Synthesis and NMR characterization of 3,4 '-dibutoxy-2,2 '-bithiophene

3,4'-Dibromo-2,2'-bithiophene was converted, in high yield, into the corresponding dibutoxy derivative. The H-1 and C-13 nmr data are discussed in comparison with those of 3,3'- and 4,4'-dibutoxy-2,2'-bithiophene in relation to regiochemistry

INTERNAL-ROTATION AROUND SINGLE BONDS AND CONFORMATIONAL PREFERENCES IN HETEROCYCLIC-ANALOGS OF BENZYL METHYL SULFOXIDE STUDIED WITH NMR TECHNIQUES

The conformational equilibrium related to the internal rotation processes occurring in sulphoxides of the type ArCH2SOCH3 (where Ar=2-thienyl, 2-furyl, 2-pyridinyl and (3-methyl)2-pyridinyl rings) were studied with H-1 and C-13 NMR spectroscopy. Proton chemical shifts and long-range coupling constants (n)J(H, H) were obtained from the iterative analysis of the multiplets and were employed, together with C-13 chemical shifts, long-range (n)J(C, H) and relaxation parameters (NOE and non-selective T-1 values) to obtain stereochemical relationships between the protons present in these molecules. Conformational predictions at a qualitative level were also derived from total molecular energies calculated with the semi-empirical AM1/MNDO method as a function of internal coordinates. The different approaches converged to indicate that the heterocyclic rings adopt an average orientation similar to the perpendicular orientation of the phenyl ring in benzyl methyl sulphoxide and, as regards rotation around the CH2-S bond, the prevalent conformer shows that the methyl group is symmetrically oriented with respect to the methylenic protons, The barriers for internal rotation are rather low and the equilibrium between conformers is dependent on the medium properties. Attempts to obtain conformational results were performed for the molecule of omeprazole, an antiulcer drug which contains the ArCH2SO-R moiety (Ar and R are substituted 2-pyridinyl and 2-benzimidazolyl groups, respectively). With respect to the other compounds examined, the orientation of the Ar ring does not significantly differ and the benzimidazole ring seems to prefer an orientation stereochemically equivalent to that of the methyl group

Synthesis of beta-butylsulfanyl alpha-oligothiophenes from 3-butylsulfanyl-2,2 '-bithiophene

beta-Butylsulfanyl quater-, sexi-, and octithiophenes were synthesized by oxidative coupling with iron(III) chloride from 3-butylsulfanyl-2,2'-bithiophene. quaterthiophene was also generated through coupling reactions. The nmr characterization of oligomers is reported and discussed

One-step synthesis of tris(butylsulfanyl)sexithiophene from 3-butylsulfanyl-2,2'-bithiophene

FeCl3 converts, in high yield, 3-butylsulfanyl-2, 2'-bithiophene into a tris(butylsulfanyl)sexithiophene, which shows interesting optical properties and forms a stable radical cation and dication

Conformational Behaviour of Organic carbonyl Compounds. Part 2. Aldehydes and Acetyl Derivatives of Condensed Aromatic Hydrocarbons

The relative conformer stability in a number of acetyl and formyl derivatives of condensed hydrocarbons has been determined by the lanthanide induced shift (LIS) method and by simulating the experimental chemical shifts. For the aldehyde of naphtalene the conformational results were confirmed by examining the nmr spectra of model compounds with known probable conformation. In condensed hydrocarbons containing carbonyl substituents the behviour found may be substantially related to three distinct situations, those comparable to the alpha- and beta -positions of naphtalene and overcrowded positions comparable to position 4 in phenanthrene. Calculation of the conformational behaviour by the semi-empirical methods provide qualitative correct results only for systems where steric interactions are small

Conformational Analysis f Organic Carbonyl Compounds. Part 3. A 1H and 13C Nuclear Magnetic Resonance Study of Formyl and Acetyl Derivatives of Benzo[b]furan

A conformational study of formyl and acetyl derivatives of benzo[b]furan provides evidences that in the case of 2- and 7-derivatives, the E,Z-conformational mixture is solvent dependent: the Z prevailing in solvent with higher polarity