1994 R.U. Lemieux Award Lecture Hydrolysis of acetals and ketals. Position of transition states along the reaction coordinates, and stereoelectronic effects

1994 ◽  
Vol 72 (10) ◽  
pp. 2021-2027 ◽  
Author(s):  
Pierre Deslongchamps ◽  
Yves L. Dory ◽  
Shigui Li
Keyword(s):  
Ab Initio ◽  
Reaction Pathway ◽  
Transition States ◽  
Experimental Results ◽  
Reaction Coordinates ◽  
Stereoelectronic Effects ◽  
Theoretical Support ◽  
Semi Empirical ◽  
Hydrolysis Of ◽  
Support Evidence

Past and recent experimental results on the formation or hydrolysis (or isomerization) of various acetals and ketals including α-and β-glycoside models are presented. Ab initio investigations of simple acetals are also briefly reviewed as well as recent experimental and theoretical support evidence for a synperiplanar effect. A detailed study using the semi-empirical Hamiltonian AM1 defining the reaction pathway in the hydrolysis of various acetals and ketals is reported. This overall study shows that the hydrolysis of acetals and ketals is controlled by powerful stereoelectronic effects.

scholarly journals Dynamics of chemical reactions of astrophysical interest

1997 ◽  
Vol 178 ◽  
pp. 271-280 ◽  
Author(s):  
M. Alagia ◽  
N. Balucani ◽  
L. Cartechini ◽  
P. Casavecchia ◽  
G.G. Volpi
Keyword(s):  
Potential Energy ◽  
Ab Initio ◽  
Chemical Reactions ◽  
Potential Energy Surfaces ◽  
Experimental Results ◽  
Empirical Potential ◽  
Beam Scattering ◽  
Scattering Technique ◽  
Energy Surfaces ◽  
Semi Empirical

The dynamics of the astrophysically relevant reactions OH + H2,OH+CO,N(2D)+C2H2 and O(1D)+H2 are studied using the crossed beam scattering technique. Comparisons of the experimental results with those of dynamics calculations on ab initio and semi-empirical potential energy surfaces are discussed.

Ab initio study of the decomposition of formamidine

2005 ◽  
Vol 83 (12) ◽  
pp. 2082-2090 ◽  
Author(s):  
M H Almatarneh ◽  
C G Flinn ◽  
R A Poirier
Keyword(s):  
Aqueous Solution ◽  
Water Molecule ◽  
Ab Initio ◽  
Gas Phase ◽  
Reaction Pathway ◽  
Transition States ◽  
Decomposition Reaction ◽  
Phase Decomposition ◽  
Free Energies ◽  
Hartree Fock

The decomposition of formamidine yielding hydrogen cyanide and ammonia has been investigated by ab initio calculations. Optimized geometries for reactants, transition states, and products were determined at the HF/6-31G(d) and MP2/6-31G(d) levels of theory. Energies were also determined at the G1, G2, G2MP2, G3, G3B3, G3MP2, and G3MP2B3 levels of theory. The role of water in the decomposition reaction of formamidine was examined. Intrinsic reaction coordinate (IRC) analysis was carried out for all transition states. Activation energies, enthalpies and free energies of activation were also calculated for each reaction pathway. G3 level of theory predicts the gas-phase decomposition of formamidine to have a high activation energy of 259.1 kJ mol–1. Adding one water molecule catalyses the reaction by forming a cyclic hydrogen-bonded transition state, reducing the barrier to 169.4 kJ mol–1 at the G3 level. Addition of a second water, which acts as a "solvent" molecule, further reduces the barrier to 151.1 kJ mol–1 at the G3 level. These values are still high and explain why rather extreme conditions are necessary to achieve this reaction experimentally. Thermodynamic properties (ΔE, ΔH, and ΔG) for each reaction pathway studied were also calculated. The G3 heats of reaction (ΔE) of the gas-phase decomposition of formamidine, its complex with one water molecule, and its complex with two water molecules are 0.9, 2.2, and –5.1 kJ mol –1, respectively. The G3 heat of reaction for the gas-phase decomposition to yield separated products is 22.3 kJ mol–1. Free energies of reaction and of activation in aqueous solution were calculated with PCM using the KLAMT cavity model. At MP2 the formamidine reaction is found to be exergonic in aqueous solution and to favour formation of the separated products (NH3 + HCN). The solvent model predicts a significant lowering of the free energy of activation (16–18 kJ mol–1) for the unimolecular reaction and 21–42 kJ mol–1 for the water-mediated reaction in aqueous solution relative to the gas phase. Key words: decomposition reaction, formamidine, Hartree–Fock, post Hartree–Fock, Gaussian-n theories, IRC, solvation models, PCM, KLAMT.

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