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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: The first total synthesis of Hypomurocin A1 (HM A1) in solution phase is described and the synthesis presented has been successfully achieved by the ‘azirine/oxazolone method’ to introduce the two Aib‐Pro sequences included in this undecapeptaibol in one step with methyl 2,2‐dimethyl‐2H‐azirines‐3‐prolinate as the building block.
Abstract: The first total synthesis of Hypomurocin Al (HM Al) in solution phase is described. As members of the peptaibol family, hypomurocins are constituted by two groups of peptides: six undecapeptides (undecamers) in the HM A group and six octadecapeptides (18-mers) in the HM B group. The synthesis presented has been successfully achieved by the 'azirine/oxazolone method' to introduce the two Aib-Pro sequences included in this undecapeptaibol in one step with methyl 2.2-dimethyl-2H-azirine-3-prolinate as the building block. The coupling reactions of the Z-protected amino acids or peptide acids involved the use of N,N,N',N'-tetramethyluronium tetrafluoroborate (TBTU) and 1-hydroxybenzotriazole (HOBt), and led to the peptides in good-to-very-good yields. The peptides were purified by reverse-phase HPLC and characterized by NMR spectroscopy ( 1 H, 1 3 C, COSY, TOCSY, HSQC, HMBC, ROESY), ESI-MS, IR, elemental analysis, optical rotation, and X-ray crystallography. An NMR analysis of HM Al was also carried out in deuterated micelles to perform a structural comparison of the helix in solution and in membranes.

31 citations

Journal ArticleDOI
TL;DR: In this article, the thiocarbonyl ylides have been prepared in situ from the corresponding 2,5-dihydro-1,3,4thiadiazoles 12.
Abstract: The thiocarbonyl ylides 13 and 1,3-thiazol-5(4H)-thiones 1 undergo a smooth reaction to yield spirocyclic 1,3-dithioIanes 14-16 (Schemes 4-6) . The 1,3-dipolar cycloadditions occur in a regioselective manner, but the orientation of the thiobenzophenone-S-methylide (13b) differs from that of the cycloalkane thione-S-methylides 13a and 13c. Whereas the 1,3-cycloadduct with 13b is formed in accordance with frontier-orbital considerations, the inverse orientation in the reactions with 13a and 13c most likely is the result of steric hindrance in the transition state. The thiocarbonyl ylides have been prepared in situ from the corresponding 2,5-dihydro-1,3,4-thiadiazoles 12. The more stable aliphatic precursors 12a and 12c undergo decomposition at 50", the unstable 12b at -30".

31 citations

Journal ArticleDOI
TL;DR: In this paper, the reaction of AgPF6 in acetonitrile with an equimolar amount of the macrocycle 1,4,7-triazacyclononane (L) and addition of [NBu4]X (X = Cl, Br, I or CN) affords colourless to yellow precipitates of [AgL(X)].
Abstract: Reaction of AgPF6 in acetonitrile with an equimolar amount of the macrocycle 1,4,7-triazacyclononane (L) and addition of [NBu4]X (X = Cl, Br, I or CN) affords colourless to yellow precipitates of [AgL(X)]. The complexes [AgL′(X)](X = SCN or CN)(L′= 1,4,7-trimethyl-1,4,7-triazacyclononane) have been prepared similarly. When the ligand to AgPF6 ratio was 2:1 in ethanolic solution, colourless crystals of [AgL2]PF6 and [AgL′2]PF6 were obtained, respectively. A binuclear species [LAg(µ-CN)AgL]PF6 has been obtained from a solution of AgPF6 and L (1:1) in pyridine upon addition of NaCN (0.5 equivalent). Mercury(II) chloride reacts in water with L (1:2) and addition of NaPF6 to yield [HgL2][PF6]2; with L′ the complex [HgL′(Cl)]PF6 was obtained. Crystals of [AgL′2]PF6 are tetragonal, space group P42/m(no. 84), with a= 10.134(1), c= 12.771(2)A, and Z= 2. Crystals of [AgL′(SCN)] are orthorhombic, space group Pcmn(no. 62), with a= 9.497(5), b= 11.837(8), c= 26.00(1)A and Z= 8.

31 citations

Journal ArticleDOI
TL;DR: The crystal structure of the title compound has been determined from x-ray diffractometer data by the heavy-atom method and refined anisotropicically by least-squares calculations as mentioned in this paper.
Abstract: The crystal structure of the title compound has been determined from x-ray diffractometer data by the heavy-atom method and refined anisotropically by least-squares calculations. Crystals are monoclinic, space groupP 21/c, with unit cell dimensions:a=7.321(1),b=14.622(2),c=14.827(2) A,β=92.95(2)∘, Z=4. The finalR index is 4.6%. The copper coordination is trigonal, involving the sulphur atoms of twoN-ethyl-1,3-imidazolidine-2-thione molecules and one chlorine atom. The structure is held together by two intramolecular N-H⋯Cl hydrogen bonds and by normal van der Waals interactions.

31 citations

Journal ArticleDOI
TL;DR: In this paper, the triclinic space group P 1 (C 1, 1, No. 2) is represented by a monoanion of pyridoxal thiosemicarbazone.

31 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