| 1. |
- Bella, M., et al.
(författare)
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Reaction of selected carbohydrate aldehydes with benzylmagnesium halides: benzyl versus o-tolyl rearrangement
- 2014
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Ingår i: Beilstein Journal of Organic Chemistry. - : Beilstein Institut. - 1860-5397. ; 10, s. 1942-1950
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Tidskriftsartikel (refereegranskat)abstract
- The Grignard reaction of 2,3-O-isopropylidene-alpha-D-lyxo-pentodialdo-1,4-furanoside and benzylmagnesium chloride (or bromide) afforded a non-separable mixture of diastereomeric benzyl carbinols and diastereomeric o-tolyl carbinols. The latter resulted from an unexpected benzyl to o-tolyl rearrangement. The proportion of benzyl versus o-tolyl derivatives depended on the reaction conditions. Benzylmagnesium chloride afforded predominantly o-tolyl carbinols while the application of benzylmagnesium bromide led preferably to the o-tolyl carbinols only when used in excess or at higher temperatures. The structures of the benzyl and o-tolyl derivatives were confirmed unambiguously by NMR spectral data and X-ray crystallographic analysis of their 5-ketone analogues obtained by oxidation of the corresponding mixture of diastereomeric carbinols. A possible mechanism for the Grignard reaction leading to the benzyl -> o-tolyl rearrangement is also proposed.
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| 2. |
- Hirsch, Jan, et al.
(författare)
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Synthesis and Molecular Structure of Methyl 4-O-methyl-α-D-glucopyranuronate
- 2005
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Ingår i: Molecules. - 1420-3049 .- 1420-3049. ; 10:1, s. 251-258
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Tidskriftsartikel (refereegranskat)abstract
- A method for the preparation of methyl 4-O-methyl-α-D-glucopyranuronate and its single crystal X-ray structure determination are reported. The molecule adopts an almost ideal 4C1 (OC3) conformation.
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| 3. |
- Langer, Vratislav, 1949, et al.
(författare)
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2-(1H-Benzimidazol-2-ylsulfanyl)butanoic acid
- 2006
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Ingår i: Acta Crystallographica Section E: Structure Reports Online. - 1600-5368. ; E62:6, s. o2138-o2140
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Tidskriftsartikel (refereegranskat)abstract
- The title compound, C11H12N2O2S, forms ionic crystals consisting of protonated benzimidazole cations and carboxylic acid anions, C11H13N2O2+·C11H11N2O2-. In both ions, the bicyclic 1H-benzimidazole core is essentially planar. The plane of the 2-alkylsulfanyl substituent is almost coplanar with the benzimidazole plane. The three-dimensional packing is stabilized by strong intermolecular N-H...O and O-H...N interactions and weak C-H...O intermolecular hydrogen bonds.
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| 4. |
- Langer, Vratislav, 1949, et al.
(författare)
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2,3:4,6-Di-O-isopropylidene-α-L-sorbofuranose and 2,3-O-isopropylidene-α-L-sorbofuranose
- 2009
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Ingår i: Acta Crystallographica Section C: Crystal Structure Communications. - 0108-2701 .- 1600-5759. ; C65:4, s. o151-o154
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Tidskriftsartikel (refereegranskat)abstract
- In the title compounds, C12H20O6, (I), and C9H16O6, (II), the five-membered furanose ring adopts a 4T3 conformation and the five-membered 1,3-dioxolane ring adopts an E3 conformation. The six-membered 1,3-dioxane ring in (I) adopts an almost ideal OC3 conformation. The hydrogen-bonding patterns for these compounds differ substantially: (I) features just one intramolecular O-H...O hydrogen bond [O...O = 2.933 (3)Å], whereas (II) exhibits, apart from the corresponding intramolecular O-H...O hydrogen bond [O...O = 2.7638 (13)Å], two intermolecular bonds of this type [O...O = 2.7708(13) and 2.7730(12) Å]. This study illustrates both the similarity between the conformations of furanose, 1,3-dioxolane and 1,3-dioxane rings in analogous isopropylidene-substituted carbohydrate structures and the only negligible influence of the presence of a 1,3-dioxane ring on the conformations of furanose and 1,3-dioxolane rings. In addition, in comparison with reported analogs, replacement of the -CH2OH group at the C1-furanose position by another group can considerably affect the conformation of the 1,3-dioxolane ring.
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| 5. |
- Langer, Vratislav, 1949, et al.
(författare)
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2-(4-Hydroxyphenyl)-4,4-dimethyl-2-oxazoline: X-ray and density functional theory study
- 2006
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Ingår i: Acta Crystallographica Section C: Crystal Structure Communications. - 0108-2701 .- 1600-5759. ; C62:7, s. o416-o418
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Tidskriftsartikel (refereegranskat)abstract
- In the crystal structure of the title compound, C11H13NO2, there are strong intermolecular O-H...N hydrogen bonds which, together with weak intramolecular C-H...O hydrogen bonds, lead to the formation of infinite chains of molecules, held together by weak intermolecular C-H...O hydrogen bonds. A theoretical investigation of the hydrogen bonding, based on density functional theory (DFT) employing periodic boundary conditions, is in agreement with the experimental data. The cluster approach shows that the influence of the crystal field and of hydrogen-bond formation are responsible for the deformation of the 2-oxazoline ring, which is not planar and adopts a 4T3 (C3TC2) conformation.
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| 6. |
- Langer, Vratislav, 1949, et al.
(författare)
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3-(4-Bromophenyl)-5-(4-dimethylaminophenyl)-1-phenyl-2-pyrazoline: X-ray and density functional theory (DFT) studies
- 2007
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Ingår i: Acta Crystallographica Section C: Crystal Structure Communications. - 0108-2701 .- 1600-5759. ; C63:6, s. o340-o342
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Tidskriftsartikel (refereegranskat)abstract
- In the crystal structure of the title compound, C23H22BrN3, a strong conjugation of the pyrazoline chromophore with the aromatic rings at positions 1 and 3 is observed, as well as a significant shift in the synclinal→synperiplanar direction. The absolute structure was unequivocally determined. In the absence of clasical hydrogen-bond donors, the structure is stabilized by weak C-H…π interactions. This paper also reports the electronic structure of the title compound using NBO (natural bond order) analysis. The contributions of lone pairs to the relevant bonds were revealed.
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| 7. |
- Langer, Vratislav, 1949, et al.
(författare)
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3-O-Benzoyl-1,2-O-isopropylidene-β-D-fructopyranose
- 2005
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Ingår i: Acta Crystallographica Section E: Structure Reports Online. - 1600-5368. ; E61:7, s. o2172-o2174
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Tidskriftsartikel (refereegranskat)abstract
- In the structure of the title compound, C16H20O7, the five-membered 1,3-dioxolane ring is disordered with two different positions, A and B (1/1); it adopts the OT4 conformation slightly distorted towards E4 for molecule A, and the 1E conformation distorted towards 1TO for molecule B. The pyranose ring adopts an almost ideal 1C4 conformation. The three-dimensional packing is stabilized by strong intermolecular O-H...O interactions and weak C-H...O hydrogen bonds.
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| 8. |
- Langer, Vratislav, 1949, et al.
(författare)
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6-O-Cyanomethyl-1,2:3,4-di-O-isopropylidene-α-D-galactopyranose
- 2005
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Ingår i: Acta Crystallographica Section E: Structure Reports Online. - 1600-5368. ; E61:3, s. o779-o781
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Tidskriftsartikel (refereegranskat)abstract
- The analysis of the title compound, C14H21NO6, revealed a highly distorted conformation of the six-membered pyranose ring. The presence of two five-membered 1,3-dioxolane rings fused to the pyranose ring at the 1,2- and 3,4-positions is responsible for the severe deviation from the usual chair conformation of the pyranose ring. The three-dimensional packing is stabilized by weak hydrogen bonds of the C-H...O type.
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| 9. |
- Langer, Vratislav, 1949, et al.
(författare)
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Crystal structures of three isomeric forms of hydoxyphenyl-2-oxazoline
- 2005
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Ingår i: Proceedings of XLVIII. Congress of Polish Chemical Society, Poznan 18-22 september 2005. - 8389936070 ; 1, s. S7-P2
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The crystal structures of three positionally isomeric compounds, 2-(2-hydroxyphenyl)-2-oxazoline, C9H9NO2, (I), 2-(3-hydroxyphenyl)-2-oxazoline, C9H9NO2, (II), and 2-(4-hydroxyphenyl)-2-oxazoline, C9H9NO2, (III), [alternative names of the title compounds are: 2-(4,5-dihydro-1,3-oxazol-2-yl)phenol, (I), 3-(4,5-dihydro-1,3-oxazol-2-yl)phenol, (II), and 4-(4,5-dihydro-1,3-oxazol-2-yl)phenol, (III)] have been determined. The title compounds were prepared in the course of our research focused at cyclic imino ethers and their utilization in polymer chemistry because hydroxyphenyl-2-oxazolines are known to produce poly(ether-amides) on heating of the monomer. In these compounds, the deviation from coplanarity of oxazoline and benzene rings is dependent on the position of the hydroxyl group at phenyl moiety. The coplanar arrangement in (I) is stabilized by a strong intramolecular O-H...N hydrogen bond. In (II) the hydroxyl group is hydrogen bonded to the ring nitrogen atom on adjacent molecule.Surprisingly, the 2-oxazoline ring of one molecule in asymmetric unit of (II) adopts 3T4 (C2TC3) conformation, while 2-oxazoline ring in the other molecule, as well as that in (I) and (III), is nearly planar, as expected. Tetramers of molecules of (II) are formed and they are bound together via weak C-H...N hydrogen bonds. In (III), strong intermolecular O-H...N hydrogen bonds and weak intramolecular C-H...O hydrogen bonds lead to the formation of an infinite chain of molecules perpendicular to the b direction. The theoretical investigation of H-bonds, based on density functional theory (DFT) employing periodic boundary conditions, has been done using Vienna Ab initio Simulation Package (VASP).
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| 10. |
- Langer, Vratislav, 1949, et al.
(författare)
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Preparation and Crystal Structure of (1S, 5S, 7S, 8R)-8-Hydroxy-7-phenyl-2,6-dioxabicyclo[3.3.0]octan-3-one
- 2003
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Ingår i: Molecules. - 1420-3049 .- 1420-3049. ; 8:7, s. 599-606
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Tidskriftsartikel (refereegranskat)abstract
- The absolute configuration at two newly formed stereogenic centres (5S, 7S) during the key steps of the total synthesis of naturally occuring goniothalesdiol was established by single-crystal X-ray diffraction analysis relative to stereocentres (1S, 8R) of the title compound (alternatively named 3,6-anhydro-2-deoxy-6-phenyl-L-ido-1,4-hexonolactone, C12H12O4). The conformation of both 5-membered lactone and furanose fused rings is also discussed.
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