrene, methyl iodide, ethyl iodide, isoprene and 2-iodopropane are investigated. The pyrene molecular radical cation is remarkably unreactive while the closed shell [ M -HI + ion is highly reactive and the [ M -H,) +' ion shows intermediate reactivity. Analogies are found between the behaviour of the pyrene molecular radical cation and the corresponding [ M -HI + 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 x-delocalization of the radical and the cation over the large aromatic system. Addition of isoprene to the (M -HI + and (M -H,j + * ions of pyrene occurs via cycloaddition reactions. A characteristic fragmentation of each adduct ion is methyl radical loss and evidence obtained using pyrene-d,, indicates that the product in the case of [ M -HI + is an ionized indene. Addition of methyl iodide, ethyl iodide and 2-iodopropane to the [ M -H j + ion of pyrene occurs to give an iodonium product (C,,H9-I+-R) which fragments by loss of I' or CH,' to give the methylpyrene or iodopyrene product ions. Reactions of ethyl iodide and Ziodopropane 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 (MS'O) are used to convert the [ 2M -HI + adduct, C,,H:, , to C32Hz' exemplifies the intriguing ion chemistry and the stability of the carbon skeleton of the adduct ions.

Evidence of neutral radical induced analyte ion transformations in APPI and Near-VUV APLI

“…7 is calculated to be in the range of ⌬G R ϭ 4.48 eV and 4.57 eV. Once the pyrenyl cation is formed it shows high reactivity towards neutral radical species and even closed shell molecules such as H 2 O [15,29,32]. The addition of O( 3 P) and OH (no.…”

Quadrupole ion trap studies of fundamental organic reactions

“…In early demonstrations of the capabilities of ion traps for studying organic reactions, Cooks and co-workers (Einhorn, Kenttamaa, & Cooks, 1991;Nourse, Cox, & Cooks, 1992;Soni et al, 1995a;Soni, Wong, & Cooks, 1995b) examined several systems including Diels Alderlike cycloaddition reactions between acyl cations and isoprene. Some of these reactions previously had been explored in great detail using triple and pentaquadrupole instruments (Eberlin & Cooks, 1993;Eberlin et al, 1995).…”

Hydrogenation and Charge States of PAHsPAHs in Diffuse Clouds. I. Development of a Model

“…First we note that the SOMO (the singly occupied molecular orbital, which is also the highest occupied molecular orbital) of a PAH cation is spread over the carbon skeleton, due to the delocalization of radical character (Nourse, Cox, & Cooks 1992). When a hydrogen atom approaches a conventional PAH`doublet such as benzene, naphthalene or pyrene cation, it will interact primarily with this SOMO, which bears only one unpaired electron (Fleming 1976).…”