Spectroscopic properties of trichlorofluoromethane CCl(3)F calculated by density functional theory

Density functional theory is used to generate local potential energy surfaces in normal coordinates for several chlorine isotopomers of trichlorofluoromethane (CCl(3)F, CFC11). An examination of predicted structures suggested that the PBE0 functional would be suitable. Anharmonic surfaces around the equilibrium geometries are reported, as determined by energies, gradients, and second derivatives. Vibrational levels for fundamentals, overtones and combination bands are reported, as well as harmonic frequencies, anharmonic constants, rotational constants, isotope shifts, and infrared intensities. These are compared with experimental information.     

Size-dependent structural evolution and chemical reactivity of gold clusters.

Ground-state structures and other experimentally relevant isomers of Au(15) (-) to Au(24) (-) clusters are determined through joint first-principles density functional theory and photoelectron spectroscopy measurements. Subsequent calculations of molecular O(2) adsorption to the optimal cluster structures reveal a size-dependent reactivity pattern that agrees well with earlier experiments. A detailed analysis of the underlying electronic structure shows that the chemical reactivity of the gold cluster anions can be elucidated in terms of a partial-jellium picture, where delocalized electrons occupying electronic shells move over the ionic skeleton, whose geometric structure is strongly influenced by the directional bonding associated with the highly localized "d-band" electrons.     

Conformational structure of some trimeric and pentameric structural units of heparin

The molecular structure of trimeric units (D-E-F and F-G-H) and the pentamer D-E-F-G-H of heparin (sodium salts and their anionic forms) was studied using the B3LYP/6-31G(d) method. The equilibrium structure of the sodium salts of the trimers and pentamer investigated in the isolated state was determined by multidentate coordination of the sodium cations with oxygen atoms of the sulfate, carboxyl, and hydroxyl (hydroxymethyl) groups, respectively. The displacement of Na+ ions from the binding sites in the sodium salt of oligosaccharides studied resulted in the appreciable change of the overall conformation of the corresponding anion. Upon dissociation, a large change in both the position of the sulfate groups and the conformation across the glycosidic bonds was observed. The stable energy conformations around the glysosidic bonds found for the pentamer investigated are compared and discussed with the available experimental X-ray structural data for the structurally related heparin-derived pentasaccharides in cocrystals with proteins.     

Stereoselective preparation of six diastereomeric quatercyclopropanes from bicyclopropylidene and some derivatives

Diastereomeric meso- and d,l-bis(bicyclopropylidenyl) (5) were obtained upon oxidation with oxygen of a higher-order cuprate generated from lithiobicyclopropylidene (4) in 50 and 31 % yield, respectively. Their perdeuterated analogues meso-[D(14)]- and d,l-[D(14)]-5 were obtained along the same route from perdeuterated bicyclopropylidene [D(8)]-3 (synthesized in six steps in 7.4 % overall yield from [D(8)]-THF) in 20.5 % yield each. Dehalogenative coupling of 1,1-dibromo-2-cyclopropylcyclopropane (6) gave a mixture of all possible stereoisomers of 1,5-dicyclopropylbicyclopropylidene 16 in 69 % yield, from which (Z)-cis-16 was separated by preparative gas chromatography (26 % yield). The crystal structure of meso-5 looks like a superposition of the crystal structures of two outer bicyclopropylidene units (3) and one inner s-trans-bicyclopropyl unit, whereas the two outer cyclopropyl moieties adopt a gauche orientation with respect to the cyclopropane rings at the inner bicyclopropylidene units in (Z)-cis-16. Birch reduction with lithium in liquid ammonia of meso-5 and d,l-5 gave two pairs of diastereomeric quatercyclopropanes trans,trans-(R*,S*,R*, S*)-17/cis,trans-(R*,S*,R*,R*)-18 and trans,trans-(R*,S*,S*,R*)-19/cis,trans-(R*,S*,S*,S*)-20 in 97 and 76 % yield, respectively, in a ratio 9:1 for every pair. The latter diastereomer was also obtained as the sole product by Birch reduction of (Z)-cis-16 in 96 % yield. Under the same conditions, tetradecadeuterio analogues trans,trans-[D(14)]-(R*,S*,R*,S*)-17/cis,trans-[D(14)]-(R*, S*,R*,R*)-18 (8:1) and trans,trans-[D(14)]-(R*,S*,S*,R*)-19/cis,trans-[D(14)]-(R*,S*,S*,S*)-20 (12:1) were prepared from meso-[D(14)]-5 and d,l-[D(14)]-5 in 37 and 63 % yield, respectively. Reduction of meso-5 with diimine gave the cis,cis-quatercyclopropane (S*,S*,R*,R*)-21 as the main product (58 % yield) along with the cis,trans-diastereomer (S*,S*,R*,S*)-18 (29 % yield). Thus, five of the six possible diastereomeric quatercyclopropanes were obtained from meso-5, d,l-5, and (Z)-cis-16. The X-ray crystal structure analyses of trans,trans-(R*,S*,R*,S*)-17 and cis,cis-(S*,S*,R*,R*)-21 revealed for the both an unusual conformation in which the central bicyclopropyl unit adopts an s-trans-(antiperiplanar) orientation with phi=180.0 degrees , and the two terminal bicyclopropyl moieties adopt a synclinal conformation with phi=49.8 and 72.0 degrees , respectively. In solution the vicinal coupling constants (3)J(H,H) in trans,trans-(R*,S*,R*,S*)-[D(14)]-17, trans,trans-(R*,S*,S*,R*)-[D(14)]-19, trans,cis-(R*,S*,R*,R*)-[D(14)]-18 and trans,cis-(R*,S*,S*,S*)-[D(14)]-20 were found to be 4.1, 4.7, 5.9 and 5.9 Hz, respectively. This indicates a predominance of the all-gauche conformer in (R*,S*,R*,S*)-17 and a decreasing fraction of it in this sequence of the other diastereomers.     

Tuning electronic eigenvalues of benzene via doping

Using variable atomic numbers within molecular grand-canonical ensemble theory, the highest occupied Kohn-Sham eigenvalue of isoelectronic benzene derivatives is tuned. The performed transmutational changes correspond to the iterative doping with boron and nitrogen. The molecular Fukui function proves to be a reliable index in order to predict the changes in the highest occupied molecular orbital eigenvalue due to doping.     

Metalated diphosphanylsiloxanes with polycyclic and polymeric structures

The reactions of the diphosphanylsiloxane O(SiiPr₂PH₂)₂ (1) with MiPr₃ (M = Ga, In) produced the polycyclic compounds [O{SiiPr₂(PH)MiPr₂}{SiiPr₂(P)MiPr}] ₂ (2, 3). Compounds 2 and 3 are composed of three M₂P₂ rings forming a ladder structure and two OSi₂P₂M rings. By reactions of 1 with n-BuLi the polymeric compound [O(SiiPr₂PHLi)₂(THF)(TMEDA)] · THF (4) was obtained.