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Experimental and theoretical investigations of trimethylchlorosilane (TMCS) interactions with =SiOH groups catalyzed by NR3 (R = C2H5, CH3) have been conducted using Aerosil samples. The potential energy surface (PES) profiles along the reaction pathway were calculated in a cluster approach by the MNDO/H and AMI methods. The comparison with CIS1H3 reactions showed that the formation of fourcentered stabilized prereaction complexes is possible unlike TMCS reactions with =SiOH groups. The catalytic effect was caused by the enthalpy factor of the rate constants predominantly. Noncatalytic reaction rate constants were calculated and compared with experimental data. interact with silica surfaces at temperatures above 570 K substitute H atoms in silanol groups at catalysts by triethylamine (TEA) practically instantaneously at T « 300 K.* 1 Similar rapid reactions were observed with alcoholization, fluorination, and hydrolysis on silica surface catalyzed by electron-donor compounds: amines, ethers, alcohols, ketones, H2O, HC1.2 The problem of catalytic effect mechanisms by electrondonor compounds at chemosorption processes remains disputable. There exists the opinion that in electrophilic substitution reactions (SeO (for example, haloidsilanes with silica) the formation of hydrogen bonds =Si-OH-XY with electron-donor molecules XY leads to polarization of the 0-H bonds and increases its ability to heterolytic splitting of the Si-Hal bond in adsorbate. At a limiting reaction stage, the sorption complex included a silanol group, haloidsilane, and electron-donor molecule, and it may be considered an intermediate of the Seí reaction.1•2 This reaction was studied on example of the system =SiOH + ClSi(CH3)3 + N(C2H5)3(1) Noncatalytic reactions =SiOH + X"Si(CH3)4_" --SiOSiX^íCHg)^+ HX X = Cl, OCH3; = 1-3 were studied by experimental methods,3-5 but activation energies obtained were strongly different and the investigations of reaction mechanism (1) were scanty.1 45'2 6'7 Experimental SectionMaterials. Dispersed pyrogenic Si02 Aerosil (A-300,99.9%) was obtained from PU "ChloroviniT (Kalush), and its BET surface area of300 m2/g was measured by using nitrogen. Silanol * Author to whom correspondence should be addressed.