A comprehensive study on the physicochemical properties of a series of mono- and diaza[5]helicenes as well as mono- and diaza[6]helicenes is reported. Through the use of both computational and experimental methods, these helically chiral pyridohelicenes with the nitrogen atom(s) in various positions are characterised according to their inversion barriers, protonation constants and redox potentials. By using DFT calculations, kinetic measurements, UV/Vis titrations, cyclic voltammetry and EPR spectroscopy, a self-contained picture of their behaviour under conventional treatment by heat, acids and oxidising/reducing agents is provided.
Spiral staircases: A general method for the preparation of optically pure [5]‐, [6]‐, and [7]heterohelicenes is based on a CoI‐ or Ni0‐catalyzed diastereoselective [2+2+2] cycloisomerization of centrally chiral triynes to deliver helicenes comprising two 2H‐pyran rings. The configuration, which can be predicted, does not depend on helicene length or functional groups present.
As we know, fi nished polyester fi bers are very diffi cult to dye, especially at low temperature (including room temperature). An exception is processes for dying undrawn fi bers. We have studied use of the crazing method to dye polyester fi bers at low temperatures with water-soluble dyes not having an affi nity for polyethylene terephthalate. We have studied the effect on sorption of cationic dyes from the composition, concentration, and temperature of the adsorption-active medium, and the dye concentration in the dye bath. The results of the study are the basis for developing a production process for obtaining colored special-purpose polyester fi bers.Polyester fi bers are very diffi cult to dye [1] due to their hydrophobicity, compact structure, and lack of a suffi cient number of functional groups in the polyethylene terephthalate (PET) macromolecules that can chemically react with active groups of the dyes. The most active centers of the PET macromolecules are the ester and terminal hydroxyl and carboxyl groups, due to which the polyester fi bers have an affi nity for disperse dyes but do not have an affi nity for direct dyes, acid dyes, or basic dyes. Surface dyeing of polyester fi bers is generally done in aqueous solutions with disperse dyes at elevated temperatures [2]. Polyester fi bers are not dyed at room temperature in practice. An exception is methods for dyeing the undrawn fi ber [3], making it possible to carry out the dyeing process directly in aqueous solutions of the dyes at low temperatures (below the glass transition temperature). The method involving crazing of polyester fi bers can be used for similar purposes.A characteristic feature of the crazing process is orientational drawing of the polyester fi lament in adsorption-active (AA) media [4]. Surface microdefects in the polymer and exposure to the medium lead to a change in the initial structure and mechanical properties of the fi laments. At the points where the liquid penetrates, stress concentrations appear and specifi c cracks are formed. In contrast to true fracture cracks, the appearance of microcracks in the polymers does not lead to their fracture. Such microcracks can sustain high loads. When the fi lament is deformed in the direction of the applied stress, orientation occurs at the locations of microcracks.When a freshly formed polyester fi lament is drawn in an adsorption-active medium in the presence of dye, the dye penetrates into the microcracks formed and when the pores are closed, it is anchored in the fi lament. For qualitative and quantitative evaluation of the dyeing process, we used the dye Cationic Red 2S, soluble in adsorption-active media. Under usual conditions, it does not dye polyester fi bers and is not chemically bound; but when it penetrates into microcracks, when the pores are closed it is mechanically held in the fi ber, ensuring saturated and permanent dyeing.Crazing of polymers in liquid media is a complicated multistep process which depends on many factors. We have studied the effect of the following pa...
A series of diverse aromatic azadienetriyne and azatriynes was synthesised. These compounds were subjected to transition metal-mediated [2+2+2] cycloisomerisation to form pentacyclic or hexacyclic helically chiral azahelicene or azahelicene-like structures mostly in moderate yields. Introducing stereogenic centre(s) into selected azatriynes, cyclisation proceeded in a stereoselective fashion providing aza[5]helicenes or aza[6]helicene-like compounds in up to a 100:0 diastereomeric ratio. Gibbs energy differences between corresponding pairs of diastereomers (calculated at the DFT(B3LYP)/TZV+P level) were in good agreement with the experimental data and allowed for the prediction of the stereochemical outcome of the reaction. This study presents for the first time asymmetric synthesis of azahelicene derivatives in high optical purities.
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