Quadrant Rule Research Articles

The role of deuterium in optical activity: the CD spectrum of (S,S)-dideuteriooxirane

The circular dichroism of (S,S)-[2,3-{sup 2}H{sub 2}]oxirane has been investigated in the gas phase over the 1800-1500-{angstrom} region. While the absorption spectrum reveals only two allowed transitions, the circular dichroism (CD) spectrum shows a third transition which is magnetic dipole allowed and electric dipole forbidden. The CD sign of the first excited state complies with a quadrant rule which was formulated for the oxirane chromophore. This consignate behavior is contrary to the role of deuterium in carbonyl compounds, where an antioctant behavior is observed. The signs of the CD signals of the first excited state for oxiranes with methyl or deuterium substituents located in the same quadrant are the same, in contrast to the antioctant behavior of deuterium in carbonyls. This leaves the chirality rule formulated for substituted oxiranes without any exceptions. 33 refs., 1 fig.

Ab initio CI study of the optical rotatory strengths of HSSH

The optical rotatory strengths for the four lower-lying electronic transitions of dihydrogen disulfide (HSSH) have been studied by a large ab initio multi-reference CI (MR CI) calculation. The dependence of the optical property on the rotation with respect to the twofold axis of symmetry has been examined. For the two lowest-lying transitions, the empirical C2-rule and the “quadrant rule” may be confirmed. However, for dihedral angles near 90°, a significant net contribution of rotatory strengths is calculated, whereas the two excited states are nearly degenerate.

An extension of the quadrant rule in oxiranes to non-alkyl substituents: the CD of R (—)- and S (+)-epichlorohydrin

The circular dichroism (CD) of epichlorohydrin (1-chloro-2,3-epoxypropane) in the gas phase reveals one structureless broad band peaked at 1710 Å. The CD sign of this band is according to the prediction made by the quadrant rule previously established for the oxirane chromophore. It seems that the quadrant rule can be applied to substituents other than alkyl groups.

The vacuum ultraviolet circular dichroism of carrageenans

The vacuum ultraviolet CD of ι- and κ-carrageenan reveals a negative band at 180 nm in solid films and in aqueous solution, with and without 3 m m KCl. In the solid (film) state a positive band at 148–150 nm is also observed. The sign of the low energy (180 nm) band is consistent with a recently proposed quadrant rule.

Circular dichroism, XCIII determination of the absolute configuration of alcohols, olefins, epoxides, and ethers from the CD of their “in situ” complexes with [Rh 2(O 2CCF 3) 4

A new, very convenient and sensitive “in situ” method has been developed for the determination of the absolute configuration of chiral compounds, which can bind to the axial position of [Rh 2(O 2CCF 3) 4] ( 5) and induce circular dichroism within its electronic absorption bands. The CD spectra of the “in situ” complexes of chiral alcohols, ethers (including epoxides), olefins, and ketons with 5 show up to 5 Cotton effects (A – E) in the 600 – 300 nm range. This method works well for chiral secondary alcohols and monoolefins. For these compounds tentative rules are proposed, which correlate the absolute stereochemistry with the sign of certain Cotton effects of their complexes. A rule for the sign of band E for alcohols and a quadrant rule for the sign of band C for olefins can be applied. Olefins induce unexpected strong Cotton effects in presence of 5 giving evidence for a relatively stable π-bond between olefin and rhodium atom.

ChemInform Abstract: Preparation and Chiroptical Properties of Optically Active Vinyl Ether‐Iron and Olefin‐Iron Complexes. A CD Quadrant Rule Correlating Absolute Configurations.

AbstractReaction of the racemic iron complex (I) with (‐)‐menthol (II) leads to a diastereomeric mixture of the optically active vinyl alcohol‐iron complexes (III) and (IV), which are in rapid equilibrium resulting in partial dynamic resolution of the complexed olefin center.

Preparation and chiroptical properties of optically active vinyl ether-iron and olefin-iron complexes. A CD quadrant rule correlating absolute configurations

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPreparation and chiroptical properties of optically active vinyl ether-iron and olefin-iron complexes. A CD quadrant rule correlating absolute configurationsM. Kohinoor Begum, Kai Hsuan Chu, Thomas S. Coolbaugh, Myron Rosenblum, and Xiao Ya ZhuCite this: J. Am. Chem. Soc. 1989, 111, 14, 5252–5259Publication Date (Print):July 1, 1989Publication History Published online1 May 2002Published inissue 1 July 1989https://doi.org/10.1021/ja00196a036RIGHTS & PERMISSIONSArticle Views245Altmetric-Citations12LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (929 KB) Get e-Alerts Get e-Alerts

Enantiomer analysis by complexation gas chromatography : Scope, merits and limitations

The application of complexation gas chromatography in contemporary enantiomer analysis was investigated. Enantiomers were separated without derivatization on Chirametal stationary phases, such as manganese(II), cobalt(II) and nickel(II) bis[3-(heptafluorobutanoyl)-(1 R)-camphorate], coated on high-resolution glass and fused-silica open-tubular columns. Enantiomeric excesses (ee) up to 99.9% can be precisely determined by complexation gas chromatography. Employing the gas chromatography-mass spectrometry (single ion monitoring) technique, the determination of ee and absolute configurations of solutes, present in complex mixtures, can be performed at the low picogram level. For the first time, pertinent sources of error in the gas chromatographic determination of ee were identified and novel experimental verifications thereof are presented. Interconversion profiles due to inversion of configuration during enantiomer separation by complexation gas chromatography have been detected. Inconsistencies of an empirical quadrant rule, correlating absolute configuration and order of elution of cyclic ethers from nickel(II) bis[3-(heptafluorobutanoyl)-(1 R)-camphorate], are reported.

Cystine peptides.

NHCH3 (X = Gly 1, Ala 2, Aib 3, Leu 4 and D‐Ala 5), have been investigated by Raman and circular dichroism (CD) spectroscopy. Solid state Raman spectra are consistent with β‐turn conformations in all five peptides. These peptides exhibit similar conformations of the disulfide segment in the solid state with a characteristic disulfide stretching frequency at 519 ± 3 cm‐1, indicative of a trans‐gauche‐gauche arrangement about the Cα—Cβ—S—S—Cβ—Cα bonds. The results correlate well with the solid state conformations determined by X‐ray diffraction for peptides 3 and 4. CD studies in chloroform and dimethylsulfoxide establish solvent dependent conformational changes for peptides 1, 3 and 5. Disulfide chirality has been derived using the quadrant rule. CD results together with previously reported nuclear magnetic resonance (n.m.r.) data suggest a conformational coupling between the peptide backbone and the disulfide segment.

Asymmetric reduction of the carbonyl group by chiral hydrides. 1. Stereochemical considerations

A quadrant rule is proposed for the enantioselective reduction of acetophenone by chiral hydrides based on LiAlH4, NaBH4, LiBH4, and BH3. This enables the configuration of the product to be explained and predicted, depending on the preferred conformations of the ligands in these hydrides.

Zum Circulardichroismus von Disulfidbrücken in Proteinen. Teil 2. Vergleichende CNDO/S- und INDO/S-CI-Rechnungen

Rotatory strengths for H2S2 conformers based on X-ray data for ribonuclease A, 2-, and 4-zinc-insuline-dimers have been calculated with some CNDO/S- and INDO/S-versions. The best agreement between their calculated signs and those predicted by the quadrant rule and Rauk’s valence basis set ab initio calculations are found with the CNDUV-version of CNDO/S. A choice of β0 s = - 11.5 eV within this method improves the calculated transition wavelengths compared to observed ones.

Vacuum ultraviolet circular dichroism of keratan sulfate

The vacuum ultraviolet CD of keratan sulfate reveals an intense negative CD band at 171 nm. Its intensity can be rationalized with a recently proposed quadrant rule in terms of the acetamido group being slightly tilted toward the hexosaminidic linkage oxygen. The same structural feature accounts for the particularly intense negative n-π ∗ CD band near 210 nm.

ChemInform Abstract: Vacuum UV Circular Dichroism of Polysaccharides

Polysaccharides are of great commercial and biological importance. At the molecular level they display a richness in structural and conformational variability, and helical structures are commonplace. Of the various experimental techniques applicable to the study of polysaccharide conformation, optical spectroscopy has been limited by the relatively high energy of the electronic excitations, the first excitation in unsubstituted saccharides being in the vacuum ultraviolet region. In the past decade, the development of VUV CD spectrometers, including the use of synchrotron radiation, has allowed the chiroptical properties of polysaccharides to be observed directly. In this brief review the major CD features of polysaccharides are summarized, and several applications are described illustrating the usefulness of VUV CD spectroscopy in the study of the polysaccharide conformation. Examples include the glucans, dextran and acetylated cellulose; the glycosaminoglycan, heparin; and the microbial polysaccharides, gellan and xanthan. A recently proposed quadrant rule which describes the sign of the 175 nm n-σ* polysaccharide CD band also is discussed. This rule is the first attempt to place the descriptionof polysaccharide VUV CD on a theoretical foundation.

Conformation of (1→ 6)-β- d-glucan by vacuum-ultraviolet circular dichroism

Gelation of pustulan [(1→ 6)-β- d-glucan] likely involves some chain ordering. To characterize the most probable conformation, we previously carried out energy calculations and identified the local energy minimums. Here, we analyze the (previously measured) vacuum-ultraviolet circular dichroism of pustulan by using a quadrant rule recently proposed for the 175-nm c.d. band and our earlier quantummechanical model for the 185-nm c.d. band. Most of the local-energy minimum conformations are shown to be inconsistent with the circular dichroism observed. Of the two distinct conformations consistent with the observed circular dichroism, one includes the global-energy minimum calculated earlier, i.e., (φ, ψ, ω) = (20°, −90°, gt).

The n–π* optical activity of a ketone predicted to be optically inactive by the octant and quadrant rules: (1R,5R)-dimethyladamantan-2-one

The title compound, which has each of its methyl groups lying in a quadrant or octant rule symmetry place, exhibits a weak positive n–π* circular dichroism Cotton effect, ΔIµ292max.=+0.009.

Vacuum UV circular dichroism of polysaccharides.

AbstractPolysaccharides are of great commercial and biological importance. At the molecular level they display a richness in structural and conformational variability, and helical structures are commonplace. Of the various experimental techniques applicable to the study of polysaccharide conformation, optical spectroscopy has been limited by the relatively high energy of the electronic excitations, the first excitation in unsubstituted saccharides being in the vacuum ultraviolet region. In the past decade, the development of VUV CD spectrometers, including the use of synchrotron radiation, has allowed the chiroptical properties of polysaccharides to be observed directly. In this brief review the major CD features of polysaccharides are summarized, and several applications are described illustrating the usefulness of VUV CD spectroscopy in the study of the polysaccharide conformation. Examples include the glucans, dextran and acetylated cellulose; the glycosaminoglycan, heparin; and the microbial polysaccharides, gellan and xanthan. A recently proposed quadrant rule which describes the sign of the 175 nm n‐σ* polysaccharide CD band also is discussed. This rule is the first attempt to place the descriptionof polysaccharide VUV CD on a theoretical foundation.

CNDO/S-CI-Rechnungen zum Circulardichroismus von Disulfidbrücken in Proteinen im nahen UV

CNDO/S-CI-calculations of rotational strengths of the disulfide moieties in Ribonuclease A, 2-zinc- and 4-zinc-insuline-dimers based on X-ray data have been performed. Appropriate R2S2- conformations (R = H, CH3 , C2H5 , CH2CH(NH2)CHO) have been considered as models for the disulfide linkages. The sign of the calculated rotatory strength of the longest wavelength transition coincides in most cases with that predicted by the quadrant rule for disulfides. For dihedral angles near 90° the energies of the two longest wavelength transitions are found to be nearly degenerate. However there is a net contribution of their rotatory strengths whereas with the quadrant rule this is expected to be negligible.

Stereoisomeric chiral 2,9-diazabicyclo[4.4.0.]decane-3,10-diones as models of dipeptide grouping: Synthesis, X-ray, IR, NMR and cd studies

Synthesis of the title optically active bicyclic dilactams I and II with cis- and trans-annelation of rings is described. The stereospecific synthesis started from (2R)-2-benzamido-2-(4-oxocyclohexyl)acetic acid ((-)-VI) whose absolute configuration was determined by chemical correlation with the known (2R)-2-amino-(4-hydroxyphenyl)acetic acid ((-)-IIIb). Relative configuration at the bridgehead atoms in I and II was assigned by 1H and 13C NMR spectroscopy and confirmed by X-ray diffraction analysis which showed the detailed conformation in crystal. According to the 1H NMR spectra in solution the trans-isomer II has the same configuration as in crystal whereas the cis-isomer I exists in two forms one of which is identical with that in crystal. This conformational analysis agrees also with the IR spectra, detecting an intramolecularly hydrogen-bonded conformation for IIbut no hydrogen bond for I. The CD spectra of both lactams were successfully interpreted using the exciton theory in the π-π region where it reflects the differences in the angles Φ and ψ (for I Φ = 110°, ψ = -143°; forII Φ = -145°, ψ = 162°). In the n-π transition region the interpretation was based on the quadrant rule and also inherent non-planarity of one of the amide groups in II.

Synthesis of condensed tannins. Part 2. Synthesis by photolytic rearrangement, stereochemistry, and circular dichroism of the first 2,3-cis-3,4-cis-4-arylflavan-3-ols

Photolytic rearrangements of those 2,3-trans-3,4-trans- and 2,3-trans-3,4-cis-4-arylflavan-3-ols in which the nucleophilicity of D-ring (4-aryl group) functionality exceeds that of the A-ring, provide the first access to 2,3-cis-3,4-cis-diastereoisomers. The circular dichroism of these new isomers is at variance with the proposed general rule for assessing the absolute configuration at C-4. In terms of the aromatic quadrant rule such discrepancies correlate with deviations from the preferred C-ring conformations.

Microbial stereodifferentiating reduction and absolute configuration of 8-deltacyclanone and 4-brendanone. An application of the quadrant rule

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMicrobial stereodifferentiating reduction and absolute configuration of 8-deltacyclanone and 4-brendanone. An application of the quadrant ruleMasao Nakazaki, Hiroaki Chikamatsu, Takeo Fujii, and Toshiharu NakatsujiCite this: J. Org. Chem. 1981, 46, 3, 585–589Publication Date (Print):January 1, 1981Publication History Published online1 May 2002Published inissue 1 January 1981https://doi.org/10.1021/jo00316a019RIGHTS & PERMISSIONSArticle Views43Altmetric-Citations8LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (692 KB) Get e-Alerts Get e-Alerts