(Aza)Acenes Share the C2 Bridge with (Anti)Aromatic Macrocycles: Local vs. Global Delocalization Paths

Breaking Global Diatropic Current to Tame Diradicaloid Character: Thiele's Hydrocarbon Under Macrocyclic Constraints

A diradical/biradical character of organic derivatives is one of the key aspects of contemporary research focusing on the fundamental studies followed by potential applicability relying on the unique optical, electronic, or magnetic properties assigned to unpaired electrons. A precise involvement of two p-phenylenes into a cyclophane-like conjugated, diatropic system creates a flexible molecule with the two different characters of both subunits (benzene and quinone) imprinting into the structure a Kekulé delocalized system. A dynamic of both carbocyclic subunits, and their mutual interaction generates a singlet open-shell state (J=-1.25 kcal/mol) as documented spectroscopically (NMR and EPR). The extended theoretical analysis has proved a correlation between dihedral angle and the diradicaloid character that shifts from a closed-shell singlet to an open-shell state, eventually showing the y0=0.86 for 78 degrees and ΔEST=-0.34 kcal/mol.

Diagnosing Ring Current(s) in Figure-Eight Skeletons: A 3D Through-Space Conjugation in the Two-Loops Crossing

The macrocyclic structures with local conjugation readily undergo a redox-triggered change in the diatropic character, leading to a global current–density pathway of the doubly charged systems. The figure-eight geometry of the neutral dimer does not significantly change upon oxidation according to the spectroscopic and computational data. The oxidation leads to 3D cross-conjugation at the intersection of the two ethylene bridges resulting in a global ring current.

Tropo(thio)ne-Embedded HomoHPHACs: Does the Tropylium Cation Induce Global Antiaromaticity in Expanded Hexapyrrolohexaazacoronene?

Tropo(thio)ne-embedded homoHPHACs and their dications were synthesised by an electrophilic annulation of secoHPHAC and successive oxidation. 13C NMR spectra of the dications represented global 22π homoaromaticity via homoconjugation, while alkylation...

Edge Decoration of Anthracene Switches Global Diatropic Current That Controls the Acene Reactivity

The 14π-electron system of anthracene has been merged with the unsaturated Z-1,2-difurylethene to form a macrocycle(s) with the retained local conjugation of all incorporated subunits that were substantially modulated with a redox activation, opening a global delocalization involving all integrated aromatics. In addition, the edge modulation of acene via the attachment of a specific isomer of the conjugated system gives steric confinements that are characteristic of small macrocycles, forcing substantially short C(H)···O electrostatic interactions that are documented spectroscopically with the support of X-ray analysis.

Reductive Dimerization of Macrocycles Activated by BBr3

A macrocyclic motif composed of carbazole and pyridine subunits linked by a carbonyl bridge (C=O) forms a skeleton with a peripheral reactivity that leads to a pinacol-like coupling activated by BBr₃, eventually entrapping a substantially elongated C–C bond. Slightly modified conditions lead to the efficient transformation of the C=O unit to a CH₂ linker that, after exposure to air, gives a dimeric molecule with multiple bonds between two macrocyclic units, as documented in spectroscopy and X-ray analysis.