On a double of a free group

We construct a double of a free group which has an unsolvable occurrence problem, and is (therefore) not LERF.     

Substitution directe de l'azote N-9 de la théophylline

In alkaline medium, 8-(2-chloroethyl)aminotheophylline (1) cyclizes into two imidazopurines: the imidazo[1,2-e]purine (2A) (cyclization on 9-N) and the imidazo[2,1-f]purine (2B) (cyclization on 7-N). The structure of each compound was determined by an unambiguous synthesis and confirmed by spectrographic methods. Synthesis of one pyrrlo[2,1-f]purine, a novel heterocycle, is described.     

A necessary condition for\mathop {A * B}\limits_{a = b} to be LERFto be LERF

This paper examines some necessary conditions for the product to be LERF.     

Polyamines and corresponding aminoacids measured together

Summary A two-column switching technique plus gradient elution have been developed to separate polyamines (putrescine, spermine and spermidine) and related aminoacids (aspartic, glutamic, glycine, taurine and gaba) as isoindole derivatives. The system uses two columns (CN and C18) arranged in series, via a valve which allows the effluent to be switched from the primary column to the secondary column or directly to the detector.     

A 13C NMR study of tautomerism in phenoxymethylisoxazol-5-ones

A ¹³C NMR study of new isoxazol-5-ones has been carried out in different solvents. Mathematical analysis of the tautomeric ring proton exchange in pyridine solvent indicates that the relative contributions of the NH, CH and OH tautomers are respectively 10 ± 5, 15 ± 3, 10 ± 8%, while the anionic form represents the remaining 65 ± 8%.