How good is a Broyden–Fletcher–Goldfarb–Shanno-like update Hessian formula to locate transition structures? Specific reformulation of Broyden–Fletcher–Goldfarb–Shanno for optimizing saddle points

Based on a study of the Broyden–Fletcher–Goldfarb–Shanno (BFGS) update Hessian formula to locate minima on a hypersurface potential energy, we present an updated Hessian formula to locate and optimize saddle points of any order that in some sense preserves the initial structure of the BFGS update formula. The performance and efficiency of this new formula is compared with the previous updated Hessian formulae such as the Powell and MSP ones. We conclude that the proposed update is quite competitive but no more efficient than the normal updates normally used in any optimization of saddle points. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 349–362, 1998     

Catalytic Diastereoselective Tandem Conjugate Addition–Elimination Reaction of Morita–Baylis–Hillman C Adducts by C?C Bond Cleavage

Through the cleavage of the C? C bond, the first catalytic tandem conjugate addition–elimination reaction of Morita–Baylis–Hillman C adducts has been presented. Various S_N2′‐like C‐, S‐, and P‐allylic compounds could be obtained with exclusive E configuration in good to excellent yields. The Michael product could also be easily prepared by tuning the β‐C‐substituent group of the α‐methylene ester under the same reaction conditions. Calculated relative energies of various transition states by DFT methods strongly support the observed chemoselectivity and diastereoselectivity.     

Is the Bis(μ-oxo)dicopper Core Capable of Hydroxylating an Arene?

Direct attack of the bis(μ-oxo)dicopper core on an arene appears feasible in tyrosinase and model complexes on the basis of studies of new [Cu^III₂(μ-O)₂]²⁺ compounds supported by bidentate imine/amine ligands. In the first demonstration of such reactivity for a bis(μ-oxo)dicopper core, decomposition of these intermediates caused hydroxylation of a pendant phenyl ring [Eq. (a)] in a reaction analogous to that catalyzed by tyrosinase.     

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As far as KRI's clients were concerned, KRI's appeal was not only in having researchers who had a high level of expert knowledge, but it was also in the efficiency with which high risk jobs were conducted, and the speed of response time, especially when corporations made comparisons with their own in‐house labs. KRI, while being a facility for contract research, is also capable of becoming a profitable corporation, mostly thanks to the adoption of this system. KRI sincerely hopes to continue serving as a group made up of quality professionals who embrace a dream, and to contribute to society through its achievements. At the same time, the company strives to be sensitive to changing needs, and, of course, to conduct R&D and consulting activities which will ensure success for its clients.     

Resonance‐Assisted Intramolecular Chalcogen–Chalcogen Interactions?

High-level B3LYP/6-311+G(3df,2p) density functional calculations have been carried out for a series of saturated chalcogenoaldehydes: CH(X)-CH(2)-CH(2)YH (X, Y=O, S, Se, Te). Our results indicate that in CH(X)-CH(2)-CH(2)YH (X=Y=O, S, Se) the X-H...X intramolecular hydrogen bond (IHB) competes in strength with the X...XH chalcogen-chalcogen interaction, while the opposite is found for the corresponding tellurium-containing analogues. For those derivatives in which X does not equal Y, X being the more electronegative atom, the situation is more complicated due to the existence of two non-equivalent X-H and Y-H tautomers. The Y-H tautomer is found to be lower in energy than the X-H tautomer, independently of the nature of X and Y. For X=O, S, Se and Y=S, Se the most stable conformer b is the one exhibiting a Y-H...X IHB. Conversely when Y=Te, the chelated conformer d, stabilized through a X...YH chalcogen-chalcogen interaction is the global minimum of the potential energy surface. Systematically the IHB and the chalcogen-chalcogen interactions observed for saturated compounds are much weaker than those found for their unsaturated analogues. This result implies that the nonbonding interactions involving chalcogen atoms, mainly Se and Te, are not always strongly stabilizing. This conclusion is in agreement with the fact that intermolecular interactions between Se and Te containing systems with bases bearing dative groups are very weak. We have also shown that these interactions are enhanced for unsaturated compounds, through an increase of the charge delocalization within the system, in a mechanism rather similar to the so call Resonance Assisted Hydrogen Bonds (RAHB). The chalcogen-chalcogen interactions will be also large, due to the enhancement of the X-->Y dative bond, if the molecular environment forces the interacting atoms X and Y to be close each other.     

Diketopyrrolopyrrole?Thiophene‐Based Acceptor–Donor–Acceptor Conjugated Materials for High‐Performance Field‐Effect Transistors

We report the synthesis, morphology, and field‐effect‐transistor (FET) characteristics of new acceptor–donor–acceptor conjugated materials that consist of diketopyrrolopyrrole (DPP) acceptor groups and one of four different thiophene moieties, that is, dithiophene (2T), thieno[3,2‐b]‐thiophene (TT), dithieno[3,2‐b:2′,3′‐d]‐thiophene (DTT), and 5,5′′′‐di‐(2‐ethylhexyl)‐[2,3′;5′,2′′;4′′,2′′′]quaterthiophene (4T). The optical band gaps of the as‐prepared materials are smaller than 1.7 eV, which is attributed to the strong intramolecular charge transfer and the backbone coplanarity of the thiophene moieties. The order of both crystallinity and FET mobility (×10^?2–×10^?4 cm² V^?1 s^?1) is TT2DPP > 4T2DPP > 2T2DPP >DTT2DP, which differ in the structure of the π‐conjugated cores and core symmetry. Well‐ordered intermolecular chain packing was confirmed by the GIXD and AFM results. In particular, the FET hole mobility of TT2DPP was further improved to 0.1 cm² V^?1 s^?1, which was attributed to the well‐interconnected structure through solution‐shearing. These experimental results suggest the potential applications of the new DPP? thiophene? DPP conjugated materials for organic electronic devices.     

Are Boryl Radicals from Amine–Boranes and Phosphine–Boranes the Most Stable Radicals?

The relative stability of the radicals that can be produced from amine–boranes and phosphine–boranes is investigated at the G3‐RAD level of theory. Aminyl ([RNH]^.:BH₃) and phosphinyl ([RPH]^.:BH₃) radicals are systematically more stable than the boryl analogues, [RNH₂]:BH₂^. and [RPH₂]:BH₂^.. Despite similar stability trends for [RNH]^.:BH₃ and [RPH]^.:BH₃ radicals with respect to boryl radicals, there are significant dissimilarities between amine– and phosphine–boranes. The homolytic bond dissociation energy of the N?H bond decreases upon association of the amines with BH₃, whereas that of the P?H bond for phosphines increases. The stabilization of the free amine is much smaller than that of the corresponding aminyl radical, whereas for phosphines this is the other way around. The homolytic bond dissociation energy of the B?H bond of borane decreases upon complexation with both amines and phosphines.