Studies on sesquiterpenoids—III Some derivatives of guaiol

When guaiol was dehydrated with such reagents as thionyl chloride-pyridine, phosphorus oxychloride-pyridine or potassium bisulphate, the isopropenyl derivative (IIa) was always obtained as a main product, together with a small amount of IIb. Catalytic reduction of IIa in alkaline media afforded -dihydroguaiene (V), while in neutral or acid media it gave a mixture of V and its double bond isomer (VI).     

ChemInform Abstract: On Squaring Triangles — Structural Motifs in Cu—In—Sb Compounds.

Two new compounds, Cu₇In_2.5Sb_0.5 (I) and Cu₂In_0.75Sb_0.25 (II) are prepared from the elements (silica ampules, 1173 K, 3 d, followed by annealing at 573—773 K for 220 d).     

NMR-untersuchungen an piperidinen—III. 1H-messungen an alkylpiperidinen

The ¹H-220 MHz spectra of several alkylpiperidines are reported. Almost complete assignments for all ring protons are possible. The effects of N-methyl and C-methyl groups on adjacent ring protons are discussed in detail.     

Heterocyclic fluorine compounds—III Monofluoroxanthones

The four monofluoroxanthones substituted in the benzene ring have been prepared by two different routes, namely by cyclisation of the appropriate carboxyfluorodiphenyl ether and by a Balz-Schiemann reaction with the corresponding aminoxanthone.     

Structural and vibrational properties of vanadium (III) oxofluoride and oxochloride—a theoretical study

The potential energy surfaces of FVO and ClVO are studied using the density functional theory. It is found that the potential energy surface of both molecules is dominated by triplet states. Several singlet states are found close in energy, though. A good agreement is found between experimental and calculated vibrational frequencies except for the V–F stretching mode, which is predicted to be too low by the present results. The frequencies corresponding to the O–V–X bending mode are provided as a guide for future experimental studies. An estimation of the force constants, mean amplitudes of vibration, and thermodynamic functions is performed, too, in order to get a deeper insight into the bond properties of the title molecules.     

Metallobiliverdin Radicals—DFT Studies

Several aspects of the molecular and electronic structure of biliverdin derivatives have been studied using density functional theory (DFT). The calculations have been performed for complexes of trianion (BvO₂)^3? and dianion [BvO(OH)]^2?, derived from two tautomeric forms of biliverdin, BvO₂H₃ and [BvO(OH)]H₂, with redox innocent metal ions: lithium(I ), zinc(II ), and gallium(III ). One‐electron‐oxidized and ‐reduced forms of each complex (cation and anion radicals) have been also considered. The molecular structures of all species investigated are characterized by a helical arrangement of tetrapyrrolic ligands with the metal ion lying in the plane formed by the two central pyrrole rings. The spin density distribution in four types of metallobiliverdin radicals—[(BvO₂^.)Mⁿ⁺]^n‐2, [{BvO(OH)^.}Mⁿ⁺]^n‐1 (cation radicals), [(BvO2^.)Mⁿ⁺]^n‐4, [{BvO(OH)^.}Mⁿ⁺]^n‐3 (anion radicals)—has been investigated. In general, the absolute values of spin density on meso carbon atoms were larger than for the β‐carbon atoms. Sign alteration of spin density has been found for meso positions, and also for the β‐carbon atoms of at least two pyrrole rings. The calculated spin density maps accounted for the essential NMR spectroscopic features of iron biliverdin derivatives, including the considerable isotropic shifts detected for the meso resonances and shift alteration at the meso and β‐positions.     

Mass spectrometry of onium salts—I. Studies on anilinium oxides

The mass spectra of the three isomeric trimethylanilinium oxides and their methyl-d₃ analogues show that the m- and p- isomers undergo intermolecular trans-O-alkylation before evaporation. In the o-isomer, only 10% transalkylated product is observed and there is strong evidence that most of this isomer evaporates without undergoing structural changes. By indirect introduction, however, the o-isomer showed only transalkylated product. The most important fragmentation patterns on electron-impact are α-cleavage on the N-methyl carbon or expulsion of the O-substituent with formation of a quinoid structure. The latter dominates for the o- and p-methyl ethers while the former is the most important pathway for the m-isomer and for the corresponding phenols. Lower fragments are of modest intensity.     

Constrained Cyclopeptides: Biaryl Formation through Pd‐Catalyzed C−H Activation in Peptides—Structural Control of the Cyclization vs. Cyclodimerization Outcome

A series of short tryptophan‐phenylalanine peptides containing an iodo substituent on the phenyl ring was subjected to Pd‐catalyzed CH activation reactions to give the corresponding aryl‐indole coupled products. Two types of adducts were generated: cyclomonomer and cyclodimeric peptides; no evidence of oligo‐ or polymerization products was detected. Contrary to standard peptide macrocyclizations, the factors controlling the fate of the reaction are the number of amino acids between the aromatic residues and the regiochemistry of the parent iodo derivative, independent of both the concentration and the cyclization mode. The method is general and allows access to novel biaryl peptidic topologies, which have been fully characterized.     

Studies on organophosphorus compounds—III: Reaction of α-substituted secondary car☐amides with HMPA—amidine and/or nitrile syntheses

Secondary car☐amides (R¹CONHR²) undergo different reactions when heated in HMPA at about 220°. If R¹ or R² can form stable carbonium ions, fragmentation reactions are observed and the corresponding nitriles R²CN or R¹CN, respectively, are formed. Also amidines are produced. N-benzyl-acetamide rearranges when heated in HMPA to give β-phenyl-propionitrile, It is suggested that in all the reactions investigated the first step is the formation of a phosphorodiamidate followed by formation of a nitrilium carbonium ion. The fragmentation reactions can be used as an alternative to the Sandmeyer reaction (nitrile synthesis).     

Polymerization of Cyclosiloxanes. I. Kinetic Studies on Living Polymer—Octamethylcyclotetrasiloxane Systems

The kinetics of the anionic polymerization of octamethylcyclotetrasiloxane (D₄) initiated by α-methylstyrene living polymer in tetrahydrofuran was studied. The following kinetic scheme was postulated: Initiation: Propagation: where S^- and M represent the initiator and D₄, respectively. At a living end concentration of 0.0377 mole/l. and a monomer concentration of 1.5 mole/l. in tetrahydrofuran at 25°C. the following kinetic data were obtained: k₁ = 2.3 × 10^?4 l./mole-sec., k₂ < 2.3 × 10^?5 sec.^?1, k₃ = 2.75 × 10^?2l./mole-sec. k₄ ≈ 1.17 × 10^?2 sec.^?1, K₁ > 10 l./mole and K₂ ≈ 2.35 l./mole. The rate constants k₁ and k₃ were found to be dependent on the concentration of anions. This is attributed to the dissociation of ion pairs to free ions at lower concentration. Under the experimental conditions studied the majority of the anions were present in the form of ion pairs. The reactivity of the free ions is about 100 times greater than that of ion pairs. There is no temperature effect on K₂, indicating zero ΔH and positive ΔS in the propagation reaction.     

Structural investigation of lac resin—II

The three fractions of lac rein viz., hard resin I, hard resin II and soft resin have been cleaved with hydriodic acid followed by deiodination. The products were separated into fatty acids and terpene acids. The former have been studied by GLC and data on the nature and distribution of the chain lengths and their relative amounts were thus obtained. Cleavage of the different fractions of the resin with hydrogen chloride followed by alkaline hydrolysis gave the total aleuritic acid quantitatively. Based on the above results, the possibility of the presence of alkali stable linkages in lac resin and the amount of aleuritic acid liberated only by acid cleavage have been determined.     

‘Untypical aging off-flavor’ in wine: formation of 2-aminoacetophenone and evaluation of its influencing factors

2-Aminoacetophenone (AAP) is known as the character impact compound responsible for the so called untypical ‘aging off-flavor’ (UTA) in Vitis vinifera wines. The formation of AAP is caused by an oxidative degradation of the phytohormone indole-3-acetic acid (IAA), triggered by sulfuration after fermentation. Using different radical generating systems (hydroxyl and/or superoxide radical generating systems) it could be shown especially that superoxide radicals are responsible for the formation of AAP. Hereby, a pyrrole ring cleavage of IAA yields 3-(2-formylaminophenyl)-3-oxo-propionic acid (FAPOP), N-formyl-2-aminoacetophenone (FAP), and AAP. Analysis of 32 grape musts and their corresponding wines revealed that wines with a higher superoxide radical scavenger activity are less prone to UTA formation. However, UTA is not correlated with the IAA content of the must or wine. Differences in the release of IAA during fermentation of musts derived from early and late harvested grapes indicate a correlation between the ripeness of the processed grapes, the IAA content at the time of sulfuration, and the UTA formation.     

Selective reagents for solvent extraction of metals—III. Picolinic acids

Alkyl-substituted pyridine-2-carboxylic acids have been found to be efficient reagents for the extraction of Cu²⁺, Fe³⁺, Co²⁺ and Ni²⁺ from aqueous sulfate solutions at pH 1.7. The effects of the position and the nature of the substituent are discussed.     

Pyrophthalone and its derivatives as ligands—I. Mode of coordination—formation of isomeric iminopyrophthalone complexes

The complex formation of Co(II), Ni(II), Zn(II) with aminopyrophthalone was studied by means of electronic, IR, EPR and ¹H-NMR spectroscopy. It was established that with Co(II) and Ni(II) two isomeric complexes are formed in contrast to Zn(II) and Cu(II) complex formation. On the basis of the spectral data obtained the coordination mode and structure of the complex species are assumed.     

Asymmetric and symmetric annellation effects—III Benzocoronenes

1:2–5:6-Dibenzocoronene (IV) was obtained from 1:2–4:5–8:9-tribenzopyrene (II) via the dianhydride (III). 1:2–4:5-Dibenzopyrene (V) condensed twice with maleic anhydride. The resulting dianhydride (VI) gave 1:2-benzocoronene (VII) on decarboxylation. 1:12-o-Phenyleneperylene (X) was obtained by a zinc dust melt from the quinone (VIII). The annellation effects passing from triphenylene and perylene to the benzocoronenes indicate the presence of a triphenylene complex within the electronic fine structure of coronene.