Algorithmic tools in the study of semiempirical potential surfaces

Liotard, D.

doi:10.1002/qua.560440505

Cited by 83 publications

(51 citation statements)

References 92 publications

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“…The most marked difference lies in the orientation of the chain at C(2). According to these authors, the most stable structure is that in which H (20) forms a H-bond with O(1). The AM1 energy difference between this structure and the most stable one is 0.3 kcal/mol; such a small difference suggests that both conformations are equally probable in the gas phase.…”

Section: Dmentioning

confidence: 98%

“…The geometries for stationary points were identified by minimization of the energy with respect to all geometric parameters using the Broyden-FletcherGoldfarb-Shanno algorithm [ 14-1 81. The approximate geometries for the transition states (TS) were refined by minimizing the gradient norm of energy using the Powell algorithm [19], followed by the full Newton algorithm (LTRD) [20]. At a later stage, stationary points were characterized by FORCE or LTRD frequency analysis, a zero index for a critical point (where 'index' refers to the number of strictly negative eigenvalues of the Hessian) being assigned to reactants, products, and intermediates, and a unity value to each TS.…”

mentioning

confidence: 99%

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Theoretical Calculations of β‐Lactam Antibiotics. Part VI. AM1 calculations of alkaline hydrolysis of clavulanic acid

Frau

Donoso

Muñoz

et al. 1994

Helvetica Chimica Acta

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The gas-phase basic hydrolysis of clavulanic acid (a) was studied by using the AM1 semi-empirical method. The results obtained show that the hydroxyethylidene side chain at C(2) is pivotal to the stability of the different reaction products involved. The products with an open oxazolidine ring are more stable than those with a closed ring fused to theg -1actam ring. This behaviour differs from that of penicillins and cephalosporins where the most stable degradation products are those with an intact thiazolidine or dihydrothiazine ring, respectively, fused to the -lactam ring. The different chemical reacivity of clavulanic acid relative to penicillins and cephalosporins could explain the disparate behaviour of the latter two types of compound towardsa -1actamases. Once the acyl-enzyme intermediate of clavulanic acid has been formed, it can evolve with cleavage of the oxazolidine ring to form a difficult to deacylate compound.

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Section: Dmentioning

confidence: 98%

mentioning

confidence: 99%

Theoretical Calculations of β‐Lactam Antibiotics. Part VI. AM1 calculations of alkaline hydrolysis of clavulanic acid

Frau

Donoso

Muñoz

et al. 1994

Helvetica Chimica Acta

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“…[18] Geometries of stationary points were determined by minimization of energy with respect to all geometric parameters. Transition states were located by the chain method [19] and characterized by one, and only one, negative eigenvalue of the Hessian matrix. Finally, the transitions states found were shown to belong to the studied reaction by intrinsic reaction coordinate (IRC).…”

Section: Theoretical Studiesmentioning

confidence: 99%

Aluminium(III) Trifluoromethanesulfonate as an Efficient Catalyst for the Intramolecular Hydroalkoxylation of Unactivated Olefins: Experimental and Theoretical Approaches

Coulombel

Rajzmann

Pons

et al. 2006

Chemistry A European J

115

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The Al(OTf)(3)-catalyzed cycloisomerization of unactivated unsaturated alcohols was studied from experimental and theoretical points of view. A series of cyclic ethers was obtained in excellent yields and regioselectivities. This catalyst system provides one of the most straightforward routes to cyclic ethers with Markovnikov-type regioselectivity under mild conditions. Theoretical and NMR studies were carried out in order to better determine the mechanism of this reaction. The NMR studies were in agreement with preferential complexation of Al(OTf)(3) to the oxygen atom of the unsaturated alcohol, but did not exclude complexation to the double bond of the alcohol. Theoretical calculations indicated strong acidification of the hydroxyl proton when Al(OTf)(3) was complexed to the alcohol oxygen atom. A plausible catalytic cycle for the Al(OTf)(3)-catalyzed intramolecular hydroalkoxylation of unactivated olefins is proposed.

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“…The procedure we use is an extension of the simulated annealing method to potential energy surfaces which present several significant minima. It is similar to the procedure developed by D. Liotard [17] based on a random exploration of the potential energy surface by using the metropolis algorithm [18]. The obtained configurations are sorted out and the selected configurations are used as starting points for a local minimization method (quasi-Newton method, BFGS [19]).…”

mentioning

confidence: 99%

Intermolecular interactions: basis set and intramolecular correlation effects on semiempirical methods. Application to (C2H2)2, (C2H2)3 and (C2H4)2

Brenner

Millié

1994

Z Phys D - Atoms, Molecules and Clusters

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Abstract.A detailed study of the intrinsic consistency of the semiempirical method of P. Claverie namely, the effects of the basis set and intramolecular correlation on the multipole distributions of molecular subunits and the influence of the electronic population of each atom in the molecular subunit on its van der Waals radius, is performed on some van der Waals dimers. The validity, limits of this model and the appropriate way to use it is established. In particular, the dependence of the geometry and the interaction energy on the basis set chosen and the intramolecutar correlation shows that the multipole distribution involved in the calculation of the electrostatic and polarization terms must be derived from a correlated wave function within an extended basis set. Associated to non local methods for finding stationary points, the method of P. Claverie reproduce reliably the intermolecular geometrical parameters observed for the equilibrium structures and the transition states of the dimer and trimer of acetylene. In addition, a study of the equilibrium structures of the ethylene dimer is presented, the aim of being to clarify the considerable uncertainty in their number and their geometry.

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Algorithmic tools in the study of semiempirical potential surfaces

Cited by 83 publications

References 92 publications

Theoretical Calculations of β‐Lactam Antibiotics. Part VI. AM1 calculations of alkaline hydrolysis of clavulanic acid

Theoretical Calculations of β‐Lactam Antibiotics. Part VI. AM1 calculations of alkaline hydrolysis of clavulanic acid

Aluminium(III) Trifluoromethanesulfonate as an Efficient Catalyst for the Intramolecular Hydroalkoxylation of Unactivated Olefins: Experimental and Theoretical Approaches

Intermolecular interactions: basis set and intramolecular correlation effects on semiempirical methods. Application to (C2H2)2, (C2H2)3 and (C2H4)2

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