Charge distribution, dipole moments and molecular structure of some organogermanium compounds

Formal charge distributions in, and the electric dipole moments of, a few simple organogermanium compounds have been evaluated by the method of R. P. Smith et al. [J. Amer. Chem. Soc., 73(1951) 2263]. The difference between the experimental and calculated moments in the case of alkylhalogermanes is explained in terms of the pπ—dπ back bonding effect outweighing the electron releasing effect. In unsaturated compounds, the differences are attributed to possible mesmeric effects involving the expansion of the germanium valence shell.

Molecular and crystal structure of deoxyguanosine 5'-phosphate

RECENT crystallographic studies of the dinucleosides ApU (ref. 1) and GpC (ref. 2) have given experimental proof for the base pairing arrangement proposed by Watson and Crick for the DNA double helix3. Another striking feature of this structure relates to the torsional angle about the C5'-C4' bond in the phosphate−sugar backbone chain. In the Crick and Watson model4, this conformation is gauche−trans (GT). Crystal structures of 5'-nucleotides, dinucleosides and dinucleotides so far studied, however, have shown only the gauche−gauche (GG) conformation about this bond. The GG conformer is also the only one found in the refined models of the proposed structure of the double helical nucleic acids and polynucleotides5−7. The only nucleotide with a GT conformation is 6-azauridine-5'-phosphate8 which is not a normal monomer unit of nucleic acids. It is also reported that 5'-dGMP assumes preferentially GT conformation in solution9.

Isotope shifts and hyperfine structure in the 555.8-nm S-1(0) -> P-3(1) line of Yb

We apply our technique of using a Rb-stabilized ring-cavity resonator to measure the frequencies of various spectral components in the 555.8-nm 1S0-->3P1 line of Yb. We determine the isotope shifts with 60 kHz precision, which is an order-of-magnitude improvement over the best previous measurement on this line. There are two overlapping transitions, 171Yb(1/2-->3/2) and 173Yb(5/2-->3/2), which we resolve by applying a magnetic field. We thus obtain the hyperfine constants in the 3P1 state of the odd isotopes with a significantly improved precision. Knowledge of isotope shifts and hyperfine structure should prove useful for high-precision calculations in Yb necessary to interpret ongoing experiments testing parity and time-reversal symmetry violation in the laws of physics.

Aromatic amines and their derivatives. Part 3. The synthesis and crystal structure of 4,4-NN-tetramethyl-NN-dinitroso-2,2-methylenedianiline

The synthesis of 4,4,N,N-tetramethyl-NN-dinitroso-2,2-methylenedianiline (1) by the route p-MeC6H4NH2+ HCHO + OH–(p-MeC6H4NMe)2CH2(7b); (7b)+ acid at 70 °C 4,N-dimethyl-6-(N-methyl-p-toluidinomethyl)aniline (4b); (4b)+ acid at 130 °C 4,4,NN-tetramethyl-2,2-methylenedianiline (3b); (3b)+ HNO2(1), is described. Aspects of the 1H n.m.r. spectra of the above and related compounds are discussed. A crystal-structure analysis of compound (1) shows one of the N-nitroso-groups to be disordered with the endo-form being in preponderance (4 : 1) over the exo-form. The other N-nitroso-group is exclusively exo in the solid state. There is little or no resonance between the benzene ring and the nitroso-group attached to the ring, the two groups being almost perpendicular to each other. In one of the N-nitroso-groups, the nitrogen atom deviates significantly from the plane of the benzene ring to which it is attached. Both amide nitrogen atoms show some pyramidal character.

Crystal and molecular structure of allo-4-hydroxy-L-proline dihydrate

allo-4-Hydroxy-L-proline crystallizes from an aqueous solution as the dihydrate. The crystals are orthorhombic, space group P212121, with a=7.08 (2), b=22.13 (3), c= 5"20 (2) A,. The structure was solved by direct methods and refined by block-diagonal least squares. The final R for 733 observed reflexions is 0.054. The molecule exists as a zwitterion with hydroxyl and carboxyl groups cis to the pyrrolidine ring. The latter is puckered at the fl-carbon atom, which deviates by -0.54 A, from the best plane formed by the four remaining atoms. The molecules are held together by a network of hydrogen bonds, the water molecules playing a dominant role in the stability of the structure.

Crystal and molecular structure of 15-bromolongibornane-8,9-dione

The crystal and molecular structure of the title compound (1) has been determined by the heavy-atom method from 1038 observed three-dimensional photographic data. Crystals are orthorhombic, with a = 20.07 ± 0.02, b= 10.05 ± 0.02, c= 7.31 ± 0.01 Å, space group P212121, with Z= 4. The structure was refined by block diagonal leastsquares to R 0.099. The conformation of the norbornane moiety is discussed. The seven-membered ring portion of the molecule adopts an approximate chair conformation. The packing of the molecules in the crystal is mainly a consequence of van der Waals interactions.

The crystal and molecular structure of the amino terminal tetrapeptide of alamethicin. A novel 310 helical conformation

The molecular structure of N-benzyloxycarbonyl-α-aminoisobutyryl-prolyl-α-aminoisobutyryl-alanyl methyl ester (Z-Aib-Pro-Aib-Ala-OMe), the amino terminal tetrapeptide of alamethicin is reported. The molecule contains two consecutive β-turns with Aib-Pro and Pro-Aib at the corners, forming an incipient 310 helix. This constitutes the first example of an X2-Pro3 β-turn in the crystal structure of a small peptide.

Structural studies of analgesics and their interactions. III. The crystal and molecular structure of amidopyrine

Amidopyrine (1-phenyl-2,3-dimethyl-4-dimethylaminopyrazolone), C13HzvN30, a dimethylamino derivative of antipyrine and an important analgesic and antipyretic agent, crystallizes in the triclinic space group P1 with four molecules in a unit cell of dimensions a= 7.458 (5), b = 10.744 (5), c= 17.486 (15)/~,, e=98.6 (2),/~= 85.6 (3), y= 108-6 (2) . The structure was solved by direct methods and refined to an R value of 0.055 for 3706 photographically observed reflexions. The dimensions of the two crystallographically independent molecules are very nearly the same. The pyrazolone moiety in the molecule has dimensions comparable to those in antipyrine. Unlike antipyrine, the molecular dimensions of amidopyrine in the free state (the present structure) are close to those found in some of its hydrogenbonded complexes. Thus it appears that the presence of the dimethylamino group makes the molecule more resistant to changes in its dimensions resulting from molecular association. An attempt has also been made to correlate the polar nature of the pyrazolone moiety and the hybridization state of the hetero nitrogen atoms in antipyrine, amidopyrine and their complexes.

The Crystal and Molecular Structure of 4-Aza-5-oxo-tricyclo[4.4.0.03,8]decane (Aza-twistanone)

Die kristalline Struktur von Aza-twistanon wurde durch eine Röntgenstruktur-analyse untersucht. Die Kristalle gehören zur monoklinen Raumgruppe P21/n mit den Zelldimensionen a = 6,662(6), b = 13,36(2), c = 8,606(9) Å, = 98,97(2)°, V = 757 Å3, Z = 4. Die Struktur wurde mit Direktmethoden gelöst und bis zu R = 0,035 verfeinert (mittlere (c) = 0,003 Å3).Die cis-Amidgruppe ist relativ stark deformiert und hat einen Torsionswinkel C -C -N-C von 14,5(4)° (Deformation aus der Ebene c = 5,0(5)° und N = 13,5(4,0)°). Die gegenüberliegende äthylenbrücke weist einen Torsionswinkel von 25,1(5)° auf. Die entsprechenden Winkel in Twistan betragen je 20°. Das tricyclische Gerüst von Aza-twistanon hat approximative.

The Crystal and Molecular Structure of l-(Diphenylmethyl)azetidin-3-ol

1-(Diphenylmethyl)azetidin-3-ol is triclinic, space group P1, with a=8.479(2), b=17.294(4),c = 10.606 (3) A, a = 118.59 (2),/~ = 100.30 (2), y = 89.63 (2) °, Z = 4. The structure was solved by multisolution methods and refined to an R of 0.044 for 2755 reflexions. The four-membered rings in the two independent molecules are puckered with dihedral angles of 156 and 153 ° . The two molecules differ in conformation with respect to rotation of the phenyl rings about the C-C bonds. The structure is stabilized by a network of O-H. • • N intermolecular hydrogen bonds.

Stereospecific photodimerization of coumarins in crystalline inclusion complexes. Molecular and crystal structure of 1:2 complex of (S,S)-(-)-1,6-bis(o-chlorophenyl)-1,6-diphenyl-hexa-2,4-diyne-1,6-diol and coumarin

Proximity of molecules is a crucial factor in many solid- state photochemical processes.'S2 The biomolecular photodimerization reactions in the solid state depend on the relative geometry of reactant molecules in the crystal lattice with center-to-center distance of nearest neighbor double bonds of the order of ca. 4 A. This fact emanates from the incisive studies of Schmidt and Cohen.2 One of the two approaches to achieve this distance requirement is the so-called "Crystal-Engineering" of structures, which essentially involves the introduction of certain functional groups that display in-plane interstacking interactions (Cl...Cl, C-He-0, etc.) in the crystal The chloro group is by far the most successful in promoting the /3- packing m ~ d e ,th~o,u~gh recent studies have shown its limitations? Another approach involves the use of constrained media in which the reactants could hopefully be aligned.

Conformational studies of the triphenylphosphazenyl side chain in cyclophosphazenes. II. Crystal and molecular structure of 2,4,4,6,6,8,8-heptachloro-2-triphenylphosphazenylcyclotetra(phosphazene), N4P4Cl7(NPPh3)

Abstract is not available.

Vertex-Fused Metallaborane Clusters: Synthesis, Characterization and Electronic Structure of [(eta(5)-C5Me5Mo)(3)MoB9H18]

The reaction of the [(eta(5)-C5Me5)MoCl4] complex with [LiBH4 - TH F] in toluene at - 70 degrees C, followed by pyrolysis at 110 degrees C, afforded dark brown [(eta(5)-C5Me5Mo)(3)MoB9H18], 2, in parallel with the known [(eta(5)-C5Me5Mo)(2)B5H9], 1. Compound 2 has been characterized in solution by H-1, B-11, and C-13 NMR spectroscopy and elemental analysis, and the structural types were unequivocally established by crystallographic studies. The title compound represents a novel class of vertex-fused clusters in which a Mo atom has been fused in a perpendicular fashion between two molybdaborane clusters. Electronic structure calculations employing density functional theory yield geometries in agreement with the structure determinations, and on grounds of density functional theory calculations, we have analyzed the bonding patterns in the structure,

The crystal and molecular structure of benzyloxycarbonyl-a-amino-isobutyryl-L-prolyl-methylamide. The observation of an X2-Pro3 Type III b-turn

The crystal and molecular structure of N-benzyloxycarbonyl-a-aminoisobutyryl-L-prolyl methylamide, the amino terminal dipeptide fragment of alamethicin, has been determined using direct methods. The compound crystallizes in the orthorhombic system with the space group P212-21. Cell dimensions are a = 7.705 A, b = 11.365 A, and c = 21.904 A. The structure has been refined using conventional procedures to a final R factor of 0.054. The molecular structure possesses a 4 - 1 intramolecular N-H--0 hydrogen bond formed between the CO group of the urethane moiety and the NH group of the methylamide function. The peptide backbone adopts the type 111 P-turn conformation, with 42 = -51.0°, +* = -39.7",&j = -65.0', $3 = -25.4'. An unusual feature is the occurrence of the proline residue at position 3 of the P-turn. The observed structure supports the view that Aib residues initiate the formation of type 111 @-turn conformations. The pyrrolidine ring is puckered in Cy-exo fashion.