Conformation of diastereoisomeric cyclo(neopentylglycyl-prolyls): NMR, X-ray, and CD studies

1987 ◽  
Vol 52 (9) ◽  
pp. 2295-2308 ◽  
Author(s):  
Karel Bláha ◽  
Miloš Buděšínský ◽  
Ivo Frič ◽  
Jan Pospíšek ◽  
Jindřich Symerský
Keyword(s):  
Chain Structure ◽  
Side Chain ◽  
Boat Conformation ◽  
X Ray Diffraction ◽  
X Ray ◽  
Butyl Group ◽  
Boat Form ◽  
Cd Studies ◽  
Twisted Boat ◽  
C Nmr

Conformation of diastereoisomeric cyclo(L-neopentylglycyl-L-prolyl) (IV) and cyclo(D-neopentylglycyl-L-prolyl) (VIII) in solution was studied by 1H and 13C NMR spectroscopy. Both compounds have approximately the same conformation of the bicyclic moiety in which the 2,5-piperazinedione ring exists in the boat form with pseudoaxial proline H(α) atom, and the proline ring is in the C(γ)-exo conformation. Rotation of the neopentyl side chain is markedly hindered. In the trans-derivative VIII the side chain occupies a pseudoaxial position with staggered rotamer about the C(α)-C(β) bond, the tert-butyl group pointing from the ring in the direction of the nitrogen atom. The preferred rotamer of the cis-isomer markedly deviates from this staggered conformation in the exo-direction relative to the piperazine ring. X-Ray diffraction analysis shows that crystal conformation of the trans-isomer VIII is very similar to that in solution. According to CD measurements, steric interactions of the acyclic side chain with the dioxopiperazine ring lead to twisted boat conformations of this ring with non-planar amide groups. From comparison with other proline-containing cyclodipeptides it follows that the effect of these interactions depends on the side chain structure. The neopentyl side chain flattens the boat conformation and reduces the deviation of the amide groups from planarity.

Crystal Structure of Dibromo(η4-1,5-cyclooctadiene)palladium(II)

1996 ◽  
Vol 61 (9) ◽  
pp. 1335-1341 ◽  
Author(s):  
Petr Štěpnička ◽  
Ivana Císařová
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Single Crystal ◽  
Boat Conformation ◽  
X Ray Diffraction ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
X Ray ◽  
Square Planar ◽  
Twisted Boat

The crystal structure of [(η4-C8H12)PdBr2] has been determined by a single crystal X-ray diffraction with R = 3.82% for 2 147 independent diffractions. The compound crystallizes with the symmetry of orthorhombic space group P212121 (No. 19) within the following parameters: a = 7.0785(5) Å, b = 11.1896(9) Å, c = 12.514(1) Å, V = 991.2(1) Å3, Z = 4. The square planar arrangement of ligands around Pd(II) is distorted due to the steric requirements of 1,5-cyclooctadiene in a twisted boat conformation. Formula units are joined by the weak C2-H2...Br1(1 + x, y, z) hydrogen bonds.

Conformational changes in serine on methylmercury complexation

1988 ◽  
Vol 66 (6) ◽  
pp. 1379-1385 ◽  
Author(s):  
Marie-Claude Corbeil ◽  
André L. Beauchamp
Keyword(s):  
Aqueous Solution ◽  
Conformational Changes ◽  
Hydroxyl Group ◽  
Side Chain ◽  
X Ray Diffraction ◽  
X Ray ◽  
Carboxylate Oxygen ◽  
Zwitterionic Complex ◽  
Ligand Conformation ◽  
C Nmr

The CH3Hg+ cation forms a zwitterionic complex CH3Hg[HOCH2CH(NH2)CO2—N,O,O] with serine in aqueous solution. X-ray diffraction (P212121, a = 5.821, b = 8.052, c = 14.307 Å, R = 0.021) shows that mercury is linearly bonded to the NH2 end of the amino acid, whereas one carboxylate oxygen and the side-chain hydroxyl group establish secondary Hg—O bonds. Coordination leads to characteristic changes in the infrared and Raman spectra of serine. From the 1H and 13C nmr spectra, N-coordination is found to be retained in aqueous solution, whereas the ligand conformation observed in the solid accounts for 76% of the conformer distribution.

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

1984 ◽  
Vol 49 (3) ◽  
pp. 712-742 ◽  
Author(s):  
Karel Bláha ◽  
Ahmed M. Farag ◽  
Dick VAN DER Helm ◽  
M. Bilayet Hossain ◽  
Miloš Buděšínský ◽  
...  
Keyword(s):  
Acetic Acid ◽  
Stereospecific Synthesis ◽  
Cd Spectra ◽  
X Ray Diffraction ◽  
Relative Configuration ◽  
X Ray ◽  
H Nmr ◽  
Chemical Correlation ◽  
Cd Studies ◽  
C Nmr

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.

An unusual reaction of a bridged triterpenoid α-diketone with acetic anhydride

1991 ◽  
Vol 56 (12) ◽  
pp. 2917-2935 ◽  
Author(s):  
Eva Klinotová ◽  
Václav Křeček ◽  
Jiří Klinot ◽  
Miloš Buděšínský ◽  
Jaroslav Podlaha ◽  
...  
Keyword(s):  
Acetic Acid ◽  
Nmr Spectroscopy ◽  
Acetic Anhydride ◽  
Spectral Methods ◽  
X Ray Diffraction ◽  
X Ray ◽  
Mild Conditions ◽  
Condensation Products ◽  
Unsaturated Lactones ◽  
C Nmr

3β-Acetoxy-21,22-dioxo-18α,19βH-ursan-28,20β-olide (IIIa) reacts with acetic anhydride in pyridine under very mild conditions affording β-lactone IVa and γ-lactones Va and VIIa as condensation products. On reaction with pyridine, lactones Va and VIIa undergo elimination of acetic acid to give unsaturated lactones VIIIa and IXa, respectively. Similarly, the condensation of 20β,28-epoxy-21,22-dioxo-18α,19βH-ursan-3β-yl acetate (IIIb) with acetic anhydride leads to β-lactone IVb and γ-lactone Vb; the latter on heating with pyridine affords unsaturated lactone VIIIb and 21-methylene-22-ketone Xb. The structure of the obtained compounds was derived using spectral methods, particularly 1H and 13C NMR spectroscopy; structure of lactone IVa was confirmed by X-ray diffraction.

Crystal structure determination of the conformation of two bicyclo[3.3.1]nonan-ones

1985 ◽  
Vol 63 (6) ◽  
pp. 1166-1169 ◽  
Author(s):  
John F. Richardson ◽  
Ted S. Sorensen
Keyword(s):  
Crystal Structure ◽  
Direct Methods ◽  
Chair Conformation ◽  
Molecular Structures ◽  
Boat Conformation ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
Final Agreement

The molecular structures of exo-7-methylbicyclo[3.3.1]nonan-3-one, 3, and the endo-7-methyl isomer, 4, have been determined using X-ray-diffraction techniques. Compound 3 crystallizes in the space group [Formula: see text] with a = 15.115(1), c = 7.677(2) Å, and Z = 8 while 4 crystallizes in the space group P21 with a = 6.446(1), b = 7.831(1), c = 8.414(2) Å, β = 94.42(2)°, and Z = 2. The structures were solved by direct methods and refined to final agreement factors of R = 0.041 and R = 0.034 for 3 and 4 respectively. Compound 3 exists in a chair–chair conformation and there is no significant flattening of the chair rings. However, in 4, the non-ketone ring is forced into a boat conformation. These results are significant in interpreting what conformations may be present in the related sp2-hybridized carbocations.

Darstellung, 11B-, 13C-, 29Si-NMR- und Schwingungsspektren von Trimethylsilylmethyl-hexahydro-closo-hexaborat, [B6H6(CH2Si(CH3)3)]- sowie Kristallstruktur von [P(C6H5)4][B6H6(CH2Si(CH3)3)] / Preparation, 11B, 13C, 29Si NMR and Vibrational Spectra of Trimethylsilylmethyl-hexahydro-clo-hexaborate, [B6H6(CH2Si(CH 3)3)]-and the Crystal Structure of [P(C6H5)4] [B6H6(CH2Si(CH3)3)]

1995 ◽  
Vol 50 (7) ◽  
pp. 1025-1029 ◽  
Author(s):  
J. Baurmeister ◽  
A. Franken ◽  
W. Preetz
Keyword(s):  
Crystal Structure ◽  
Monoclinic Space Group ◽  
29Si Nmr ◽  
X Ray Diffraction ◽  
Nmr Spectrum ◽  
X Ray ◽  
Quadrupole Coupling ◽  
Stretching Vibration ◽  
Ir And Raman ◽  
C Nmr

By reaction of [N(C4H9 )4]2 [B6H6] with iodomethyl-trimethylsilane in acetonitrile a solution with trimethylsilylm ethyl-closo-hexaborate(1-)anions, [B6H6 (CH2Si(CH3)3)]-, is formed. The crystal structure of [P(C6H5 )4][B6H6(CH2Si(CH3)3)] has been determined by single crystal X-ray diffraction analysis; monoclinic, space group P21/n with a = 16.140(2), b = 11.646(8), c = 16.731(3) Å, β 109.664(11)°. The 11B NMR spectrum reveals features of a mono hetero substituted octahedral B6 cage. The 13C NMR spectrum exhibits a quartet at +0.18 ppm with 1J(C,H) = 118 Hz for the three methyl groups and a weak multiplet at -0.65 ppm for the methylene bridge due to quadrupole coupling with the boron atoms. In the 29Si NMR spectrum a decet at +2.25 ppm with 2J(C,H ) = 6.9 Hz is observed. The B -C stretching vibration is observed at 1155 cm-1 in the IR and Raman spectrum.

Syntheses, Structural Characterization and Fluorescence of Zn(II) and Cd(II) Polymers from 5-(Pyridin-2-ylmethylamino)isophthalic acid

2013 ◽  
Vol 68 (9) ◽  
pp. 1007-1014 ◽  
Author(s):  
Xiao-Chun Cheng ◽  
Xiao-Hong Zhu ◽  
Hai-Wei Kuai
Keyword(s):  
Water Clusters ◽  
Hydrothermal Reaction ◽  
Reaction System ◽  
Chain Structure ◽  
Isophthalic Acid ◽  
Auxiliary Ligand ◽  
X Ray Diffraction ◽  
X Ray ◽  
Alkaline Reaction ◽  
A Chain

The hydrothermal reaction of Zn(II) nitrate with 5-(pyridin-2-ylmethylamino)isophthalic acid (H2L) yields the complex [Zn(L)(H2O)] 2H2O (1). When 2,2'-bipyridine (bpy) as auxiliary ligand and Cd(II) nitrate were used in the alkaline reaction system, [Cd(L)(H2O)(bpy)] 3H2O (2) was obtained. Complexes 1 and 2 have been characterized by single-crystal and powder X-ray diffraction, IR, elemental and thermogravimetric analyses. Complex 1 shows a 2D fes network structure with uninodal 3-connected (4.82) topology, which is further linked by hydrogen bonding to give rise to a 3D supramolecular framework; complex 2 displays a chain structure. Interestingly, tetranuclear water clusters were generated in 1, which are interlinked to fabricate a water chain structure. The fluorescence properties of 1 and 2 were investigated

47,49Ti NMR in Metals, Inorganics, and Gels

2000 ◽  
Vol 55 (1-2) ◽  
pp. 291-297 ◽  
Author(s):  
T. J. Bastow
Keyword(s):  
Solid State ◽  
Titanium Oxide ◽  
Recent Progress ◽  
Titanium Isopropoxide ◽  
Metallic State ◽  
X Ray Diffraction ◽  
X Ray ◽  
Hydrolysis Of ◽  
C Nmr

Some recent progress in solid state 47,49Ti NMR is described and reviewed. The metallic-state work described covers metals such as hep titanium, TiB2 , a number of intermetallics such as TiAl2 and TiAl3· The inorganic work covers the various titanium oxide based materials including the TiO2 polymorphs, anatase, rutile and brookite. The gel work covers the evolution of crystalline titania from gels formed by hydrolysis of titanium isopropoxide. Some complementary data from 17O and 13C NMR and powder X-ray diffraction is also included.

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