Expanding and Testing a Computational Method for Predicting the Ground State Reduction Potentials of Organic Molecules on the Basis of Empirical Correlation to Experiment

A method for predicting the ground state reduction potentials of organic molecules on the basis of the correlation of computed energy differences between the starting S-0 and one-electron-reduced D-0 species with experimental reduction potentials in acetonitrile has been expanded to cover 3.5 V of potential range and 74 compounds across 6 broad families of molecules. Utilizing the conductor-like polarizable continuum model of implicit solvent allows a global correlation that is computationally efficient and has improved accuracy, with r(2) \u3e 0.98 in all cases and root mean square deviation errors of(mean absolute deviationsmV) for either B3LYP/6-311+G(d,p) or B3LYP//6-31G(d) with an appropriate choice of radii (UAKS or UA0). The correlations are proven to be robust across a wide range of structures and potentials, including four larger (27-28 heavy atoms) and more conformationally flexible photochromic molecules not used in calibrating the correlation. The method is also proven to be robust to a number of minor student mistakes or methodological inconsistencies

Synthesis of 5,6-Diaminoacenaphthylene by Reduction of Sterically Crowded Nitro Groups with Sodium Dithionite

5,6-Diaminoacenaphthylene was synthesized in four steps from acenaphthene. This seemingly simple molecule provides unique synthetic challenges because it is relatively difficult to reduce the nitro groups and the molecule contains a particularly reactive double bond. It was determined that the only feasible sequence for the synthesis was to nitrate acenaphthene, then brominate, eliminate, and finally selectively reduce. Several reduction methods were attempted before finding one that would completely reduce both nitro groups while leaving the double bond intact

Synthesis and Structural Investigation of an \u27Oxazinoquinolinespirohexadienone\u27 That Only Exists as Its Long-Wavelength Ring-Opened Quinonimine Isomer

The spirocyclic oxazinoquinolinespirohexadienone (OSHD) photochromes are computationally predicted to be an attractive target as electron deficient analogues of the perimidinespirohexadienone (PSHD) photochromes, for eventual application as photochromic photooxidants. We have found the literature method for their preparation unsuitable and present an alternative synthesis. Unfortunately the product of this synthesis is the long wavelength (LW) ring-opened quinonimine isomer of the OSHD. We have found this isomer does not close to the spirocyclic short wavelength isomer (SW) upon prolonged standing in the dark, unlike other PSHD photochromes. The structure of this long wavelength isomer was found by NMR and X-ray crystallography to be exclusively the quinolinone (keto) tautomer, though experimental cyclic voltammetry supported by our computational methodology indicates that the quinolinol (enol) tautomer (not detected by other means) may be accessible through a fast equilibrium lying far toward the keto tautomer. Computations also support the relative stability order of keto LW over enol LW over SW

Radical ion probes. 11. Reaction of 1,1-dimethyl-5,7-di-t-butylspiro[2.5]octa-4,7-dien-6-one with 5-hexenyl magnesium bromide

In an ongoing effort to establish 1,1-dimethyl-5,7-di-t-butylspiro[2.5]octa-4,7-dien-6-one (1) as a mechanistic probe for the detection of single electron transfer (SET), the reaction of1 with 5-hexenyl magnesium bromide was examined in the hopes of observing cyclization of any intermediate 5-hexenyl radicals to cyclopentylcarbinyl radicals. A polar process dominated the reaction, but in the less prevalent SET process, the 5-hexenyl → cyclopentylcarbinyl rearrangement was extensive, indicative of freely diffusing paramagnetic intermediates

Efficient Computational Methods for Accurately Predicting Reduction Potentials of Organic Molecules

A simple computational approach for predicting ground-state reduction potentials based upon gas phase geometry optimizations at a moderate level of density functional theory followed by single-point energy calculations at higher levels of theory in the gas phase or with polarizable continuum solvent models is described. Energies of the gas phase optimized geometries of the S0 and one-electron-reduced D0 states of 35 planar aromatic organic molecules spanning three distinct families of organic photooxidants are computed in the gas phase as well as well in implicit solvent with IPCM and CPCM solvent models. Correlation of the D0 − S0 energy difference (essentially an electron affinity) with experimental reduction potentials from the literature (in acetonitrile vs SCE) within a single family, or across families when solvent models are used, yield correlations with r2 values in excess of 0.97 and residuals of about 100 mV or less, without resorting to computationally expensive vibrational calculations or thermodynamic cycles

Cyclopropylcarbinyl → Homoallyl-Type Ring Opening of Ketyl Radical Anions. Structure/Reactivity Relationships and the Contribution of Solvent/Counterion Reorganization to the Intrinsic Barrier

Following a protocol developed by Mathivanan, Johnston, and Wayner (J. Phys. Chem. 1995, 99, 8190−8195), the radical anions of several cyclopropyl- and oxiranyl-containing carbonyl compounds were generated in an effort to measure the rate constants for their ring opening (ko) by laser flash photolysis. The results of these experiments are compared to those obtained from earlier electrochemical studies, and the combined data set is used to rationalize the kinetics of radical anion ring opening in a general context by using Savéant\u27s theory pertaining to stepwise dissociative electron transfer (Acc. Chem. Res. 1993, 26, 455−461). Compared to cyclopropylcarbinyl → homoallyl rearrangements of neutral free radicals, at comparable driving force, the radical anion ring openings are slightly slower. The small difference in rate is attributed to the contribution of an additional, approximately 2 kcal/mol, solvent reorganization component for the radical anion rearrangements. The solvent reorganization energy for ring opening of these radical anions is believed to be small because the negative charge does not move appreciably in the progression reactant → transition state → product

Quantum Amplified Isomerization: A New Chemically Amplified Imaging System in Solid Polymers

A new imaging system based on a photoinitiated electron transfer chain reaction is reported. Specifically, irradiation of 9,10-dicyanoanthracene (sensitizer) leads to the conversion of Dewar benzene derivatives (reactants) to benzene derivatives (products) within solid polymer films. The mechanism of the reaction may involve chemical amplification with cation radicals ( holes ) as the catalytic species. We present herein studies of both molecularly doped polymers and polymers containing Dewar benzene moieties attached to side chains. The refractive index of the materials could be tuned within a narrow range using this photochemical reaction, as demonstrated by the writing of persistent gratings in forced Rayleigh scattering experiments

Radical Ion Probes. 8. Direct and Indirect Electrochemistry of 5,7-Di-tert-butylspiro[2.5]octa-4,7-dien-6-one and Derivatives

Results pertaining to the direct and indirect electrochemistry of 5,7-di-tert-butylspiro[2.5]octa-4,7-dien-6-one (1a), 1-methyl-5,7-di-tert-butylspiro[2.5]octa-4,7-dien-6-one (1b), and 1,1,-dimethyl-5,7-di-tert-butylspiro[2.5]octa-4,7-dien-6-one (1c) are reported. Product analyses reveal that reduction of all these substrates leads to cyclopropane ring-opened products; ring opening occurs with modest selectivity leading to the more substituted (stable) distonic radical anion. The direct electrochemistry of these compounds is characterized by rate limiting electron transfer (with α ≈ 0.5), suggesting that while ring opening is extremely rapid, the radical anions do have a discrete lifetime (i.e., electron transfer and ring opening are not concerted). Utilizing homogeneous redox catalysis, rate constants for electron transfer between 1a, 1b, and 1c and a series of aromatic radical anions were measured; reduction potentials and reorganization energies were derived from these rate constants by using Marcus theory