Sign Of Optical Rotation Research Articles

Chirality induction in cyclopolymerization. VI. Enantioselective cationic cyclopolymerization of divinyl ethers with chiral 10-camphorsulfonic acid/zinc chloride initiating system

Cyclopolymerization of benzaldehyde divinyl acetal (1) and 1,2-divinyloxybenzene (4) was carried out using (+)- or (−)-camphorsulfonic acid [(+)- or (−)-2]/ZnCl2 initiating system. Polymer 3 obtained from monomer 1 consisted essentially of cyclic repeating units, whereas polymer 5 from 4 possessed a small amount of residual vinyloxy groups. Both polymers 3 and 5 using (+)-2/ZnCl2 showed optical activity with a negative sign of optical rotation. The molar optical rotation values of polymer 3 using ZnCl2 · OEt2 were larger than those using ZnCl2. The CD spectra of the polymer with [Φ] = −30.1° ((−)-3) and (4S,6S)-4,6-dimethyl-2-phenyl-1,3-dioxane showed a negative Cotton effect at 210 nm, whereas the polymer with [Φ] = +24.1° ((+)-3) and (4R,6R)-4,6-dimethyl-2-phenyl-1,3-dioxane had mirror image CD curves with a positive Cotton effect at 210 nm. The absolute configurations of the major chiral cyclic units in (−)- and (+)-3 were the SS- and RR-forms, respectively. © 1997 John Wiley & Sons, Inc.

Chirality induction in cyclopolymerization. VI. Enantioselective cationic cyclopolymerization of divinyl ethers with chiral 10‐camphorsulfonic acid/zinc chloride initiating system

Cyclopolymerization of benzaldehyde divinyl acetal (1) and 1,2-divinyloxybenzene (4) was carried out using (+)- or (−)-camphorsulfonic acid [(+)- or (−)-2]/ZnCl2 initiating system. Polymer 3 obtained from monomer 1 consisted essentially of cyclic repeating units, whereas polymer 5 from 4 possessed a small amount of residual vinyloxy groups. Both polymers 3 and 5 using (+)-2/ZnCl2 showed optical activity with a negative sign of optical rotation. The molar optical rotation values of polymer 3 using ZnCl2 · OEt2 were larger than those using ZnCl2. The CD spectra of the polymer with [Φ] = −30.1° ((−)-3) and (4S,6S)-4,6-dimethyl-2-phenyl-1,3-dioxane showed a negative Cotton effect at 210 nm, whereas the polymer with [Φ] = +24.1° ((+)-3) and (4R,6R)-4,6-dimethyl-2-phenyl-1,3-dioxane had mirror image CD curves with a positive Cotton effect at 210 nm. The absolute configurations of the major chiral cyclic units in (−)- and (+)-3 were the SS- and RR-forms, respectively. © 1997 John Wiley & Sons, Inc.

Correlation between optical rotation sign and conformation of γ-butyrolactones

trans-4,5-Disubstituted-γ-butyrolactones are found to adopt different conformations by NMR spectroscopy; their optical rotation signs are found to depend on the conformations they assume.

Total synthesis of micropine and epimicropine

Abstract The enantioselective total synthesis of micropine, an unusual 2,6-disubstituted piperidine alkaloid, and epimicropine, through mercuric trifluoroacetate-catalysed intramolecular alkenylamide cyclisation is described. The synthesis proceeds from L -serine and affords material of the same positive sign of optical rotation as the natural product thereby confirming the absolute stereochemistry of micropine.

Direct HPLC Separation of Indenolol Enantiomers Using a Cellulose Chiral Stationary Phase

Racemic indenolol was resolved into its individual enantiomers by high performance liquid chromatography (HPLC) using a commercially available cellulose tris (3,5-dimethylphenyl carbamate) chiral stationary phase, known as Chiralcel OD. Indenolol contains two positional isomers, giving it a total of four enantiomers. The enantiomeric ratio was validated and peak identification for each enantiomer was established according to their optical rotation sign.

Stereochemistry of the formation of endocyclic sulfoximides from o-carboxyphenyl sulfoxides

Abstract The stereochemistry of the amination and subsequent cyclodehydration of optically active 2-(octylsulfinyl)benzoic acid to yield the corresponding endocyclic sulfoximide (1-octyl-3-oxo-benzo[d]-isothia(IV)azole 1-oxide) was studied using two different amination reagents, viz. hydrazoic acid and O-(mesitylenesulfonyl)hydroxylamine (MSH), respectively. It was found that while the reaction with hydrazoic acid yielded a partially racemized product having the same sign of optical rotation as the sulfoxide precursor, MSH gave essentially complete formation (>94%) of enantiopure product with the opposite sign of rotation. This difference in stereochemistry is likely to be caused by a neighbouring carboxyl group participation taking place in the strong acid medium used in the first case.

Anionic polymerization of optically active oxiranes

AbstractThe anionic bulk polymerization of optically active (2R, 3S)‐3,4‐epoxy‐1,2‐O‐isopropylidenebutane‐1,2‐diol (1) and its (2 S, 3 S) diastereomer 2 was studied. Molecular weights and optical activity measurements as well as carbon and proton NMR spectra are reported. The polymers show solvent dependent inversion of the sign of optical rotation. The NMR spectra are consistent with isotactic polymer chains.

Stereocomplex formation between enantiomeric poly(lactic acid)s. X. Binary blends from poly(D‐lactide‐CO‐glycolide) and poly(L‐lactide‐CO‐glycolide)

AbstractBinary blend films from lactide‐rich poly(D‐lactide‐co‐glycolide) (PDLG) and poly(L‐lactide‐co‐glycolide) (PLLG) were obtained by casting methylene chloride solutions of the two mixed copolymers with different D‐ and L‐lactide contents (XDI and XLI), and their crystallization was studied by differential scanning calorimetry (DSC). Four combinations were selected from the binary (A‐B) blends: mixing of the same polymer [XDI(A) = XDI(B) or XLI(A) = XLI(B)], blending under XDI(B) = XLI(A), blending of a D‐lactide homopolymer [XDI(B) = 1] with other PDLGs, and blending of a D‐lactide homopolymer [XDI(B) = 1] with other PLLGs. Racemic crystallites were exclusively formed between PDLG and PLLG when they had high lactide unit contents. The melting point and enthalpy of fusion of the racemic crystallites decreased with a decrease in XDI of PDLG or XLI of PLLG, suggesting that glycolide units in the polymer disturbed the growth of the racemic crystallites. A similar behavior was also observed for the homocrystallization in nonblended copolymer films. Homocrystallites composed entirely either of D‐lactide unit or L‐lactide unit sequences were formed when one component was crystallizable and the other component had the same sign of optical rotation or very different lactide content. An interesting finding was that even nonhomocrystallizable lactide‐poor PDLG and PLLG could form racemic crystallites when both were blended. © 1994 John Wiley & Sons, Inc.

Determining the sign of optical rotation in linearly birefringent crystal sections

The problem of determining the sign of optical rotation in a linearly birefringent crystal section is examined. This problem has not been fully addressed in recent publications describing techniques for these measurements. It is shown in this paper that there is considerable scope for error in the determination of the sign and particular care must be taken in certain situations. It is important to know this sign as theories that seek to correlate optical rotation with crystal structure cannot be tested without this information.

Preparative enantiomer separation with modified cyclodextrins as chiral stationary phases

Preparative gas chromatographic enantiomer separation was achieved by using a packed column with heptakis(2,6-di-O-methyl-3-O-pentyl)-β-cyclodextrin (2,6-Me-3-Pe-β-CD) as a chiral stationary phase. Depending on the selectivity factor up to milligram amounts of almost pure enantiomers or at least enantiomeric mixtures, sufficiently enriched to determine the sign of optical rotation, could be obtained with only one injection of a racemate. This technique may be very useful for stereochemical assignments, for attaining pure enantiomers for bioassays, pharmacokinetic and metabolic studies and investigations of fragrance and flavour compounds.

Correlating the optical rotation of α-quartz with a skew matrix of a dielectric tensor

A beam of polarized light propagating along the helical axis of α-quartz interacts with SiO4/2 groups consecutively. When a skew matrix of a resultant dielectric tensor is compared to a skew matrix of a rotation matrix, the polarizability components of an SiO4/2 group, with two sets of results, may be derived since the specific rotation along the helical axis is known for 5892.9 A light at 293 K. Both sets have the same mean value for the components. The mean is close to an empirical result based on the bond refractivity of Si–O. In comparison with the optical rotation sign (+ or −) along the optic axis, an opposite rotation sign is derived along the directions perpendicular to both the optic axis and any diad axis. In α-quartz, the inactive directions 33.83° from its optic axis are interpreted. The diad-axis directions are predicted to be inactive directions. Bunn's empirical formula is interpreted.

High-performance liquid chromatographic separation of chiral metallocenic ketones and alcohols

The enantiomers of chiral (arene)tricarbonylchromium ketones and alcohols were separated by high-performance liquid chromatography with a Chiralcel OD column. The absolute configuration of the ketones was assigned on the basis of the sign of optical rotation determined with an on-line detector.

Optical resolution of some biologically active compounds by chiral liquid chromatography on BSA‐silica (resolvosil) columns

AbstractOptical resolution on the analytical scale of a number of racemic pharmaceuticals and some other biologically active compounds has been studied using immobilized bovine serum albumin (BSA) as the stationary phase. For some of the compounds the elution order was determined by the use of optically enriched fractions obtained from a preceding passage of a sample through a preparative column containing microcrystalline triacetylcellulose (MCTA). The reversal in the sign of optical rotation shown in the polarimetric elution profile from the latter, combined with the integrated peak area ratio obtained on resolution on the analytical column, gave directly the order of elution. For one of the benzothiadiazines studied (bendroflumethiazide), increasing the pH of the mobile phase produced opposite effects on the retention of the two enantiomers, leading to a large effect on the separation factor. For many of the compounds studied, high separation factors (α > 2) could be achieved.

Synthesis, NMR study, partial resolution and redox-demercuration of chiral 2-bromomercuri-4-dimethylaminobutane

The preparation and 1H, 13C NMR spectra are reported for chiral 2-bromomercuri-4-dimethylaminobutane ( A), a novel useful organomercurial model having both a mercury atom attached to a chiral carbon centre and a tertiary nitrogen in the γ-position. Racemic A has been resolved partially using dibenzoyl- d tartaric acid. Redox-demercuration with a palladium(0) complex was shown to give an optically active palladium metallocycle ( B), the signs of optical rotation of A and B being the same.

Studies on the optical active alternating copolymer of benzofuran or 1,3‐cyclooctadiene with acrylic monomers

AbstractIn the presence of an optical active amyloxyaluminum or menthoxyaluminum chloride the asymmetric‐induction alternating copolymerization of benzofuran or 1,3‐cyclooctadiene and acrylonitrile or methacrylonitrile was investigated. The sign of optical rotation of copolymers was positive or negative, depending on the kind of catalyst used. The optical activity of copolymers of benzofuran and acrylonitrile attains a maximum value at an equimolar composition. The highest specific rotation [α]D of copolymers of benzofuran and acrylonitrile prepared in the presence of stoichiometric amount of (—)‐menthoxyaluminum dichloride with respect to acrylonitrile was about −8°. The stereo‐structure of acrylonitrile unit may be controlled by the optical active aluminum compound onto which a strong coordination of acrylonitrile may occur.

On the rotatory dispersion in cholesteric liquid crystals

It is shown that the dynamical theory of light propagation in a cholesteric liquid crystal does not predict a reversal in the sign of optical rotation on the long wavelength side of the reflection band. This conforms with the results of exact electromagnetic treatment.

Polymerization of epoxyorganosilanes. II. Asymmetric selective polymerization of epoxyorganosilanes

AbstractThe asymmetric selective polymerizationIn PINO's words : stereoselective polymerization, cf. J. Polymer Sci. C 16 (1968) 3265. of epoxyethyltrimethylsilane (ETMS) and of (2.3‐epoxypropoxy)trimethylsilane (EPOS) were studied using a catalyst system formed by an organometallic compound reacted with an optically active reagent. Optically active polymers were obtained in both cases but the asymmetric selectivity of EPOS polymerization was low, considering the weak optical activity of glycidol derived from the hydrolysis of recovered monomer. Concurrently, this experiment permitted us to deduce that dextrotatory EPOS has the same configuration as dextrorotatory glycidol.A polymer of EPOS was submitted to a series of reactions leading to a polymer identical to polypropylene oxide (PPO). The optical behaviour of this polymer, studied in comparison with PPO, also confirmed the relation between the absolute configuration of EPOS and its optical rotation sign. This is the first example, in which the absolute configuration can be determined by utilizing the asymmetric selective polymerization.

Association Involving Optically Active Ions. II. Association Constants of Tris(ethylenediamine)cobalt(III) and Tris(propylenediamine)-cobalt(III) Ions with Some Anions

Abstract Association constants of [Co en3]3+ (en=ethylenediamine) and d- and l-[Co d-pn3]3+ (pn=propylenediamine; d- and l- refer to the sign of optical rotation at sodium D-line) with some anions have been determined spectrophotometrically. Values are as follows: [Co en3]3+·SO42−49, [Co-en3]3+·glycollate− ∼5, d-[Co d-pn3]3+·SO42− 70, d-[Co d-pn3]3+·d-tart2− (tart2−=bivalent tartrate anion) 30, d-[Co d-pn3]3+·l-tart2− 28, l-[Co d-pn3]3+·SO42− 43, l-[Co d-pn3]3+·d-tart2− ∼7, l-[Co-d-pn3]3+·l-tart2− ∼16. These association constants are discussed in terms of the microscopic interaction between the ions. The effect of outer-sphere association on the circular dichroism and optical rotatory dispersion is also discussed.

Optical rotatory dispersion of crystals of sodium chlorate and sodium bromate

The rotatory dispersion of crystals of NaClO3 and NaBrO3 has been measured in the visible and ultraviolet region of the spectrum. Apart from a small infrared contribution, the rotatory dispersion of both crystals can be expressed as a difference of two terms. For NaClO3 the positive term has a greater strength than the negative one, whereas for NaBrO3 the reverse is the case. Thus corresponding configurations of the two crystals have opposite signs of optical rotation. The important point is brought out that calculations of optical activity in terms of atomic refractivities but neglecting rotatory dispersion, such as those carried out recently for these two crystals, arc necessarily inconclusive.

5-thio- D-ribopyranose : Part I. The free sugar and the methyl glycosides

5-Thio- D-ribose has been synthesised from methyl 2,3-isopropylidene-5- O-toluene- p-sulphonyl-β- D-ribofuranoside. Two crystalline forms of the sugar having different signs of optical rotation were obtained although, more commonly, they co-crystallised. The absence of an SH absorption in their infrared spectra indicates the dextrorotatory and laevorotatory forms to be the α- D-pyranose and β- D-pyranose isomers, respectively. Their mutarotation curves are simple, in contrast to that of β- D-ribopyranose, suggesting the absence of furanoid forms in the equilibria. Methyl 5-thio-α- and β- D-ribopyranosides are the major products of the Fischer reaction of the sugar with methanolic hydrogen chloride. The two thiopyranosides undergo acidic hydrolysis more readily than the corresponding methyl α- and β- D-ribopyranosides.