Reactivity Controlling Factors for an Aromatic Carbon‐Centered σ,σ,σ‐Triradical: The 4,5,8‐Tridehydroisoquinolinium Ion

The chemical properties of the 4,5,8‐tridehydroisoquinolinium ion (doublet ground state) and related mono‐ and biradicals were examined in the gas phase in a dual‐cell Fourier‐transform ion cyclotron resonance (FT‐ICR) mass spectrometer. The triradical abstracted three hydrogen atoms in a consecutive manner from tetrahydrofuran (THF) and cyclohexane molecules; this demonstrates the presence of three reactive radical sites in this molecule. The high (calculated) electron affinity (EA=6.06 eV) at the radical sites makes the triradical more reactive than two related monoradicals, the 5‐ and 8‐dehydroisoquinolinium ions (EA=4.87 and 5.06 eV, respectively), the reactivity of which is controlled predominantly by polar effects. Calculated triradical stabilization energies predict that the most reactive radical site in the triradical is not position C4, as expected based on the high EA of this radical site, but instead position C5. The latter radical site actually destabilizes the 4,8‐biradical moiety, which is singlet coupled. Indeed, experimental reactivity studies show that the radical site at C5 reacts first. This explains why the triradical is not more reactive than the 4‐dehydroisoquinolinium ion because the C5 site is the intrinsically least reactive of the three radical sites due to its low EA. Although both EA and spin–spin coupling play major roles in controlling the overall reactivity of the triradical, spin–spin coupling determines the relative reactivity of the three radical sites.     

Introducing the theory of relativity

A simple way of introducing the theory of relativity to chemistry students is presented. This is based on experimental observations of the variation in the mass of an electron with speed. Analysis of these generates the equations chemists use, and provides a basis for critical discussion of the theory.     

The first nitrosyl derivatives of high nuclearity carbonyl clusters: Synthesis and X-ray analysis of the [(Ph3P)2N]+ salts of the anions [Os10C(CO)24(μ2-NO)]− and [Os10C(CO)23(NO)]−

The carbido dianion [Os₁₀C(CO)₂₄]^2? reacts with NOBF₄ in MeCN to give [OS₁₀C(CO)₂₄(μ₂-NO)]^? (1) in which the nitrosyl ligand adopts a novel bonding mode bridging the wingtips of a “butterfly” indentation of metal atoms. The anion 1 undergoes rearrangement and CO loss in solution to give [OS₁₀C(CO)₂₃(NO)]^? (2); the overall molecular geometry of 2 is close to that previously found for the dianion [Os₁₀C(CO)₂₄]^2? with the nitrosyl ligand bonded in a terminal fashion to the tetrahedral Os₁₀ metal skeleton. Crystals of the [(Ph₃P)₂N]⁺ salt of 1 are triclinic, space group P$\text{1}$, with a 20.389(4), b 14.670(3), c 12.333(3) Å, α 99.55(3), β 94.43(3), γ 103.03(3)°, Z = 2, refinement of atomic parameters using 2699 absorption corrected data converged at R = 0.0952. The [(Ph₃P)₂N]⁺ salt of 2 crystallises with one molecule of CH₂Cl₂ in the triclinic space group P$\text{1}$, with a 19.374(3), b 16.813(3), c 11.791(2) Å, α 85.00(3), β 101.81(3), γ 99.43(3)°, Z = 2, refinement of atomic parameters using 8736 absorption corrected data converged at R = 0.0943.     

Gas phase ion molecule reactions of organometallic compounds; protonation of selected η6-arenetricarbonylchromium complexes and η6-cycloheptatriene complexes of the Group VI metals with various Brønsted acid reagent ions

η⁶-Arenetricarbonylchromium(0) complexes, (with the η⁶-arene = benzene, toluene, methylbenzoate and acetophenone) and η⁶-cycloheptatrienetricarbonyl complexes of chromium(0), molybdenum(0) and tungsten(0) undergo reactions in the gas phase with the Brønsted acid reagent ions H₃⁺, CH₅⁺, t-C₄H₉⁺, (NH₃)_nH⁺ which depend on the Brønsted acid strengths of these ions and also on the basicity of the metal complexes. Processes which involve either metal or ligand proton attachment, as well as charge exchange, electrophillic addition and rearrangement reactions have been identified. Some comparisons are drawn between these gas phase observations and the solutions phase behaviour of these compounds.     

Investigation of ternary cyclodextrin complexes by fluorescence spectrometry

Ternary complexes of cyclodextrin are apparently formed in the presence of saturated alcohols, glycols and acids. The role of third components in these complexes is investigated. Pyrene is used as a probe to determine the degree of compartmentalization, the change in the hydrophobicity of the microenvironment, and the formation constant.