Theoretical investigation of electrocyclic reactions for torquoselectivity, probes of hydrogen-bonding, and molecular devices

Recent reports of inward torquoselectivities in thermal electrocyclic ring-opening reactions of 3-silylcyclobutenes have revealed a new mechanism involving fully saturated substituents. Orbital interactions involving the substituents and the orbitals associated with the breaking bonds are found to produce these contrasteric torquoselectivities, with minor contributions from electrostatic effects. Reaction energetics and transition states for electrocyclic ring-opening reactions of 3-substituted cyclobutenes are reported to complement previous extensive studies of unsaturated substituents. Inward stereoselectivities are predicted for silyl-, protonated phosphonyl, and boryl substituted cyclobutenes.; An interconversion between substituted benzocyclobutene and o-xylylene is studied for its potential application as a molecular device activated by redox activation. The reversible stability of the system by redox activation has led to a proposal of a diphenylnaphthocyclobutene system as a potential molecular field effect transistor or rectifier. Its energy of activation, reaction, and standard redox potentials were investigated. The conversion from diphenylbenzoquinodimethane to diphenylnaphthocyclobutene has an activation energy of 7.1 kcal/mol and the energy of reaction is predicted to be −16.1 kcal/mol. The radical cation is predicted to spontaneously open once a standard redox potential of 1.8V is applied. To better understand the chemistry of o-xylylenes, the dimerization process was also investigated computationally.; The strength of intramolecular C-FH-O interactions was studied computationally by exploring the equilibrium between various substituted benzocyclobutenes with these substituents interacting upon ring-opening to o-xylylenes.{09}The C-FH-O interaction is estimated 3–4 kcallmol, relative to C-HH-O. This value is comparable to the C-OH-O interaction in this system.; The ground-state geometries and excited singlet and lowest triplet energies of polyacenes from benzene through nonacene are predicted with calculations and compared to experimental data where available. The polyacenes and cyclacenes have geometries consisting of two fully delocalized nonalternating ribbons joined by relatively long bonds. Polyacenes are predicted to have smaller band gaps than the corresponding polyenes and triplet ground states for nine or more benzene rings. Findings are rationalized in terms of a simple MO model, and the results are compared to extensive prior theoretical work in the literature. Predictions about the electronic structure of analogues containing polyacene units are made.