- A zwitterionic carbanion frustrated by boranes - Dihydrogen cleavage with weak lewis acids via an "inverse" frustrated lewis pair approach
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The synthesis, structural characterization, and acid-base chemistry of [C(SiMe2OCH2CH2OMe)3]Na (2), a sterically encumbered zwitterionic organosodium compound, is reported. 2 is a strong Bronsted base that forms frustrated Lewis pairs (FLPs) with a number of boron-containing Lewis acids ranging from weakly Lewis acidic aryl and alkyl boranes to various alkyl borates. These intermolecular FLPs readily cleave H2, which confirms that even poor Lewis acids can engage in FLP-mediated H2 cleavage provided that the present bulky base is of sufficiently high Bronsted basicity.
- Li, Hui,Aquino, Adelia J. A.,Cordes, David B.,Hung-Low, Fernando,Hase, William L.,Krempner, Clemens
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- Method of preparation of methyl-benzyl-ketone
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A process for producing phenylacetic acid is provided. The process includes combining sodium, chlorobenzene, toluene, and a catalyst to form a suspension. This suspension is mixed to form phenylsodium. Upon boiling, the suspension forms benzylsodium. The suspension is then carbonized and acidified to form phenylacetic acid.
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Page/Page column 4-5
(2008/06/13)
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- QUANTUM CHEMICAL CALCULATIONS AND NUCLEAR MAGNETIC RESONANCE MEASUREMENTS ON BENZYL-TYPE CARBANIONS. PART 2. INFLUENCE OF COUNTERCATIONS AND INTERACTING UNSATURATED SYSTEMS
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Quantum chemical calculations, n.m.r. and spectrophotometric measurements are carried out to study the influence of countercations and interacting unsaturated systems on the structural and electronic properties of benzyl-type carbanions.The calculated geometry of benzyl-Li compares favourably with X-ray data on a related structure. (13)C, (1)H n.m.r. shifts and 1JCH coupling constants of benzyl, o- and p-CH3O-benzyl-Li, -Na, and -K compounds show a fair overall agreement with the ab initio-calculated charge distributions and structural parameters for the terminal members of the Li-, Na-, and K- series, the Li compound and the free carbanion, modelling the K salt.Both theory and experiment indicate that, when passing from the anion to the alkali-metal compound, an important destruction of the resonance saturation, present in the CH3O derivatives, occurs due to the presence of the countercation, the reduction being more important with decreasing cation radius.The n.m.r. data for α-alkyl-substituted compounds suggest that steric factors make the position of the cation in the Cα region less favourable, the effect being more pronounced for larger cation radius.The resonance saturation effect in the above mentioned systems may also be influenced by intermolecular effects, e.g. it may change during a chemical reaction.Ab initio calculations on the interaction energy between the benzyl-type carbanions and unsaturated systems showing increasing delocalization possibilities for incoming negative charge indicate that the larger this delocalization possibility (ethene butadiene styrene), the more important the destruction of resonance saturation.Along this series the parallel conformation of the CH3O group in the p-CH3O compounds gradually becomes less disfavoured.The calculated effect is however not strong enough yet in order to show full agreement with the observed increase in the k(-) value for the addition reaction to 1,1-diphenylethene when passing from polystyryl to poly-p-methoxystyryl carbanions.Larger basis sets and extensive geometry optimization should be carried out in order to settle this problem.
- Vanermen, Guido,Toppet, Suzanne,Van Beylen, Marcel,Geerlings, Paul
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p. 707 - 714
(2007/10/02)
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- Dissociation Behavior of Benzylalkali Compounds in Tetrahydrofuran: Effect of Countercation, Aromatic Methoxy Substitution, and α-Alkyl Substitution
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Conductometric measurements are carried out on different benzylalkali compounds (benzylcesium, -potassium, -sodium, and -lithium, and their o-CH3O and p-CH3O derivatives) in tetrahydrofuran at various temperatures, in order to get information on their dissociative behavior and on the influence of the alkali cation, aromatic methoxy substitution, and α-alkyl substitution on the carbon-metal bond strength.The dissociation constants of the organometallic compounds are determined by using the Kraus and Bray equation, the Fuoss equation, the Wooster equation, or by curve fitting depending on which species are involved in the solution conductance.Temperature variation of Kd is used to determine the enthalpy and entropy of dissociation.The information previously acquired by quantum chemical calculations and NMR measurements on the electronic structure of benzyl-type carbanions and the corresponding organometallic compounds appears to be of great value in interpreting the dissociation behavior of the benzyl- and styrylalkali compounds (which are also included in the study).The resonance saturation phenomenon encountered in the quantum chemical and NMR study turns out to be an important factor in the dissociative behavior of p-CH3O compounds, as compared to the unsubstituted cases.The smaller dissociation costants of the o-CH3O compounds also parallel the results of the quantum chemical calculations, showing an additional interaction between the cation and the CH3O group.The weakening of the carbon-metal bond upon α-alkyl substitution parallels the increase of dissociation capability when alkyl or polymer chain substituents are present on the α-carbon atom.
- Vanermen, G.,Beylen, M. Van,Geerlings, P.
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p. 603 - 607
(2007/10/02)
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