Molecular mechanism for rapid autoxidation in α-pinene ozonolysis

Aerosol affects Earth’s climate and the health of its inhabitants. A major contributor to aerosol formation is the oxidation of volatile organic compounds. Monoterpenes are an important class of volatile organic compounds, and recent research demonstrate that they can be converted to low-volatility aerosol precursors on sub-second timescales following a single oxidant attack. The α-pinene + O3 system is particularly efficient in this regard. However, the actual mechanism behind this conversion is not understood. The key challenge is the steric strain created by the cyclobutyl ring in the oxidation products. This strain hinders subsequent unimolecular hydrogen-shift reactions essential for lowering volatility. Using quantum chemical calculations and targeted experiments, we show that the excess energy from the initial ozonolysis reaction can lead to novel oxidation intermediates without steric strain, allowing the rapid formation of products with up to 8 oxygen atoms. This is likely a key route for atmospheric organic aerosol formation.

Targeted Synthesis of Regioisomerically Pure Dodecasubstituted Type I Porphyrins Through the Exploitation of Peri-Interactions

A targeted synthesis of dodecasubstituted type I porphyrins that utilizes the reaction of unsymmetrical 3,4-difunctionalized pyrroles and sterically demanding aldehydes was developed. This way, type I porphyrins could be obtained as the only type isomers, likely due to a minimization of the steric strain arising from peri-interactions. Uniquely, this method does not depend on lengthy precursor syntheses, the separation of isomers, or impractical limitations of the reaction scale. In addition, single crystal X-ray analysis elucidated the structural features of the macrocycles.

Targeted Synthesis of Regioisomerically Pure Dodecasubstituted Type I Porphyrins Through the Exploitation of Peri-Interactions

A targeted synthesis of dodecasubstituted type I porphyrins that utilizes the reaction of unsymmetrical 3,4-difunctionalized pyrroles and sterically demanding aldehydes was developed. This way, type I porphyrins could be obtained as the only type isomers, likely due to a minimization of the steric strain arising from peri-interactions. Uniquely, this method does not depend on lengthy precursor syntheses, the separation of isomers, or impractical limitations of the reaction scale. In addition, single crystal X-ray analysis elucidated the structural features of the macrocycles.

Diketopyrrolopyrrole Derivatives Functionalized with N-Annulated PDI and Se-Annulated PDI by Direct (Hetero)Arylation Methods

<p>We report on the synthesis of diketopyrrolopyrrole (DPP) derivatives functionalized with N-annulated and Se-annulated perylene diimide (NPDI and SePDI, respectively) <i>via </i>direct (hetero)arylation methods. DPP is symmetrically bifunctionalized with SePDI (SePDI–DPP–SePDI) and unsymmetrically functionalized with SePDI and NPDI (SePDI–DPP–NPDI). The effects of Se substitution compared to N substitution on physical, electrochemical, and optical properties are investigated along with performance as non-fullerene acceptors in photovoltaic devices. It is found that Se substitution increases the electron affinity of the p-conjugated molecule and blue shifts the optical absorption spectra, observations that were supported by computational analysis. Steric strain between the PDI endcap and DPP core prevent complete electronic communication along the p-conjugated backbone and results in the unsymmetrical compound, SePDI‒DPP‒NPDI, having electronic and optical properties that are a linear combination of both the symmetrical SePDI and NPDI based compounds. Different is that the SePDI‒DPP‒NPDI compound has a distinct melt observed at 343 °C and organic photovoltaic devices based on this compound had lower than expected open-circuit voltages, suggesting a unique solid-state packing arrangement. SePDI-based compounds performed worse than the NPDI-based compound in organic photovoltaic devices using the donor polymer PTB7-Th. </p>

Diketopyrrolopyrrole Derivatives Functionalized with N-Annulated PDI and Se-Annulated PDI by Direct (Hetero)Arylation Methods

<p>We report on the synthesis of diketopyrrolopyrrole (DPP) derivatives functionalized with N-annulated and Se-annulated perylene diimide (NPDI and SePDI, respectively) <i>via </i>direct (hetero)arylation methods. DPP is symmetrically bifunctionalized with SePDI (SePDI–DPP–SePDI) and unsymmetrically functionalized with SePDI and NPDI (SePDI–DPP–NPDI). The effects of Se substitution compared to N substitution on physical, electrochemical, and optical properties are investigated along with performance as non-fullerene acceptors in photovoltaic devices. It is found that Se substitution increases the electron affinity of the p-conjugated molecule and blue shifts the optical absorption spectra, observations that were supported by computational analysis. Steric strain between the PDI endcap and DPP core prevent complete electronic communication along the p-conjugated backbone and results in the unsymmetrical compound, SePDI‒DPP‒NPDI, having electronic and optical properties that are a linear combination of both the symmetrical SePDI and NPDI based compounds. Different is that the SePDI‒DPP‒NPDI compound has a distinct melt observed at 343 °C and organic photovoltaic devices based on this compound had lower than expected open-circuit voltages, suggesting a unique solid-state packing arrangement. SePDI-based compounds performed worse than the NPDI-based compound in organic photovoltaic devices using the donor polymer PTB7-Th. </p>

Alder-ene reactions driven by high steric strain and bond angle distortion to form benzocyclobutenes

A unique aryne-based Alder-ene reaction to form benzocyclobutene is described.