Search results for "Electronic effect"
showing 10 items of 45 documents
3-(Pyridin-2-yl)[1,2,3]triazolo[1,5-a]quinoline: A Theoretical and Experimental Analysis of Ring-Chain Isomerisation
2009
In the course of the synthesis of new fluorophores for molecular recognition an experimental (1H NMR) and theoretical (DFT) study of the ring-chain isomerism of 3-(pyridin-2-yl)[1,2,3]triazolo[1,5-a]quinoline derivatives (A) into 2-([1,2,3]triazolo[1,5-a]pyridin-3-yl)quinoline derivatives (B) has been carried out. The rearrangement is influenced by steric and electronic effects of the substituents present on the quinoline ring. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
2,2’Bipyrimidine: A Useful Tool in Designing Polynuclear Complexes of Controlled Nuclearity
1996
The versatility of a simple ligand such as 2,2’-bipyrimidine (bpym) which can adopt chelating and bis(chelating) coordination modes facilitates the preparation of both mononuclear and polynuclear complexes whose nuclearity can be controlled by playing with the metal to bpym molar ratio, the nature of the counterion and the presence of additional ligands. In this work, we summarize our results dealing with the preparation and the structural and magnetic characterization of complexes between first-row transition metal ions and bpym. Examples of orbital reversal and tunable exchange in bpym-containing copper(II) complexes are presented and discussed. The influence of the number of unpaired ele…
Chiroptical inversion of a planar chiral redox-switchable rotaxane.
2019
Reversible redox-switching of a planar chiral [2]rotaxane with a tetrathiafulvalene-bearing crown ether macrocycle generates a complete sign reversal of the main band in the ECD spectrum, as shown by experiment and rationalised by DFT calculations.
1H,13C,17O and19F NMR spectroscopic study of isomeric ring-substituted monofluoro-(E)-3-phenylpropenals
1993
Isomeric ring substituted monofluoro-(E)-3-phenylpropenals (cinnamaldehydes) were synthesized in order to provide, with the NMR-active 19F nucleus, an insight into the influence of substituents and the transmission of electronic effects between the aromatic ring and the side-chain. Their 1H, 13C and 17O NMR chemical shifts and their nJ(H,H), nJ(H,F), nJ(C,H) and nJ(C,F) values were determined. Generally, the nJ(C,F) coupling constants correlate with the length of the coupling route and thus simplify the assignments of the 13C NMR spectra. Only the side-chain carbons C-2 and C-3 in the ortho-substituted compounds showed an exception to this rule. Many long-range nJ(H,F) (n = 4–7) values were…
ChemInform Abstract: Conjugated Compounds Based on Vinylthiazole Units.
2008
Conjugated oligomers attract increasing attention because of their interesting properties in materials science [1]. Moreover, they are model compounds for conjugated polymers. Molecules polarized by electronic effects, in particular push-pull systems having terminal donor-acceptor substitution represent a special class of such oligomers [2]. Their major applications are in the field of nonlinear optics (NLO), twophoton absorption (TPA), two-photon induced fluorescence (TPIF), and photorefractive materials (PR). Fig. 1 illustrates known 2,5-thienylenevinylenes with zwitterionic resonance structures 1 (D = NR2; A = NO2, CHO, SO2R; n = 1, 2) [3, 4]. The corresponding compounds 2 with thiazole …
Substituent effects on axle binding in amide pseudorotaxanes: comparison of NMR titration and ITC data with DFT calculations
2012
The binding behaviour of differently substituted diamide axle molecules to Hunter/Vögtle tetralactam macrocycles was studied with a combination of NMR titration, isothermal titration calorimetry (ITC) experiments and calculations employing density functional theory (DFT), along with dispersion-corrected exchange-correlation functionals. Guests with alkyl or alkenyl chains attached to the diamide carbonyl groups have a significantly higher binding affinity to the macrocycle than guests with benzoyl amides and their substituted analogues. While the binding of the benzoyl and alkenyl substituted axles is enthalpically driven, the alkyl-substituted guest binds mainly because of a positive bindi…
On the use of multi-parameter free energy relationships: the rearrangement of (Z)-arylhydrazones of 5-amino-3-benzoyl-1,2,4-oxadiazole into (2-aryl-5…
2010
Abstract By using a multi-parameter approach (a combination of Hammett/Ingold-Yukawa-Tsuno/Fujita-Nishioka free energy relationships) the mononuclear rearrangements of heterocycles (MRH) rates for five new ortho-substituted and ten new di-, tri-, or tetra-substituted (Z)-arylhydrazones of 5-amino-3-benzoyl-1,2,4-oxadiazole into the relevant (2-aryl-5-phenyl-2H-1,2,3-triazol-4-yl)ureas (in dioxane/water and in a large range of pS+ values) have been related to the electronic and proximity effects exerted by the present substituents, also considering previous results on some mono meta- and para-substituted (Z)-arylhydrazones. In every case, excellent correlation coefficients have been calculat…
Insight into the synthesis of N-methylated polypeptides
2020
The ring-opening polymerization (ROP) of N-carboxy anhydrides (NCAs) is mostly divided into two classes: NCAs of α-substituted amino acids and N-methylated NCAs of α-unsubstituted glycine derivatives (NNCAs). The use of both monomer types offers different mechanistic features and results in a multitude of functional materials. To combine these properties, the synthesis and ROP of α-substituted and N-methylated NCAs (αNNCAs) of several amino acids were investigated. The current study provides insight into the influence of polymerization conditions and the limitations caused by the enhanced steric demand of the amino acid NCA monomers and their N-methylated derivatives. Namely, the effects of…
Synthesis of N-methyl alkylaminomethane-1,1-diphosphonic acids and evaluation of their complex-formation abilities towards copper(II)
2015
Abstract A series of N -methyl alkylaminomethane-1,1-diphosphonic acids ( 3a – g ) with a common tertiary nitrogen atom (CH 3 –N–R) bearing linear or branched alkyl, cycloheptyl or phenylalkyl R substituents was synthesized in the reaction of diethylphosphonate with triethyl orthoformate and secondary amine followed by hydrolysis, and by the Eschweiler–Clarke methylation of the alkylaminomethane-1,1-diphosphonic acids with formic acid and formaldehyde. Complex-formation abilities of 3a – g towards copper(II) in solution were studied by means of pH-potentiometry, ESI-MS spectrometry, UV–Vis and EPR methods. Evaluation of stability constants for the Cu(II) complexes of 3a – g has revealed the…
Conjugated Compounds Based on Vinylthiazole Units
2007
Conjugated oligomers attract increasing attention because of their interesting properties in materials science [1]. Moreover, they are model compounds for conjugated polymers. Molecules polarized by electronic effects, in particular push-pull systems having terminal donor-acceptor substitution represent a special class of such oligomers [2]. Their major applications are in the field of nonlinear optics (NLO), twophoton absorption (TPA), two-photon induced fluorescence (TPIF), and photorefractive materials (PR). Fig. 1 illustrates known 2,5-thienylenevinylenes with zwitterionic resonance structures 1 (D = NR2; A = NO2, CHO, SO2R; n = 1, 2) [3, 4]. The corresponding compounds 2 with thiazole …