Na2C2 und K2C2: Synthese,Kristallstruktur und spektroskopische Eigenschaften

Na₂C₂ and K₂C₂: Synthesis, Crystal Structure, and Spectroscopic Properties By the reaction of sodium or potassium solved in liquid ammonia with acetylene and subsequent heating in high vacuum Na₂C₂ and K₂C₂ could be synthesised as single phase products. The crystal structures described by Föppl could be confirmed by X-ray and neutron diffraction experiments (K₂C₂) on powdered samples. Both compounds crystallise in a tetragonal structure (I4₁/acd, no. 142, Z = 8) which can be described as a distorted variant of the antifluorite-structure type. At temperatures above room temperature (Na₂C₂: 580 K, K₂C₂: 420 K) a reversible phase transition (1^st order transition) to a cubic modification (Fm 3 m, no. 225, Z = 4) has been observed, analogous to the alkaline earth metal acetylides. This high temperature modification represents an undistorted antifluorite structure with disordered C₂^2– dumbbells. The results of raman- and ¹³C-MAS-NMR-spectroscopic investigations are in agreement with acetylide dumbbells in the title compounds and allow a comparison to the respective monoalkalimetal and alkaline earth metal acetylides.     

2β, 13-Oxido-apotrichothecane: Synthese,chemische und physikalische Eigenschaften. Verrucarine und Roridine, 23. Mitteilung

Starting from the 12,13-epoxy-trichothecanes roridin C (trichodermol) ( 1 ), verrucarol ( 15 ) and trichothecolone ( 25 ), the isomeric 2β, 13-epoxy-apotrichothecanes 9, 20 and 33 have been synthesized. In these compounds the oxetane group proved to be unexpectedly stable to mineral acids and complex metal hydrides, probably due to its fusion to a cyclopentane ring. The IR. and NMR. spectra of the oxetanes are discussed.     

Organylselenoacetylene und selenocyanate; 77Se- und 13C-NMR-chemische verschiebungen und 77Se- 13C-spin-kopplungskonstanten

⁷⁷Se and ¹³C NMR chemical shifts and ⁷⁷Se-¹³C spinspin coupling constants of mono- and bis(organylseleno)acetylenes and organyl selenocyanates are shown. The changes of ⁷⁷Se chemical shifts caused by variation of the organyl groups are well reflected by known increments. The δ(⁷⁷Se) and ¹J(⁷⁷Se¹³C) values of the investigated compounds are discussed in relation to the corresponding alkyl- and vinyl-selenides. The ¹J(⁷⁷Se¹³C) values of the selenoacetylenes and selenocyanates as well as alkyl- and vinyl-selenides are linearly dependednt (i) on ¹J(¹³C¹H) values of the corresponding hydrocarbons, hydrogen cyanide respectively and (ii) on the product of the s-characters of the coupled Se and C atoms. These linear correlations prove the predominance of the Fermi contact term for changes of the one-bond ⁷⁷Se¹³C coupling in dependence on hybridization.     

13C,13C coupling constants from a mixture of isotopomers (13C) of substituted aromatic compounds; 1-nitronaphthalenes

¹³C Homonuclear decoupling experiments led to the assignment of the carbon-carbon coupling constants of ¹³C-enriched 1-nitronaphthalene obtained by nitration of [1-¹³C]naphthalene. The effects of substituents on coupling constants can be explained on the basis of the electronegativity of the first atom of the substituent, and the observed substituent effects are shown to be parallel to previous data for oxygen containing substituents.     

Darstellung und Charakterisierung der Fulleren-Kokristallisate C60 · 12 C6H12, C70 · 12 C6H12, C60 · 12 CCl4, C60 · 2 CHBr3, C60 · 2 CHCl3, C60 · 2 H2CCl2

Synthesis and Characterization of the Fullerene Co-Crystals C₆₀ · 12 C₆H₁₂, C₇₀ · 12 C₆H₁₂, C₆₀ · 12 CCl₄, C₆₀ · 2CHBr₃, C₆₀ · 2CHCl₃, C₆₀ · 2H₂CCl₂ By crystallization of fullerenes from non-polar solvents (C₆H₁₂, CCl₄, CHBr₃, CHCl₃, H₂CCl₂) compounds of the following compositions were obtained: C₆₀ · 12C₆H₁₂, C₇₀ · 12C₆H₁₂, C₆₀ · 12CCl₄, C₆₀ · 2CHCl₃, C₆₀ · 2CHBr₃ and C₆₀ · 2H₂CCl₂. Lattice parameters have been determined by X-ray diffraction of powder samples; according to single-crystal examinations on C₆₀ · 12C₆H₁₂, C₆₀ · 12CCl₄ and C₆₀ · 2CHBr₃ the fullerene is orientationally disordered. C₆₀ · 12C₆H₁₂, cubic, a = 28.167(1) Å; C₇₀ · 12C₆H₁₂, cubic, a = 28.608(2) Å; C₆₀ · 12CCl₄, cubic, a = 27.42(1) Å; C₆₀ · 2CHBr₃, hexagonal, a = 10.212(1), c = 10.209(1) Å; C₆₀ · 2CHCl₃, hexagonal, a = 10.08(1), c = 10.11(2) Å; C₆₀ · 2H₂CCl₂, tetragonal, a = 16.400(1) Å, c = 11.645(7) Å.     

Unterscheidung symmetrisch substituierter Kohlenstoffringe durch 13C,13C-Spin-Spin-Kopplung. Vergleich von herkömmlicher und INADEQUATE-13C-NMR-Spektroskopie

Distinction of Symmetrically Substituted Carbocyclic Compounds by ¹³C, ¹³C Spin-Spin Coupling. Comparison of Conventional and INADEQUATE¹³C-NMR Spectroscopy ¹³C,¹³C spin-spin couplings allow an easy distinction of symmetrically substituted carbocyclic compounds. On the basis of the number and ratio of ¹³C,¹³C satellite pairs, for instance head to head and head to tail products of photodimerisations can be distinguished. The informations derived from a conventional and an INADEQUATE ¹³C-NMR spectrum are compared.     

13C,13C coupling constants of conjugated dienes

One bond ¹³C,¹³C- and ¹³C,¹H-coupling constants have been measured for some 1,2-dimethylene-cycloalkanes, as well as for 2,3-dimethylbuta-1,3-diene and methylenecyclobutane. The results for 2,3-dimethylbuta-1,3-diene confirm the findings for buta-1,3-diene, i.e. that J(C-1, C-2) is smaller for the diene than for the correspondingly substituted monoene. No differences have been found between the ¹J(CC) exocyclic coupling constants of the dimethylene and monomethylene cycloalkanes.     

Synthese und NMR-Spektren einiger 13C-markierter Thio- und Seleno-äther, -acetale und -orthoester

Synthesis and NMR Spectra of Some ¹³C-Labelled Thio- and Seleno-ethers, -acetals, and -orthoesters Twenty-seven different open-chain and cyclic derivatives (RX)_nCH_4-n and (RX)_nCH_3-nR′ with n = 1?3, X = S or Se, R,R′ = alkyl or aryl, 1,3,5-trithiane, and bis-(dimethylsulfonio)methane and -methanide with single or multiple ¹³C-labelling have been synthesized. The ¹³C-NMR spectra of the sulfur and selenim compounds have been measured, and the dependence of the chemical shifts (δ_c) and coupling constants [′J(C,H), ′J(Se,C)] from the substitution pattern in discussed (Fig. 1) and compared with the polyhalogeno-methanes (Fig. 2).     

Suppressing one‐bond homonuclear 13C,13C scalar couplings in the J‐HMBC NMR experiment: application to 13C site‐specifically labeled oligosaccharides

Site‐specific ¹³C isotope labeling is a useful approach that allows for the measurement of homonuclear ¹³C,¹³C coupling constants. For three site‐specifically labeled oligosaccharides, it is demonstrated that using the J‐HMBC experiment for measuring heteronuclear long‐range coupling constants is problematical for the carbons adjacent to the spin label. By incorporating either a selective inversion pulse or a constant‐time element in the pulse sequence, the interference from one‐bond ¹³C,¹³C scalar couplings is suppressed, allowing the coupling constants of interest to be measured without complications. Experimental spectra are compared with spectra of a nonlabeled compound as well as with simulated spectra. The work extends the use of the J‐HMBC experiments to site‐specifically labeled molecules, thereby increasing the number of coupling constants that can be obtained from a single preparation of a molecule. Copyright © 2014 John Wiley & Sons, Ltd.