Two trans‐4‐aminoazoxybenzenes

Two isomeric trans‐4‐amino­azoxy­benzenes, trans‐1‐(4‐amino­phenyl)‐2‐phenyl­diazene 2‐oxide (α, C₁₂H₁₁N₃O) and trans‐2‐(4‐amino­phenyl)‐1‐phenyl­diazene 2‐oxide (β, C₁₂H₁₁N₃O), have been characterized by X‐ray diffraction. The α isomer is almost planar, having torsion angles along the C_aryl—N bonds of only 4.9 (2) and 8.0 (2)°. The relatively short C_aryl—N bond to the non‐oxidized site of the azoxy group [1.401 (2) Å], together with the significant quinoid deformation of the respective phenyl ring, is evidence of conjugation between the aromatic sextet and the π‐electron system of the azoxy group. The geometry of the β isomer is different. The non‐substituted phenyl ring is twisted with respect to the NNO plane by ca 50°, whereas the substituted ring is almost coplanar with the NNO plane. The non‐oxidized N atom in the β isomer has increased sp³ character, which leads to a decrease in the N—N—C bond angle to 116.8 (2)°, in contrast with 120.9 (1)° for the α isomer. The deformation of the C—C—C angles (1–2°) in the phenyl rings at the substitution positions is evidence of the different character of the oxidized and non‐oxidized N atoms of the azoxy group. In the crystal structures, mol­ecules of both isomers are arranged in chains connected by weak N—H?O (α and β) and N—H?N (β) hydrogen bonds.     

How far the substituent effects in disubstituted cyclohexa-1,3-diene derivatives differ from those in bicyclo[2.2.2]octane and benzene?

Structural Chemistry - Substituents effects in cyclic diene derivatives are studied using quantum chemical modeling and compared to the corresponding effects in aromatic (benzene) and fully...     

Synthesis,structures, and conformational characteristics of calixarene monoanions and dianions

The synthesis, complete characterization, and solid state structural and solution conformation determination of calix[n]arenes (n = 4, 6, 8) is reported. A complete series of X-ray structures of the alkali metal salts of calix[4]arene (HC4) illustrate the great influence of the alkali metal ion on the solid state structure of calixanions (e.g., the Li salt of monoanionic HC4 is a monomer; the Na salt of monoanionic HC4 forms a dimer; and the K, Rb, and Cs salts exist in polymeric forms). Solution NMR spectra of alkali metal salts of monoanionic calix[4]arenes indicate that they have the cone conformation in solution. Variable-temperature NMR spectra of salts HC4.M (M = Li, Na, K, Rb, Cs) show that they possess similar coalescence temperatures, all higher than that of HC4. Due to steric hindrance from tert-butyl groups in the para position of p-tert-butylcalix[4]arene (Bu(t)C4), the alkali metal salts of monoanionic Bu(t)C4 exist in monomeric or dimeric form in the solid state. Calix[6]arene (HC6) and p-tert-butylcalix[6]arene (Bu(t)C6) were treated with a 2:1 molar ratio of M(2)CO(3) (M = K, Rb, Cs) or a 1:1 molar ratio of MOC(CH(3))(3) (M = Li, Na) to give calix[6]arene monoanions, but calix[6]arenes react in a 1:1 molar ratio with M(2)CO(3) (M = K, Rb, Cs) to afford calix[6]arene dianions. Calix[8]arene (HC8) and p-tert-butylcalix[8]arene (Bu(t)()C8) have similar reactivity. The alkali metal salts of monoanionic calix[6]arenes are more conformationally flexible than the alkali metal salts of dianionic calix[6]arenes, which has been shown by their solution NMR spectra. X-ray crystal structures of HC6.Li and HC6.Cs indicate that the size of the alkali metal has some influence on the conformation of calixanions; for example, HC6.Li has a cone-like conformation, and HC6.Cs has a 1,2,3-alternate conformation. The calix[6]arene dianions show roughly the same structural architecture, and the salts tend to form polymeric chains. For most calixarene salts cation-pi arene interactions were observed.     

CO substitution in Ru3(CO)12 by 2,3-bis(diphenylphosphino)-N-phenyl-maleimide (bppm). X-ray diffraction structure of Ru2(CO)6(bppm)

The cluster Ru₃(CO)₁₂ reacts with the diphosphine ligand 2,3-bis(diphenylphosphino)-N-phenyl-maleimide (bppm) in toluene solution at 100C by fragmentation to give a 2:1 mixture of the donor–acceptor complex Ru₂(CO)₆(-bppm) and the phosphido-bridged species Ru₂(CO)₆ , respectively. The new diruthenium compounds have been isolated by chromatography and characterized in solution by IR and NMR (¹H and ³¹P) spectroscopies, in addition to X-ray diffraction analysis in the case of Ru₂(CO)₆( ₂ -bppm). Ru₂(CO)₆( ₂ -bppm), which exists as two crystallographically independent molecules in the unit cell, crystallizes in the orthorhombic space group Pbca, a = 18.8441(9), b = 21.352(2), c = 36.510(2) Å, V = 14,690(1) ų, z = 16, D _calc = 1.649 g/cm³; R = 0.0356, and R _w = 0.0812 for 17732 observed reflections. The reactivity of the bis(diphenylphosphino)-N-phenyl-maleimide ligand with Ru₃(CO)₁₂ under thermolysis conditions is contrasted with the related diphosphine ligands 2,3-bis(diphenylphosphino)maleic anhydride (bma) and 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd).     

Cage-annulated thiacrown ethers and thiacryptands

A series of cage-annulated sulfur-containing crown ethers and cryptands have been synthesized as possible specific metal host systems. The synthesis and structures of seven compounds are described, including a thiacryptand complex with Hg(II). The trishomocubane cage is essentially spherical except for a methylene group, which imparts no steric restrictions, and two disordered superimposed orientations occur in most structures. This superposition of four- and five-membered rings usually cannot be resolved into separate entities, resulting in distorted distances, angles, and thermal parameters for the cage. (3) I4₁ cd, a = 13.207(3) Å, b = 13.207(3) Å, c = 35.876(12) Å; (10) C2, a = 14.551(2) Å, b = 10.028(1) Å, c = 10.491(1) Å, = 107.108(2)°; (14) P2₁/n, a = 10.6277(8) Å, b = 9.8488(7) Å, c = 21.822(2) Å, = 97.945(2)°; (19) P2₁/c, a = 15.381(3) Å, b = 6.667(1) Å, c = 18.158(3) Å, = 94.838(4)°; (25) C2/c, a = 34.386(4) Å, b = 11.318(1) Å, c = 13.409(2) Å, = 110.044(2)°; (28) , a = 10.4487(8) Å, b = 11.5677(9) Å, c = 13.354(1) Å, = 71.042(1)°, = 87.344(1)°, = 65.839(1)°; (29) P2₁/c, a = 10.8138(5) Å, b = 16.4949(8) Å, c = 22.054(1) Å, = 96.087(1)°.     

Characterizations of Some Free Random Variables by Properties of Conditional Moments of Third Degree Polynomials

We investigate Laha–Lukacs properties of noncommutative random variables (processes). We prove that some families of free Meixner distributions can be characterized by the conditional moments of polynomial functions of degree 3. We also show that this fact has consequences in describing some free Lévy processes. The proof relies on a combinatorial identity. At the end of this paper we show that this result can be extended to a \(q\) -Gausian variable.     

1‐[(1‐Ethoxypropylidene)amino]‐2‐ethyl‐4‐(4‐hydroxybenzyl)imidazol‐5(4H)‐one

The racemic title compound, C₁₇H₂₃N₃O₃, isolated from the reaction of l ‐(−)‐tyrosine hydrazide with triethyl orthopropionate in the presence of a catalytic quantity of p‐toluenesulfonic acid (p‐TsOH), crystallizes with Z′ = 1 in a centrosymmetric monoclinic unit cell. The molecule contains two planar fragments, viz. the benzene and imidazole rings, linked by two C—C single bonds. The dihedral angle between the two planes is 59.54 (5)° and the molecule adopts a synclinal conformation. The HOMA (harmonic oscillator model of aromaticity) index, calculated for the benzene ring, demonstrates no substantial interaction between the two π‐electron delocalization regions in the molecule. In the crystal structure, there is an O—H...N hydrogen bond that links the molecules along the c axis.     

The substituent effect of π-electron delocalization in N-methylamino-nitropyridine derivatives: crystal structure and DFT calculations

Structural Chemistry - The crystal and molecular structures of 3-(N-methylamino)-2-nitropyridine, 5-(N-methylamino)-2-nitropyridine and 2-(N-methylamino)-5-nitropyridine have been characterized by...     

DFT and experimental studies on structure and spectroscopic parameters of 3,6-diiodo-9-ethyl-9H-carbazole

Structural Chemistry - The first report on crystal and molecular structure of 3,6-diiodo-9-ethyl-9H-carbazole is presented. Experimental room-temperature X-ray and 13C chemical shift studies were...