Structure of 4-Cyclohexyl-3,4-dihydro-2-hydroxy-2-methyl-2\u3ci\u3eH\u3c/i\u3e,5\u3ci\u3eH\u3c/i\u3e-pyrano[ 3,2-\u3ci\u3ec\u3c/i\u3e][1]benzopyran-5-one

C19H22O4, monoclinic, P21/c, a = 2·515 (2), b = 17·472 (3), c = 7·489 (1) Å, β = 00·40 (1)°. The structure was solved by direct methods. The cyclohexyl group is pseudo-equatorial and trans to the axial hydroxyl; the dihydropyran ring is a half-chair distorted towards the d,e-diplanar conformation. Hydrogen bonding between the coumarin carbonyl and the hydroxyl groups at an O···O distance of 2·834 (4) Å is found. In CDC13 solution, this compound exists predominantly in the open-chain keto form

A Structure Containing Diastereomers, (2\u3ci\u3eS\u3c/i\u3e,4\u3ci\u3eR\u3c/i\u3e)-\u3ci\u3etrans\u3c/i\u3e- and (2\u3ci\u3eR\u3c/i\u3e,4\u3ci\u3eR\u3c/i\u3e)-\u3ci\u3ecis\u3c/i\u3e-2-hydroxy-2,4-dimethyl-3,4-dihydro-2\u3ci\u3eH\u3c/i\u3e,5\u3ci\u3eH\u3c/i\u3e-pyrano[3,2-\u3ci\u3ec\u3c/i\u3e][1]benzopyran-5-one, C\u3csub\u3e14\u3c/sub\u3eH\u3csub\u3e14\u3c/sub\u3eO\u3csub\u3e4\u3c/sub\u3e

Mr = 246·3, monoclinic, P21, a = 7·804 (3), b = 18·248 (8), c = 8·752 (5) Å, β = 99·59°, V = 1233 Å3, Z = 4 (2 molecules/asymmetric unit), Dx = 1·33 g cm-3, λ(Mo Kα) = 0·71067 Å, μ = 0·91 cm,-1, F(000) = 520, T = 293 K. Final R = 0·066 for 1123 observed independent intensities. The structure consists of diastereomers approximately inversionrelated through a pseudocenter of symmetry at x = 0·241 (4), z = 0·281 (3) except the 4-methyl groups. The dihydropyran rings are half chairs distorted towards the eƒ-diplanar conformation. Like molecules are hydrogen-bonded between hydroxyl and carbonyl groups along a, O···O distances being 2·781 (7) (trans) and 2· 780 (7) Å (cis)

Electron diffraction studies of supersonic jets. V: Low temperature crystalline forms of SF\u3csub\u3e6\u3c/sub\u3e, SeF\u3csub\u3e6\u3c/sub\u3e, TeF\u3csub\u3e6\u3c/sub\u3e

Condensation of SF6, SeF6, and TeF6 in nozzle flows with inert carrier gases produces microcrystals of these materials. All form the higher temperature body‐centered cubic structure at higher partial pressures of hexafluoride. At lower partial pressures and colder nucleation conditions a lower symmetry form of each has been produced. Electron diffraction powder patterns are consistent with the space group Pnma to which metal hexafluorides of UF6 type belong. Low temperature phases of the present materials differ from those of the metal compounds, however, in being less dense than the cubic forms. Aspects of the gas dynamics affording a control over nucleated species are briefly discussed

Electron diffraction studies of supersonic jets. VI. Microdrops of benzene

Large clusters of benzene were generated in supersonic flow through a Laval nozzle with carrier gases He, Ne, or Ar. Benzene concentration and carrier pressures were varied over wide ranges. Diffraction patterns recorded from s=0.8 to 12 Å−1 revealed strong intermolecular interference features indicative of supercooled bulk liquid at 100–200 K. Computer simulations of nucleation and cluster growth were carried out and agreed with the following observations. An initial benzene partial pressure of ∼0.1 bar expanded through a nozzle of our design requires a carrier pressure of 2–3 bar to give reasonably complete condensation. Cluster diameter and fraction condensed decrease if (1) benzene mole fraction is reduced at constant carrier pressure, (2) carrier pressure is reduced at constant benzene partial pressure, and (3) carrier molecular weight is decreased. The simulations identify the factors accounting for the trends. Cluster intensities are compared with those calculated for small clusters proposed by Williams, small crystal fragments, and bulk fluid according to the statistical mechanical algorithm RISM. None of the models reproduce observed results within experimental error but comparisons provide information about size, temperature, and structure. Intrinsic deficiencies of RISM are indicated by the present experiments.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70115/2/JCPSA6-80-4-1451-1.pd

Dihydropyran Ring Conformations. I. Structures of 2-Methoxy- and 2-Hydroxy-2, 4-dimethyl-3, 4-dihydro-2\u3ci\u3eH\u3c/i\u3e, 5\u3ci\u3eH\u3c/i\u3e-Pyrano[3,2-\u3ci\u3ec\u3c/i\u3e][1]benzopyran-5-ones

Conformations of embedded 3,4-dihydro-2H-pyrans (DHP\u27s) are studied in a closely related series of nine molecular structures, including the cis and trans isomers of both racemic and resolved homologs of 2,4-dimethyl-3,4-dihydro-2H,5H-pyrano[3,2-c][l]-benzopyran-5-one. DHP rings in these structures display a range of conformations near the half-chair form but distorted variously toward each of the two inequivalent d,e- and e,f-diplanar forms. Factor analysis reveals the coordination of torsional motions associated with a principal ring-bending mode based on the various ring conformations. Two methyl ketals and an hemiketal structure are reported. (I): (2S,4S)-cis-2-methoxy, C15H16O4, Mr = 260·30, trigonal, P3221, a = 9·579 (5), c = 24·938 (15) Å (hexagonal axes), V = 1981·7 (33) Å, Z = 6, Dx = 1·309 g cm-3, λ(Mo Kᾱ)= 0·71073 Å, μ = 0·884 cm- 1, F(000) = 828, T = 295 K, R = 0·040 for 1470 observations. (II): (2R,4S)-trans-2-methoxy, C15H16O4, Mr = 260·30, monoclinic, P21, a = 9·254 (4), b = 11·970 (5), c = 12·736 (5) Å, β = 105·64 (4)°, V = 1358·5 (22) Å3, Z = 4 (two molecules per asymmetric unit), Dx = 1·274 g cm-3, λ(Mo Kᾱ) = 0·71073 Å, μ = 0·860 cm-1, F(000) = 552, T = 295 K, R = 0·043 for 2923 observations. (III): (2S,4S)-cis-2-hydroxy, C14H14O4, Mr = 246·27, orthorhombic, P212121, a = 6·816 (3), b = 12·826 (7), c = 13·949 (6) Å, V = 1219·4 (17) Å3 , Z = 4, Dx = 1·340 g cm-3, λ(Mo Kᾱ) = 0·71073 Å, μ= 0·919 cm-1, F(000) = 520, T = 293 K, R = 0·046 for 1291 observations

Electron diffraction studies of supersonic jets. VII. Liquid and plastic crystalline carbon tetrachloride

Carbon tetrachloride at 3–11 mol % in neon carrier produces clusters of CCl4 molecules in flow through a Laval nozzle. Electron diffraction patterns of the clusters formed at a total pressure below 2.5 bar are intermediate between x‐ray diffraction patterns of bulk liquid CCl4 and neutron patterns of the amorphous material formed by condensation at 10 K. Strong, sharp interference features at low angle imply appreciable long range order, perhaps beyond 50 Å, in the clusters, whose temperatures are about 210 K. When carrier partial pressure is increased beyond 2.6 bar, clusters begin to exhibit crystallinity. Crystallites belong to the rhombohedral plastic‐crystalline phase Ib, a=14.27 Å and α=90.0°.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70299/2/JCPSA6-80-4-1458-1.pd

Electron diffraction studies of supersonic jets. V. Low temperature crystalline forms of SF6, SeF6, and TeF6

Condensation of SF6, SeF6, and TeF6 in nozzle flows with inert carrier gases produces microcrystals of these materials. All form the higher temperature body‐centered cubic structure at higher partial pressures of hexafluoride. At lower partial pressures and colder nucleation conditions a lower symmetry form of each has been produced. Electron diffraction powder patterns are consistent with the space group Pnma to which metal hexafluorides of UF6 type belong. Low temperature phases of the present materials differ from those of the metal compounds, however, in being less dense than the cubic forms. Aspects of the gas dynamics affording a control over nucleated species are briefly discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70232/2/JCPSA6-79-6-2683-1.pd

Structure of (Phenyl)bis( 4-hydroxybenzo-2\u3ci\u3eH\u3c/i\u3e-pyran-2-one-3-yl)methane*

A derivative of dicoumarol, C25H16O6, Mr, = 412·41, orthorhombic, P212121, a = 7·959(2), b = 12·865 (3), c = 18·606 (6) Å, V = 1905·3 (22) Å3, Z = 4, Dx = 1.44 g cm-3, λ(Mo Kα) = 0·71073 Å , μ = 0·965 cm-1, F(000) = 856, T = 293 K, final R = 0·042 for 2031 observations. The 4-hydroxycoumarins are intramolecularly hydrogen bonded between hydroxyls and carbonyls, O···O separations are 2·624 (3) and 2·718 (3)Å, a scheme which imparts a dis-symmetry to the otherwise achiral molecule and underlies packing in a polar space group

α-L-Aspartylglycine Monohydrate

C6H10N2O5, H2O, orthorhombic, P212121, a = 4·844 (5), b = 9·916 (3), c = 18·070(4) Å, V = 868·05 Å3, Z = 4, Dc = 1·59, Dm (flotation in chloroform/iodoform) = l·60 (1) Mg m-3; R1 = 0·040, R2 = 0·033 for 1088 observations. The dipeptide crystallizes as a zwitterion with the main-chain carboxyl ionized and the side-chain amino group protonated. The overall dipeptide conformation is highly extended and the molecule is extensively hydrogen bonded

α-L-Glutamylglycine

C7H12N 2O5, orthorhombic, P212121, a = 5·525(5), b = 12·565(4), c = 13·211(6) Å, Z = 4, Dc = l·48, Dm (flotation in chloroform/ methylene chloride) = 1·48(1) Mg m-3, R1 = 0·039, R2 = 0·040 for 1172 observations. The dipeptide crystallizes as a zwitterion with the main-chain carboxyl ionized and the amino terminus protonated. The conformation of the peptide group is trans; the glutamyl side chain is extended, but the carboxy terminus is held by hydrogen bonding in a non-extended conformation with a torsional angle ΦGly = -74.1°