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Journal ArticleDOI

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.
Citations
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Journal ArticleDOI
TL;DR: In this article, the synthesis and structure of new monocyclooctatetraenyl complexes of Yttrium, Terbium, and Lutetium was discussed.
Abstract: Organometallic Compounds of the Lanthanoids, 73[1]. – Synthesis and Structure of New Monocyclooctatetraenyl Complexes of Yttrium, Terbium, and Lutetium [(C8H8)Ln(μ1-Cl)(THF)]2 (LnY, Lu) react with NaOR (RPh, C6H3Me2-2,6) to give the dinuclear cyclooctatetraenyl rare earth alkoxides [(C8H8)Ln(μ1-OR)(THF)]2 [RPh, LnY (1a), Lu (1b); RC6H3Me2-2,6, LnY (2a), Lu (2b)]. The reactions of [(C8H8)Ln(μ1-Cl)(THF)]2 with LiOC(tBu)3, NaOSiPh3, and NaC5H3tBu2 result in the formation of (C8H8)LnOC(tBu)3(THF) [LnY (3a), Lu (3b)], (C8H8)LnOSiPh3(THF) [LnY (4a), Lu (4b)], and (C8H8)Tb(C5H3tBu2) (5), respectively. Treatment of (C8H8)Y(C5Me5) with acetylacetone yields (C5Me5)Y(acac)2 (6). The 1H-and 13C-NMR and mass spectra of the new compounds as well as the X-ray crystal structures of 1a and 5 are discussed.

26 citations

Journal ArticleDOI
TL;DR: In this paper, the conformation of Boc-L-α-phenylalanine in solution (CDCl3 and CD2Cl2) was studied by 1H NMR spectroscopy.
Abstract: Die Konformation von Boc-L-α-Phenylalanin in Losung (CDCl3 und CD2Cl2) wurde mit 1H-NMR-Spektroskopie und im Kristall durch Rontgenstrukturanalyse untersucht. Die asymmetrische Einheit enthalt zwei Molekule, die nahezu zentrosymmetrisch zueinander angeordnet sind. In beiden nehmen die Urethangruppen die E-Konformation ein. Vergleichbare Bindungs-abstande und -winkel stimmen fur beide Molekule innerhalb weniger Standardabweichungen uberein. Durch je zwei Wasserstoffbrucken zwischen den Molekulen wird eine Blattstruktur parallel zur α-Achse ausgebildet. In Losung ist dagegen nach Aussage der NMR-Spektren die Z-Konformation an der Urethanbindung stabiler. Die gemeinsame Auswertung der Aquilibrierung E Z bei 209–216 K und der Linienformanalyse ergibt die thermodynamischen und kinetischen Parameter in Tab. 7. Die Struktur und die Barriere der E,Z-Isomerisierung werden diskutiert. tert-Butoxycarbonyl-L-α-phenylalanine. Crystal Structure and Conformational Changes in Solution The conformation of Boc-L-α-phenylalanine in solution (CDCl3 and CD2Cl2) was studied by 1H NMR spectroscopy. The crystal structure was solved by X-ray analysis. The two independent molecules in the asymmetric unit adopt both the E-conformation at the urethane bond. They are linked by a pseudo-centre of symmetry. They have very similar interatomic distances and angles. The crystal structure is formed by hydrogen bonds to give sheets in the direction of the a-axis. The Z-conformation is more stable in solution according to our NMR data. The equilibration E Z was studied at 209 – 216 K. The evaluation of these data together with total line shape data yields the thermodynamic and kinetic parameters in table 7. The structure and the barrier of the E,Z-isomerization are discussed.

26 citations

Journal ArticleDOI
TL;DR: In this article, the structure of a tri-p-tolylphosphine and azobenzene with bis(1,5-cyclooctadiene)nickel in hexane has been determined at room temperature from three-dimensional X-ray data collected by counter methods.

26 citations

Journal ArticleDOI
TL;DR: In this paper, the benzyl complex of a hexamethyl-substituted compound has been crystallographically characterised and it has been shown that the ligand is relatively distorted and this is borne out by crystallographic comparison of the model complexes cis-[W(CO)4{(S,S)-R2C([graphic omitted])2}](R = H or Me).
Abstract: Reaction of [RuCl2(NCMe)2(cod)] with bis(dihydrooxazoles) gave [RuCl2(cod){(S,S)-R12C-([graphic omitted])2}](cod = cycloocta-1,5-diene; R1= H, R2= CH2Ph or Pri; R1= Me, R2= Pri). The benzyl complex has been crystallographically characterised. The IR spectra of the complex of the hexamethyl-substituted compound suggest that the ligand is relatively distorted and this is borne out by crystallographic comparison of the model complexes cis-[W(CO)4{(S,S)-R2C([graphic omitted])2}](R = H or Me). Mechanistic studies of the epoxidation of styrene and stilbenes in the presence of isobutyraldehyde and molecular oxygen using the ruthenium complexes as catalysts in the presence and absence of 4-tert-butylcatechol as a radical trap revealed that the metals act as promoters for the production of PriCO3H and that this carries out the epoxidation, either directly or by formation of oxo-ruthenium species.

26 citations

Journal ArticleDOI
TL;DR: The 18‐membered Aib‐containing cyclohexapeptides, cyclo(‐Gly‐AIB‐Aib‐A ib‐Gy‐Phe(2Me)‐A Hib‐A‐ib‐gly‐a‐ib-Phe (24a, 24b, and 25), have efficiently been synthesized by solution‐phase techniques and the solid‐state conformations of the linear hexapeptide 1d, 16 and 27,
Abstract: The 18-membered Aib-containing cyclohexapeptides, cyclo(-Gly-Aib-Aib-Gly-Aib-Phe-) (22), cyclo(-Gly- Aib-Phe(2Me)-Gly-Aib-Aib-) (24a), cyclo(-Gly-Phe(2Me)-Aib-Gly-Aib-Aib-) (24b), and cyclo(-Gly- Phe(2Me)-Aib-Gly-Aib-Phe-) (25), have efficiently been synthesized by solution-phase techniques. The linear precursors 1a-1d were prepared by combining the 'azirine/oxazolone method' for incorporation of alpha,alpha-disubstituted alpha-amino acids (Aib, Phe(2Me)) into the peptide chains by classical peptide coupling methods for segment condensations. Deprotection of the amino and carboxy termini of 1a - 1d, followed by cyclization with DEPC as the coupling reagent, gave the above-mentioned cyclic hexapeptides 22, 24a, 24b, and 25 in good yields (26 - 57%) . The solid-state conformations of the linear hexapeptides 1d, 16 and 27, and of the cyclohexapeptides 22 and 25 have been established by X-ray crystallography.

26 citations

References
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Journal ArticleDOI
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

Journal ArticleDOI
S. C. Wang1
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

Journal ArticleDOI
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