Double Bond Distance Research Articles

C−C Plasticity in Boron Chemistry: Modulation of the Cc···CcDistance in Mixed Pyrrolyl/Dicarbollide Complexes

The single, double, and triple bond distances are well defined in conventional organic compounds. Cluster boron chemistry, in particular the o-carboranes, provides the possibility to modulate the C−C distance in an almost continuous way within the same family of compounds. As an example, mixed pyrrolyl/dicarbollide sandwich cobalt complexes derived from closo-[3-Co(η5-NC4H4)-1,2-C2B9H11] (1) display a continuous range of Cc···Cc distances between 1.640(7) for the parent compound and 1.919(6) for closo-[3-Co(η5-NC4H4)-1,2-(SCH3)2-1,2-C2B9H9] (5). Here, Cc represents the cluster carbon atom. The Cc···Cc modulation was achieved merely by modifying the substituents on the carbon of the cluster compound. The complexes studied were synthesized by reaction of the appropriate closo cluster, e.g., 1,2-(SCH3)2-1,2-C2B10H10 with a suspension of K[NC4H4] and anhydrous CoCl2. The new compounds are closo-[3-Co(η5-NC4H4)-1,2-(SCH3)2-1,2-C2B9H9] (5), closo-[3-Co(η5-NC4H4)-1,2-(SC6H5)2-1,2-C2B9H9] (6), and closo-[3-Co(η5-...

Preparation, Properties, and Crystal Structure of the Rare Earth Ruthenium Carbides R3Ru2C5 (R=Y, Gd–Er)

The title compounds were prepared from the elemental components by arc-melting and subsequent annealing. While Gd3Ru2C5 and Tb3Ru2C5 are present in the as-cast samples, the others are formed during the annealing process. The magnetic properties of the four compounds R3Ru2C5 (R=Gd–Ho) were investigated with a SQUID magnetometer. They show very soft ferromagnetism. The highest Curie temperature was observed for the gadolinium compound with TC=84(1) K. Electrical conductivity measurements for Tb3Ru2C5 indicate metallic behavior. The crystal structure of these isotypic compounds has been determined from single-crystal X-ray data of Gd3Ru2C5: P63/m, Z=4, a=1147.0(1) pm, c=504.7(1) pm, R=0.052 for 500 F values and 43 variable parameters. Structure refinements of another crystal of the gadolinium compound with a slightly different composition and of the terbium compound gave similar results. In all three structure refinements a ruthenium position on the hexagonal axis had to be refined with split occupancy. The adjacent lanthanoid positions reflect this disorder. The refinement of the occupancy parameters of the three data sets resulted in the compositions Gd3Ru1.851(1)C4.86(2), Gd3Ru1.862(2)C4.97(3), and Tb3Ru1.776(4)C4.95(1). The structure contains C2 pairs and isolated carbon atoms. The C–C distances in the three refinements vary between 133(1) and 142(3) pm, close to the typical double-bond distance of 134 pm. The structure contains trigonal polyanionic clusters of the composition Ru3C10, and in addition there are ruthenium atoms which have no carbon neighbors. Chemical bonding in these compounds is briefly discussed on the basis of the 18- and 8-electron rules.

A curiously short carbon–carbon double bond?

The discrepancy between the ‘curiously short’ carbon–carbon double bond distance in 3-ethynylcyclopropene, as measured experimentally by X-ray analysis [1.255(2) A], compared with the value derived from high level ab initio calculations (ca. 1.28 A), is largely due to neglect of corrections for molecular motion in the crystal.

INFRARED SPECTRAL, VALENCE BOND SUM ANALYSIS AND SINGLE CRYSTAL X-RAY STRUCTURE DETERMINATION OF 2,2′-BIS (PHTHALIMIDOETHYL) AMMONIUM 2,2′-BIS (PHTHALIMIDO-ETHYL)DITHIOCARBAMATE

Synthesis and X-ray crystal structure of 2,2′-bis(phthalimidoethyl) ammonium 2,2′-bis(phthalimido ethyl)dithiocarbamate ((padtc)−(paH)+) is reported. Crystal parameters are : space group : Pl, a = 10.252(2), b = 13.692(3), C = 15.072(4)Å, α = 103. 680 (1)°; β = 99.710(1)°; v = 107.300(1)°, Z = 2, R = 0.048 for 6288 reflections. The two, C-S distances significantly differ from each other and are in between the single and double bond distances [C(41)-S(1) = 1.701(3)Å and C(41)-S(2) = 1.682(4)Å]. Asymmetry in the C-S distances shows localization of high electron density between the C and S bonds. Contribution of thioureide form to the dithiocarbamate is explicitly supported by the thioureide distance observed. The valence bond sum (VBS) was found to be 1.4 for the thioureide C-N bond indicating a partial double bonded nature.

Insecticidal and repellent properties of nine volatile constituents of essential oils against the American cockroach,Periplaneta americana(L.)

The toxic and repellent properties of nine major constituents of essential oils, comprising benzene derivatives and terpenes, were evaluated against Periplaneta americana (L.). Contact and fumigant toxicities to adult females and repellency to nymphs were determined. The decreasing order of knockdown activity via contact was methyl-eugenol>isosafrole=eugenol>safrole. The killing effect via contact was in the order eugenol=methyl-eugenol=isosafrole>safrole. Fumigant toxicity was only observed for safrole and isosafrole, with safrole being the more potent. Isoeugenol and the tested terpenes had neither contact nor fumigant toxic effect. The decreasing order of repellency to nymphs was safrole>isosafrole>methyl-eugenol=α-pinene> eugenol>isoeugenol. The benzene derivatives were generally more toxic and repellent to P. americana than the terpenes. The distance of the side chain double bond from the aromatic ring and the substitution of a methoxy group to these compounds appeared to be important determinants of their toxicity and repellency. © 1998 Society of Chemical Industry

Intermolecular N-H...O Hydrogen Bonding Assisted by Resonance. II. Self Assembly of Hydrogen-Bonded Secondary Enaminones in Supramolecular Catemers

The crystal structures of 15 compounds containing the 2-en-3-amino-1-one heterodienic system and forming intermolecular N—H...O hydrogen bonds assisted by resonance (RAHB) are reported: (1) 3-phenylamino-2-cyclohexen-1-one; (2) 3-(4-methoxyphenylamino)-2-cyclohexen-1-one; (3) 3-(4-chlorophenylamino)-2-cyclohexen-1-one; (4) 3-(4-methoxyphenylamino)-2-methyl-2-cyclohexen-1-one; (5) 3-(4-methoxyphenylamino)-5-methyl-2-cyclohexen-1-one; (6) 3-isopropylamino-5,5-dimethyl-2-cyclohexen-1-one; (7) 3-phenylamino-5,5-dimethyl-2-cyclohexen-1-one; (8) 3-(3-methoxyphenylamino)-5,5-dimethyl-2-cyclohexen-1-one; (9) N,N-3-aza-pentane-1,5-bis[1-(3-oxo-5,5-dimethyl-1-cyclohexenyl)]; (10) 3-phenylamino-6,6-dimethyl-2-cyclohexen-1-one; (11) 3-(2-methoxyphenylamino)-6,6-dimethyl-2-cyclohexen-1-one; (12) 3-(3-chlorophenylamino)-6,6-dimethyl-2-cyclohexen-1-one; (13) 3-(4-chlorophenylamino)-6,6-dimethyl-2-cyclohexen-1-one; (14) 1-(4-chlorophenyl)-4-(4-chlorophenylamino)-6-methyl-2-pyridone; (15) 3-(4-chlorophenylamino)-5-phenyl-2-cyclopenten-1,4-dione. All compounds form intermolecular N—H...O=C hydrogen bonds assisted by resonance connecting the heteroconjugated enaminonic groups in infinite chains. Chain morphologies are analyzed to find out crystal engineering rules able to predict and interpret the crystal packing. Simple secondary enaminones [i.e. (1)–(13) together with a number of structures retrieved from the Cambridge Structural Database] are found to form hydrogen bonds having π-delocalizations, as characterized by a C=O bond-length average of 1.239 ± 0.004 Å, and hydrogen-bond strengths, represented by the N...O average distance of 2.86 ± 0.05 Å, very similar to those previously found for amides. Enaminones, however, can be easily substituted by chemical groups able to influence both π-conjugations and N...O hydrogen-bond distances. Some substituted enaminones, retrieved from the literature, display, in fact, N...O hydrogen-bond distances as short as 2.627 Å and large π-delocalizations with C=O double-bond distances as long as 1.285 Å. These effects appear to be associated with (a) the presence of further π-conjugated systems involving the C=O and NH groups of the enaminone moiety or (b) the transformation of the enaminone carbonyl group in an amidic function.

R structure of difluoromethanimine, CF2=NH, from microwave spectra of isotopic species

The microwave spectra of the 13C-, 15N-, and 15N, D-substituted species of difluoromethanimine, CF2=NH, have been measured and assigned, and the rotational, centrifugal distortion, and quadrupole coupling constants have been determined. The ground state rotational constants of four isotopic molecules were sufficient to determine six independent parameters of the r0 structure. The difference between the C–F distances was indeterminate. The structure and the quartic centrifugal distortion constants are compared with the results from ab initio calculations with and without electron correlation. The r0 C=N double bond distance is 1.240(5) Å, halfway between the distance determined from single crystal x-ray diffraction and the ab initio distance (MP2/6-31G*). The molecular electric dipole moment forms an angle of about 8° with the direction of the N–H bond.

3-Hydroxy-6-methyl-2-pyridylmethyl Isopropylphosphonate Sesquihydrate

The title compound, C10H16NO4P.{{3}\over{2}}H2O, contains a zwitterion with a negative charge on the unsubstituted phosphonate O atoms and a positive charge on the N atom of the pyridine ring. The distances between the P and the two unsubstituted phosphonate O atoms [1.503 (2) and 1.483 (2) Å] lie between P—O single- and double-bond distances. The bond angle at the P atom between these O atoms [116.4 (1)°] is larger than the other O—P—O angles. Hydrogen bonds link the unsubstituted phosphonate O atoms through water molecules to the pyridyl N atoms of neighbouring molecules. The presence of the H atom on the N atom of the pyridine ring is associated with a large C—N—C bond angle [124.6 (2)°].

(meso-4,8-Diaza-3,9-dimethyl-6,6-trimethyleneundecane-2,10-dione dioximato-N,N',N'',N''')oxotechnetium(V), [TcO(C14H25N4O2)

The title compound was synthesized and analyzed by X-ray diffraction, in addition to IR, NMR, visible-UV and mass spectral studies. The coordination geometry about the TcV atom is five-coordinate square pyramidal, with four N atoms in equatorial positions and an O atom in the axial position. The Tc=O double-bond distance is 1.664 (5) Å. The two amide Tc—N bond lengths are shorter than the two oxime Tc—N bond lengths. The central six-membered ring has a boat conformation with the Tc-bonded O atom `hanging' above. The intramolecular hydrogen-bond length between the two O atoms of the oxime groups is 2.432 (9) Å. The cyclobutyl C atoms are, more or less, in a square plane.

3-Methyl-5-(2,6,6-trimethyl-1-cyclohexenyl)-2(5H)-furanone

The title compound, C 14 H 20 O 2 , can be regarded as a synthetic derivative resembling tobacco isoprenoids and is structurally related to primary precursor α- and β-ionones. The double bond distance C(3)=C(4) in the furanone ring is 1.329 (8) A and the double bond distance C(1')=C(2') in the cyclohexene ring is 1.331 (6) A. The bond between the rings, C(5)-C(2'), is 1.513 (7) A and the bond torsion angle O(1)-C(5)-C(2')-C(1'), which describes the relative twist of the rings, is ±51.3 (7)°

Crystal structures and physical properties of the ternary carbides ScT1–xC2(T = Fe, CO, Ni)

The crystal structures of the title compounds, originally determined for ScCoC2, have been refined from single-crystal X-ray data to residuals of R= 0.037 (154 structure factors), R= 0. 031 (433 F values) and R= 0.049 (161 F values) each with 12 variable parameters, for the Fe, Co and Ni compounds, respectively. The C–C distances in the carbon pairs are 138.1(9), 139.7(3) and 135(2) pm. They are thus close to the double-bond distance of 134 pm in alkenes. The refinement of the occupancy parameters showed that the iron, cobalt and nickel positions are occupied to only 88, 88 and 83% in the crystals used for the structure refinements. In general, interatomic distances in the three compounds are very similar. This is rationalized by the counterbalancing effects of the electron counts and electronegativity of the transition-metal component. The structure consists of two-dimensional infinite layers of composition ScC2 which have a CaC2-like structure. These layers are separated by sheets of the transition elements, possibly with two-dimensional metallic conductivity. Compact polycrystalline samples of the three compounds are very weakly paramagnetic and show semiconducting behaviour.

Synthesis and properties of 1,2-difluorodinitroethylene

1,2-Difluorodinitroethylene was synthesized by flash vacuum pyrolysis of 1,2-difluorotetranitroethane. X-ray crystallography showed that one of the two nitro groups is out of the plane of the rest of molecule and that the C-C double-bond distance in unusually short at 1.284 {angstrom}. 1, 2-Difluorotetranitroethane reacted with alcohols to give alkyl fluoronitroacetates and with anthracene and cyclopentadiene to give Diels-Alder adducts.

Structural and spectroscopic studies on the trinuclear clusters Re 3Cl 9(PMe 3) 3 and Re 3Cl 9(η 1-dppm) 3 (dppm  Ph 2PCH 2PPh 2)

The reactions of the trinuclear cluster Re 3Cl 9 with various phosphine ligands in ethanol have been used to prepare the new complexes Re 3Cl 9(PMe 2Ph) 3, Re 3Cl 9(η 1-dppm) 3, Re 3Cl 9(dmpm) 1.5, Re 3Cl 9(η 1-arphos) 3 and Re 3Cl 9(arphos) 1.5, where dppm = Ph 2PCH 2PPh 2, dmpm = Me 2PCH 2PMe 2 and arphos = Ph 2PCH 2CH 2AsPh 2. The 1H and 31P{ 1H} NMR spectra of several of these complexes and of Re 3Cl 9(PMe 3) 3 and Re 3Cl 9(PMePh 2) 3 are described, including studies of the dissociative ligand exchange in Re 3Cl 9(η 1-dPPM) 3. The structures of Re 3Cl 9(PMe 3) 3 and Re 3Cl 9(η 1-dppm) 3 have been established by X-ray crystallography. Crystallographic data for Re 3Cl 9(PMe 3) 3: hexagonal space group P6 3/ m, a = b = 11.614(1), c = 11.209(2) Å, α = β = 90, γ = 120°, V = 1309.4(5) Å 3 and Z = 2. The structure was refined to R = 0.038 ( R w = 0.064) for 524 data with I > 3.0σ( I). Crystallographic data for Re 3Cl 9(η 1-dppm) 3 · C 7H 8: triclinic space group P 1 , a = 11.883(3), b = 18.233(4), c = 20.102(5) Å, α = 103.32(1), β = 99.18(1), γ = 95.88(1)°, V = 4139(3) Å 3 and Z = 2. The structure was refined to R = 0.039 ( R w = 0.050) for 7190 data with I > 3.0σ( I). Both structures resemble that of the previously reported Re 3Cl 9(PEt 2Ph) 3, with Re  Re double bond distances spanning the narrow range of 2.471(1)–2.488(1) Å. The Re  P bond lengths are 2.634(4) Å for the Me 3P complex, and between 2.693(3) and 2.727(3) Å for Re 3Cl 9(η 1-dppm) 3; the presence of three monodentate dppm ligands is confirmed in the latter structure.

Structural aspects and conformational analysis of 1,1-dichloro-2,2-bis[p-(N,N-dimethylamino)phenyl]ethane

The crystal and molecular structure of 1,1-dichloro-2,2-bis[p-(N,N-dimethylamino)phenyl]ethane, a structural analogue of the degradation product of the insecticide DDT, has been determined from three dimensional diffractometric data using Mo-Kα radiation. The compound crystallises in the monoclinic space group P21/c with unit cell dimensions a= 8.091 (4), b= 6.145(2), c= 34.384(10)Å, β= 91.50(3)°. The structure was solved by direct methods and refined by full-matrix least-squares analysis to a final R value of 0.075 for 1 522 observed reflections. The ethylenic double bond distance is 1.328(11)Å. The twist about the ethylenic bond is 7.1 (5)°. The C–Cl distances are 1.731 (9) and 1.743(8)Å. The conformational parameters of this compound are compared with those of other analogous insecticides studied by X-ray diffractometry methods. The conformational angles are low in comparison with the other active insecticides.

Ternary carbides of the rare earth and iron group metals with CeCoC 2- and CeNiC 2-type structure

32 carbides RTC 2 (R ≡ rare earth metal, T ≡ Fe, Co, Ni), 18 for the first time, were prepared by arc melting of the elemental components and subsequent annealing in evacuated silica tubes. Most of them crystallize in the orthorhombic CeNiC 2-type structure. The carbides LnCoC 2 (Ln ≡ La, Ce, Pr, Nd) have the related monoclinic CeCoC 2-type structure. SmCoC 2 is of CeCoC 2 type at low temperature and of CeNiC 2 type at high temperature. The crystal structures of DyCoC 2 and DyNiC 2 were refined from singlecrystal X-ray data to residuals of R = 0.012 (581 structure factors) and R = 0.023 (971 structure factors) for 17 variable parameters. The carbon atoms in these compounds form pairs. The C-C distances of 1.37 Å come close to the double bond distances of 1.34 Å in alkenes. The hydrolysis of DyCoC 2 in diluted hydrochloric acid, however, yields only little ethene, mainly ethane and some propane and methane. The cell volumes indicate that cerium and ytterbium are essentially trivalent in these compounds, whereas the corresponding europium compounds cannot be prepared under similar conditions.

Vibrational frequencies for silaacetylene and its silylidene and vinylidene isomers

The molecular structures, vibrational frequencies, and relative energies of silaacetylene and its vinylidene and silyidene isomers have been investigated via nonempirical molecular electronic theoretical methods. Basis sets of double Zeta (DZ) and double-Zeta plus d function quality have been used for this purpose in conjunction with self-consistent-field (SCF) and configuration interaction (CI) wave functions. The largest CI included in a completely variational manner 8 001 configurations, and analytic CI gradient methods were used to determine the structure and harmonic vibrational frequencies of silaacetylene itself. The absolute minimum on the potential energy hypersurface is the silyidene, :Si==CH/sub 2/, which lies approx.50 kcal below the linear silaacetylene. The vinylidene isomer H/sub 2/Si==C: is either an extremely shallow minimum, or, more likely, not a genuine relative minimum at all. Silaacetylene is predicted to have a trans bent equilibrium geometry, with HSiC angle 128.8/sup 0/, HCSi angle 150.1/sup 0/, and a silicon-carbon bond distance of 1.635 A about 0.08 angstrom, about 0.08 angstrom shorter than a ''standard'' Si==C double-bond distance. The silicon-carbon stretching vibrational frequency is predicted to be approx. 1100 cm/sup -1/, or 10% higher than found experimentally for dimethylsilaethylene. It is concluded that the silicon-carbon linkage in trans-bent silaacetylene is intermediate betweenmore » a double and triple bond. There appears to be no cis isomer of silaacetylene.« less

Polarized ethylenes: structures of (1,3-dimethyl-2-imidazolidinylidene)malononitrile and (1,3-dimethyl-2-perhydropyrimidinylidene)malononitrile

Crystal structures of the title compounds, (I) and (II), have been determined by three-dimensional diffraction methods. Crystals of CsHIoN 4 (I) are monoclinic, space group P21/a with Z = 4, Mr= 162, a = 7.965 (1), b = 16.232 (2), c = 7.343 (1) A, fl = 113.54 (1) °, V = 890.7 A 3, D,n = 1.218, D x = 1.208 gcm -3, g(Cu Ka, 2 = 1.5418/~) = 6.47 em -1, F(000) = 344. The crystals of C9H12N4 (II) are orthorhombic, space group P21en, with Z = 4, Mr = 176, a = 7.983 (3), b = 8.075 (2), c = 14.652 (3) ./k, V = 44.43/~3, Dm= 1.219, D x = 1.237 g cm -3, #(Mo Ka, ). = 0.7107 ,/k) = 0.868 cm -1, F(000) = 376. Both structures were solved by direct methods and refined to R = 5.8% for (I) and 5.3 % for (II). The C-C double-bond distances are 1.407 (3) in (I) and 1.429 (6)/~ in (II), appreciably longer than normal. The steric and push-pull effects result in rotation about the C=C bond, the rotation angles being 20.2 (3) in (I) and 31.5 (6) o in (II).

Oxepine, VI. Dehydratisierungsprodukte von 2,5‐Cyclohexadien‐1,4‐diolen; die Kristallstruktur von 3,7‐Di‐tert‐butyl‐5‐phenyl‐2‐(p‐tolyl)‐oxepin

Oxepins, VI1). Dehydration Products of 2,5‐Cyclohexadiene‐1,4‐diols; the Crystal Structure of 3,7‐Di‐tert‐butyl‐5‐phenyl‐2‐(p‐tolyl)oxepinX‐ray analysis of the product of dehydration of 2,6‐di‐tert‐butyl‐4‐phenyl‐1‐(p‐tolyl)‐2,5‐cyclohexadiene‐1,4‐diol (4a) proves the structure as 3,7‐di‐tert‐butyl‐5‐phenyl‐2‐(p‐tolyl)oxepin (1a), in agreement with former IR, 1H NMR and 13C NMR spectroscopic results. The double and single bond distances show a certain degree of equalization.

Carbon–carbon double bonds can be catalytically hydrogenated on hydrated alumina

We use inelastic electron tunneling spectroscopy to study catalytically induced hydrogenation of several unsaturated dicarboxylates chemisorbed on undried, hydrated alumina. Using isotope substitution we estabilish that hydroxyl groups on the alumina are the source of hydrogen. Fumarate and maleate hydrogenate completely at room temperature forming a succinate species. Gutaconate, hydromuconate, and muconate hydrogenate in a way that is exponentially temperature dependent, only slightly pressure dependent, and time independent in the range of a few minutes to an hour. We have investigated the temperature dependence over the range 25–400 °C, and we believe it is related to the thermal dehydration mechanism in alumina. From the variation in temperature dependence among the surface species we develop an index of the relative ease of hydrogention that correlates well with double bond distance from the surface and with bond resonance stabilization. Species whose double bonds are constrained to be closer to the surface hydrogenate more easily, and conjugated double bonds stabilize a species against hydrogenation. The alumina surface can be regenerated with water vapor and used for further hydrogenation.

Separation of Isomeric Insect Pheromonal Compounds Using Reversed-Phase HPLC with AgNO3 in the Mobile Phase

Using reversed-phase HPLC and a polar mobile phase containing silver nitrate, rapid separations of geometrical isomers of mono-, di-, and polyunsaturated open chain olefins were achieved. These olefins represented various chain lengths of acetates, alcohols, aldehydes, and hydrocarbons. Separations of adjacent positional isomers of dodecenyl acetate were also attempted; the degree of success was dependent on double bond distance from the acetate group. Advantages of the mobile Ag+/reversed-phase technique over commonly used methods for geometrical isomer separation are discussed.