Synthesis and characterization of a semiflexible liquid crystalline polyester with a broad nematic region

In this paper, we report on the synthesis and detailed characterization of a new semiflexible nematic liquid crystalline polyester which could serve as a 'model' polyester for a variety of physical and physico-chemical investigations. The polymer is a nematic liquid over a wide temperature range-from the glass transition temperature at ∼95°C to the isotropic transition at ∼240°C. We expect this polyester to be particularly useful for studying the effect of flow on the orientation of liquid crystalline polymers, as well as the production and removal of disclinations.     

PROPERTIES OF AN UNUSUAL PHOTOPRODUCT OF U.V. IRRADIATED THYMIDYLYL-THYMIDINE

Abstract— One of the four major photoproducts formed by UV irradiation of TpT in aqueous solution has a number of unusual properties. This compound, which we arbitrarily call TpT⁴, is produced irreversibly from TpT with single-hit kinetics and seems to represent a novel pathway for TpT photolysis different from the conventional cyclobutane ring dimer formation. This communication describes the preparative isolation of TpT⁴ by ion-exchange chromatography on DEAE-cellulose and its UV, fluorescence and IR spectra. TpT⁴ has an absorption maximum at 325 mμ, fluoresces at 405 mμ when excited at 325 mμ, and has an IR spectrum consistent with the assumption that one of the thymine rings has been converted to a pyrimidin-2-one structure. In addition, TpT⁴ appears to have both pyrimidine rings linked together and does not contain a peroxide group as previously supposed. Spectrophotometric titration shows that TpT⁴ has a pKâ of 10.75 and is unstable to prolonged treatment at extreme pH. A model structure consistent with the present data is given. This model contains the glycosidic and phosphodiester bonds intact with a 5-methylpyrimidine-2-one ring and a thymine ring joined in ether linkage at the C₄ positions, with an OH at the C₄ position in the thymine ring.     

Application of Arene-Ruthenium Chemistry to a Formal Total Synthesis of OF 4949 III

A convergent formal total synthesis of OF 4949 III is described. Arene-ruthenium chemistry was used in the construction of the diaryl ether linkage in high yield, and cycloamidation under high dilution conditions (0.005 M) was achieved using DPPA as coupling reagent. SmI(2) was used to reductively remove the 2-iodoethyl ester protecting group in the presence of DMPU or HMPA.     

A new paradigm for cationic cyclization of iron tricarbonyl diene complexes with pendant alkenes and arenes

A new example of stereospecific cationic cyclization of iron tricarbonyl diene complexes with pendant alkenes and arenes is provided. Protonation of a double bond vicinal to the iron tricarbonyl diene moiety is employed to trigger the cyclization, rather than the previously reported Lewis/protic acid dehydroxylation of diastereomeric alcohols, eliminating one step of separation and avoiding some reactivity problems previously encountered for one of the alcohol diastereoisomers. [reaction: see text]     

Liquid extraction of molybdophosphoric and molybdoarsenic acids: application to the determination of phosphorus in the presence of arsenic

The radioisotopes phohphorus-32 and arsenic-74 have been used to study the extraction of molybdophosphoric and molybdoarsenic acids from aqueous solution with various organic solvents. A method is described for the gravivmetric determination of phosphorus in the presence of arsenic which makes use of solvent extraction with n-butyl acetate. The results obtained for the determination of phosphorus in various types of iron and steel are described.     

Vibrational spectroscopy of 3,4-difluorocyclobutenes: cis-d0, trans-d0 and trans-d4 species

Infrared and Raman spectra were recorded for cis-3,4-difluorocyclobutene (cDFCB) and trans-3,4-difluorocyclobutene-d4. Unscaled density functional theory (DFT) calculations of frequencies and intensities at the B3LYP/6-311++G(d,p) level supported the complete assignment of the vibrational fundamentals. The previous assignment of fundamentals of trans-3,4-difluorocyclobutene was revised. An unusual blue shift occurs for the methylenic CH-stretching frequencies of cis-3,4-difluorocyclobutene in going from the gas phase to the liquid phase. This hydrogen bond effect is related to similar observations recently reported and interpreted. The blue shift does not occur for the vinylic CH bonds of the cis isomer and does not occur for either type of CH bond in the trans isomer.