Gas Phase Reactions of Carbon Cluster Ions with Crotononitrile

Abstract

Ion/molecule reactions of carbon cluster ions (Cn'+, n = 10-20) in the gas phase with crotononitrile (CRN) were investigated by Fourier transform ion cyclotron resonance spectrometry (FT-ICR). The carbon cluster ions studied were generated by electron impact ionization of perchlorinated aromatic compounds and subsequent elimination of all C1 substituents from the molecular ion. Clear pseudo-first-order reactions were observed for the carbon cluster ions Cn*+ thus formed without any sign of isomeric clusters of different reactivity. AM1 calculations of the stability of C&l, ( x = 4 , 6 , 8 ) derived from octachloronaphthalene indicate that the most stable monocyclic C,'+ are formed by this method. The reactions of C,'+ with C R N at a low operating pressure (1.2 X 1o-S-8.0 X le7 mbar) include the formation of adduct ions stabilized by radiative emission or/and loss of a neutral species (H or HCN) from the adduct ion. Rate constants for the reaction with C R N are distinctly larger than for the cluster reactions with H C N and acrylonitrile, and an exceptionally large reaction efficiency is found for C13*+ and C17*+. This correlates inversely with the thermochemical stability of the carbon clusters. The nature of the reaction products depends on the C number of C,'+. Consecutive reactions of the primary product ions Cn+4H4N+, formed by loss of H from the adduct ion, were observed only for reactions of even numbered Cn'+. On collision induced dissociation (CID) the adduct ions from Cn*+ ( n = 11, 13) redissociate to the original cluster ion while the adduct ions of C17*+ lose C3 and c 6 (2C3). A reaction model explaining these observations is proposed.

Gas-phase reactions of carbon cluster ions with isomeric chloropropenes

“…The efficiencies for the reactions both with AC and CP exhibit a clear dependence on the size of the carbon cluster ion and are especially large for Cic and CiT compared to their neighbors. An analogous dependence of reactivity on cluster size has been observed for the reactions of CA+ with acrylonitrile [8], crotononitrile [9], and benzene [6]. In the latter case Dunbar and Pozniak were able to extend this series of cluster ions with (4r + 1) carbon atoms and enhanced reactivity to C;:.…”

“…Thus, Cic reacts about two times faster with CP than with AC, while for Cij+ a factor of five and for the less reactive "aromatic" Ci;' and Gil a factor of 30 and > 100, respectively, is observed. A similar systematic difference in C,+ reactivity was observed for the reactions with acrylonitrile and crotononitrile in favour of the latter reagent [9]. This was not attributed to the increased number of degrees of freedom of crotononitrile which increase the lifetime of the collision complex, but to the lower IE of crotononitrile (10.22 eV [17]) compared to acrylonitrile (10.91 eV [17]).…”

“…As has been discussed elsewhere [9], one expected for isomeric CA+. In view of the mechanism to account for the transformation large excess of energy which has to be of a polycyclic perchloroarene into a monoimparted to the arene molecular ions for cyclic carbon cluster is a sequence of retroexhaustive dechlorination, it is likely that Bergman cyclizations [15] depicted in Fig.…”

“…Contrary to these latter reactions no adduct ions are formed, but ions Cn+3 Hz are formed exclusively by loss of Cl from the adducts. The loss of H from adduct ions was already observed as an additional reaction channel for the reactions with crotononitrile [9] and benzene [6], but only for odd numbered CA+. However, in spite of the exclusive formation of C,, 3H; from all CA+ by reactions with AC and CP, the nature of the product ions is clearly different for odd and even numbered CA+ also in these cases.…”

“…Recently, we have shown that the reactions of CA+ (n = 10-20) with acrylonitrile [S] and crotononitrile [9] yield adduct ions, very likely by radiative stabilization, analogous to the reaction with HCN. However, for it = 10 and 13 the rate constants of the reactions with these unsaturated nitriles are about 100 times larger than those with HCN [lo].…”