Structural effects on valence tautomerism : VII. An NMR and molecular mechanics study of the steric effects of t-butyl substituents on the cycloheptatriene-norcaradiene equilibrium of 7-cyano-7-m

7-Cyano-7-methylcycloheptatrienes containing one t-butyl group on the 1-position ($\text{2}$) or two t-butyl groups on the 1- and 3-, 1- and 4-, or 1- and 5-positions ($\text{3}$, $\text{4}$, or $\text{5}$, respectively) were synthesized and their cyclo- heptatriene (CHT)-norcaradiene (NCD) equilibria measured by variable-temperature ¹H NMR for CS₂-CD₂Cl₂ solutions. The ¹H NMR chemical shifts of the 7-methyl group indicate that these compounds are composed of essentially one CHT and one NCD tautomer with an endo geometry of the methyl group. The introduction of a t-butyl group at the 1-position of 7-cyano-7-methylcycloheptatriene ($\text{1}$) markedly shifts the equilibrium to the NCD side and the addition of the second t-butyl group further favors the NCD form, with the NCD populations for $\text{2}$, $\text{3}$, $\text{4}$, and $\text{5}$ at 25 °C 70.9, 96.5, 92.3, and 99.3%, respectively. An application of molecular mechanics (MMPI) calculations to various t-butylated CHT-NCD systems suggests that the t-butyl groups sterically destabilize the CHT form more than the NCD form, bringing about increased NCD populations.     

Organothallium compounds XII NMR spectra of some polyfluorophenylthallium (III) compounds

The PMR and ¹⁹F NMR spectra of the complexes R₂TlBr (R = C₆F₅, $\text{o}$-HC₆F₄, $\text{m}$-HC₆F₄, 3,5-H₂C₆F₃, or 3,6-H₂C₆F₃ and R₃Tl(diox) (R = C₆F₅, $\text{m}$-HC₆F₄, or 3,5-H₂C₆F₃; diox = 1,4-dioxan) have been recorded. Proton and fluorine chemical shifts, thallium-proton, thallium-fluorine, fluorine-fluorine, and fluorine-proton coupling constants, and thallium substituent chemical shifts are given and discussed     

Flash vacuum thermolysis of spirocyclohexadienones

In an attempt to prepare short-bridged hydroxymetacyclophanes $\text{1b-d}$, the spirocyclohexadienones $\text{2b-d}$ were pyrolyzed by flash vacuum thermolysis (FVT). Instead of $\text{1b-d}$, variable amounts of 4-(5-hexenyl)phenol ($\text{4b}$), β-hydroxybenzocycloalkenes ($\text{5b-d}$) and 4-(trans-1-alkenyl) phenols ($\text{6c-d}$) were obtained. The formation of these products is explained by invoking cleavage of a spiro bond in $\text{2}$ under formation of the intermediate diradical $\text{3}$ which, depending on the length of the aliphatic chain and on the temperature, has several pathways open for isomerization to spin-paired products.     

H3N·PF5 and H2NPF5−, new compounds in the system H3N/PF5

Phosphorus pentafluoride was reported long ago to give adducts 2 PF₅ ·5 NH₃ (1) and nNH₃·PF₅ (n= 1 ? 4) (2). None of the compounds was characterised in detail. Repeating the reaction of PF₅ and NH₃ we found the adduct H₃N·PF₅, $\text{1}$, in 8% yield besides (H₂N) ₂PF₃ (3) and NH₄PF₆. However, HF and (F₂P=N)₃ gave $\text{1}$ in 41% yield. The ¹H, ¹⁹F, and ³¹P n.m.r. spectra of $\text{1}$ exhibit ¹⁴NH, ¹⁴NPF(cis), and ¹⁴NP coupling. The x-ray structure determination shows almost perfect octahedral geometry at phosphorus with a PN bond length of 1.842 ā. Compound $\text{1}$ is soluble in water without decomposition. Treatment with NH₃ leads to the anion H₂NPF₅^?. Upon heating $\text{1}$ forms in good yield H₂NPF₄ and NH₄PF₆. Without a solvent $\text{1}$ and NH₃ react to give (H₂N) ₂PF₃. A mechanism for the ammonolysis of PF₅ is proposed.     

Crystal and molecular structure of 9,10-diphenylbicyclo[6.2.0]decapentaene a 10 π aromatic compound

X-ray analysis of 9,10-diphenylbicyclo[6.2.0]decapentaene $\text{2b}$ has revealed good planarity of the decapentaene nucleus, remarkably long bond length of the central bond, and appreciably small alternation of the peripheral bonds. It is thus concluded that $\text{2b}$ is a pericyclic 10 π aromatic compound.     

Synthesis and NMR spectroscopy of 2′, 3′, 4′, 5′, 6′ - pentafluoroformanilide

Pentafluoroformanilide was prepared by a new synthetical route. The ¹H, ¹³C, and ¹⁹F chemical shifts for the compound indicated the presence of $\text{cis}$ and $\text{trans}$ isomers in chloroform with a rotational energy barrier of 13.4 Kcal mol^-1 for the N-C(O) bond.N, N′-Bis(2,3,4,5,6-pentafluorophenyl) formamidine was obtained from pentafluoroformanilide.     

The crystal structure of N-sodiohexamethyldisilazane,Na[N{Si(CH3)3}2]

The crystal structure of Na[N{Si(CH₃)₃}₂] has been determined from single-crystal x-ray diffraction data collected by counter methods. N-sodiohexamethyldisilazane crystallizes in the mono-clinic space group p21/n with unit cell parameters $\text{a}$ = 9.426(3), $\text{b}$ = 6.921(3), c = 17.974(5)Å, β = 93.83(2)°, and ?_calc = 1.04 g cm^?3 for z = 4 formula units. Least-squares refinement gave a final conventional R value of 0.034 for 1244 independent observed reflections. In the solid state the compound exists in a polymeric arrangement with an average Na-N distance of 2.355(4)Å. The methyl group are configured such that the angle of rotation of the trimethylsilyl moiety about the Si-N bond is 30° from the eclipsed position. The Si-N bond length is 1.690(5)Å, and the Si-N-Si bond angle is 125.6(1)°.     

Reaction of 5,5-diphenyl-2-thiohydantoin with 1,2-dibromoethane.crystal and molecular structures of 2,3-dihydro-6,6-diphenylimi-dazo-[2,1-b]-thiazol-5(6h)-one and 2,3-dihydro-5,5-diphenylimi-dazo-[2,-1-b]-thiazol-6(5h)-one and their reactivity

The crystal and molecular structures of the title isomeric compounds $\text{1}$ and $\text{2}$, obtained by intramolecular N,S--dialkylation of 5,5-diphenyl-2-thiohydantoin with 1,2-dibro-moethane, have been determined from X-ray diffractometer data. 2,3-Dihydro-6,6-diphenylimidazo-[2,1-b]-thiazol-5(6H)-one $\text{1}$ crystallizes in space group P2₁2₁2₁ with a=11.376(3), b=12,255(5), c=8.434(3) Å and Z=4. Crystals of $\text{2}$, containing one molecule of benzene, are monoclinic,space group P2₁/c with a=11.539(6), b=10.242(3), c=16.353(5) Å, β=95.45(5)° and Z=4. In both cases a planar geometry of the two fused five-membered heterocyclic rings was found. The selected bond lengths in $\text{1}$ and $\text{2}$, as well as those analogous imidazothiazinones $\text{3}$ and $\text{4}$, were used to calculate E_HOSE (Harmonic Oscillation Stabilization Energy). The problem of stability and chemical reactivity of compounds $\text{1}$ to $\text{4}$ is also discussed.     

v-Triazolines. part XXI. Spiro[bicyclo[2.2.1]hept-2-ene[54']1',2'.s'-triazole]derivatives from cyclopentadiene and 5-amino-4-methylene-v-triazolines

1R^*, 4R^*, 5S^*, 5'S^*-5'-Amino-1'-(4-nitrophenyl)-4',5'-dihydrospiro[bicyclo [2.2. 1]hept-2-ene[5.4]-1',2',3'-triazoles]$\text{2}$ have been obtained both by ?4 +2]-cycloaddition of cyclopentadiene to amino-methylene-1-(4-nitrophenyl)-4,5-dihydro-v-triazoles $\text{1}$ and by [3+2]-cycloaddition of 4-nitrophenylazide to 5-aminomethylene-2-norborenes $\text{4}$. The configuration has been fully established by X-ray crystallographic analysis. The course of the cycloaddition and the thermal behaviour of $\text{2}$ are discussed.     

Bonding information in tungsten(VI) compounds from directly bonded fluorine and fluorophenoxy subtituents

The series of compounds (FC₆H₄O)_nWF_6-n, where n = 1-6 and F is meta or para to oxygen, has been prepared and all fluorine nmr chemical shifts determined. The W-$\text{F}$, para-$\text{F}$, and meta-$\text{F}$ resonances all shift upfield as a function of n with approximate relative sensitivities of 1, 1/20, and 1/30, respectively. All chemical shifts are also found to be sensitive to molecular stereochemistry, with subtituents trans to oxygen shifted to higher field than those trans to fluorine. ¹⁹F data is also reported for the complete series (C₆H₅O)_nWF_6-n     

Substituent effects on fluorine - 19 chemical shifts in benzobicyclo(2.2.2)octen-1-yl fluorides

Inverse ¹⁹F substituent chemical shifts (SCS) of $\text{m}$- and $\text{p}$-substituted benzylfluorides are shown to have their origin in hyperconjugation involving the CF δ - bond.     

Metal—metal bonding in dinuclear complexes of platinum(I). The crystal and molecular structure of carbonyl(chloro)-bis-μ-[bis(diphenylphosphino)methane]diplatinum hexafluorophosphate

The structure of [Pt₂Cl(CO) (μ-Ph₂PCH₂PPh₂)₂] [PF₆] was determined by $\text{X}$-ray methods and refined to $\text{R}$ = 0.082, using diffractometric intensities of 5646 independent reflections. The crystals are monoclinic, space group $\text{P}$2₁/$\text{n}$, $\text{a}$ = 12.919(3), $\text{b}$ = 15.576(6), $\text{c}$ = 25.151(5)Å, β = 94.82(3)°, $\text{Z}$ = 4. They are built of octahedral hexafluorophosphate anions and dinuclear platinum(I) cations. The latter contain PtCl and PtCO fragments linked to one another by a PtPt σ-bond and by two bridging bis(diphenylphosphino)methane ligands. The platinum atoms are in square planar environments and the dihedral angle between the two coordination planes is 40.1°. Selected bond lengths are: PtPt 2.620(1), PtCl 2.384(5), PtC 1.89(3) and PtP 2.291(5) – 2.308(5)Å.     

Preparation of some highly halogenated derivative of furan

Direct chlorination of 2-(2H-hexafluoropropyl)-tetra- hydrofuran $\text{1}$ gave high yield of 2-(2-chlorohexafluoropropyl)- pentachloro-2,5-dihydrofuran $\text{2}$. Bromination of $\text{1}$ gave very complex mixture of products, from which three compounds, $\text{viz}$. 2-bromo-5-(2H-hexafluoropropyl)-furan $\text{3}$, 3-bromo-5-(2H-hexafluoropropyl)-furan $\text{4}$, and 2,4-dibromo-5-(2H-hexafluoropropyl)furan $\text{5}$ were isolated. Exchange fluorination of $\text{2}$ with dry KF at 240 – 300° led to a stepwise substitution of fluorines for chlorines to give mixtures of chloro-fluoro-2-(2-chlorohexafluoropropyl)-dihydrofurans $\text{7}$,$\text{8}$,$\text{9}$ and $\text{10}$, together with small amounts of 2-(2-chlorohexafluoropropyl)-3,4,5-trichlorofuran $\text{6}$.Exchange fluorination of 3,4-dihalo-2,2,5,5-tetrafluoro- 2,5-dihydrofurans $\text{11a}$ and $\text{11b}$ led to a substitution of fluorine for one vinylic halogen to give 3-halo-2,2,4,5,5-pentafluoro-2,5-dihydrofurans $\text{12a}$ and $\text{12b}$ in good yields.Compounds $\text{2}$ – $\text{12}$ were characterised by n.m.r., m.s., and i.r. spectroscopy and elemental analysis.     

13C-NMR of some ajmalane alkaloids

The ¹³C-NMR spectra of the alkaloid ajmaline ($\text{1}$) and its stereoisomers isoajmaline ($\text{2}$), sandwichine ($\text{3}$) and isosandwichine ($\text{4}$) are reported. The different stereochemistry at C (17), C(20) and C(21) of the four isomers can be directly ascertained by chemical shifts data.     

1H NMR spectra of 1-alkyl-1,2,3,4-tetrahydro-2-oxo-3-azocine-carboxylic acid derivatives and their analogues

¹H NMR spectra of 1-alkyl-1,2,3,4-tetrahydro-2-oxo-3-azocinecarboxylates and -carbonitriles indicated that the geminal protons at the 1-α-position were located in noneqnivalent magnetic environments. The difference in the chemical shifts amounted to as much as 0.73 ppm in the case of methyl 1-ethyl-1,2,3,4-tetrahydro-2-oxo-3-azocinecarboxylate at 26°, and the free energy of activation for the coalescence was estimated to be larger than 23 $\text{kcal}\text{mol}$. The same type of nonequivalence and coalescence phenomena were also observed even with dimethyl protons at the 1-γ-position of 1-isobutyl-1,2,3,4-tetrahydro-2-oxo-3-azocinecarboxylate (ΔG^≠_c = 19 $\text{kcal}\text{mol}$). The situation was hardly affected by the reduction of the CC double bonds. The nonequivalence was not observed, however, if the substituent at the 3-position was absent. Therefore, these novel ¹H NMR spectra of 1-alkyl protons in the title compounds were concluded to be due to strong coupling between the restricted rotation around N(1)—C(α) bond and inversion of the 2-oxoazocine ring which required high energy of activation.     

Chiral recognition of alkene and arene hydrocarbons by 1H and 13C NMR. determination of enantiomeric purity

Simultaneous presence of the salt $\text{1}$ and one of the lanthanide complexes (+)-$\text{2}$, (+)-$\text{3}$, or (+)-$\text{4}$ splits ¹H or ¹³C NMR signals of the chiral alkenes $\text{5}$, $\text{6}$, and $\text{8}$ as well as of the chiral arene $\text{7}$; the enantiomeric purity of a mixture of (+)- and (?)-$\text{8}$ was determined successfully.     

Correlation between the isotropic 29Si chemical shifts and the mean silicon-oxygen bond lengths in silicates

Using known NMR and structural data of solid silicates the linear correlation $\text{δ}\text{-}$ = 1.1$\text{87 × 10}$⁴$\text{d}\text{(SiO)}$ - 2014 between the isotropic ²⁹Si NMR chemical shifts $\text{δ}\text{-}$ (ppm) and the “isotropic” mean bond lengths $\text{d}\text{(SiO)}$ (nm) has been established. The results of semi-empirical calculations are in good agreement with this equation.     

Isolation and structural elucidation of heliangolidin,a new sesquiterpene lactone from artemisia canariensis

A new heliangolide has been isolated from aerial parts of $\text{Artemisia canariensis}$, and identified as (6$\text{E}$,10$\text{Z}$)(3$\text{S}$,3a$\text{R}$,4$\text{S}$,lla$\text{R}$)-3a,5,8,11a--tetrahydro-4-acetoxy-3,6, 1O-trimethyl-2,9 (3$\text{H}$, 4$\text{H}$) -cyclodeca[b] furandione. The structural elucidation of the new compound, named heliangolidin, was carried out by spectral means (MS, IR, ¹H and ¹³C NMR, and two dimensional ¹H-¹³C chemical shift correlations) and X-ray diffraction analysis.     

The crystal structures of α- and β-CdUO4

The structural parameters of α- and β-CdUO₄ crystals are determined by X-ray powder diffraction technique. α-CdUO₄ is rhombohedral and cell parameters are a = 6.233(3) Å and α = 36.12(5)°. β-CdUO₄ crystallizes in a C-centered orthorhombic cell with a = 7.023(4), b = 6.849(3), c = 3.514 (2) Å. The space groups are $\text{R}\text{3}\text{m}$ for α-CdUO₄ and Cmmm for β-CdUO₄. α-CdUO₄: 1U in (000), 1Cd in ($\text{1}\text{2}\text{1}\text{2}\text{1}\text{2}$), 2O(1) in ±(uuu), 2O(2) in ±(vvv); u = 0.113, v = 0.350, Z = 1. β-CdUO₄: 2U in ($\text{000;}\text{1}\text{2}\text{1}\text{2}\text{0}$), 2Cd in ($\text{1}\text{2}\text{0}\text{1}\text{2}\text{; 0}\text{1}\text{2}\text{,}\text{1}\text{2}$), 4O(1) in ($\text{0, ±y, 0;}\text{1}\text{2}\text{,}\text{1}\text{2}\text{±y, 0}$), 4O(2) in ($\text{±x, 0,}\text{1}\text{2}\text{;}\text{1}\text{2}\text{±x,}\text{1}\text{2}\text{,}\text{1}\text{2}$); x = 0.159, y = 0.278, Z = 2. β-CdUO₄ contains collinear uranyl UO²⁺₂ groups with a UO(1) distance of 1.91 Å, located either along or parallel to the c axis whereas the UO(1) bond length in α-CdUO₄ is 1.98 Å which is longer than the usual uranyl bond length.