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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 …