A series
of N-arylimide molecular balances
were developed to study and measure carbonyl–aromatic (CO−π)
interactions. Carbonyl oxygens were observed to form repulsive interactions
with unsubstituted arenes and attractive interactions with electron-deficient
arenes with multiple electron-withdrawing groups. The repulsive and
attractive CO−π aromatic interactions were well-correlated
to electrostatic parameters, which allowed accurate predictions of
the interaction energies based on the electrostatic potentials of
the carbonyl and arene surfaces. Due to the pronounced electrostatic
polarization of the CO bond, the CO−π aromatic
interaction was stronger than the previously studied oxygen−π
and halogen−π aromatic interactions.
The attractive interaction between carbonyl oxygens and the π-face of aromatic surfaces was studied using N-phenylimide molecular rotors. The CO•••Ar interactions could stabilize the transition states but were half the strength of comparable CO•••C O interactions. The CO•••Ar interaction had a significant electrostatic component but only a small orbital delocalization component. Letter pubs.acs.org/OrgLett
Substituent–π interactions associated with aromatic stacking interactions were experimentally measured using a small N-phenylimide molecular balance model system.
We demonstrate the use of para-polybenzimidazole (PBI)
membranes
as replacements for Nafion membranes in aqueous HCl oxygen-depolarized
electrolyzers. Both para-PBI and densified para-PBI membranes reduce
the cell voltage needed at 0.5 A cm–2 by ≥100
mV. We examine the effect of HCl(aq) flow rate, back-pressure, electrolyzer
temperature, and, for the densified para-PBI membranes, H3PO4 swell time on electrolyzer performance. Increased
proton conductivity, measured as reduced area-specific membrane resistance,
is identified as the primary mechanism to explain the improved performance
of the electrolyzer.
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