Showing papers by "Paul von Ragué Schleyer published in 1983"
TL;DR: The relatively small diffuse function-augmented basis set, 3-21+G, is shown to describe anion geometries and proton affinities adequately as discussed by the authors.
Abstract: The relatively small diffuse function-augmented basis set, 3-21+G, is shown to describe anion geometries and proton affinities adequately. The diffuse sp orbital exponents are recommended for general use to augment larger basis sets.
5,916 citations
TL;DR: In this article, negative anionic hyperconjugation was studied for anions and related neutral systems using ab initio split valence basis sets, 3−21+G and 4−31+G, which are augmented by a set of diffuse s and p functions on the non-hydrogen atoms.
287 citations
TL;DR: In this paper, the authors calculate MO ab initio des surfaces d'energie potentielle for des systemes a nombre pair d'electrons: isomeres singulets les moins stables, barrieres pour les reactions de deplacement 1,2 de l'hydrogene, structures triplets a l'equilibre, etc.
Abstract: Calculs MO ab initio des surfaces d'energie potentielle pour des systemes a nombre pair d'electrons: isomeres singulets les moins stables, barrieres pour les reactions de deplacement 1,2 de l'hydrogene, structures triplets a l'equilibre, etc.
190 citations
TL;DR: In this paper, Li-Li defined three stables: energies totales, energies de dissociation, and distributions of charge electronique and conformations, and showed that ces molecules ne seraient pas hypervalentes au sens strict, les electrons excedentaires andant mis en jeu dans des liaisons.
Abstract: Calculs ab initio indiquant des molecules tres stables: energies totales, energies de dissociation. Distributions de charge electronique et conformations: ces molecules ne seraient pas hypervalentes au sens strict, les electrons excedentaires etant mis en jeu dans des liaisons Li-Li
149 citations
TL;DR: In this article, the MO ab initio (3 -21G, 6-21G and 6-31G) is computed for the composition of Na et Li, and the composition de Mg.
82 citations
78 citations
TL;DR: In this article, Hartree-Fock et al. discuss de la stabilite et de la structure des α,ω-dilithioalcanes par des methodes MNDO et ab initio.
Abstract: Etude de la stabilite et de la structure des α,ω-dilithioalcanes par des methodes MNDO et ab initio (theorie de Hartree-Fock); l'instabilite des dilithio-1,2 ethane et dilithio-1,3 propane est attribuee a de faciles eliminations-transpositions intermoleculaires au profit de complexes LiH plus stable thermodynamiquement
55 citations
51 citations
TL;DR: In this paper, the second metallization of 1-Lithionaphthalene (2) and 9-lithioanthracene (12) undergo specific metallations whereby a second lithium is introduced at the adjacent peri-positions (5, 18) (in the presence of n-butyllithium/N,N, N′,N′-tetramethylethylenediamine (TMEDA)).
Abstract: Sowohl 1-Lithionaphthalin (2) als auch 9-Lithioanthracen (12) werden durch n-Butyllithium in Gegenwart von N,N,N′,N′-Tetramethylethylendiamin (TMEDA) spezifisch metalliert, wobei ein zweites Lithiumatom in der benachbarten peri-Position eingefuhrt wird (5, 18). MNDO-Berechnungen liefern eine Erklarung fur solche gerichteten Zweitmetallierungen, fur die andere Beispiele bekannt sind. Nicht nur sind die dilithiierten Produkte durch symmetrische doppelte Uberbruckung stabilisiert (thermodynamische Triebkraft), sondern es werden auch die aktivierten Wasserstoffatome in den monolithiierten Vorstufen richtig erkannt. Die LUMO-Koeffizienten und die CH-Bindungslangen sind hier am grosten. Realistischere Modelle fur die Verbindungen in Losung, namlich Dimere, zeigen die gleiche Charakteristik.
Regioselective Metallation of Aromatic Compounds, II. Second Metallation of 1-Lithionaphthalene and 9-Lithioanthracene
Both 1-lithionaphthalene (2) and 9-lithioanthracene (12) undergo specific metallations whereby a second lithium is introduced at the adjacent peri-positions (5, 18) (in the presence of n-butyllithium/N,N,N′,N′-tetramethylethylenediamine (TMEDA)). Explanations for such directed second metallations, for which other examples are known, are provided by MNDO calculations. Not only are the dilithiated products stabilized by symmetrically double bridging (implying a thermodynamic driving force) but also the activated hydrogens in the monolithio precursors are indicated clearly. The LUMO-coefficients on these hydrogens are largest and the CH bond lengths longest. Dimers, more realistic models for the solution species, show these characteristics as well.
49 citations
48 citations
TL;DR: Corrections de correlation MP2 a des calculs anterieurs 4-21P, 6-31G and 4 -21P+fonctions de polarisation de type : la forme a pont symetrique (C s ) serait le seul minimum sur la surface d'energie potentielle as mentioned in this paper.
Abstract: Corrections de correlation MP2 a des calculs anterieurs 4-21P, 6-31G et 4-21P+fonctions de polarisation de type : la forme a pont symetrique (C s ) serait le seul minimum sur la surface d'energie potentielle
TL;DR: Etude de la structure du silabenzene, du silaboicyclohexadiene, and des silacyclo-hexadienylidenes a partir de calculs ab initio et MNDO des energies relatives of ces isomeres; sur les bases de distributions de charges and de structures electroniques calcules, est envisagee la stabilisation de differents isomere par des substituants as discussed by the authors.
Abstract: Etude de la structure du silabenzene, du silabicyclohexadiene, et des silacyclohexadienylidenes a partir de calculs ab initio et MNDO des energies relatives de ces isomeres; sur les bases de distributions de charges et de structures electroniques calcules, est envisagee la stabilisation de differents isomeres par des substituants
01 Jan 1983
TL;DR: The octet rule fails to predict the stoichiometrics of binary lithium compounds of first row elements as mentioned in this paper, and it is shown that a simple interpretation assigns only an octet of electrons to the central atom, and any additional electrons to a surrounding lithium cage.
Abstract: The octet rule fails to predict the stoichiometrics of binary lithium compounds of first row elements. There is now gas phase experimental evidence for OLi3, OLi4, OLi5, and OLi5; many similar perlithiated species are predicted computationally to be highly stable thermodynamically towards all possible dissociation modes. The structures of NLi4, OLi4, and FLi4, for example, are tetrahedral while CLi5, NLi5, and OLi5 favor trigonal bipyramidal (D3h) symmetries. CLi6, and CLi6 are octahedral. The extra (ninth and tenth) valence electrons occupy totally symmetric (a1) molecular orbitals, largely lithium-lithium bonding in character. A simple interpretation assigns only an octet of electrons to the central atom, and any additional electrons to the surrounding lithium cage.
TL;DR: The potential energy surface of the singlet carbenoid CH 2 FLi has been examined using ab initio methods including electron correlation and zero-point energy corrections as mentioned in this paper, and three non-tetrahedral structures found earlier are confirmed to be minima, but only the lowest energy structure 1 should be experimentally observable.
TL;DR: In this article, the proton affinity of SiH 4 exceeds than of CH 4 by ≈25 kcal/mol. But the heat of hydrogenation of Si H 4 is smaller than that of CH + 3 by nearly the same amount.
TL;DR: In this article, the low-lying singlet and triplet structures of H 2 CBe and HCBeH were examined using molecular orbital theory, and the results showed that the lowest energy singlet structure is the ( 1 B 1 ) open-shell singlet, also with C 2v symmetry.
TL;DR: In this paper, an exceptionally large 1,2-hydride shift barrier, over 40 kcal/mol, was indicated by high-level theoretical calculations for the phenyl cations, which is the state-of-the-art.
Abstract: An exceptionally large 1,2-hydride shift barrier, over 40 kcal/mol, is indicated by high-level theoretical calculations for the phenyl cations.
TL;DR: In this article, the reaction of ethylene with an H3B·OH2 complex (a model for hydroboration in ether solvents) is indicated by ab initio calculations to resemble an SN2 displacement of the solvent by thy olefin; the solvent plays essentially no role in the transition state.
Abstract: The reaction of ethylene with an H3B·OH2 complex (a model for hydroboration in ether solvents) is indicated by ab initio calculations to resemble an SN2 displacement of the solvent by thy olefin; the solvent plays essentially no role in the transition state, but BH3 never becomes free during the reaction.
TL;DR: In contrast to the reported difficulties in preparing the tetraphenyl-substituted cyclobutadienyl dianion 3-2K, dilithiation of 2-benzyl-1,3-diphenyl 1-propene (1) to give the title 2-2Li, is a facile reaction as discussed by the authors.
Abstract: The Tribenzylidenemethane Dianion
In contrast to the reported difficulties in preparing the tetraphenyl-substituted cyclobutadienyl dianion 3-2K, dilithiation of 2-benzyl-1,3-diphenyl-1-propene (1) to give the title dianion, 2-2Li, is a facile reaction. An analysis of the charge distribution by means of the 13C NMR chemical shifts further confirms conclusions reached on the basis of MNDO calculations: Y-conjugated trimethylenemethane dianions are more stable than cyclobutadienyl dianions. Huckel theory does not give reliable predictions for small doubly charged systems which are dominated by electrostatic repulsions.
TL;DR: In this article, the effects of metal hydride elimination of cyclic olefins directly to give conjugated anions and polyanions in a single operation were investigated.
Abstract: Equimolar mixtures of n-butyllithium and potassium tert-amyloxide effect metallation and metal hydride elimination of cyclic olefins directly to give conjugated anions and polyanions in a single operation. 1-Methyl-1-cycloalkenes or methylenecycloalkanes are particularly well suited and give highly unsaturated products. Odd-membered rings eliminate better than their even-membered counterparts, and eight-membered rings eliminate particularly slowly. Reactions with methyl iodide and trimethylsilyl chloride proceed smoothly in high yield.
Die Metallierungs-Eliminierungs-Reaktion, II. Monocyclische Anionen und Polyanionen
Aquimolare Mischungen von n-Butyllithium und Kalium-tert-amyloxid bewirken Metallierung und Metallhydrid-Eliminierung an cyclischen Olefinen und fuhren direkt in einer Eintopf-Reaktion zu konjugierten Anionen und Polyanionen. 1-Methyl-1-cycloalkene oder Methylencycloalkane sind besonders gut geeignet und geben stark ungesattigte Produkte. Ringe mit ungerader Kohlenstoffzahl eliminieren besser als die geradzahligen. Achtgliedrige Ringe eliminieren extrem langsam. Reaktionen mit Methyliodid und Trimethylsilychlorid verlaufen glatt und in guter Ausbeute.
TL;DR: Quench reactions, 13C nmr spectra and MNDO molecular orbital calculations all suggest the title dianion to prefer the exo,exo -conformation, like the 1,3-diphenyl allyl anion, but in contrast to 2-substituted 1, 3-dipshenyl al lyl anions as discussed by the authors.
TL;DR: Cumulenic amines R1CHCC(R3)NR22 (R1 and R2H or alkyl, R3H or Me) are converted rapidly at 20 °C into enyne amines with methanol or water under neutral conditions as discussed by the authors.
Abstract: Cumulenic amines R1CHCC(R3)NR22(R1 and R2H or alkyl, R3H or Me) are converted rapidly at 20 °C into enyne amines R1CC–CHC(R3)NR22 with methanol or water under neutral conditions.
TL;DR: In this article, it was shown that isopropyl-benzenes react with n-butyl-lithium-potassium t-pentyl oxide mixtures to give coupling products characteristic of styrene radical anions which are postulated to arise from one-electron oxidation of the styrene dianion intermediates.
Abstract: Ethyl- or isopropyl-benzenes react with n-butyl-lithium–potassium t-pentyl oxide mixtures to give coupling products characteristic of styrene radical anions which are postulated to arise from one-electron oxidation of styrene dianion intermediates.