Thin-Layer Chromatographic Determination of the pKa Values of Organic Acids and Bases

JPC – Journal of Planar Chromatography – Modern TLC -     

Use of Structural Descriptors to Predict the RM Values of m- and p-Alkoxyphenols in RP TLC

JPC – Journal of Planar Chromatography – Modern TLC - Selected meta- and para-alkoxyphenols have been separated by RP TLC on cellulose impregnated with ethyl oleate, with ethanol-water,...     

O-Methyloximes of Testosterone and of 17α-Methyltestosterone: TLC and QSPR Study of RF Values

JPC – Journal of Planar Chromatography – Modern TLC - The Z (1b and 2b, respectively) and E diastereomers (1c and 2c, respectively) of the O-methyloximes of testosterone (1a) and...     

Influence of the Regression Technique on the Extrapolated Retention Values of Single-Point Adsorption Compounds on Silica Gel

JPC – Journal of Planar Chromatography – Modern TLC - The retention (RM) values of nine one-point adsorption model compounds: diphenylamine, indol, 2-naphtol, 1-naphtol, 1-naphtylamine,...     

Changes of 1,2,4-Triazole Retention and Lipophilicity Descriptor Values in RP-TLC and MLC–TLC Systems in the Presence of an External Magnetic Field

JPC – Journal of Planar Chromatography – Modern TLC - As it was shown in earlier experiments, magnetic field can influence various processes taking part in nature. One of them might be...     

Investigation of the Correlation between RM Values and Selected Topological Indexes for Higher Alcohols,Higher Fatty Acids and their Methyl Esters in RPTLC

JPC – Journal of Planar Chromatography – Modern TLC - Homologous series of higher fatty acids, higher alcohols, and methyl esters of higher fatty acids have been separated by RPTLC. The...     

4‐Substituted 2,3‐Dihydroisoxazoles as Masked Azomethine Ylides: Access to Pyrrole Derivatives by 1,5‐ and 1,7‐Dipolar Electrocyclizations of Enynyl Derivatives

The enynyl‐substituted 2,3‐dihydroisoxazoles (‘isoxazolines') 9 – 14 were prepared by highly (Z)‐selective Peterson olefination reaction from the corresponding carbaldehydes 6 – 8 . On short‐time thermolysis (280 – 406°/10 s) the TMS derivatives 9 – 11 give rise to the annulated pyrrolines 18 – 20 , which, in some cases, suffer CH₄ elimination affording the pyrroles 15 – 17 . In contrast, thermolysis of the terminal alkyne derivatives 12 – 14 leads to the bicyclic compounds 21 – 23 . The reaction pathways are discussed on the basis of the formation of conjugated azomethine ylides as key intermediates, which either undergo a 1,5‐cyclization to 18 – 20 or a 1,7‐ring‐closure affording cycloallene intermediates of type V , which are further transformed into the azepino pyrroles 21 – 23 .     

结构化学中可观测物理量的确定值与平均值

以类氢原子轨道的组合态为体系,分析了能量和轨道角动量具有确定值的条件。并结合实例讨论了非本征态下的位置、能量和轨道角动量平均值的计算中容易出现的若干问题。     

Preparation of optically active cyclohexenones: Chirons for the lipophilic moiety of flowery- and woody-like odorant ketones

Optically active 2,5,6,6- and 2,4,4,5-tetraalkylcyclohex-2-en-1-ones ((+)- 2a – d and (?)- 5a – d ), important building blocks for flowery- and woody-like odorants, have been prepared. Compounds (+)- 2a – d and (?)- 5a – d were obtained by ozonolysis of the corresponding cyclopentenic precursors, followed by intramolecular aldol condensation. Alternatively, enones (+)- 2a – d were reduced to the corresponding allylic alcohols ad converted to enones (-)- 5a – d via acidic isomerization and oxidation. ¹³C-NMR assignments are presented.     

Acid/Alkali Gated Photochromism of Diarylethenes with Quinoline Derivatives

Three new diarylethenes 1 – 3 combined with quinoline derivatives have been synthesized. Through controlled chemical condition of deprotonation/protonation, they presented some new irreversible photochromic phenomenons under UV/Vis light irradiation in chloroform solution. It was found that 1 – 3 had well photoisomerization upon UV/Vis light irradiation in neutral chloroform solution. Addition of acid to the solution of the ring‐opening isomers of 1 – 3 produced 1oa – 3oa , which performed reversible photochromic behavior under UV/Vis light irradiation and reversed back to 1 – 3 under neutralizing with adding lewis base. However, addtion of base to neutral soluton of the ring‐opening isomers of 1 – 3 produced 1ob – 3ob , which could not change to the deprotonated ring‐closing isomers under UV light irradiation.     

Efficient Synthesis of α‐Benzylidene‐γ‐methyl‐γ‐butyrolactones

A concise synthesis of α‐benzylidene‐γ‐methyl‐γ‐butyrolactones 5a – g from substituted benzaldehydes is described. Compounds 1a – g on reaction with phosphorane 2 , provide the pentenoates 3a – g , which can be hydrolyzed to the acids 4a – g . The latter are cyclized to the corresponding butyrolactones 5a – g in excellent yields. The pentenoates 3a – g , on acid catalyzed cyclization, also provide 5a – g in very high yields.     

Syntheses of the Macrocyclic Spermine Alkaloids (±)‐Budmunchiamine A – C

The syntheses of four macrocyclic spermine alkaloids, (±)‐budmunchiamine A – C ( 1a – c ) and (±)‐budmunchiamine L4 ( 1 ), were accomplished by Michael addition of spermine to the α,β‐unsaturated esters 3a – d , followed by cyclization of the resulting α,ω‐tetraamino esters 4a – d with triethoxyantimony; N‐methylation of the amino lactams 6a – c yielded the budmunchiamines A – C ( 1a – c ).     

Laser-Induced Hydrogen Radical Removal in UV MALDI-MS Allows for the Differentiation of Flavonoid Monoglycoside Isomers

Negative-ion matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectra and tandem mass spectra of flavonoid mono-O-glycosides showed the irregular signals that were 1 and/or 2 Da smaller than the parent deprotonated molecules ([M – H]^–) and the sugar-unit lost fragment ions ([M – Sugar – H]^–). The 1 and/or 2 Da mass shifts are generated with the removing of a neutral hydrogen radical (H*), and/or with the homolytic cleavage of the glycosidic bond, such as [M – H* – H]^–, [M – Sugar – H* – H]^–, and [M – Sugar – 2H* – H]^–. It was revealed that the hydrogen radical removes from the phenolic hydroxy groups on the flavonoids, not from the sugar moiety, because the flavonoid backbones themselves absorb the laser. The glycosyl positions depend on the extent of the hydrogen radical removals and that of the homolytic cleavage of the glycosidic bonds. Flavonoid mono-glycoside isomers were distinguished according to their TOF MS and tandem mass spectra.

Mass spectrometry of 3-substituted 4-hydroxyisoquinolines and their derivatives

Under electron impact, 3-aryl-4-hydroxyisoquinolines form [M – H]⁺, [M – CO]⁺ and [M – H – CO]⁺ ions with a subsequent elimination of HCN or CH₃CN. A cyclic structure for the [M – H]⁺ ion is suggested. The primary act of fragmentation of the corresponding methyle ether derivatives is the loss of CH₃?, as well as H?; the further fragmentatio is similar to that described above. It has been established that the unusual [M – H]⁺, [M – OH]⁺ and [M – CH₅?]⁺ ions are formed when 8 fragments. Fragmentation schemes for all compounds are proposed based upon high resolution mass spectra and deuterated analogues.     

Separation of Red Paprika Color Components by use of Thin-Layer Chromatography on a Variety of Supports

JPC – Journal of Planar Chromatography – Modern TLC -     

Regioselective 1,3‐Dipolar Cycloadditions of (1Z)‐1‐(Arylmethylidene)‐5,5‐dimethyl‐3‐oxopyrazolidin‐1‐ium‐2‐ide Azomethine Imines to Acetylenic Dipolarophiles

The 5,5‐dimethylpyrazolidin‐3‐one ( 4 ), prepared from ethyl 3‐methylbut‐2‐enoate ( 3 ) and hydrazine hydrate, was treated with various substituted benzaldehydes 5a – i to give the corresponding (1Z)‐1‐(arylmethylidene)‐5,5‐dimethyl‐3‐oxopyrazolidin‐1‐ium‐2‐ide azomethine imines 6a – i . The 1,3‐dipolar cycloaddition reactions of azomethine imines 6a – h with dimethyl acetylenedicarboxylate (=dimethyl but‐2‐ynedioate; 7 ) afforded the corresponding dimethyl pyrazolo[1,2‐a]pyrazoledicarboxylates 8a – h , while by cycloaddition of 6 with methyl propiolate (=methyl prop‐2‐ynoate; 9 ), regioisomeric methyl pyrazolo[1,2‐a]pyrazolemonocarboxylates 10 and 11 were obtained. The regioselectivity of cycloadditions of azomethine imines 6a – i with methyl propiolate ( 9 ) was influenced by the substituents on the aryl residue. Thus, azomethine imines 6a – e derived from benzaldehydes 5a – e with a single substituent or without a substituent at the ortho‐positions in the aryl residue, led to mixtures of regioisomers 10a – e and 11a – e . Azomethine imines 6f – i derived from 2,6‐disubstituted benzaldehydes 5f – i gave single regioisomers 10f – i .     

Use of Ninhydrin for Detection of Silylated Amino Acids

JPC – Journal of Planar Chromatography – Modern TLC -     

Identification of the aromatic hydroxylamine group by mass spectrometry

The mass spectra of aromatic hydroxylamines are diagnostic; [M], [M – 2], [M – 16] and, in most instances, [M – 17] ions are observed.     

Thin-Layer Chromatographic Monitoring of Sonolytic Degradation of Surfactants in Wastewaters

JPC – Journal of Planar Chromatography – Modern TLC -     

Determination of the Lipophilicity of Xanthines by Reversed-Phase Liquid Chromatography

JPC – Journal of Planar Chromatography – Modern TLC -