Modeling the Chemistry of Gaseous Cations Derived from Tricarbon Dioxide.

Cations CpOq+ (p ≤ 7 with q = 1,2) and CpO3+ (p = 4-7) and corresponding neutrals are modeled by B3LYP/jun-cc-pVTZ to rationalize previous mass spectrometric observations of ion reactions with neutral C3O2. Modeling yields optimized potential energies, geometries, Mulliken spin populations, electric dipole moments, electron configurations, and thermochemical parameters. Lewis diagrams are derived. Mono- and dioxide cations typically have unbranched carbon chains, but trioxides are branched. The ions are most stable as spin doublets, but low-lying quartets are found for monoxides with even p. For trioxide ions, the quartets for p = 5,7 are lower-lying than for p = 4,6. For neutral mono- and dioxides resulting from possible electron transfer to the ions, triplets are more stable than singlets for even p. Neutral trioxides are most stable as triplets except C5O3 with a singlet slightly more stable. Singlet C4O3 and C6O3 are unstable with respect to CO loss. Charge transfer is likely only for CpO+ (p = 1-3) and CpO3+ (p = 4, 6). Monocarbon insertion by C3O2 is understood as two sequential CO losses without a hypothetical C6O4+• intermediate and is thermochemically favorable for all ions considered.

Crystal structure of 9-methacryloylanthracene.

In the title compound, C18H14O, with systematic name 1-(anthracen-9-yl)-2-methyl-prop-2-en-1-one, the ketonic C atom lies 0.2030 (16) Šout of the anthryl-ring-system plane. The dihedral angle between the planes of the anthryl and methacryloyl moieties is 88.30 (3)° and the stereochemistry about the Csp (2)-Csp (2) bond in the side chain is transoid. In the crystal, the end rings of the anthryl units in adjacent mol-ecules associate in parallel-planar orientations [shortest centroid-centroid distance = 3.6320 (7) Å]. A weak hydrogen bond is observed between an aromatic H atom and the O atom of a mol-ecule displaced by translation in the a-axis direction, forming sheets of parallel-planar anthryl groups packing in this direction.

Gaseous cation chemistry and chain-length effects in electron ionization and collision-induced dissociation mass spectra of symmetric 1,n-bis(9-anthracenyl)alkanes.

The behavior of the gaseous cations resulting from EI (30 and 70 eV) of the bichromophoric title compounds 1-5 (for n = 1-5, respectively) is examined by ion-trap mass spectrometry, including collision-induced dissociation (CID) with variation in collision energy. These results are compared with those from anthracene and 9-methylanthracene and with previously reported mass spectrometric results for 3 and dicarbazolylalkanes. Rather than using the kinetic method to obtain ion energetics where the fragmentation mechanism is clear, as commonly done, the method is used here with relative complementary-ion abundances from CID to test the proposed fragmentation mechanisms using B3LYP calculations of relative ionization energies and optimized geometries of ionic and neutral fragments. Hydrogen migrations are common, and skeletal rearrangements including formation of expanded, fused and spiro rings are proposed in several cases. Of the chain cleavages, α-homolysis giving C(15) H(11) (+) , likely as dibenzotropylium, is most important for each of 1-5 except 3, where ß-cleavage to C(16) H(13) (+) dominates with a proposed methyldibenzotropylium structure. α-Cleavage was important also in the dicarbazolylalkanes. A previous inference of a McLafferty rearrangement to explain C(15) H(12) (+•) from 3 is not supported by the present results. The fragmentation behavior of 1-5 depends strongly on n and implies significant interchromophoric interaction between anthracenyl groups.