13C NMR shifts and conformations of substituted indans

¹³C NMR spectra of indan derivatives bearing substituents in the 1, 2, 5 and 6 positions are reported and assigned by LIS measurements and other techniques. Epimeric indanes bearing vicinal oxygen and phenyl or benzyl substituents show ring carbon shielding in the cis relative to the trans isomers, which is compared with corresponding cyclopentane shifts, and indicates the predominance of envelope conformations with pseudoaxial oxygen substituents for the cis isomers. Acetylation shifts show consistently larger shielding at C-β for the trans compounds. Introduction of oxygen at C-5 leads to asymmetric shielding effects at the ortho carbon atoms as soon as there is a substituent in the para position which can participate in mesomeric forms.     

Intramolecular noncovalent interactions: Bis(toluene)chromium(0) conformers

The structure of trans- and cis-conformers of bis(toluene)chromium(0) and the intramolecular interactions in them are studied by means of MP2 and density functional theory along with topological and NBO analyses. It was concluded for the first time that the locations of two hydrogen atoms of each methyl group between the phenyl ring planes in the most stable cis-conformer of bis(toluene)chromium(0) are largely determined by the stabilizing interactions of methyl C-H bonds and their hydrogen atoms with the metal atom and chromium-carbon bonds. It was concluded from the obtained data that the C-H...Cr contacts in the studied conformers should be considered as hydrogen bonds rather than agostic interactions. Contrary to the existing conception of the quantum theory of atoms in molecules, repulsive interaction is shown to occur between the pairs of hydrogen atoms of the two methyl groups in bis(toluene)chromium(0) cis-conformers rather than the stabilizing hydrogen-hydrogen interactions.     

Stereochemical effects in the electron impact mass spectra of cis-trans isomeric 1,2,3,4-tetramethylcyclohexanes

The mass spectra of six cis-trans isomeric 1,2,3,4-tetramethylcyclohexanes are discussed. The intensity ratio of [M? CH₃]⁺/[M? C₂H₅]⁺ correlates with the strain energies of the stereoisomers. Therefore, the identification of cis-trans isomers is possible by means of their mass spectra. The mass spectra of deuterium labelled compounds demonstrate favoured fragmentation of the axial methyl groups and ring opening between the cis substituted carbon atoms of the cyclohexane.     

An X‐ray powder diffraction study of cis‐dichloridobis(2‐methyl‐2H‐tetrazol‐5‐amine‐κN4)platinum(II), a tetrazole‐containing analogue of cisplatin

The structure of the title compound, cis‐[PtCl₂(C₂H₅N₅)₂], was analysed using in‐house X‐ray powder diffraction data at room temperature. The structure was solved by direct methods and refined using Rietveld analysis. A slightly distorted square‐planar coordination geometry is formed around the Pt atom by two Cl atoms and two ring N atoms of the 2‐methyl‐2H‐tetrazol‐5‐amine ligands, which are in a cis configuration. The planes of the tetrazole rings are inclined at 79.7 (7) and 73.8 (6)° with respect to the coordination plane, with their substituents oriented in such a way that the complex as a whole has approximate C₂ symmetry. Intermolecular N—H...Cl hydrogen bonds mediate the formation of a three‐dimensional supramolecular network.     

Crystal Structure of Mixed Crystals of the Tetra(n-butyl)ammonium Salts of cis-Tetrafluorophthalocyaninato(2−)tantalate(V) and cis-Trifluorophthalocyaninato(2−)tantalate(IV)

cis-Trichlorophthalocyaninato(2?)tantalate(V) reacts with excess tetra(n-butyl)ammonium fluoride trihydrate yielding mixed crystals of the tetra(n-butyl)ammonium salts of cis-tetrafluorophthalocyaninato(2?)tantalate(V) and cis-trifluorophthalocyaninato(2?)tantalate(IV) in the ratio five to four. These crystallize in the monoclinic space group P2₁/ n with cell parameters: a = 13.368(2) Å, b = 13.787(2) Å, c = 23.069(3) Å, β = 93.35(1)°, Z = 4. Ta^v is octacoordinated with four F atoms and four N_iso atoms in an antiprismatic cis-arrangement. The Ta^v-F distance varies from 1.919(7) to 1.966(4) Å. Ta^IV is heptacoordinated with three F atoms in a cis-arrangement. The Ta^IV-F distance varies from 1.74(1) to 1.966(4) Å. The Ta atom is located out of the centre of the N₄ plane towards the F atoms by 1.234(3) Å. The Ta–N distances range from 2.261(6) to 2.310(6) Å.     

12H-dibenzo[d,g][1,3,2]dioxaphosphocins: Synthesis,structures and “through-space” spin-spin coupling in their NMR spectra

A series of 12H-dibenzo[d,g][1,3,2]dioxaphosphocins has been prepared by the reactions of bisphenols with either ethyl phosphorodichloridate or phosphorus pentasulfide. The structures of a pair of cis and trans isomers in this series were elucidated by X-ray crystallography. Both isomers adopt the boat-chair conformation in the solid state with the bulky group at C-12 in the pseudo-equatorial position. Some flattening of the heterocyclic ring due to the pseudo-axial ethoxy group was observed in the cis isomer. A novel transannular cyclisation reaction was observed in the mass spectra of the cis isomers and this has allowed us to assign the configurations of all the isomers in the series. The pmr spectra of the compounds have been explained in terms of the rigid boat-chair conformation; however, as bulky groups were introduced at C-12, signs of mobility were observed for the cis isomers and an equilibrium was established with mobile boat forms. A stereospecific long-range coupling between P and the proton at C-12 could be transmitted “through space” by the antiperiplanar lone-pair electrons on the ring oxygen atoms.     

Zur Lokalisierung funktioneller Gruppen in Steroiden mit Hilfe der Massenspektrometrie: XIII—Massenspektren von 3,7,17-Trihydroxyandrostanen und 7,17-Dihydroxyandrostan-3-onen

Androstanes with a trans connected A/B ring system and hydroxy groups in positions 3, 7 and 17 show in their mass spectra key ions of mass 99 and 178. The ion of mass 99 contains the carbon atoms of ring D, and the ion of mass 178 those of the A/B ring system and C-11. If the rings A and B are cis connected, the ion of mass 178 is produced with much lower abundance and the ion of mass 99 is almost absent. The α or β position of a hydroxy group in position 7 can be deduced from the spectra of corresponding trimethylsilyl derivatives: a fragment of [M ? 131] dominated by presence of a 7α-trimethylsilyl ether group and trans connection of the A/B ring system. Determination of the configuration of the hydroxy group in position 3 is very difficult. Analogous fragments are observed in the spectra of the corresponding 7, 17-dihydroxyandrostan-3-ones.     

13C FT-NMR spectra of alkyl substituted furans. A study of the influence of steric interactions

The ¹³C FT-NMR spectra of thirteen furans, monodi- or trisubstituted with methyl and/or t-butyl groups, were studied in detail. Substituent effects of methyl and t-butyl groups on the chemical shifts of ring carbon atoms are additive in nonsterically hindered furans. Steric shifts for the ring carbon atoms are found in furans with bulky neighbouring substituents, but the hybridisation of the carbon atoms in these hindered furans is not changed. The chemical shifts of the substituents are calculated according to the Grant-Cheney formula. No simple relationship between steric shift and steric hindrance can be ascertained.     

Hydrogen bonding in polyamino‐polyalcohols: a monohydrated cocrystal of 1,3‐diamino‐5‐azaniumyl‐1,3,5‐trideoxy‐cis‐inositol iodide and 1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol

In the title monohydrated cocrystal, namely 1,3‐diamino‐5‐azaniumyl‐1,3,5‐trideoxy‐cis‐inositol iodide–1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol–water (1/1/1), C₆H₁₆N₃O₃⁺·I⁻·C₆H₁₅N₃O₃·H₂O, the neutral 1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol (taci) molecule and the monoprotonated 1,3‐diamino‐5‐azaniumyl‐1,3,5‐trideoxy‐cis‐inositol cation (Htaci⁺) both adopt a chair conformation, with the three O atoms in axial and the three N atoms in equatorial positions. The cation, but not the neutral taci unit, exhibits intramolecular O—H...O hydrogen bonding. The entire structure is stabilized by a complex three‐dimensional network of intermolecular hydrogen bonds. The neutral taci entities and the Htaci⁺ cations are each aligned into chains along [001]. In these chains, two O—H...N interactions generate a ten‐membered ring as the predominant structural motif. The rings consist of vicinal 2‐amino‐1‐hydroxyethylene units of neighbouring molecules, which are paired via centres of inversion. The chains are interconnected into undulating layers parallel to the ac plane, and the layers are further held together by O—H...N hydrogen bonds and additional interactions with the iodide counter‐anions and solvent water molecules.     

Conformational preferences of 2-methoxypyridine from 1H and 13C NMR and from STO-3G molecular orbital calculations

Observable coupling over five formal bonds between the methoxy group protons and the ortho ring proton in 2-methoxypyridine, coupliugs between the methoxy group carbon and ring protons, and methoxy carbon spin-lattice relaxation times are all consistent with a preference for the planar cis conformer, in which conjugation is favoured and repulsions between the methyl group and the ortho hydrogen are reduced. Small-amplitude torsioas about the C-2–O bond may carry the methoxy group away from this orientation, but more distant conformations can probably be excluded. Methyl group rotation is less hindered in the cis than in the trans conformer. Molecular orbital calculations at the STO-3G level, with complete geometry optimization, support the conduskus drawn from experimental evidence.     

N.m.r. spectra of cyclic amines. II—Factors influencing the chemical shifts of α-protons in aziridines

Proton magnetic resonance spectra of trans and cis-2,3-diphenylaziridine (1 and 2) and their N-ethyl derivatives 3 and 4 were measured in carbon tetrachloride, chloroform, and benzene-d₆ at low temperatures (1 and 3) and in dry conditions (1 and 2). On the basis of these results it was concluded that an N-ethyl group exerts a shielding influence on a cis ring proton and a deshielding influence on a trans ring proton. From results obtained by measuring the ¹H n.m.r. spectra of 1–4 in deuterochlorofom-trifluoroacetic acid it was derived that the lone pair of the aziridine nitrogen exerts a shielding influence on cis related ring hydrogens. In most N-alkylaziridines the effect of the N-alkyl group predominates.     

Configurationally and conformationally homogeneous cyclicN-aryl sulfimides. II.13C-and1H NMR spectra

The configuration and (in case of mobile ring systems) the preferred conformation in a series of thiane- and ofcis-andtrans-1-thiadecalin-1-N-4-chlorophenyl imides were assigned by means of¹³C- and¹H nmr spectroscopy.¹H nmr criteria known to be valid for determination of the stereochemistry of cyclic sulfoxides may be applied (with limitations) to cyclicN-aryl sulfimides, if both isomers (S–N bond equatorial and axial, respectively) are known. The assignments are easier, and unambiguous for single isomers, by comparison of¹³C nmr chemical shifts of ring carbon atoms of sulfimides and sulfides. The influence of equatorially and axially oriented sulfimide groups on the chemical shifts of neighbouring protons, and on the carbon atoms of the heterocyclic rings are discussed in detail.

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Konfigurativ und konformationell einheitliche cyclische N-Aryl-sulfimide. II.¹³C- und¹H-NMR-Spektroskopie

Zusammenfassung Die Konfiguration und (bei beweglichen Ringsystemen) die bevorzugte Konformation einer Reihe von Thian- und voncis- undtrans-1-Thiadekalin-1-N-4-chlorophenylimiden wurde durch¹³C- und¹H-NMR-Spektroskopie bestimmt. Bekannte¹H-NMR-Kriterien zur Festlegung der Stereochemie cyclischer Sulfoxide sind (mit Einschränkungen) auch bei cyclischenN-Arylsulfimiden anwendbar, wenn beide Isomere (S–N-Bindung äquatorial bzw. axial) bekannt sind. Leichter, und auch bei Vorliegen von nur einem Isomeren eindeutig, gelingt die Zuordnung durch Vergleich der¹³C-NMR-Verschiebungen der Ringkohlenstoffatome von Sulfimiden und Sulfiden. Die Einflüsse äquatorial oder axial orientierter Sulfimidgruppen auf die chemischen Verschiebungen benachbarter Wasserstoffe und der Kohlenstoffe des Heterorings werden diskutiert.

     

Conformation and hydrogen bonding for the bicyclic compound 3‐thiabicyclo[3.2.0]heptane‐6,7‐dicarboxylic acid 3,3‐dioxide

The initial goal of this work was to verify the geometry of the product of a photochemical reaction, viz. the title compound, C₈H₁₀O₆S, (II). Our crystallographic study firmly establishes the cis–anti–cis nature of the substituents on the cyclobutane ring. The geometry is also designated as exo, where exo signifies that the five‐membered ring is on the opposite side of the central cyclobutane ring from the carboxylic acid substituents. The structure determination reveals two molecules, A and B, in the asymmetric unit that display substantially different conformations of the bicyclic core: the cyclobutane ring puckering angles are 22 and 3°, and the sulfolane ring conformations are twist (S‐exo) and envelope (S‐endo). Intrigued by this variation, we then compared the conformations of other molecules in the Cambridge Structural Database that have sulfolane rings fused to cyclobutane rings. In this class of compound, there are five examples of saturated cyclobutane rings, with ring puckering angles ranging from 3 to 35°. The sulfolane rings were more similar: four of the six molecules exhibit envelope conformations with S‐endo, as in molecule B of (II). Despite the conformational differences, the hydrogen‐bonding scheme for both molecules is similar: carboxyl –OH groups form hydrogen bonds with carboxyl and sulfone O atoms. Alternating A and B molecules joined by hydrogen bonds between sulfone O atoms and carboxyl –OH groups form parallel chains that extend in the ac plane. Other hydrogen bonds between the carboxyl groups link the chains along the b axis.     

Synthesis and Crystal Structure of Mercury(II) Metal Crown Ether with N‐Heterocyclic Carbene Linkage

The mercury(II) metal crown ether ( 2a ) was obtained in high yield by reaction of the carbene precursor 1,2‐bis[N‐(1‐naphthylmethylene)imidazoliumethoxy]benzene dihexafluorophosphate ( 1 ) and Hg(OAc)₂. Addition of NaI to the acetone solution of 2a resulted in precipitation of pale yellow solid 2b . The structures of 2a and 2b were determined by single‐crystal X‐ray diffractometry. Both molecules display a helical conformation with a torsional cycle. The mercury atom in complex 2a is tricoordinated by two intramolecular carbene carbon atoms and an acetate oxygen atom. The mercury atom in complex 2b is tetracoordinated by two intramolecular carbene carbon atoms and two cis‐iodine atoms.     

Synthesis and stereochemistry of indano[1,2‐d][1,3]oxazines and thiazines,new ring systems

A set of structurally varied indano[1,2‐d][1,3]oxazines and thiazines, which are new ring systems, were prepared by ring‐closure reactions of amino alcohols 4–6. The reactions of cis‐ and trans‐1‐amino‐ and cis‐ 1‐benzylamino‐2‐hydroxymethylindane (4–6) with 1 equivalent of an aromatic aldehyde in methanol at room temperature resulted in three‐component equilibria (15a‐g), or a Schiff base (16), or a ring‐closure product alone (17a‐c), respectively, depending on the substitution or configuration of the starting amino alcohol. The ring‐chain tautomeric equilibria can be described by an equation of Hammett type.     

Asperuloside monohydrate

The title compound, [2aS‐(2aα,4aα,5α,7bα)]‐5‐(β‐d ‐gluco­pyran­osyl­oxy)‐2a,4a,5,7b‐tetra­hydro‐1‐oxo‐1H‐2,6‐dioxa­cyclo­pent­[cd]­inden‐4‐yl­methyl acetate monohydrate, C₁₈H₂₂O₁₁·H₂O, was extracted from the Turkish plant Putoria calabrica (L. fil.) DC. The three fused rings have envelope or distorted envelope conformations and form a bowl in which ring strain causes distortion of some bond angles and significant pyramidalization of two of the Csp² atoms. The ring junction H atoms are all cis to one another and the glycosidic linkage is in the β axial position. The structure incorporates two symmetry‐independent water mol­ecules, each of which is located on a twofold axis. Intermolecular hydrogen bonds involving all the hydroxy groups and water mol­ecules link the mol­ecules into a complex three‐dimensional framework.     

Caesium cis‐tetrachloridodioxidorhenate(VII)

The title crystal structure, Cs[ReCl₄O₂], consists of cis‐tetrachloridodioxidorhenate(VII) anions and caesium cations. The distorted octahedral anion has nearly C_2v symmetry, with a cis arrangement of the oxide ligands. The Re—Cl bond lengths for the Cl atoms trans to the oxide ligands are affected by the trans influence of the Re—O bonds and are longer than for the Cl atoms cis to the oxide ligands [average of 2.472 (2) Åversus average of 2.322 (2) Å, respectively]. There are ten Cl atoms from six cis‐tetrachloridodioxidorhenate(VII) anions in the neighbourhood of the caesium cation.     

Conformation et Spectrometrie de RMN. III. Spectres 13C de Diméthylamino Cyclanols et Dérivés

The ¹³C NMR spectra of 2-dimethylaminocyclohexanols and the four trans-3-dimethylamino-2-decahydronaphtols are described. The gauche interactions allow precise estimation of chemical shifts for each carbon atom; thus, band attribution can be resolved without mistake. In the case of the cis and the trans diequatorial compounds, the conformational perturbations which we have suggested before are verified by our present measurements on the substituted carbon atoms. We also show effects on adjacent atoms, which were unobservable with the usual IR and ¹H NMR techniques.     

Repetierbare Ringerweiterungen durch [2,3]-sigmatropische Umlagerungen in cyclischen Allylsulfonium-allyliden; Synthese von mittleren und grossen Thiacyclen. Vorläufige Mitteilung

Repeatable ring expansions by [2,3]-sigmatropic shifts in cyclic allylsulfonium allylides; synthesis of medium- and large-sized thiacycles Allylation of a 2-vinyl thiacyclus with allyl bromide in 2,2,2-trifluoroethanol followed by ylide generation by use of aqueous potassium hydroxide results in a [2,3]-sigmatropic rearrangement with formation of a new 2-vinyl thiacyclus enlarged by three carbon atoms (Scheme 1). In this way, starting from the 5-membered ring 1 , a series of four ring enlargement sequences leads to the 17-membered thiacycles 9 and 10 via the 8-, 11- and 14-membered rings 4 , 7 and 8 (Scheme 2).     

Synthesis of a Strained Spherical Carbon Nanocage by Regioselective Alkyne Cyclotrimerization

The smallest spherical carbon nanocage so far, [2.2.2]carbon nanocage, has been synthesized by the cationic rhodium(I)/H₈‐binap complex‐catalyzed regioselective intermolecular cyclotrimerization of a cis‐1‐ethynyl‐4‐arylcyclohexadiene derivative followed by the triple Suzuki–Miyaura cross‐couplings with 1,3,5‐triborylbenzene and reductive aromatization. This cage molecule is highly strained, and its ring strain is between those of [6] and [5]cycloparaphenylenes. A significant red‐shift of an emission maximum was observed, compared with that of known [4.4.4]carbon nanocage. The sequential cyclotrimerizations of a cis‐1,4‐diethynylcyclohexadiene derivative with the same rhodium(I) catalyst followed by reductive aromatization failed to afford [1.1.1]carbon nanocage; instead, a β‐graph‐shaped cage molecule was generated.