Search results for "Intramolecular force"

The effect of 2,2-dicyanovinyl groups as electron acceptors in push–pull substituted oligo(1,4-phenylenevinylene)s

2003

Abstract The newly synthesized oligo(1,4-phenylenevinylene) series 2a–d with bis(2-hexyloctyl)amino groups as electron donors and 2,2-dicyanovinyl groups as electron acceptors represents conjugated oligomers with strong push–pull effects. Due to the decrease of the intramolecular charge transfer with increasing numbers of repeat units (n=1–4), the long-wavelength transition shows a particularly great hypsochromic shift for the extension of the chromophore.

Reaktionen bei der Bestrahlung von poly(N-chloramid)en

1980

On irradiating poly(N-chloroamide)s in films or in solution in the range of 325–375 nm carboxamide groups are formed. The irradiated polymer contains chlorine which is linked to C-atoms. This reaction can certainly not be explained with an intramolecular photorearrangement but with a sequence of photoreactions and dark reactions satisfactorily accounting for all observations.

Gas-liquid chromatography and lipophilicity of esters of benzoic acids

1987

Abstract The use of gas-liquid chromatographic (GLC) retention indices for the determination of lipophilicity was studied for a series of alkyl and arylalkyl esters of substituted benzoic acids. The regression relationships between the logarithms of the partition coefficients and the retention characteristics measured on two cpillary columns, SE-30 and OV-351, were evaluated. The behaviour of arylalkyl esters and of alkyl esters cannot be expressed in terms of a single regression equation. This is probably a consequence of the effect of the intramolecular hydrophobic interaction upon the retention of arylalkyl esters under GLC conditions. An analysis of the isokinetic relationships revealed…

A slow process in confined polymer melts: layer exchange dynamics at a polymer solid interface

2010

Employing Molecular Dynamics simulations of a chemically realistic model of 1,4-polybutadiene between graphite walls we show that the mass exchange between layers close to the walls is a slow process already in the melt state. For the glass transition of confined polymers this process competes with the slowing down due to packing effects and intramolecular rotation barriers.

Inter- and intramolecular non-covalent interactions in 1-methylimidazole-2-carbaldehyde complexes of copper, silver, and gold

2014

Abstract Three new imidazole compounds, [CuBr2(mimc)2] (1), [Ag(mimc)2][CF3SO3] (2), and [AuCl3(mimc)] (3) (mimc = 1-methylimidazole-2-carbaldehyde), have been synthesized, structurally characterized, and further analyzed using the QTAIM analysis. The compounds exhibit self-assembled 3D networks arising from intermolecular non-covalent interactions such as metallophilic interactions, metal-π contacts, halogens–halogen interactions, and hydrogen bonds. These weak interactions have a strong impact on the coordination sphere of the metal atoms and on the packing of compounds 1, 2, and 3.

Pauson–Khand reaction of fluorinated compounds

2020

The Pauson–Khand reaction (PKR) is one of the key methods for the construction of cyclopentenone derivatives, which can in turn undergo diverse chemical transformations to yield more complex biologically active molecules. Despite the increasing availability of fluorinated building blocks and methodologies to incorporate fluorine in compounds with biological interest, there have been few significant advances focused on the fluoro-Pauson–Khand reaction, both in the inter- and intramolecular versions. Furthermore, the use of vinyl fluorides as olefinic counterparts had been completely overlooked. In this review, we collect the advances both on the stoichiometric and catalytic intermolecular an…

Experimental and theoretical investigations of the contact ion pairs formed by reactions of the anions [(EPR2)2N]- (R = (i)Pr, (t)Bu; E = S, Se) with…

2010

Reactions of the sodium salts [(EPR(2))(2)N]Na(TMEDA) (R = (i)Pr, (t)Bu; E = S, Se) with the iodide salts [(TePR(2))(2)N]I (R = (i)Pr, (t)Bu) in toluene produce the mixed-chalcogen systems [(EPR(2))(2)N][(TePR(2))(2)N] (6b, E = Se, R = (t)Bu; 6c, E = S, R = (t)Bu; 7b, E = Se, R = (i)Pr; 7c, E = S, R = (i)Pr). Compounds 6b, 6c, 7b, and 7c have been characterized in solution by variable-temperature multinuclear ((31)P, (77)Se, and (125)Te) NMR spectroscopy and in the solid state by single-crystal X-ray crystallography. The structures are comprised of contact ion pairs linked by bonds between Te and S or Se atoms. For the tert-butyl derivatives 6b and 6c, the anionic half of the molecule is co…

1983

The first dissociation constant of oligonuclear phenolic compounds consisting of one nitrophenol unit besides further alkyl phenol units (10 dinuclear, 15 trinuclear, 6 tetranuclear compounds, and 4 nitrophenols as model) was determined spectroscopically in water/methanol (50/50 by vol.) at 25°C. For the ortho-linked title compounds with the nitrophenol unit at the end of the molecule a decrease of pK1 is observed which becomes stronger with increasing chain length. The introduction of bulky groups in ortho-position of the dissociating phenolic unit, as well as at the opposite end of the molecule causes a further decrease of pK1. The lowest value is found for a p-nitrophenol unit in the mid…

High Enantiocontrol in the Intramolecular Cyclopropanation of Diazo Ketones Catalyzed by Dirhodium(II) Complexes with Ortho-Metalated Aryl Phosphine …

2001

[reaction: see text]. Chiral dirhodium(II) complexes, Rh2(O2CCF3)2(PC)2, [PCH = (p-CH3C6H4)3P, (m-CH3C6H4)3P], provide an excellent yield and a high enantiocontrol in the cyclopropanation of alpha-diazo ketones with gamma and delta double bonds. The ee values are significantly dependent on the solvent used; the best results are obtained using pentane.

The conformation cis of N-acetyl-N-methyl-α,β-dehydroalanine N′-methylamide and saturated analogues

2007

A series of three homologous amino acids derivatives: N-acetyl-N-methyl-α,β–dehydroalanine N′-methylamide (1), N-acetyl-N-methyl-L-alanine N′-methylamide (2), and N-acetyl-N-methyl-DL-alanine N′-methylamide have been synthesised. The racemic species undergoes spontaneous separation into L and D-enantiomers. From these two chiral forms, the structure of L-enantiomer (3) was analysed. The molecules of 1 – 3 adopt the cis arrangement of the N-terminal amide bond. The molecular conformations are similar for 1 (φ, ψ = 94.6(1)°, −1.7(1)°) and 3 (φ, ψ = 111.5(1)°, −23.8(1)°), and also 2 (φ, ψ = −114.8(2)°, 29.5(2)°), if inversion through the chiral C2 carbon is considered. They are stabilised by i…