The two title reactions were investigated by means of ab initio molecular orbital calculations. Under neutral conditions, the hydrolysis of methylmethoxydihydroxysilane was examined, and the water-trimer cluster was found to be a reactant for ready bond interchange. The condensation of methyltrihydroxysilane was caused by the participation of the water dimer. Two of the observed reactions involved a front-side nucleophilic attack to the silicon center or a similar mechanism. Acid-and base-promoted hydrolyses were also examined, and their enhanced reactivities were ascribed to the stability of the silyl cation and a hypervalent intermediate, respectively.
Ab initio calculations were performed for eight Claisen rearrangements, eqs 1-8. Transition-state (TS) structures of [3,3] sigmatropic rearrangements of reactions 1-4 are similar, but their activation energies (E(a)'s) are different, E(a)(1) < E(a)(2) and E(a)(3) < E(a)(4). From the intermediate of reaction 3, a hydrogen is moved intermolecularly to form the product, o-allyl phenol. The lower reactivities of reactions 2 and 4 relative to reactions 1 and 3 are ascribed to large endothermicities in the sigmatropic rearrangements, respectively. Chair-type transition states are more favorable than boat-type transition states in reactions 1-4. The allyl group is released from the in-plane C-X (X = O or N) sigma bond and is captured by the pi-type lone-pair electrons. The sulfur- and phosphorus-containing rearrangements, reactions 5-8, are computed to have smaller activation energies but are to be less exothermic than those of oxgyen- and nitrogen-containing rearrangements.
ABSTRACT:Title reactions were investigated with ab initio calculations.Methyl isocyanate and ethylene oxide were adopted as model reactants. The products, 2-oxazolidones and isocyanurates, cannot be yielded without a base catalyst. The 2-oxazolidone may be produced by a dual S N 2 reaction, where the catalyst base (e.g., Cl − ) is a nucleophile and a leaving group on the ethylene-oxide carbon. Isocyanurate is generated by the stepwise association of three isocyanate molecules, where one of the molecules is initially linked with a base. The six-membered ring isocyanurate is isomerized stepwise into the components isocyanate and 2-oxazolidone. A tetrahedral type of complex between the isocyanurate and a base-catalyzed ethylene oxide is the key intermediate for the isomerization.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.