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Articles 1 - 30 of 108
Full-Text Articles in Chemistry
Does Methane Invert Through Square Planar?, Mark S. Gordon, Michael Schmidt
Does Methane Invert Through Square Planar?, Mark S. Gordon, Michael Schmidt
Mark S. Gordon
MCSCF calculations using a triple-t basis set augmented with diffuse and polarization functions are used to probe that part of the singlet methane potential energy surface that pertains to the inversion of CH4 from one t~trahedral structure t.o another. The true inversion transition state is found to have a distorted C, structure, quite different both ge?me.tncally ~nd energetically from the previously presumed square planar saddle point. At the secondorder configuration mte.ractl~n.level of theory, the barrier to inversion is predicted to be just 7-8 kcaljmol higher in energy than the bond diSSOCiation energy for the first C-H bond cleavage in methane.
Experimental And Computational Studies Of Four-Coordinate Aluminum: The Reaction Of Aluminates And Acids, Robert Damrauer, Michèle Krempp, Niels H. Damrauer, Michael W. Schmidt, Mark S. Gordon
Experimental And Computational Studies Of Four-Coordinate Aluminum: The Reaction Of Aluminates And Acids, Robert Damrauer, Michèle Krempp, Niels H. Damrauer, Michael W. Schmidt, Mark S. Gordon
Mark S. Gordon
The gas-phase reactions of trimethylaluminates with a variety of acids are considered from both an experimental and computational perspective. The experimental work involves product and kinetic studies of ten aluminates, [(CH3hAlX]- (X= H, CH3, NH2, OH, F, SiH3, PH2, SH, Cl, and OCH3). Both X and methyl cleavage pathways are observed in these reactions. X cleavage occurs with several aluminates (X = H, NH2, OH, and PH2), in contrast to the thermochemical predictions of ab initio computations performed at the MP2/6-31 ++G(d,p) level. These indicate that methyl cleavage is favored in the reaction of nine aluminates (OCH3 was not computed) …
Insertion Reactions Of Monovalent Silicon: A Nonvanishing Barrier For The Silylidyne Plus Hydrogen Reaction Sih + H2, Mark S. Gordon, Yaoming Xie, Yukio Yamaguchi, Roger S. Grev, Henry F. Schaefer Iii
Insertion Reactions Of Monovalent Silicon: A Nonvanishing Barrier For The Silylidyne Plus Hydrogen Reaction Sih + H2, Mark S. Gordon, Yaoming Xie, Yukio Yamaguchi, Roger S. Grev, Henry F. Schaefer Iii
Mark S. Gordon
Ab initio quantum mechanical methods have been applied to the SiH (X zrr) insertion into the Hz molecule. The transition state has no elements of symmetry. The classical barrier height is predicted to be 5.6 :I: I kcaljmol. The barrier is qualitatively consistent with an estimate from Jasinski's experimental reaction rates, which are much slower than those observed for the related CH + Hz, SiH + SiH4, and SiH2 + Hz reactions.
Π-Bond Strengths Of H2x=Yh2: X = Ge Or Sn, And Y = C, Si, Ge, Or Sn, Theresa L. Windus, Mark S. Gordon
Π-Bond Strengths Of H2x=Yh2: X = Ge Or Sn, And Y = C, Si, Ge, Or Sn, Theresa L. Windus, Mark S. Gordon
Mark S. Gordon
The molecular structures and 1r-bond strengths are determined using both MP2 and MCSCF + CI energies for a series of H2X=YH2 compounds, where X = Ge or Sn and Y = C, Si, Ge, or Sn. These strengths are estimated both by evaluating the rotation barriers and by investigating the appropriate thermochemical cycles. The results show that C > Si ,.., Ge > Sn in their ability to form The molecular structures and 1r-bond strengths are determined using both MP2 and MCSCF + CI energies for a series of H2X=YH2 compounds, where X = Ge or Sn and Y = C, Si, …
Uncatalyzed Peptide Bond Formation In The Gas Phase, Jan H. Jensen, Kim K. Balgridge, Mark S. Gordon
Uncatalyzed Peptide Bond Formation In The Gas Phase, Jan H. Jensen, Kim K. Balgridge, Mark S. Gordon
Mark S. Gordon
Several levels of electronic structure theory are used to analyze the formation of a peptide bond between two glycine molecules. Both a stepwise and concerted mechanism were considered. The energetic requirements for the stepwise and concerted mechanisms are essentially the same within the expected accuracy of the methods used. A simpler model system comprised of formic acid and ammonia is found to provide a good representation of the essential features of dipeptide formation. Total electron densities and localized molecular orbitals are used to interpret the mechanisms.
Strategies Tor Designing A High-Valent Transition-Metal Silylidene Complex, Thomas R. Cundiari, Mark S. Gordon
Strategies Tor Designing A High-Valent Transition-Metal Silylidene Complex, Thomas R. Cundiari, Mark S. Gordon
Mark S. Gordon
The electronic structure of complexes arising from the formation of a double bond between a silylene ligand (Si(R)R') and a high-valent transition-metal fragment have been investigated using ab initio wave functions including the effects of electron correlation. Using the analogy of carbon, these complexes may be referred to as Scbrock-type silylenes or silylidenes. A prime motivation for this work is that complexes of this type, unlike their carbon analogues, have so far eluded attempts at experimental characterization. Several conclusions are reached as a result of these calculations. (a) The inclusion of electron correlation is necessary to adequately describe the MSi …
Hypercoordination In Group Iv Mh5 And Mh5- Systems, Marshall T. Carroll, Mark S. Gordon, Theresa L. Windus
Hypercoordination In Group Iv Mh5 And Mh5- Systems, Marshall T. Carroll, Mark S. Gordon, Theresa L. Windus
Mark S. Gordon
The energetics and bonding of the group IV hypervalent MH5 and MH5- D3h structures (M = C, Si, Ge, Sn) are examined in this paper. Ab initio all-electron calculations are used to predict the energies and geometries of the systems. The resulting electron densities are analyzed using the topological theory of atoms in molecules. It is found that the anion energetically is more stable than the neutral radical for M = Si, Ge, and Sn but not for M = C. Further distinguishing carbon from the other members of the group is the fact that the CH bond mostly is …
Experimental And Theoretical Evidence In Support Of An Intermediate Complex In The Insertion Reaction Of Silylene Into Silane, R. Becerra, H. M. Frey, B. P. Mason, R. Walsh, Mark S. Gordon
Experimental And Theoretical Evidence In Support Of An Intermediate Complex In The Insertion Reaction Of Silylene Into Silane, R. Becerra, H. M. Frey, B. P. Mason, R. Walsh, Mark S. Gordon
Mark S. Gordon
The reaction between silylene, SiH2, and silane, SiH4, viz. SiH2 + SiH4 - Si2H6 (1) may reasonably be considered the prototype Si-H insertion process of silicon hydride chemistry. This reaction, which is also the second step in the thermolysis of silane1 leading ultimately to solid silicon and silicon hydride deposition, is known to be fast. Experimental measurements of the rate constant2-4 show the reaction to proceed at close to the collisional limit. Theoretical calculations of the energy surface for the decomposition of Si2H6 show that it possesses no energy barrier at the threshold of dissociation,5 which suggests a zero barrier …
Theoretical Investigatlons Of Olefin Metathesis Catalysts, Thomas R. Cundiari, Mark S. Gordon
Theoretical Investigatlons Of Olefin Metathesis Catalysts, Thomas R. Cundiari, Mark S. Gordon
Mark S. Gordon
An ab initio analysis of the electronic structure of high-valent, transition-metal alkylidenes as models for olefm metathesis catalysts is presented. The catalyst models studied fall into three categories: "new" metathesis catalyst models-tetrahedral M(0Hh(XH)(CH2) complexes; "old" metathesis catalyst models-tetrahedral MCMY)(CH2) complexes and alkylidene-substituted Mo metathesis catalysts, Mo( OHMNH)(=C(H)Z). The effect on the bonding caused by modification of either the metal, ligands, or alkylidene substituents is considered. For the new models the minimum energy structures result from maximum metal d1rligand p11' bonding and minimum competition among the ligands for the same d11' AO. Rotation about the MC axis increases this competition. The …
Nature Of The Transition Metal-Silicon Double Bond, Thomas R. Cundiari, Mark S. Gordon
Nature Of The Transition Metal-Silicon Double Bond, Thomas R. Cundiari, Mark S. Gordon
Mark S. Gordon
The nature of the metal-silicon double bond is investigated using ab initio wavefunctions. Electron correlation is specifically included in the calculations at the FORS-MCSCF (full optimized reaction space multiconfiguration self-consistent field) level of theory. Silylene complexes of the form MSiH2 +,containing metals from the first transition series (M = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni), are chosen for this study. An analysis of the bonding and electronic structure among the silylene complexes is presented. The silylene complexes are compared to representative car bene analogues, MCH2 +, and to CrGeH2 + and CrSnH2+.
High-Valent Transition-Metal Alkylidene Complexes: Effect Of Ligand And Substituent Modification, Thomas R. Cundiari, Mark S. Gordon
High-Valent Transition-Metal Alkylidene Complexes: Effect Of Ligand And Substituent Modification, Thomas R. Cundiari, Mark S. Gordon
Mark S. Gordon
An ab initio investigation into the effects of ligand and substituent modification on the metal-carbon double bond is reported. Prototypical group IVB (Ti, Zr, HO and Group VB (Nb, Ta) alkylidenes are chosen for this study. The MC/LMO/CI (multiconfigurationjlocalized molecular orbital/configuration interaction) procedure is used to examine the electronic structures of these complexes in terms of the prime resonance contributors to the ground-state wave function. The main conclusion drawn from this work is that the intrinsic nature of the metal-carbon double bond can typically be changed only within certain limits by modification of the electronegativity of the ligands (L) and …
An Analytical Representation Of The Lowest Potential Energy Surface For The Reaction O(3 P)+Hcl (X 1Σ+)→Oh(X 2Π)+Cl(2 P), H. Koizumi, George C. Schatz, Mark S. Gordon
An Analytical Representation Of The Lowest Potential Energy Surface For The Reaction O(3 P)+Hcl (X 1Σ+)→Oh(X 2Π)+Cl(2 P), H. Koizumi, George C. Schatz, Mark S. Gordon
Mark S. Gordon
We present a new analytical representation of the lowest 3 A‘ energy surface for the reaction O(3 P)+HCl(X 1Σ+)→OH(X 2Π)+Cl(2 P). This surface is derived by fitting a b i n i t i o calculations, and adjustments are made to the barrier height so that rate constants derived from accurate quantum scattering calculations match the room temperature thermal rate constants. Contributions to thermal and state resolved rate constants arising from reaction on the lowest 3 A’surface are also considered. Comparisons of thermal and state resolved rate constants with experiment are good except at high temperature where the 3 A’ …
The Conformational Potential Energy Surface Of Glycine: A Theoretical Study, Jan H. Jensen, Mark S. Gordon
The Conformational Potential Energy Surface Of Glycine: A Theoretical Study, Jan H. Jensen, Mark S. Gordon
Mark S. Gordon
The conformational potential energy surface of nonionized glycine has been studied by using ab initio (6-310*, ST0-20) and semiempirical (AM1, PM3) methods. The MP2/6-31G*/ /RHF/6-310* potential energy surface was then used to calculate the Boltzmann equilibrium distribution and kinetics of conformational interconversion at various temperatures. The results of this study are compared to previous computational and experimental investigations of gas-phase glycine.
Structures And Bonding Of Group Iv Sulfur And Oxygen Propellane Derivatives, Kiet A. Nguyen, Marhsall T. Carroll, Mark S. Gordon
Structures And Bonding Of Group Iv Sulfur And Oxygen Propellane Derivatives, Kiet A. Nguyen, Marhsall T. Carroll, Mark S. Gordon
Mark S. Gordon
The RHF, ROHF, and GVB structures and energetics of group IV 2,4,5-trioxa[l.l.l]metallapropellanes, 2,4,5- trithia [ l.l.l]metallapropellanes, and their bicyclopentane analogues have been determined from ab initio molecular orbital theory by using both the 6-31G(d) basis set for all-electron calculations and the valence basis set with effective core potentials (ECP) developed by Stevens, Basch, and Krauss. Although they have extremely short bridgehead distances, these species possess fairly large natural orbital occupation numbers in the lowest unoccupied molecular orbitals, indicating significant diradical character. Structures and other properties determined by ECP calculations are in good agreement with the 6-31 G(d) all-electron calculations.
Predicted Enthalpies Of Formation For Methyl-Substituted Silaethylenes And Disilenes, Jerry A. Boatz, Mark S. Gordon
Predicted Enthalpies Of Formation For Methyl-Substituted Silaethylenes And Disilenes, Jerry A. Boatz, Mark S. Gordon
Mark S. Gordon
Enthalpies of formation of the methyl-substituted silaethylenes (CH3).H2_,Si=CH2 (n = 1, 2) and disilenes (CH3),.H~i=Si(CH3),H:~-m (n, m = Q-2) are predicted by using isodesmic reactions which relate the compound of interest to the parent silaethylene (H2Si=CH2) or disilene (H~i=SiH2), for which accurate enthalpies of formation have recently been determined. In turn, the enthalpies of formation of these methyl-substituted compounds are used in conjunction with homodesmic reactions to reevaluate the enthalpies of formation of the silicon-substituted cyclobutenes C.Si4-0H6 (n = Q-4).
Stabilization Of Β Positive Charge By Silicon, Germanium, Or Tin, Kiet A. Nguyen, Mark S. Gordon, Gen-Tai Wang, Joseph B. Lambert
Stabilization Of Β Positive Charge By Silicon, Germanium, Or Tin, Kiet A. Nguyen, Mark S. Gordon, Gen-Tai Wang, Joseph B. Lambert
Mark S. Gordon
Ab initio molecular orbital theory is used to study the β effect of carbon, silicon, germanium, or tin on the carbenium ions in H2R'MCH2CHR+ (R' = H; R = H, CH3). The relative stabilization energies of carbenium ions provided by M (M = C, Si, Ge, Sn) were determined by calculating the energy change in an isodesmic reaction using MP2/3-21G(d) (at SCF /3-21G* geometries) and MP2/6-31G(d) (at SCF /6- 31G(d) geometries) wave functions. The magnitude of the β effect is predicted to increase in the order C < Si < Ge < Sn. For R = H, the nonvertical cyclic structure is favored for the cations, whereas methyl substitution appears to stabilize the vertical acyclic arrangement.
Ab Initio Study Of Some Methylene And Silylene Insertion Reactions, David R. Gano, Mark S. Gordon, Jerry A. Boatz
Ab Initio Study Of Some Methylene And Silylene Insertion Reactions, David R. Gano, Mark S. Gordon, Jerry A. Boatz
Mark S. Gordon
The theoretical barriers and reaction energetics have been determined, using ab initio calculations at the MP4/6-3IG(d) level, with 3-2IG* geometries, for the insertions of methylene and silylene into the X-Y bonds of ethane, methylsilane, disilane, and cyclopropane and into the X-H bonds of disilane and ethane. A correlation was observed between barrier heights and lengths of substrate bonds. The largest barriers were observed for methylene and silylene inserting into the C-C bonds of ethane. The barriers became successively lower for the C-Si and Si-Si bonds. Steric interactions thus appear to be a major factor in determining barrier heights. The observed …
Nature Of The Si-N Bond In Silatranes, Mark S. Gordon, Marshall T. Carroll, Jan H. Jensen, Larry P. Davis, Larry W. Burggraf, R. Martin Guidry
Nature Of The Si-N Bond In Silatranes, Mark S. Gordon, Marshall T. Carroll, Jan H. Jensen, Larry P. Davis, Larry W. Burggraf, R. Martin Guidry
Mark S. Gordon
Both ab initio and semiempirical calculations are used to investigate the structure and bonding in substituted silatranes. In agreement with gas-phase experiments, which fmd Si-N distances that are 0.25-0.35 A longer than those in the crystal phase, the Si-N distance (for example, in methylsilatrane) is predicted to be much larger than that observed in the crystal. Nonetheless, a bond critical point is found between Si and N, suggesting the existence of an Si-N bond in these compounds. It is found that the energy cost for constraining the Si-N distance in hydroxysilatrane to a value similar to that observed in the …
Systematic Survey Of Cyclic Silicon-Oxygen Compounds, Michael W. Schmidt, Kiet A. Nguyen, Mark S. Gordon, John A. Montgomery Jr.
Systematic Survey Of Cyclic Silicon-Oxygen Compounds, Michael W. Schmidt, Kiet A. Nguyen, Mark S. Gordon, John A. Montgomery Jr.
Mark S. Gordon
Compounds with 0, 1, 2, or 3 oxygen atoms bridging 2 silicon atoms are investigated by ab initio calculations. Two such series of compounds, with and without a formal central Si-Si bond, are considered. The triplet states of the former set are also examined. For some of these compounds, the present calculations represent the first time they have been examined at a sufficiently rigorous level of theory. For the compounds that are formally bonded, this level is two configuration SCF (TCSCF) for singlets and ROHF for triplet states, using split valence polarized basis sets. The main result is that no …
A Theoretical Study Of Some Reactions Of Hcsi-, Michael W. Schmidt, Mark S. Gordon
A Theoretical Study Of Some Reactions Of Hcsi-, Michael W. Schmidt, Mark S. Gordon
Mark S. Gordon
The ions HCSi- and H2CSiH- produced in recent flowing afterglow experiments are characterized structurally. Reactivity of the former ion with four molecules (C02, OCS, CS2, S02) is examined. Three of these species react in a sequence of intermediates of cyclic followed by acyclic structures, before reaching the final products.
Principal Resonance Contributors To High-Valent, Transition-Metal Alkylidene Complexes, Thomas R. Cundiari, Mark S. Gordon
Principal Resonance Contributors To High-Valent, Transition-Metal Alkylidene Complexes, Thomas R. Cundiari, Mark S. Gordon
Mark S. Gordon
The results of ab initio calculations are reported for prototypical high-valent, alkylidene complexes. Stationary points on each potential energy surface are characterized and compared to experimental information where available; as long as a suitably flexible valence basis set is used, good agreement between theoretically calculated and experimentally determined geometries is obtained. The complexes of interest include group IVB (Ti, Zr and Hf) and group VB (Nb and Ta) alkylidenes with hydride ligands as well as models for the four-coordinate, olefin metathesis catalysts (Mo-, W-, and Re-alkylidenes) which have been recently synthesized and characterized. In light of the fact that much …
A New Twist On Pseudorotation, Theresa L. Windus, Mark S. Gordon, Larry W. Burggraf, Larry P. Davis
A New Twist On Pseudorotation, Theresa L. Windus, Mark S. Gordon, Larry W. Burggraf, Larry P. Davis
Mark S. Gordon
For pentacoordinated structures in a trigonal bipyramidal ar· rangement, Berry1 proposed a "pseudorotation" mechanism whereby two such isomers can interconvert through a tetragonal transition state (TS). This Berry pseudorotation mechanism was demonstrated explicitly for SiH5- by following the MP22/6· 31G(d)3 minimum energy path4 (MEP).
Gas-Phase Chemistry Of The Dimethylaluminum Oxide Ion And Related Aluminum Oxide Ions: Comparison Of Reactivity With Siloxide Ions, Robert Damrauer, Michèle Krempp, Michael W. Schmidt, Mark S. Gordon
Gas-Phase Chemistry Of The Dimethylaluminum Oxide Ion And Related Aluminum Oxide Ions: Comparison Of Reactivity With Siloxide Ions, Robert Damrauer, Michèle Krempp, Michael W. Schmidt, Mark S. Gordon
Mark S. Gordon
The anion [(CH3hAIOt (1) has been prepared in a flowing afterglow selected ion flow tube (FA-SIFT) by ion selection from the reaction mixture of trimethylaluminum dimer and hydroxide. This unusual ion is quite reactive and has been extensively studied. It reacts with halogen-containing compounds of several types, including fluorobenzene, chlorobenzene, bromofluorobenzene, acetyl chloride, and HF, to give [(CH3hAI(OH)Xt, where X = F, Cl, and Br. Its chemistry with hexafluorobenzene and silicon tetrafluoride has also been detailed as have a number of reactions with carboxylic acids, esters, anhydrides, sulfur-containing neutrals, alcohols, water, and ammonia. The dominant reaction pattern of 1 involves …
Effect Of Hydration And Dimerization Of The Formamidine Rearrangement, Kiet A. Nguyen, Mark S. Gordon, Donald G. Truhlar
Effect Of Hydration And Dimerization Of The Formamidine Rearrangement, Kiet A. Nguyen, Mark S. Gordon, Donald G. Truhlar
Mark S. Gordon
Ab initio molecular orbital theory is used to predict the geometry of the transition state and the energy barrier for the double-proton transfer in formamidine dimer, using SCF /6-31 G(d,p) and MP2/6-31 G(d,p) wave functions, respectively. Intramolecular hydrogen transfer in the uncomplexed monomer (I) and double-proton transfer in the mixed dimer of formamidine and water (2) are also investigated at several levels of theory. All computational levels predict the barrier for the uncomplexed reaction (I) to be approximately twicdhat for the hydrated reaction (2). Isomerization by double-proton transfer in the dimer (3) is predicted to be the most favorable process. …
Matrix-Infrared Spectra Of Structural Isomers Of The Phosphorus Oxysulfide P4s3o, Zofia Mielke, Lester Andrews, Kiet A. Nguyen, Mark S. Gordon
Matrix-Infrared Spectra Of Structural Isomers Of The Phosphorus Oxysulfide P4s3o, Zofia Mielke, Lester Andrews, Kiet A. Nguyen, Mark S. Gordon
Mark S. Gordon
Photolysis of the P 4S3--03 molecular complex in solid argon with red light produced two sets of new infrared absorptions including terminal PO and symmetric P-S-P stretching modes, which are assigned to structural isomers of P4S30 with terminal oxygen at the apex and base phosphorus positions of P4S3. Further ultraviolet photolysis produced evidence for oxo-bridged P4S30 and a secondary product, P4S30 2.
Structure And Stability Of Hexacoordinated Sila Dianions, Mark S. Gordon, Marshall T. Carroll, Larry P. Davis, Larry W. Burggraf
Structure And Stability Of Hexacoordinated Sila Dianions, Mark S. Gordon, Marshall T. Carroll, Larry P. Davis, Larry W. Burggraf
Mark S. Gordon
The structures and stabilities of hexacoordinated silicon-containing dianions SiX6 2- have been investigated by using both ab initio (X= H, F) and semiempirical AMI (X= H, F, OH, Me, Cl) calculations. Both methods predict the hexacoordinated structures to be minima on the potential energy surfaces, although the semiempirical barriers for the reactions SiX6 2- -+ Six5- + x- appear to be rather overestimated based on the ab initio results for X = H, F. The positive charge on the central silicon atom actually increases as the number of ligands increases, and the role of d orbitals on that atom appears …
Theoretical Study Of Pseudorotation Of Pentacoordinated Silicon Anions: The Prototypical Sih5-, Mark S. Gordon, Theresa L. Windus, Larry W. Burggraf, Larry P. Davis
Theoretical Study Of Pseudorotation Of Pentacoordinated Silicon Anions: The Prototypical Sih5-, Mark S. Gordon, Theresa L. Windus, Larry W. Burggraf, Larry P. Davis
Mark S. Gordon
Ab initio and semiempirical calculations are used to analyze the minimum energy path for the pseudorotation of SiH5-. Both AMI and MP2/6-31++G(d,p) predict pseudorotation barriers of 2.4 kcal/mol. A decomposition of the projected vibrational frequencies along the path is used to assist in the interpretation of the process.
Predicted Enthalpies Of Formation For Silaethylene, Disilene, And Their Silylene Isomers, Jerry A. Boatz, Mark S. Gordon
Predicted Enthalpies Of Formation For Silaethylene, Disilene, And Their Silylene Isomers, Jerry A. Boatz, Mark S. Gordon
Mark S. Gordon
Enthalpies of formation of silaethylene (SiH2=CH2), methylsilylene (HSiCH3), disilene (SiH2=SiH2), and silylsilylene (HSiSiH3) are predicted by using the recently developed GAUSSIAN-! method for computing accurate molecular energies. The predicted enthalpies of formation of the silylenes are compared with enthalpies of formation determined from isodesmic reactions. Very good agreement is found between these two methods and improved values for the enthalpies of formation of silaethylene and disilene are suggested.
Theoretical Studies Of The Metallacyclopropenes C-[Mx2c2h2] (M = C, Sl, Ge, Sn; X = H, F), Jerry A. Boatz, Mark S. Gordon, Lawrence R. Sita
Theoretical Studies Of The Metallacyclopropenes C-[Mx2c2h2] (M = C, Sl, Ge, Sn; X = H, F), Jerry A. Boatz, Mark S. Gordon, Lawrence R. Sita
Mark S. Gordon
The geometries of the metallacyclopropenes c-[MX 2C2H2] (M = C, Si, Ge, Sn; X= H, F) are predicted by using the 3-21G(d) basis set and SCF wave functions. The nature of the ring bonding is investigated via analysis of the total electron density and is found to have little or no 11'-complex character. As a further probe of the electronic structure, bent bond lengths and intrinsic vibrational frequencies are computed. The classical barrier heights and the thermodynamics of the reaction MX 2 + HC==CH-- c-[MX 2C2H2] are predicted by using MP2/3-21G(d) energies.
Thermal Decomposition Processes For Sllanol, Mark S. Gordon, Lisa A. Pederson
Thermal Decomposition Processes For Sllanol, Mark S. Gordon, Lisa A. Pederson
Mark S. Gordon
Six alternative decomposition modes of silanol are examined with ab initio electronic structure theory. Geometries determined at the MP2/6-31 G( d,p) level of computation and single-point energetics obtained with MP4/MC-311 G{d,p) wave functions predict that the I, 1- and I ,2-eliminations of molecular hydrogen are both thermodynamically and kinetically competitive, with all other processes requiring at least 10 kcaljmol more energy to occur. At the highest level of theory, silanone is predicted to be 2.7 kcaljmollower in energy than hydroxysilylene.