Synthesis of a Highly Aromatic and Planar [10]Annulene

As the next neutral structure following Hückels rule, a planar and aromatic [10]annulene is ideal to study the link between ring size and aromaticity. However, the puckered geometry of the parent [10]annulene suggests that the aromatic stabilization energy is not sufficient to overcome the ring strain that exists when the system is forced into planarity. It has been shown computationally that this ring strain can be alleviated through the addition of two or more cyclopropane rings to the periphery, thereby creating theoretically aromatic structures. An alternative strategy to eliminating the issue of ring strain was demonstrated experimentally with the successful preparation of the highly aromatic 1,6-didehydro[10]annulene. However, the system rapidly cyclizes at -40°C to a naphthalene diradical due to the close proximity of the in-plane p-orbitals present in the system. Here we show that cyclopropanating one side of the unstable annulene successfully prevents the destabilizing cross-ring interaction while maintaining a highly aromatic structure. Remarkably, the formed [10]annulene is bench stable and can be stored for extended periods of time.<br>

Synthesis of a Highly Aromatic and Planar [10]Annulene

As the next neutral structure following Hückels rule, a planar and aromatic [10]annulene is ideal to study the link between ring size and aromaticity. However, the puckered geometry of the parent [10]annulene suggests that the aromatic stabilization energy is not sufficient to overcome the ring strain that exists when the system is forced into planarity. It has been shown computationally that this ring strain can be alleviated through the addition of two or more cyclopropane rings to the periphery, thereby creating theoretically aromatic structures. An alternative strategy to eliminating the issue of ring strain was demonstrated experimentally with the successful preparation of the highly aromatic 1,6-didehydro[10]annulene. However, the system rapidly cyclizes at -40°C to a naphthalene diradical due to the close proximity of the in-plane p-orbitals present in the system. Here we show that cyclopropanating one side of the unstable annulene successfully prevents the destabilizing cross-ring interaction while maintaining a highly aromatic structure. Remarkably, the formed [10]annulene is bench stable and can be stored for extended periods of time.<br>

REVIEW ON LIGNIN MODIFICATIONS TOWARD NATURAL UV PROTECTION INGREDIENT FOR LIGNIN-BASED SUNSCREENS

Lignin is a natural UV-blocking material; it exhibits excellent UV absorption ability owing to its aromatic structure and the presence of numerous phenolic, ketone, and intramolecular hydrogen bonds. Recently, the...

Simultaneous extraction and controlled chemical functionalization of hardwood lignin for improved phenolation

Lignin is a promising candidate for the replacement of fossil-based materials, due to its natural abundance and aromatic structure. This same structure poses major challenges to lignin’s exploitation for material...

Thienoquinolinone as a new building block for wide bandgap semiconducting polymer donors for organic solar cells

A new heterocyclic aromatic structure, thieno[3,2-c]quinolin-4(5H)-one (TQO), was designed and synthesized as an electron-accepting building block for donor–acceptor-type copolymers.