Grazing‐incidence X‐ray diffraction study of rubrene epitaxial thin films

The growth of organic semiconductors as thin films with good and controlled electrical performances is nowadays one of the main tasks in the field of organic semiconductor‐based electronic devices. In particular it is often required to grow highly crystalline and precisely oriented thin films. Here, thanks to grazing‐incidence X‐ray diffraction measurements carried out at the ELETTRA synchrotron facility, it is shown that rubrene thin films deposited by organic molecular beam epitaxy on the surface of tetracene single crystals have the structure of the known orthorhombic polymorph, with the (2 0 0) plane parallel to the substrate surface. Moreover, the exact epitaxial relationship between the film and the substrate crystalline structures is determined, demonstrating the presence of a unique in‐plane orientation of the overlayer.     

Ipso nitration. Nitrodeformylation reactions in nitrothiophenealdehydes

Nitration of 4-nitro-2-thiophenealdehyde afforded 2,4-dinitrothiophene and small quantities of 4,5-dinitro-2-thiophenealdehyde; 5-nitro-2-thiophenealdehyde gave instead 3,5-dinitro-2-thiophenealdehyde as the main product and some 2,5-dinitrothiophene. The two dinitrothiophenes form through a nitrodeformylation reaction which represents an interesting example of the nitration at an ipso position in a strongly deactivated substrate.     

Misure euclidee,hermitiane, simplettiche e potenze esterne di uno spazio vettoriale quaternionale

Riassunto SiaV _n uno spazio vettoriale quaternionale destro n-dimensionale e V_4n lo spazio vettoriale reale ? immagine reale ? diV _n. Una metrica hermitiana inV _n e le metriche euclidea e simplettica ad essa associate danno luogo (attraverso la considerazione di determinanti sul corpo dei quaternioni) a tre diversi tipi di metriche per i multivettori semplici di ∧^t V_4n. Le nozioni introdotte permettono, tra l’altro, di associare ad ogni sottospazio V_t di V_4n un ben determinato angolo (deviavione caratteristica assoluta di V_t) e di generalizzare ai multivettori la disuguaglianza di Cauchy-Schwarz. Lavoro eseguito nell’ambito dell’attività del Contratto di Ricerca n. 9 del Comitato per la matematica del C.N.R. Entrata in Redaz’one il 25 giugno 1970.     

Optimal strategy to model the electrodialytic recovery of a strong electrolyte

In this work, mostly Nernst–Planck derived relationships were used to simulate the electrodialytic recovery of a strong electrolyte, namely sodium chloride. To this end, it was set up a five-step experimental procedure consisting of zero-current leaching, osmosis, and dialysis, electro-osmosis, desalination, current–voltage and validation tests. The contribution of leaching and solute diffusion across the electro-membranes was found to be negligible with respect to the electro-migration. On the contrary, solvent diffusion tended to be important as the solute concentration difference at the membrane sides increased or current density was reduced. The electro-osmosis and desalination tests yielded the water and solute transport numbers.

By performing several limiting current tests at different solute concentrations and feed flow rates using anionic or cationic membranes, it was possible to determine simultaneously the limiting current intensity, the ratio of the differences between the counter-ion transport numbers in the anion- and cation-exchange membranes and solution, the overall resistance of the electro-membranes, the effective membrane surface area, and the solute mass transfer coefficient.

All these process and design parameters allowed the time course of the solute concentration in the concentrating (C) and diluting (D) compartments, as well as the voltage applied to the electrodes, to be reconstructed quite accurately without any further correction factors. The capability of the above parameters to simulate the performance of the electrodialysis (ED) unit was checked by resorting to a few validation tests, that were performed in quite different operating conditions from those used in the training tests, that is by filling tank C with a low feed volume with a low solute concentration and applying a constant current intensity to magnify the effect of electro-osmosis or by changing the current intensity step-wisely to simulate the continuous-mode operation of a multistage ED unit. Finally, a parameter sensitivity analysis made the different contribution of the process and design parameters to be assessed, thus yielding a straightforward procedure for designing or optimising accurately ED desalination units up to a final salt concentration of about 1.7 kmol m⁻³.     

Polymethyl derivatives of furo[3,4-c]pyran4-one,furo[3,4-c] pyridin-4-one and pyrrolo[3,4-c]pyran-4-one

The: title compounds were prepared from Michael adducts, obtained from acetoacetic esters and trans-3-hexene-2,5-dione, and from the corresponding dehydration products, by direct cyclization to oxygen rings or by reaction with ammonia (or methylamine) to give nitrogen rings.     

Intramolecular addition of carbon radicals to aldehydes: synthesis of enantiopure tetrahydrofuran-3-ols

A simple and efficient substrate-controlled asymmetric synthesis of enantiopure tetrahydrofuran-3-ols by a 5-exo-trig radical cyclization is described. This cyclization occurs when a δ-carbon radical adds intramolecularly to the carbonyl group of an aldehyde. The δ-carbon radicals can be efficiently produced from the tin hydride mediated deselenenylation of 5-phenylseleno-3-oxapentanals, which were easily prepared starting from commercially available enantiopure epoxides or chlorohydrins.     

A simple synthesis of (R)-3-aminooctanoic acid (D-BAOA) from (S)-1-octyn-3-ol

A simple substrate-controlled asymmetric synthesis of (R)-3-aminooctanoic acid (D-BAOA) is described. The present method involves the conversion of commercially available (S)-1-octyn-3-ol into the protected propargylic amine, with complete inversion of configuration, and the successive transformation of the (phenylseleno)acetylene intermediate into the Se-phenyl selenocarboxylate, which is then easily converted into the carboxylic group. The phthalimido group was eventually removed by treatment with hydrazine hydrate.     

The 1:1 complex of cytosine and 5‐fluorouracil monohydrate revisited

The monohydrated molecular adduct cytosine–5‐fluorouracil–water (1/1/1) (denoted CytFur) [systematic name: 4‐aminopyrimidin‐2(1H)‐one–5‐fluoropyrimidine‐2,4(1H,3H)‐dione–water (1/1/1)], C₄H₅N₃O·C₄H₃FN₂O₂·H₂O, was determined some 40 years ago [Voet & Rich (1969). J. Am. Chem. Soc. 91 , 3069–3075] and is widely cited as the first example of an intermolecular complex between two pyrimidinic nucleobases. In view of the importance of these base associations, CytFur has been reinvestigated with modern laboratory equipment to higher precision and with the location and free refinement of the H atoms. The new experiment reaffirms the results of the original and clarifies the tautomeric form exhibited by the compounds. The asymmetric unit comprises a hydrogen‐bonded adduct of the canonical amino–oxo tautomers in an exact 1:1 ratio and a water molecule of crystallization. This cyclic dimer forms a layered structure approximately parallel to the bc plane by joining through hydrogen bonds other such cyclic dimers. Disordered water molecules run through tunnels formed by surrounding molecular adducts along the a axis.