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Density functional theory calculations were conducted on the title reactions with water molecules. Malonaldehyde, acetylacetone, and malonic acid were adopted as reactants. A reaction of malonaldehyde and (2 + 2) water molecules was found to proceed by a small (ca. 7 kcal/mol) activation energy. Two are reactant and two are catalyst molecules, respectively. The intramolecular hydrogen bond in the enol form is disrupted by the intermolecular one. Tautomerization transition-state geometries for acetylacetone and malonic acid are similar to that of malonaldehyde. Without the enhanced reactivity of water hydrogen-bond networks, tautomerization reactions undergo large activation energies. Various reaction models of (malonaldehyde) n (n = 2, 3, and 4) have given the energetic result. The keto−enol tautomerization has an analogy with the bimolecular nucleophilic elimination (E2) mechanism.

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.

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Gas-phase equilibria for clustering reactions of both halide ions (X -) with methane and chloride ions with chloromethanes (CH 4-m Cl m ) were measured with a pulsed electron-beam high-pressure mass spectrometer. The bond energies were found to show irregular decreases for F -(CH 4 ) n , with n ) 6 and 8, for Cl -(CH 3 Cl) n , with n ) 2, 4, and 6, and for Cl -(CH 2 Cl 2 ) n , with n ) 2 and 4. These even numbers indicate that the core ions are preferably solvated by the ligands with these n values. The theoretical calculation revealed that the cluster ion Cl -(CCl 4 ) has the structure of [Cl...ClCCl 3 ]rather than Cl -...Cl 3 CCl. The unexpectedly large bond energy for Cl -(CCl 4 ) (13.4 kcal/mol) is due to the charge dispersal in the complex [Cl...ClCCl 3 ] -.