Bruce S. Ault

Bio: Bruce S. Ault is an academic researcher from University of Cincinnati. The author has contributed to research in topics: Matrix isolation & Infrared spectroscopy. The author has an hindex of 30, co-authored 269 publications receiving 4190 citations. Previous affiliations of Bruce S. Ault include University of Virginia.

Theoretical Study of the Reaction Mechanism and Role of Water Clusters in the Gas-Phase Hydrolysis of SiCl4

Abstract: The energies and thermodynamic parameters of the elementary reactions involved in the gas-phase hydrolysis of silicon tetrachloride were studied using ab initio quantum chemical methods (up to MP4//MP2/6-311G(2d,2p)), density functional (B3LYP/6-311++G(2d,2p)), and G2(MP2) theories. The proposed mechanism of hydrolysis consists of the formation of SiCl 4-x(OH)x (x ) 1-4), disiloxanes Cl4-x(OH)x-1Si-O-SiCl4-x(OH)x-1, chainlike and cyclic siloxane polymers [-SiCl2sO-]n, dichlorosilanone Cl2SidO, and silicic acid (HO)2SidO. Thermodynamic parameters were estimated, and the transition states were located for all of the elementary reactions. It was demonstrated that the experimentally observed kinetic features for the hightemperature hydrolysis are well described by a regular bimolecular reaction occurring through a four-membered cyclic transition state. In contrast, the low-temperature hydrolysis reaction cannot be described by the traditionally accepted bimolecular pathway for SisCl bond hydrolysis because of high activation barrier (Ea ) 107.0 kJ/mol, ¢G q ) 142.5 kJ/mol) nor by reactions occurring through three- or four-molecular transition states proposed earlier for reactions occurring in aqueous solution. The transition states of SiCl 4 with oneand two-coordinated water molecules were located; these significantly decrease the free energy of activation ¢G q (to 121.3 and 111.5 kJ/mol, correspondingly). However, this decrease in ¢G q is not sufficient to account for the high value of the hydrolysis rate observed experimentally under low-temperature conditions.

Photolysis of (3-methyl-2H-azirin-2-yl)-phenylmethanone: direct detection of a triplet vinylnitrene intermediate.

Abstract: The photoreactivity of (3-methyl-2H-azirin-2-yl)-phenylmethanone, 1, is wavelength-dependent (Singh et al. J. Am. Chem. Soc. 1972, 94, 1199−1206). Irradiation at short wavelengths yields 2P, whereas longer wavelengths produce 3P. Laser flash photolysis of 1 in acetonitrile using a 355 nm laser forms its triplet ketone (T1K, broad absorption with λmax ∼ 390–410 nm, τ ∼ 90 ns), which cleaves and yields triplet vinylnitrene 3 (broad absorption with λmax ∼ 380–400 nm, τ = 2 μs). Calculations (B3LYP/6-31+G(d)) reveal that T1K of 1 is located 67 kcal/mol above its ground state (S0) and has a long C–N bond (1.58 A), and the calculated transition state to form 3 is only 1 kcal/mol higher in energy than T1K of 1. The calculations show that 3 has significant 1,3-carbon iminyl biradical character, which explains why 3 reacts efficiently with oxygen and decays by intersystem crossing to the singlet surface. Photolysis of 1 in argon matrixes at 14 K produced ketene imine 7, which presumably is formed from 3 intersyste...

Matrix Isolation and Density Functional Study of the Reaction of OVCl3 with CH3OH: Synthesis and Characterization of Cl2V(O)OCH3

Abstract: The matrix isolation technique has been employed to investigate the reaction of OVCl3 with CH3OH. Using twin jet deposition, the initial intermediate in the mechanism was identified as a weakly bound molecular complex. This species is characterized by perturbations to the C−O, VO, and V−Cl stretching modes. Merged jet deposition, with a room-temperature reaction zone, led to complete conversion to Cl2V(O)OCH3, the second intermediate in the reaction sequence, through HCl elimination from the initial complex. This species was identified by use of extensive isotopic labeling, the observation of HCl as an additional reaction product, and by comparison to density functional calculations. All of the fundamental vibrational modes of this species that lie above 400 cm-1 were observed, some with very high intensities. Heating the reaction zone above 150 °C led to destruction of this intermediate, and production of both CH2O and CH3Cl.

The density functional formalism, its applications and prospects

Abstract: A scheme that reduces the calculations of ground-state properties of systems of interacting particles exactly to the solution of single-particle Hartree-type equations has obvious advantages. It is not surprising, then, that the density functional formalism, which provides a way of doing this, has received much attention in the past two decades. The quality of the energy surfaces calculated using a simple local-density approximation for exchange and correlation exceeds by far the original expectations. In this work, the authors survey the formalism and some of its applications (in particular to atoms and small molecules) and discuss the reasons for the successes and failures of the local-density approximation and some of its modifications.

The Halogen Bond

Abstract: The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

Organic Azides: An Exploding Diversity of a Unique Class of Compounds

Abstract: Since the discovery of organic azides by Peter Griess more than 140 years ago, numerous syntheses of these energy-rich molecules have been developed. In more recent times in particular, completely new perspectives have been developed for their use in peptide chemistry, combinatorial chemistry, and heterocyclic synthesis. Organic azides have assumed an important position at the interface between chemistry, biology, medicine, and materials science. In this Review, the fundamental characteristics of azide chemistry and current developments are presented. The focus will be placed on cycloadditions (Huisgen reaction), aza ylide chemistry, and the synthesis of heterocycles. Further reactions such as the aza-Wittig reaction, the Sundberg rearrangement, the Staudinger ligation, the Boyer and Boyer-Aube rearrangements, the Curtius rearrangement, the Schmidt rearrangement, and the Hemetsberger rearrangement bear witness to the versatility of modern azide chemistry.

Photoremovable Protecting Groups in Chemistry and Biology: Reaction Mechanisms and Efficacy

Abstract: The review covers the knowledge on photoremovable protecting groups and includes all relevant chromophores studied in the time period of 2000–2012; the most relevant earlier works are also discussed.