15 papers from the Heron5 Conference held July 10–16, 2010, are highlighted in this issue.

The prototypical directional weak interactions, hydrogen bonding and σ-hole bonding (including the special case of halogen bonding) are reviewed in a united picture that depends on the anisotropic nature of the molecular electrostatic potential around the donor atom. Qualitative descriptions of the effects that lead to these anisotropic distributions are given and examples of the importance of σ-hole bonding in crystal engineering and biological systems are discussed.

Flash vacuum thermolysis or vacuum gas solid reactions coupled with ultraviolet photoelectron spectroscopy and quantum chemical calculations is a very useful and powerful tool set for the synthesis and direct characterization instrument for the electronic structure studies of highly reactive species in the gas phase.

A kinetic analysis of the denitrogenation of 7,7-dimethoxy-1,4-diaryl-2,3-diazabicyclo[2.2.1]hept-2-ene derivatives with a variety of aryl groups was performed in the present study. The observed substituent effect was highly correlated with the radical-stabilizing parameters of benzylic-type radicals. Thus, stepwise denitrogenation is a mechanism for the thermal denitrogenation reaction.

There is a clear borderline of chemoselectivity in the reactions of organogold(i) complexes with donors of electrophilic halogen. While with I⁺, Br⁺, and Cl⁺ a halogenation is observed, with F⁺ an oxidative dimerization of the organic residue is induced.

An air-stable curved π-radical bearing a directly attached tert-butylnitroxide moiety has been synthesized and isolated. The extensive spin-delocalized nature of the corannulene skeleton and its high stability has allowed us to identify the origin of a dynamic electronic-spin behaviour, i.e. the temperature-dependent conformational change of the nitroxide moiety, with the help of density functional theory calculations.

The isomeric diradicals α,2-didehydrotoluene and α,4-didehydrotoluene have been isolated in argon matrices at 5 K and characterized by EPR spectroscopy. The triplet ground states of these species resemble both a phenyl radical and a benzyl radical. Alternatively, a carbene type structure can be formulated. Both didehydrotoluenes are π,σ-diradicals with a high spin triplet ground state. The figure shows the spin density distribution in α,2- (left) and α,4-didehydrotoluene (right), respectively.

The preparation of an isolable triplet carbene was attempted by the oxidation of an allene compound having two thioxanthene moieties (5). Relatively weak oxidants gave a monocationic vinyl species 8 via one-electron oxidation, whereas relatively strong oxidants furnished the dicationic ketal 9 as a consequence of two-electron oxidation and demethylation.

Photolysis of m- and p-azidomethylacetophenones results in the formation of long-lived triplet alkylnitrene intermediates. In competition with nitrene formation, these azides undergo cleavage to form benzyl and azido radicals. The triplet alkyl nitrenes react as scavengers and intercept the benzyl radicals.

Three routes are reported for the synthesis of the title compounds starting from dialkyl squarates. After introduction of unsaturated side chains, ring expansion is achieved to give 4-aminophenols, 4-amino-1-naphthols, or cyclopenta-annulated quinolines from 4-vinyl, 4-aryl, and 4-alkynyl derivatives, respectively.

N-Protected and propargylated 1-amino-2-aryl-2-cyclohexenes, which are readily prepared from the illustrated gem-dibromocyclopropane, readily engage in a Pd⁰-catalyzed intramolecular Alder–ene reaction to give C3a-arylhexahydroindoles, a motif encountered in a number of important alkaloids including tazettine.

A chemistry rationale is presented that provides a set of conceptual and practical tools for designing organic-inorganic materials of any conceivable nano-scaled structure whose arrangement can be predicted with quite reasonable accuracy. The confinement of organic molecules within layered zirconium phosphate leads to unusual properties in the solid state concerning the fields of recognition, chemically-driven porosity changes, supramolecular chirality, luminescence signalling, photoinduced electron-transfer, and gas storage.

Acetonitrile N-sulfide, CH₃CNS, is generated in a cryogenic argon matrix from 3,4-dimethyl-1,2,5-thiadiazole by UV irradiation, and the molecule is investigated by IR and UV spectroscopy. The structure and stability (uni- and bimolecular reactions) of this unstable species are studied by B3LYP, CCSD(T), and MR-AQCC quantum-chemical methods.

Thioketenes 7 and iminopropadienethiones 8 are generated sequentially by flash vacuum thermolysis of isoxazolones 6 and characterized by matrix-isolation IR spectroscopy, comparison with density functional theory-calculated spectra, and chemical trapping affording thioamides and thioquinolones.

[2]Paracyclo[2](2,7)pyrenophane and its constitutional isomer [2]metacyclo[2](2,7)pyrenophane have been synthesized using a valence isomerization/dehydrogenation reaction that proceeds rapidly at room temperature. Two structural parameters (Δd and θ) suggested that the latter system should be the more challenging target, but the former cyclophane proved to be tougher.

N-Acyloxy-N-alkoxyamides are anomeric amides that are stable at room temperature, but at elevated temperatures, in non-polar solvent, they undergo the characteristic HERON reaction of N,N-bisheteroatom-substituted amides. In this case, anhydrides and alkoxynitrenes are generated.