Conformational effects on optical rotation. 2-Substituted butanes

The specific rotations of 2-substituted butanes (X = F, Cl, CN, and HCC) were calculated at the B3LYP/aug-cc-pVDZ level as a function of the C-C-C-C torsion angle. The results for the four compounds are remarkably similar, despite large differences in the electronic transition energies. The temperature dependence of the specific rotations for 2-methylbutyronitrile and for 2-chlorobutane was studied to give experimental information about the effect of the torsion angle on the specific rotation. The results were in good accord with B3LYP/aug-cc-pVDZ calculations. The specific rotations derived from the study of 2-chlorobutane are similar to those previously obtained for 3-chloro-1-butene, indicating that the double bond does not have a large effect on the optical rotations, but it did lead to a large difference between calculated and observed specific rotations.     

Chiral recognition and resolution of the enantiomers of supramolecular triangular hosts: synthesis, circular dichroism, NMR, and X-ray molecular structure of [Li subset(R,R,R)-[CpRh(5-chloro-2,3-dioxopyridine)]3][Delta-Trisphat

The racemic triangular supramolecular host [CpRh(5-chloro-2,3-dioxopyridine)](3) (1) was prepared in high yield. Treatment with LiCl followed by addition of silver salt AgOTf gave the triflate salt species [Li subset[CpRh(5-chloro-2,3-dioxopyridine)](3)][OTf] (2). Subsequent anion metathesis using the optically pure chiral shift reagent [Cinchonidinium][Delta-Trisphat] produced a pair of diastereomers [Li subset(R,R,R)-[CpRh(5-chloro-2,3-dioxopyridine)](3)][Delta-Trisphat] (3a) and [Li subset(S,S,S)-[CpRh(5-chloro-2,3-dioxopyridine)](3)][Delta-Trisphat] (3b). The resolution of these diastereomers was achieved by fractional crystallization, and their stereochemistry relationship was established by circular dichroism studies. The X-ray molecular structure of 3a is reported and shows as an outstanding feature a chiral recognition between the Delta-Trisphat anion and a single enantiomer cation [Li subset(R,R,R)-[CpRh(5-chloro-2,3-dioxopyridine)](3)](+) manifested through a pi-pi interaction. (1)H NMR and circular dichroism studies in solution support the solid-state behavior.     

Studies on the constituents of Gentiana species. II. A new triterpenoid,and (S)-(+)- and (R)-(-)-gentiolactones from Gentiana lutea

A new triterpenoid, 12-ursene-3beta, 11alpha-diol 3-O-palmitate (1), has been isolated from the rhizomes and roots of Gentiana lutea, together with the artificial diene derivative, 9 (11), 12-ursadien-3beta-ol 3-O-palmitate (1a) and five known compounds (3-7). Their structures were established on the basis of spectral analysis. In addition, (+/-)-gentiolactone [(+/-)-2], isolated from this plant, was successfully separated into its enantiomers [(+)-2, (-)-2] for the first time, and the absolute configurations at C-9 of (+)-2, (-)-2 were assigned as S and R, respectively, from the optical rotations and the circular dichroism (CD) spectral data.     

Vibrational absorption and circular dichroism studies of (-)-camphanic acid

Vibrational absorption and circular dichroism (VCD) spectra of (-)-(1S,3R)-camphanic acid have been measured in deuterated chloroform solutions at different concentrations (0.005, 0.045, and 0.200 M) in the mid-infrared spectral range. Experimental spectra have been compared with the density functional theory (DFT) absorption and VCD spectra, calculated using the B3PW91 functional and cc-pVTZ basis set for three conformers of both the monomer and the dimer forms of (-)-(1S,3R)-camphanic acid. These calculations indicate that, in the dilute solution, the conformer with intramolecular hydrogen-bonding between the hydroxyl and lactone groups is of lowest energy and represents 70% of the different monomer conformers at room temperature, whereas, in concentrated solution, the dimer formed by intermolecular hydrogen-bonding of carboxyl groups of the two distinct monomer conformations is stabilized. The vibrational absorption and circular dichroism spectra calculated from the Boltzmann population of the individual monomer and dimer conformers are in very good overall agreement with the corresponding experimental spectra, allowing the absolute conformation and configuration of (-)-(1S,3R)-camphanic acid in dilute and concentrated solution, respectively. Experiments were also performed on (-)-(1S,3R)-camphanic chloride for which the populations predicted by DFT calculations are found to be in disagreement with those deduced from experimental spectra.     

Absolute configuration and conformational stability of (+)-2,5-dimethylthiolane and (-)-2,5-dimethylsulfolane

Enantiopure (+)-2,5-dimethylthiolane and (-)-2,5-dimethylsulfolane were prepared using literature procedures and investigated using vibrational circular dichroism (VCD). Experimental absorption and VCD spectra of (+)-2,5-dimethylthiolane and (-)-2,5-dimethylsulfolane in CCl(4) solution in the 2000-900 cm(-)(1) region were compared with the ab initio predictions of absorption and VCD spectra obtained with density functional theory using the B3LYP/6-311G(2d, 2p) basis set for different conformers of (2R,5R)-2,5-dimethylthiolane and (2R,5R)-2,5-dimethylsulfolane. This comparison indicates that (+)-2,5-dimethylthiolane is of the (2R,5R)-configuration and has two predominant conformations in CCl(4) solution. In addition, (-)-2,5-dimethylsulfolane is of (2R,5R)-configuration and has only one predominant conformation. The stereochemical assignment is in agreement with literature.     

Structural analysis of (R)-3-methylcyclohexanone conformers

Structural Chemistry - The electronic circular dichroism (CD) spectra as a function of temperature for R-(?+)-3-methylcyclohexanone (R3MCH) were reported in 11 solvents of wide polarity range...     

Ab initio optical rotatory dispersion and electronic circular dichroism spectra of (S)-2-chloropropionitrile

Coupled-cluster and density-functional methods have been used to determine specific rotations and electronic circular dichroism (ECD) rotational strengths for (S)-2-chloropropionitrile. Coupled-cluster specific rotations using both the length- and velocity-gauge representations of the electric-dipole operator, computed with basis sets of triple-zeta quality containing up to 326 functions, compare very well with recently reported gas-phase cavity-ring-down polarimetry data. ECD rotational strengths for the six lowest-lying excited states are found to vary in sign, and the second excited state, which has a larger rotational strength than the first by a factor of 4, was found to yield a much larger contribution (by a factor of 10) to the overall negative specific rotation observed both experimentally and theoretically. However, both valence and Rydberg states appear to make substantial contributions to the total rotation, often of opposite sign from the converged/linear-response result. Furthermore, the sum-over-states approach was found to be inadequate for reproducing the specific rotations derived from the linear-response approach, even when 100 excited states (well beyond the estimated ionization limit) were included in the summation. Density-functional specific rotations using the B3LYP functional with basis sets of quadruple-zeta quality containing up to 588 functions are found to be too large compared to experiment by approximately a factor of 2. This error appears to be related to both the underestimation of the electronic excitation energies, as well as concomitant overestimation of the corresponding ECD rotational strengths. Although earlier studies reported good agreement between density-functional specific rotations and experiment when electric-field-dependent functions were used in conjunction with a double-zeta-quality basis set, the results reported here, which are near the basis-set limit, suggest that this agreement may be fortuitous.     

Determination of the absolute configuration of [3(2)](1,4)barrelenophanedicarbonitrile using concerted time-dependent density functional theory calculations of optical rotation and electronic circular dichroism

The technique of time-dependent density functional theory (TDDFT) has very recently been applied to the calculation of both transparent spectral region optical rotations and electronic circular dichroism (CD). Here, we report the concerted application of the new methodologies to the determination of the absolute configuration (AC) of [3(2)](1,4)barrelenophanedicarbonitrile, 1, the first optically active barrelenophane. 1 is conformationally flexible: the two three-carbon bridges of 1 can each exhibit two conformations, leading to three inequivalent conformations of 1: a, b, and c. Conformational structures and energies are predicted using DFT at the B3LYP/6-31G level. Comparison of the calculated structures to structures obtained via X-ray crystallography of (+)-1 shows that (remarkably) all three conformations a-c are simultaneously present in crystalline (+)-1. The sodium D line specific rotations, [alpha](D), and CD spectra of a-c are calculated using TDDFT at the B3LYP/aug-cc-pVDZ level. Comparison of the conformationally averaged specific rotation and CD spectrum to the experimental data of Matsuda-Sentou and Shinmyozu leads to the AC 9S,12S(+)/9R,12R(-). The same AC is obtained both from [alpha](D) and from the CD, strongly supporting its reliability.     

Synthesis of (R)-2-Benzyloxy-1-iodo-3-butene—A New Chiral Synthon from L-(+)-Tartaric Acid: Its Application to (R)-ν-Caprolactone

A practical synthesis of (R)-2-benzyloxy-1-iodo-3-butene, a bifunctional chiral synthon from (R,R)-tartaric acid and its application to (R)-ν-caprolactone, a pheromone of Trogoderma species, is described.     

The interactions of (-)-(R)-2-aminomethylpyrrolidine (1,1-cyclobutanedicarboxylato)platinum(II) monohydrate (DWA2114R) and related compounds with deoxyribonucleic acid.

The interactions of a new antitumor platinum (Pt) complex, (-)-(R)-2-aminomethylpyrrolidine(1,1-cyclobutanedicarboxylato++ +) platinum(II) monohydrate (DWA2114R, 2) and its related compounds, cis-diamminedichloroplatinum(II) (CDDP, 1), trans-diamminedichloroplatinum(II) (TDDP, 3), (+)-(S)-2-aminomethylpyrrolidine(1,1-cyclobutanedicarboxylato++ +) platinum(II) monohydrate (DWA2114S, 4), (R)-2-aminomethylpyrrolidinedichloroplatinum(II) (5) and cis-diammine(1,1-cyclobutanedicarboxylato)platinum(II) (CBDCA, 6), with calf-thymus deoxyribonucleic acid (DNA) and DNA nucleosides were investigated by ultraviolet (UV) and circular dichroism (CD) spectrometry. The UV spectra of the DNAs treated with these Pt complexes exhibited both bathochromic shift and hyperchromicity, showing a binding of Pt to the heterocyclic groups of these DNA as well as an alteration in the secondary structure of DNA. The reaction rates of the Pt complexes with DNA, however, differed from one another, and the order was CDDP, TDDP, 5 much greater than DWA2114R, S greater than CBDCA. The CD spectra of the DNAs treated with the Pt complexes, except TDDP, at a low Pt ratio (less than approximately (ca.) 0.1 of Pt bound to DNA/DNA base molar ratio) exhibited an increase of ellipticity at ca. 275 nm. The melting temperature of the DNAs treated with DWA2114R or CDDP were almost the same as the native DNA, while the melting temperature with TDDP was higher by 7-8 degrees C than that of the native DNA. All the Pt complexes reacted with 2'-deoxyguanosine (dG), 2'-deoxyadenosine and 2'-deoxycytidine, but none reacted with thymidine. The CD spectral change of the dG was largest. DWA2114R reacted faster with dG than other nucleosides.     

(3R,4aR,5S,6R)-6-Hydroxy-5-methylramulosin: a new ramulosin derivative from a marine-derived sterile mycelium

(3R,4aR,5S,6R)-6-Hydroxy-5-methylramulosin (1) was isolated from a culture of a sterile mycelium, which was derived from the green alga, Codium fragile, along with (-)-5-methylmellein (2), (-)-5-hydroxymethylmellein (3), and (-)-(3R,4R)-cis-4-hydroxy-5-methylmellein (4). The absolute configuration of 1 was determined by the NMR data along with the lactone sector rule by circular dichroism (CD). Compound 1 exhibited moderate cytotoxic activity against HeLa cells.     

采用通透性处理的安大略假丝酵母全细胞高效合成(R)-2-氯-1-(3-氯苯基)乙醇(英文)

考察了利用安大略假丝酵母(Candida ontarioensis)静息细胞不对称催化2-氯-1-(3-氯苯基)乙酮合成(R)-2-氯-1-(3-氯苯基)乙醇的转化反应条件.结果表明,当底物浓度为10g/L时,在最适转化条件下反应72h,产物的ee值和产率分别达到99.9%和99.0%.采用4g/L十六烷基三甲基溴化铵对Candida ontarioensis细胞于4℃通透性处理20min后,全细胞的酶活提高2倍以上.当底物浓度提高为30g/L,转化24h后,产物的ee和产率分别达到99.9%和97.5%.该研究为高效制备(R)-2-氯-1-(3-氯苯基)乙醇提供了可行途径,并为生物催化合成芳基手性醇类手性中间体提供了理论指导。     

Conformational changes in photoexcited (R)-(+)-1,1'-bi-2-naphthol studied by time-resolved circular dichroism

Conformational changes following photoexcitation of ( R)-(+)-1,1'-bi-2-naphthol are studied with a time-resolved circular dichroism (CD) experiment. Two wavelengths are investigated. For lambda = 237 nm, we observe a bleaching of the ground-state absorption and a transient CD structure. Thanks to a coupled-oscillator calculation, we can attribute this effect to a decrease of the dihedral angle. For lambda = 245 nm, excited-state absorption and CD are observed. All these effects are solvent-dependent. In particular, it is shown that dynamics is slower in a protic solvent, which is attributed to hydrogen-bonding of the hydroxy groups with the solvent.     

Determination of absolute configuration using concerted ab Initio DFT calculations of electronic circular dichroism and optical rotation: bicyclo[3.3.1]nonane diones

The concerted use of ab initio time-dependent density functional theory (TDDFT) calculations of transparent spectral region optical rotation and of circular dichroism has recently become practicable, permitting the concerted use of transparent spectral region optical rotation and circular dichroism in determining the absolute configurations of chiral molecules. Here, we report concerted TDDFT calculations of the transparent spectral region specific rotations and of the circular dichroism spectra originating in n --> pi C=O group excitations of four bicyclo[3.3.1]nonane diones, 1-4. Comparison to experiment yields absolute configurations for 1-4. For each dione, specific rotations and circular dichroism spectra give identical absolute configurations. Our results are consistent with previous work, with the exception of the Octant Rule-derived absolute configuration of the 2,9-dione.     

Studies on Pd(II)-catalyzed coupling-cyclization of alpha- or beta-amino allenes with allylic halides

The palladium-catalyzed coupling-cyclization of alpha- or beta-amino allenes with allylic halides leading to 3-allylic 2,5-dihydropyrroles and 1,2,3,6-tetrahydropyridines, respectively, was studied. The starting materials are easily available. The skeletons of both two classes of products were established by the X-ray diffraction studies of 7i and 9b. Through the study of the reaction of 2b with 3-chloro-1-butene, 1-chloro-2-butene, and pi-allyl palladium species and the stereochemical outcome of the coupling cyclization of (S)-2m and (R)-2n, it is believed that the current transformation most likely proceeded via a Pd(II)-catalyzed pathway, although a Pd(0) pathway cannot be completely excluded.     

Determination of the absolute configuration of chiral alpha-aryloxypropanoic acids using vibrational circular dichroism studies: 2-(2-chlorophenoxy) propanoic acid and 2-(3-chlorophenoxy) propanoic acid

The enantiomers of 2-(2-chlorophenoxy) propanoic acid and 2-(3-chlorophenoxy) propanoic acid were resolved on a chiral HPLC column and investigated using mid-infrared vibrational circular dichroism (VCD). Experimental infrared vibrational absorption and VCD spectra were measured in CDCl3 solution in the 2000-900 cm-1 region and compared with the ab initio predictions of absorption and VCD spectra. The predicted spectra were obtained with density functional theory using B3LYP/6-31G* basis set for the stable and dominant conformers. But the predicted spectra did not provide unambiguous structural information due to intermolecular hydrogen bonding in solution. To eliminate the hydrogen bonding effects, the acids were converted to the corresponding methyl esters and the experimental absorbance and VCD spectra of methyl esters were measured. B3LYP predicted spectra were also obtained for the stable and dominant conformers of the esters. From a comparison of the experimental VCD spectra of methyl esters with corresponding ab initio predictions, the absolute configurations of esters, and therefore of their parent acids, are unambiguously determined to be (+)-(R).     

Kinetics, products, and stereochemistry of the reaction of chlorine atoms with cis- and trans-2-butene in 10-700 Torr of N2 or N2/O2 diluent at 297 K

The reactions of Cl atoms with cis- and trans-2-butene have been studied using FTIR and GC analyses. The rate constant of the reaction was measured using the relative rate technique. Rate constants for the cis and trans isomers are indistinguishable over the pressure range 10-900 Torr of N2 or air and agree well with previous measurements at 760 Torr. Product yields for the reaction of cis-2-butene with Cl in N2 at 700 Torr are meso-2,3-dichlorobutane (47%), DL-2,3-dichlorobutane (18%), 3-chloro-1-butene (13%), cis-1-chloro-2-butene (13%), trans-1-chloro-2-butene (2%), and trans-2-butene (8%). The yields of these products depend on the total pressure. For trans-2-butene, the product yields are as follows: meso-2,3-dichlorobutane (48%), dl-2,3-dichlorobutane (17%), 3-chloro-1-butene (12%), cis-1-chloro-2-butene (2%), trans-1-chloro-2-butene (16%), and cis-2-butene (2%). The products are formed via addition, addition-elimination from a chemically activated adduct, and abstraction reactions. These reactions form (1) the stabilized 3-chloro-2-butyl radical, (2) the chemically activated 3-chloro-2-butyl radical, and (3) the methylallyl radical. These radicals subsequently react with Cl2 to form the products via a proposed chemical mechanism, which is discussed herein. This is the first detailed study of stereochemical effects on the products of a gas-phase Cl+olefin reaction. FTIR spectra (0.25 cm(-1) resolution) of meso- and DL-2,3-dichlorobutane are presented. The relative rate technique was used (at 900 Torr and 297 K) to measure: k(Cl + 3-chloro-1-butene) = (2.1 +/- 0.4) x 10(-10), k(Cl + 1-chloro-2-butene) = (2.2 +/- 0.4) x 10(-10), and k(Cl + 2,3-dichlorobutane) = (1.1 +/- 0.2) x 10(-11) cm3 molecule(-1) s(-1).     

Absolute configuration of tert-butyl-1-(2-methylnaphthyl)phosphine oxide

The enantiomers of tert-butyl-1-(2-methylnaphthyl)phosphine oxide 1 have been separated using a homemade HPLC column and an analytical gradient system. Vibrational absorption and circular dichroism spectra for both enantiomers have been measured in CD2Cl2 and CH2Cl2 solutions in the 2000-900 cm(-1) region. The fully relaxed potential energy surface of (S)-tert-butyl-1-(2-methylnaphthyl)phosphine oxide, obtained using the B3LYP functional with a 6-31G basis set, indicated two stable conformers with their populations in a approximately 2:1 ratio. The vibrational absorption and VCD spectra are predicted for these two conformers using the B3LYP functional with a 6-31G basis set. The comparison of predicted and experimental spectra indicated that (+)-tert-butyl-1-(2-methylnaphthyl)phosphine oxide is in the (S)-configuration. This assignment is supported by the ab initio prediction of positive optical rotation for the most stable conformer with an (S)-configuration and the nonequivalence sense of the tert-butyl group chemical shift observed in the 1H NMR spectrum of this enantiomer measured in the presence of (+)-(S)-mandelic acid as a chiral solvating agent.     

[(R)-2-Methyl-1,4,7-triazacyclononane] [1,1,1-tris(aminomethyl)ethane]-cobalt(III) and some Mono[(R)-2-methyl-1,4,7-triazacyclononane]-cobalt(III) Complexes

Summary [(R)-2-Methyl-1,4,7-triazacyclononane][1,1,1-tris(aminomethyl)ethane]cobalt(III) has been prepared and separated into two isomers which show weak Cotton effects in the¹A₁¹T₁ region (d-electron transition) compared with that of bis[(R)-2-methyl-1,4,7-triazacyclononane]cobalt(III). The effect is comparable to that of tetraammine[(R)-1,2-diamino propane]cobalt(III). The circular dichroism spectra of the mono complex change markedly upon addition of sodium sulphate. The chelate rings are more flexible in the mono than in the bis complex. Some other related mono[(R)-2-methyl 1,4,7-triazacyclononane]cobalt(III) and [(R)-2-methyl-1,4,7 triazacyclononane][1,1,1-tris(aminomethyl)ethaneI nickel (II) complexes have also been prepared and characterized.     

Vibronically resolved electronic circular dichroism spectra of (R)-(+)-3-methylcyclopentanone: a theoretical study

The vibrationally resolved electronic circular dichroism (ECD) spectra of the two dominant conformers of (R)-(+)-3-methylcyclopentanone in gas phase are computed by density functional response theory, with a full account of Franck-Condon and Herzberg-Teller vibrational contributions at the harmonic level. Proper inclusion of the latter contributions was made possible by the recent implementation of effective-scaling computations of vibrational overlaps and of analytical gradients of time dependent DFT. The Coulomb-attenuated Becke three parameters Lee-Yang-Parr (CAM-B3LYP) functional reproduces both the position and the intensity of the experimental peaks, providing a remarkable improvement over the spectra obtained with the popular hybrid B3LYP functional, and allowing a confident assignment of the CD fine vibrational structure. Franck-Condon and Herzberg-Teller contributions are discussed in detail. The computed decrease of the CD intensity in the gas phase upon increase of the temperature of the sample follows the trend observed experimentally in different solvents.