Search results for "Spectroscopy"
showing 10 items of 10293 documents
Supramolecular arrangements of novel clickable 4-substituted 3,6-bis(2′-pyridyl)pyridazine molecules
2020
Abstract The clickable reaction between the starting 3,6-bis(2′-pyridyl)-1,2,4,5-tetrazine (bptz) with a series of terminal alkynes-containing functional biomolecules [prop-2-yn-1-ol, 4-(prop-2′-yn-1′-yl)morpholine and D-galactose] by means of an inverse electron demand Diels-Alder pathway has been studied and four new 4-substituted 3,6-bis(2′-pyridyl)pyridazine derivatives (4-Rdppn) were isolated, namely 4-(hydroxymethyl)-3,6-di(pyridin-2-yl)pyridazine (1), 4-((prop-2-yn-1-yloxy)methyl)-3,6-di(pyridin-2-yl)pyridazine (2) obtained by post-etherification reaction of 1, 4-(morpholinemethyl)-(3,6-dipyridin-2-yl)pyridazine monohydrate (3) and 3,6-di(pyridin-2-yl)-4-((2,2,7,7-tetramethyltetrahyd…
Concave macrobicycles: Absorption spectra, luminescence properties, and endocavital complexation of neutral organic guests
1996
By a mild modified Eglinton coupling a series of diynebridged macrobicyclic hosts capable of endocavital complexation were synthesized and their structures and complexation properties investigated by X-ray analysis. The inclusion of DMSO in 7 suggests a direct correlation between steric fit and orientation of the guest. On the basis of this hypothesis, the orientation of acetone in an endocavital inclusion of 2 was predicted and verified by X-ray analysis. Comparison of the single-crystal X-ray structures of the vacant macrobicycle 3 and of a family of macrobicycles showing endocavital or “pocket” complexation of neutral organic guests suggests that torsion of the cavities upon complexation…
Halogenomercury Salts of Sterically Crowded Triazenides - Convenient Starting Materials for Redox-Transmetallation Reactions
2010
Diaryl-substituted triazenides Ar(Ar′)N3HgX [Ar/Ar′ = Dmp/Mph, X = Cl (2a), Br (3a), I (4a); Ar/Ar′ = Dmp/Tph, X = Cl (2b), I (4b) with Mph = 2-MesC6H4, Mes = 2,4,6-Me3C6H2, Tph = 2′,4′,6′-triisopropylbiphenyl-2-yl and Dmp = 2,6-Mes2C6H3] were synthesized by salt-metathesis reactions in ethyl ether from the readily available starting materials Ar(Ar′)N3Li and HgX2. These compounds may be used for redox-transmetallation reactions with rare-earth or alkaline earth metals. Thus, reaction of 4b or 2b with magnesium or ytterbium in tetrahydrofuran afforded the triazenides Dmp(Tph)N3MX(thf) (5b: M = Mg, X = I; 6b: M = Yb, X = Cl) in good yield. All new compounds were characterized by melting poin…
13C-NMR Based Evaluation of the Electronic and Steric Interactions in Aromatic Amines
2005
Abstract: Chemical shifts of the para carbon atoms, δ(13C-4), in a series of aromatic amines were used to calculate the Ãp, ÃR and ÃOR substituent constants for different amino groups. 1-Pyrrolidino, N,N-di-n-butylamino and N,N-diethylamino groups were found to be the most strong electron-donors. ortho-Substitution decreases the donor properties of the amino group. The amino groups in 2,6-di-i-propylaniline and N,N-2,6-tetramethylaniline have very weak electron-donor properties. The nitrogen atom in benzoquinuclidine and N,N-dimethyl-2,6-di-i-propylaniline have an electron-acceptor character. The calculated substituent constants of the amino groups studied are consistent with the s…
Self-Sorting Effects in the Self-Assembly of Metallosupramolecular Rhombi from Chiral BINOL-Derived Bis(pyridine) Ligands
2013
Four BINOL-based bis(4-pyridyl) ligands were synthesised in enantiopure and racemic form. These ligands form metallosupramolecular [(dppp)2M2L2] rhombi with cis-protected [(dppp)Pd]2+ and [(dppp)Pt]2+ ions. In principle, racemic ligands can self-assemble into three stereoisomeric rhombi. The degree of self-sorting in the self-assembly process crucially depends on the substitution pattern and the resulting bend angle of the V-shaped ligands as well as the degree of steric crowding within the assembly when racemic ligands are used. Thus, these processes either lead to homochiral assemblies in a narcissistic self-recognition manner, to heterochiral assemblies in a social self-discriminating ma…
Role of Halide Ion in the Mechanism of Protonolysis of the Pt-C Bond in Pt(II) Alkyl and Aryl Complexes.
1985
Abstract A mechanistic study is described for the electrophilic cleavage of the Pt C σ bond in complexes cis -[PtPh 2 (PEtPh 2 ) 2 ] and trans -[PtXR(PEt 3 ) 2 ] (X = Cl and Br, R = Me, Et, n-Pr, n-Bu, CH 2 Ph) by the proton in the presence of halide ions in aqueous methanol (MeOH/H 2 O, 91v/v) which yields cis -[PtClPh(PEtPh 2 ) 2 ] and trans -[PtX 2 (PEt 3 ) 2 ], respectively. The reactions are first-order in substrate for both systems and the general bivariate rate law k obs = [H + ]{ k H + k x K [[X − ]}/(1 + K [[X − ]) is obeyed. The proposed mechanism involves a fast pre-equilibrium formation (K) of a platinum(II) anionic intermediate via interaction of the halide with the square-plan…
Comparison of calculated DFT/B3LYP and experimental 13C and 17O NMR chemical shifts, ab initio HF/6-31G* optimised structures, and single crystal X-r…
2003
Abstract Single crystal X-ray structures (monoclinic space group P2 1 ) for methyl 3-oxo-5β-cholan-24-oate and methyl 3,12-dioxo-5β-cholan-24-oate have been solved and compared with HF/6-31G* optimised structures. In the crystalline packings the side chains are connected with weak OC(sp 3 ) H ⋯ O -type of interactions between C25– H and C24– O –C25 and the keto ends with weak C(sp 3 ) H ⋯ O C-type of interactions between C4– H and O C3. The orientations of the side chains, which steric configurations are of great importance to the biological activity of the molecules, are compared with the experimental structure of methyl 3α-hydroxy-5β-cholan-24-oate. Probable reasons for the observed dif…
Micelles formed from photochemically active amphiphiles: structural characterization by small-angle neutron scattering
1996
Abstract A novel class of photochemically active amphiphiles has been synthesized containing a ketone moiety as a biradical or radical pair precursor on the hydrophobic tail of sodium sulfate surfactants. Alteration of the molecular structure of each ketone-containing surfactant allows for the systematic and predictable manipulation of the micellar size and shape, both of which are important in determining the coupling between the unpaired electrons confined within the micelle and the intraradical dynamics. The structure of the resulting aggregates has been analyzed by small-angle neutron scattering (SANS). The results show that the amphiphiles form ellipsoidal micelles with aggregation num…
1H, 13C and 15N NMR study of 2-alkylnitrosoamino-4-nitropyridines and N-oxides: An example on restricted inversion of sp3 nitrogen
2007
Abstract The 1 H, 13 C and 15 N NMR chemical shifts of seven 2-alkylnitrosoamino-4-nitropyridines and seven 2-alkylnitrosoamino-4-nitropyridine N -oxides have been assigned. The GIAO/DFT 13 C chemical shifts of energetically optimized structures have been calculated. The results were compared to the chemical shifts of previously studied 2-alkylamino and 2-alkylnitramino derivatives of 4-nitropyridine and 4-nitropyridine N -oxide. In sterically crowded ortho -substituted congener (2-ethylnitrosoamino-3-methyl-4-nitropyridine N -oxide) restricted inversion of pyramidal amino nitrogen forms a chiral center in the molecule and makes the geminal protons of N–CH 2 -moiety diastereotopic. In 5- an…
Zinc-salophen complexes as selective receptors for tertiary amines
2007
Zinc-salophen compounds 1-3 incorporating in the given order 1,2-diaminobenzene, 2,3-diaminonaphthalene, and 9,10-diaminophenantrene moieties were synthesised. Their binding properties toward a series of tertiary amines were assessed by UV-Vis and fluorescence spectroscopy in chloroform solution. Unprecedented selectivities of quinuclidine vs. triethylamine higher than 105 were recorded, thereby revealing the dramatic influence of steric effects on axial coordination of tertiary amines. X-Ray diffraction analyses showed that in the solid state compound 2 is dimeric, but its 1 : 1 quinuclidine complex is monomeric. Strong indications were obtained that both free receptors and their amine add…