Coherent X‐Ray Scattering for the Hydrogen Atom in the Hydrogen Molecule
01 May 1965-Journal of Chemical Physics (American Institute of PhysicsAIP)-Vol. 42, Iss: 9, pp 3175-3187
TL;DR: In this paper, the x-ray form factors for a bonded hydrogen in the hydrogen molecule have been calculated for a spherical approximation to the bonded atom, and the corresponding complex scattering factors have also been calculated.
Abstract: The x‐ray form factors for a bonded hydrogen in the hydrogen molecule have been calculated for a spherical approximation to the bonded atom. These factors may be better suited for the least‐squares refinement of x‐ray diffraction data from organic molecular crystals than those for the isolated hydrogen atom. It has been shown that within the spherical approximation for the bonded hydrogens in H2, a least‐squares refinement of the atomic positions will result in a bond length (Re value) short of neutron diffraction or spectroscopic values. The spherical atoms are optimally positioned 0.07 A off each proton into the bond. A nonspherical density for the bonded hydrogen atom in the hydrogen molecule has also been defined and the corresponding complex scattering factors have been calculated. The electronic density for the hydrogen molecule in these calculations was based on a modified form of the Kolos—Roothaan wavefunction for H2. Scattering calculations were made tractable by expansion of a plane wave in spheroidal wavefunctions.
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TL;DR: Pivaloyl-L-Pro-Aib and N-methylamide NH structures have been shown to possess one intramolecular hydrogen bond in (CD&SO) solution, by 'H-nmr methods, suggesting the existence of p-turns, with the corner residues of the pivaloyal-l-pro-aib as the corner residue.
Abstract: Pivaloyl-L-Pro-Aib-N-methylamihdaes been shown to possess one intramolecular hydrogen bond in (CD&SO solution, by 'H-nmr methods, suggesting the existence of p-turns, with
Pro-Aib as the corner residues Theoretical conformational analysis suggests that Type II P-turn conformations are about 2 kcal mol-' more stable than Type 111 structures A crystallographic study has established the Type I1 /%turn in the solid state The molecule crystallizes in the space group P21 with a = 5865 8, b = 11421 A, c = 12966 A, /3 = 9755", and 2 = 2 The structure has been refined to a final R value of 0061 The Type I1 p-turn conformation
is stabilized by an intramolecular 4 - 1 hydrogen bond between the methylamide NH and the pivaloyl CO group The conformational angles are @pro= -578", $pro = 1393',
@Aib = 614', and $Ajb = 251' The Type 11 /%turn conformation for Pro-Aib in this peptide is compared with the Type I11 structures observed for the same segment in larger peptides
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TL;DR: In this article, an aliphatischen Amin 1,3,5-trimethyl-1,3-5-triazinane (TMTA) was used as an unidentate ligand to the zinc atom.
Abstract: Bis[bis(trimethylsilyl)methyl]zink reagiert in n-Pentan mit dem aliphatischen Amin 1,3,5-Trimethyl-1,3,5-triazinan (TMTA) unter Bildung des 1:1-Adduktes, wobei das TMTA-Molekul als einzahniger Ligand an das Zinkatom bindet. Das Bis[bis(trimethylsilyl)methyl]zink · TMTA kristallisiert in der triklinen Raumgruppe P1 mit {a = 897,7(3); b = 1 114,4(4); c = 1627,6(6) pm; α = 90,52(1); β = 103,26(1); γ = 102,09(1)°; Z = 2}. Das zentrale C2ZnN-Fragment weist mit einer nahezu T-formigen Konfiguration einen CZnC-Winkel von 157° und ZnC-Bindungslangen von 199 pm auf. Der ZnN-Abstand von 239 pm ist auserordentlich lang und spricht fur eine nur lockere Koordination des Amins, die durch eine weitgehende Dissoziation dieses Komplexes in Benzol bestatigt wird. Die Addition aliphatischer Amine wie TMEDA oder TMTA zu einer aquimolaren etherischen Losung von Lithium-bis(trimethylsilyl)methanid und Bis[bis(trimethylsilyl)methyl]-zink fuhrt zur Bildung der Amin-Addukte des Lithium-tris[bis(trimethylsilyl)methyl]zinkats. Das Lithium-tris-[bis(trimethylsilyl)methyl]zinkat · TMEDA · 2 Et2O kristallisiert in der orthorhombischen Raumgruppe Pbca mit {a = 1 920,2(4); b = 2 243,7(5); c = 2 390,9(5) pm; Z = 8}. Es liegen solvensgetrennte Ionen vor; das Lithiumkation ist verzerrt tetraedrisch von den Stickstoffatomen des TMEDA-Liganden und den Sauerstoffatomen der beiden Diethylether-Molekule umgeben. Das Zinkatom ist trigonal planar koordiniert, die langen ZnC-Bindungen von 209 pm erklaren sich aus der sterischen und elektrostatischen Abstosung der drei carbanionischen Bis(trimethylsilyl)methyl-Substituenten.
Synthesis, Properties, and Structure of the Amine Adducts of Lithium Tris[bis(trimethylsilyl)methyl]zincates.
Bis[bis(trimethylsilyl)methyl]zinc and the aliphatic amine 1,3,5-trimethyl-1,3,5-triazinane (tmta) yield in n-pentane the 1:1 adduct, the tmta molecule bonds as an unidentate ligand to the zinc atom. Bis[bis(trimethylsilyl)methyl]zinc · tmta crystallizes in the triclinic space group P1 with {a = 897.7(3); b = 1 114.4(4); c = 1 627.6(6) pm; α = 90.52(1); β = 103.26(1); γ = 102.09(1)°; Z = 2}. The central C2ZnN moiety displays a nearly T-shaped configuration with a CZnC angle of 157° and ZnC bond lengths of 199 pm. The ZnN distances of 239 pm are remarkably long and resemble the loose coordination of this amine; a nearly complete dissociation of this complex is also observed in benzene. The addition of aliphatic amines such as tmta or tmeda to an equimolar etheral solution of lithium bis(trimethylsilyl)methanide and bis[bis(trimethylsilyl)methyl]zinc leads to the formation of the amine adducts of lithium tris[bis(trimethylsilyl)methyl]zincate. Lithium tris[bis(trimethylsilyl)methyl]zincate · tmeda · 2 Et2O crystallizes in the orthorhombic space group Pbca with {a = 1 920.2(4); b = 2 243.7(5); c = 2 390.9(5) pm; Z = 8}. In the solid state solvent separated ions are observed; the lithium cation is distorted tetrahedrally surrounded by the two nitrogen atoms of the tmeda ligand and the oxygen atoms of both the diethylether molecules. The zinc atom is trigonal planar coordinated; the long ZnC bonds with a value of 209 pm can be attributed to the steric and electrostatic repulsion of the three carbanionic bis(trimethylsilyl)methyl substituents.
38 citations
TL;DR: In this article, the dimeric tris(allyl)lanthanum dioxane complex [La(η3-C3H5)3 · (C4H8O2)1.5] was characterized by elemental analysis, 1H, 13C and 139La NMR spectroscopy.
38 citations
TL;DR: In this article, both isomers of NN-dimethyl benzamidoxime have been obtained for the first time and their configurations assigned by NMR and X-ray studies.
38 citations
TL;DR: The tripeptide L‐alanyl‐L‐ alanyl‐ L‐alanine has been crystallized from a water/dimethyl‐formamide solution in an unhydrated form, with cell dimensions a = 11.849, b = 10.004, c = 9.862 Å, monoclinic space group P21.
Abstract: The tripeptide L-alanyl-L-alanyl-L-alanine has been crystallized from a water/dimethylformamide solution in an unhydrated form, with cell dimensions a = 11.849, b = 10.004, c = 9.862 A, beta = 101.30 degrees, monoclinic space group P21 with 4 molecules per cell (2 independent molecules in the asymmetric unit). The structure was determined by direct methods and refined to a discrepancy index R = 0.057. The tri-L-alanine molecules are packed in a parallel pleated sheet arrangement with unusually long amide nitrogen-carbonyl oxygen contacts within sheets. Comparisons are made with the antiparallel pleated sheet structure of tri-L-alanine hemihydrate, previously crystallized from the same solvent system.
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TL;DR: In this article, the quantum mechanical wave functions of molecules are discussed and an attempt is made to effect a simultaneous regional and physical partitioning of the molecular density, the molecular pair density, and the molecular energy, in such a way that meaningful concepts can be associated with the density and energy fragments thus formed.
Abstract: The quantum mechanical wave functions of molecules are discussed. An attempt is made to effect a simultaneous regional and physical partitioning of the molecular density, the molecular pair density, and the molecular energy, in such a way that meaningful concepts can be associated with the density and energy fragments thus formed. The origin of chemical binding is interpreted in terms of the concepts formulated in the partitioning process. (T.F.H.)
768 citations
576 citations
TL;DR: The solution of Schroedinger's equation for the normal hydrogen molecule is approximated by the function $C[{e}^{\ensuremath{-}\frac{z({r}_{1}+{p}_{2})}{a}}+{e^{\ensem{-]-{m{e})+{m}−m{n}−n}]$ where m is the distance of one of the electrons to the two nuclei, and r is the distances of one electron to the other electron.
Abstract: The solution of Schroedinger's equation for the normal hydrogen molecule is approximated by the function $C[{e}^{\ensuremath{-}\frac{z({r}_{1}+{p}_{2})}{a}}+{e}^{\ensuremath{-}\frac{z({r}_{2}+{p}_{1})}{a}}]$ where $a=\frac{{h}^{2}}{4{\ensuremath{\pi}}^{2}m{e}^{2}}$, ${r}_{1}$ and ${p}_{1}$ are the distances of one of the electrons to the two nuclei, and ${r}_{2}$ and ${p}_{2}$ those for the other electron. The value of $Z$ is so determined as to give a minimum value to the variational integral which generates Schroedinger's wave equation. This minimum value of the integral gives the approximate energy $E$. For every nuclear separation $D$, there is a $Z$ which gives the best approximation and a corresponding $E$. We thus obtain an approximate energy curve as a function of the separation. The minimum of this curve gives the following data for the configuration corresponding to the normal hydrogen molecule: the heat of dissociation = 3.76 volts, the moment of inertia ${J}_{0}=4.59\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}41}$ gr. ${\mathrm{cm}}^{2}$, the nuclear vibrational frequency ${\ensuremath{
u}}_{0}=4900$ ${\mathrm{cm}}^{\ensuremath{-}1}$.
292 citations
TL;DR: In this paper, a simple wave function for the normal state of the hydrogen molecule, in which both the atomic and ionic configurations are taken into account, was set up and treated by a variational method.
Abstract: A simple wave function for the normal state of the hydrogen molecule, in which both the atomic and ionic configurations are taken into account, was set up and treated by a variational method. The dissociation energy was found to be 4.00 v.e. as compared to the experimental value of 4.68 v.e. and Rosen's value of 4.02 v.e. obtained by use of a function involving complicated integrals. It was found that the atomic function occurs with a coefficient 3.9 times that of the ionic function. A similar function with different screening constants for the atomic and ionic parts was also tried. It was found that the best results are obtained when these screening constants are equal. The addition of Rosen's term to the atomic‐ionic function resulted in a value of 4.10 v.e. for the dissociation energy.
253 citations
133 citations