Multiple Quantum Coherence Spectroscopy Research Articles

Pulse overlap ambiguities in multiple quantum coherence spectroscopy.

Coherent two-dimensional electronic spectroscopy probes ultrafast dynamics using femtosecond pulses. In the case where the time scale of the studied dynamics become comparable to the pulse duration, pulse overlap effects may compromise the experimental data. Here, we perform one-dimensional coherence scans and study pulse overlap effects in clean two-level systems. We find parasitic multiple-quantum coherences as a consequence of the arbitrary time ordering during the temporal pulse overlap. Surprisingly, the coherence lifetimes exceed the pulse coherence time by a factor of 1.85. These findings have important implications for the interpretation of higher-order coherent two-dimensional and related spectroscopy experiments.

Synthesis and properties of biobased mono-benzoxazine resins from natural renewable pterostilbene

Two novel fully biobased mono-benzoxazine resins have been designed and synthesized using pterostilbene, furfurylamine/stearylamine and paraformaldehyde via a solventless reaction. The structures of newly obtained mono-benzoxazine monomers have been characterized by nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and high-resolution mass spectrometry (HR-MS). The detailed assignments for oxazine-ring protons and carbons in each benzoxazine are identified using 1H–13C heteronuclear multiple quantum coherence spectroscopy (HMQC). Besides, the polymerization processes of benzoxazine resins are studied by differential scanning calorimetry (DSC) and in situ FT-IR spectroscopy, and the thermal stability of their corresponding polybenzoxazines are investigated by thermogravimetric analysis (TGA). Moreover, coatings of both polybenzoxazines on glass slides and low-carbon steels have also been prepared to evaluate their anticorrosion performance. The results indicate that both polybenzoxazines possess good thermal stability and can play efficient roles for shielding corrosion as coatings. Therefore, the current study highlights the utility of the natural renewable pterostilbene as a promising candidate to prepare high-performance bio-based polybenzoxazines.

Characterization of liquid deproteinized natural rubber prepared via oxidative degradation

AbstractIn the present work, liquid deproteinized natural rubber (LDPNR) was prepared by oxidative depolymerization of deproteinized natural rubber using hydrogen peroxide (H2O2) and sodium nitrite (NaNO2) as oxidizing reagents. Structural characterization of LDPNRs was performed using FT‐IR, 1H‐NMR, 13C‐NMR, and Heteronuclear Multiple Quantum Coherence (HMQC) spectroscopy. After degradation, the intensity of vibration mode at 1660 cm‐1 (νC=C) decreased, indicating the decrease in the number of C=C bonds in the NR chain. 1H‐NMR signals at 1.6 ppm and 13C‐NMR signals at 40.0 ppm appeared in the NMR spectra of LDPNR prepared in acidic condition suggesting the occurrence of isomerization from cis‐1,4‐isoprene units to trans‐1,4‐isoprene units. Epoxidation also occurred during degradation of DPNR as a side reaction. End groups of LDPNRs were found to depend on pH of reacted latex. LDPNR prepared in pH 5‐6 contains aldehyde end group, while LDPNR prepared at pH 8‐9 has a hydroxyl end group. The gel content of LDPNRs was found to reduce compared to that of DPNR, significantly. GPC was employed to determine molecular weight of LDPNRs. The results show that the degradation in acidic medium behaves more effectively in comparison to in alkaline medium.

Unique self-catalyzed cationic ring-opening polymerization of a high performance deoxybenzoin-based 1,3-benzoxazine monomer

An asymmetric bis(1,3-benzoxazine) monomer based on deoxybenzoin has been synthesized through Mannich condensation. The chemical structure of this deoxybenzoin-based monomer has been confirmed using 1H NMR, 13C NMR, FT-IR and elemental analysis. The assignments for the oxazine protons and carbon atoms in the asymmetric structure have also been confirmed using two-dimensional (2D) NMR techniques, including 1H-1H nuclear Overhauser effect spectroscopy (NOESY) and 1H-13C heteronuclear multiple quantum coherence spectroscopy (HMQC). In addition, the effect of incorporation of deoxybenzoin on the mode of polymerization of benzoxazine has been investigated using differential scanning calorimetry (DSC), in situ FT-IR and 1H NMR spectroscopy. This deoxybenzoin containing bis(benzoxazine) exhibits a low polymerization temperature resulting from a unique self-catalyzed cationic polymerization mechanism. Furthermore, the thermal stability of the resulting polybenzoxazine has been studied using thermogravimetric analysis (TGA). This deoxybenzoin-based polybenzoxazine exhibits high thermal stability and low flammability, with a Td5 temperature of 403 °C, a high char yield value (68%) and low total heat release (THR of 11.4 kJ/g).

Unique nuclear magnetic resonance behaviour of γ-cyclodextrin in organic solvents

The nuclear magnetic resonance (NMR) behaviour of dry α-, β-, and γ-cyclodextrin (CyD) in non-aqueous solutions with the solvents pyridine-d5, N,N-dimethyl formamide-d7 (DMF-d7), and dimethyl sulfoxide-d6 (DMSO-d6) were examined in order to study the interactions among hydroxyl groups on the rims of CyD. All signals were assigned using H-H correlation spectroscopy (COSY) and 1H-detected multiple quantum coherence spectroscopy (HMQC) spectra. In pyridine-d5, the hydroxyl groups of γ-CyD and water were observed as appreciably broad signals. Over 95 °C, a white precipitate appeared immediately, and after 4 days, it disappeared completely. All signals of α- and β-CyDs were sharp and exhibited a high field shift as the temperature increased. These spectral changes were reversible, but in the case of γ-CyD in dry pyridine-d5, the time temperature-fall for reaching the equilibrium state took longer than that of temperature rise. The dependency of NMR spectroscopy of γ-CyD on the solvent, the concentration of water, and temperature suggested that hydroxyl groups on γ-CyD are sufficiently flexible to interact via intermolecular hydrogen bond formation and to form insoluble aggregates.

Formation of Ligno-Polyols: Fact or Fiction

The physical and chemical characteristics of several lignin-polyol blends were investigated by qualitative and quantitative methods from the view of biobased polyurethane applications. Four differently isolated biomass lignins from forestry and agricultural residues were blended with polyester polyol, and one was blended with polyethylene glycol. The isolated products were examined thoroughly to elucidate the subsequent lignin and polyol interactions during the premixing stage of biobased polyurethane formulation. Polyol was detected in lignin even after vigorous washings with several organic solvents and Soxhlet extraction. The experimental data coupled with two-dimensional heteronuclear multiple quantum coherence (HMQC) and nuclear magnetic resonance (NMR) spectroscopy confirmed the formation of ligno-polyols via strong intermolecular attractions, as well as some linkages between several lignin hydroxyl and polyol functional groups.

Two new bioactive salsolanol and biphenylsalsinol from the aerial parts of Salsola villosa Delile. ex Schul. (Chenopodiaceae) growing in Saudi Arabia

ObjectiveTo isolate and characterize the bioactive secondary metabolites from aerial parts of widespread Chenopodiaceae taxa growing in Saudi Arabia: Salsola villosa Delile. ex Schul. MethodsAntibacterial activities of chloroformic extract, fractions and isolate compounds was evaluated against five bacterial strains (Escherichia coli, Pseudomonas aeruginosa, Salmonella typhimurium, Staphylococcus aureus and Staphylococcus epidermidis), using a paper disc diffusion method. The purification of compound(s) of chloroform extract was done by chromatographic column of silica gel. The structure elucidation was determined by extensive spectroscopic analysis (1H and 13C nuclear magnetic resonance, correlation spectroscopy, heteronuclear multiple bond correlation, heteronuclear multiple quantum coherence and nuclear overhauser enhancement spectroscopy) and high resolution electrospray ionization mass spectroscopy analysis. ResultsBioactivity guided fractionation of the chloroformic extract led to the isolation of two bioactive compounds: 4-(4′-hydroxy-2′-methylcyclopent-2′-enyloxy)-4-methylcyclopent-2-enol (1) named salsolanol and 4′-[3-(hydroxymethyl)oxiran-2-yl]-3-[(E)-3-hydroxyprop-1-en-1-yl]-6, 2′-dimethoxy [1, 1′-biphenyl]-2-ol (2) named biphenylsalsinol. The antibacterial effects of the chloroform extracts, fractions and isolated compounds 1 and 2 were also evaluated in this work. Results showed that the compounds 1 and 2 exhibited antibacterial activities against four strains: Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli and Pseudomonas aeruginosa with diameter of zone of inhibition ranging between (9.33 ± 0.94) to (26.33 ± 0.94) mm. ConclusionsBased on data presented here, two new natural compounds secondary cyclic alcohol 1 and biphenylpropanoid 2 isolated from bioactive chloroformic extract from aerial parts of Salsola villosa can be responsible for its antibacterial activities.

Structure, mechanism and application of vinyl alcohol oligomers grafted onto poly(3-hydroxybutyrate): a proposal

AbstractOligomers of poly(vinyl alcohol) were grafted onto poly(3-hydroxybutyrate) (PHB) by radiation-induced polymerization. The aim of this study was to elucidate the structure of these copolymers using nuclear magnetic resonance (heteronuclear multiple quantum coherence) spectroscopy supported by dynamic light scattering (DLS) and atomic force microscopy (AFM). It was concluded that vinyl alcohol (VA) was grafted onto PHB for the methylenic and methynic sites. A mechanism for the grafting reaction was proposed based on the experimental evidence. AFM and DLS allowed the characterization of the particles obtained from P(HB-g-VA). The prepared materials showed suitable properties for use in drug delivery systems.

Understanding the structure–emulsification relationship of gum ghatti – A review of recent advances

This paper is based on a series of physical and chemical investigations to understand the structure–function properties of gum ghatti. After elucidating the detailed molecular structure of two gum ghatti fractions, the structure of its component glycoprotein was investigated whereby, the protein sequence and hydrophobicity were identified, followed by the conformational analysis of the gum and its fractions. Many techniques were used for the elucidation of the fine structures, which included methylation analysis-GC-MS, Maldi-TOF MS and 2D NMR spectroscopy, homonuclear 1H/1H correlations spectroscopy (COSY, TOCSY), heteronuclear 13C/1H multiple-quantum coherence spectroscopy (HMQC) and heteronuclear multiple bond correlation (HMBC). Conformational properties were studied using a modeling system (Insight II) to relate the hydrophobicity of the protein moieties with the complex structures of the carbohydrates. These studies now provide an explanation for the excellent emulsification properties of gum ghatti in oil-in-water emulsions, which enable its application in the food, cosmetic and/or pharmaceutical industries.

Triterpenoid Saponins of Pulsatilla koreana Root Have Inhibition Effects of Tumor Necrosis Factor-α Secretion in Lipopolysaccharide-Induced RAW264.7 Cells

In the present study, a new oleanane-type triterpenoid saponin, pulsatilloside F (1), along with 21 known compounds (2-22), were isolated from the root of Pulsatilla koreana. Their chemical structures were elucidated by mass, (1)H-, (13)C-NMR, correlation spectroscopy (COSY), heteronuclear multiple quantum coherence (HMQC) and heteronuclear multiple bond connectivity (HMBC) spectroscopy. Anti-inflammatory effects of the compounds were evaluated in terms of inhibitory of tumor necrosis factor α (TNF-α) secretion in the lipopolysaccharide (LPS)-stimulated murine RAW264.7 macrophage cell line. Compounds 19 and 20 exhibited particularly inhibitory effects with respective IC50 values of 0.32 and 0.65 µm. Compounds 1-4, 7 and 10-13 exhibited inhibitory effects with inhibition rates up to 41.55-73.76% at a concentration of 5 µm, respectively.

Antiinflammatory and Antioxidant Flavonoids and Phenols from Cardiospermum halicacabum (倒地鈴 Dào Dì Líng)

Seventeen compounds, quercetin-3-O-α-l-rhamnoside (1), kaempferol-3-O-α-l-rhamnoside (2), apigenin-7-O-β-d-glucuronide (3), apigenin 7-O-β-d-glucuronide methyl ester (4), apigenin 7-O-β-d-glucuronide ethyl ester (5), chrysoeriol (6), apigenin (7), kaempferol (8), luteolin (9), quercetin (10), methyl 3,4-dihydroxybenzoate (11), p-coumaric acid (12), 4-hydroxybenzoic acid (13), hydroquinone (14), protocathehuic acid (15), gallic acid (16), and indole-3-carboxylic acid (17), were isolated from the ethanol extract of Taiwanese Cardiospermum halicabum. All chemical structures were determined by physical and extensive spectroscopic analyses such as 1H Nuclear Magnetic Resonance spectroscopy (NMR), 13C NMR, 1H-1H Correlation spectroscopy (1H-1H COSY), Heteronuclear Multiple Quantum Coherence spectroscopy (HMQC), Heteronuclear Multiple-bond Correlation spectroscopy (HMBC), and Nuclear Overhauser Effect spectroscopy (NOESY), as well as comparison with literature values. Furthermore, the High-Performance Liquid Chromatography-Photodiode Array Detector (HPLC-DAD) fingerprint profile was established for the determination of major constituents in the EtOAc extract and retention times of the isolated compounds. All isolated compounds were also evaluated for antiinflammatory and antioxidant activities.

Antiinflammatory and Antioxidant Flavonoids and Phenols from Cardiospermum halicacabum ( Dào Dì Líng).

Seventeen compounds, quercetin-3-O-α-l-rhamnoside (1), kaempferol-3-O-α-L-rhamnoside (2), apigenin-7-O-β-D-glucuronide (3), apigenin 7-O-β-D-glucuronide methyl ester (4), apigenin 7-O-β-D-glucuronide ethyl ester (5), chrysoeriol (6), apigenin (7), kaempferol (8), luteolin (9), quercetin (10), methyl 3,4-dihydroxybenzoate (11), p-coumaric acid (12), 4-hydroxybenzoic acid (13), hydroquinone (14), protocathehuic acid (15), gallic acid (16), and indole-3-carboxylic acid (17), were isolated from the ethanol extract of Taiwanese Cardiospermum halicabum. All chemical structures were determined by physical and extensive spectroscopic analyses such as 1 H Nuclear Magnetic Resonance spectroscopy (NMR), 13C NMR, 1H-1H Correlation spectroscopy (1H-1H COSY), Heteronuclear Multiple Quantum Coherence spectroscopy (HMQC), Heteronuclear Multiple-bond Correlation spectroscopy (HMBC), and Nuclear Overhauser Effect spectroscopy (NOESY), as well as comparison with literature values. Furthermore, the High-Performance Liquid Chromatography- Photodiode Array Detector (HPLC-DAD) fingerprint profile was established for the determination of major constituents in the EtOAc extract and retention times of the isolated compounds. All isolated compounds were also evaluated for antiinflammatory and antioxidant activities.

Early detection of radiation therapy response in non-Hodgkin's lymphoma xenografts by in vivo 1H magnetic resonance spectroscopy and imaging.

The purpose of the study was to investigate the capability of (1)H MRS and MRI methods for detecting early response to radiation therapy in non-Hodgkin's lymphoma (NHL). Studies were performed on the WSU-DLCL2 xenograft model in nude mice of human diffuse large B-cell lymphoma, the most common form of NHL. Radiation treatment was applied as a single 15 Gy dose to the tumor. Tumor lactate, lipids, total choline, T(2) and apparent diffusion coefficients (ADC) were measured before treatment and at 24 h and 72 h after radiation. A Hadamard-encoded slice-selective multiple quantum coherence spectroscopy sequence was used for detecting lactate (Lac) while a stimulated echo acquisition mode sequence was used for detection of total choline (tCho) and lipids. T(2)- and diffusion-weighted imaging sequences were used for measuring T(2) and ADC. Within 24 h after radiation, significant changes were observed in the normalized integrated resonance intensities of Lac and the methylenes of lipids. Lac/H(2)O decreased by 38 +/- 15% (p = 0.03), and lipid (1.3 ppm, CH(2))/H(2)O increased by 57 +/- 14% (p = 0.01). At 72 h after radiation, tCho/H(2)O decreased by 45 +/- 14% (p = 0.01), and lipid (2.8 ppm, polyunsaturated fatty acid)/H(2)O increased by 970 +/- 36% (p = 0.001). ADC increased by 14 +/- 2% (p = 0.003), and T(2) did not change significantly. Tumor growth delay and regression were observed thereafter. This study enabled comparison of the relative sensitivities of various (1)H MRS and MRI indices to radiation and suggests that (1)H MRS/MRI measurements detect early responses to radiation that precede tumor volume changes.

Fully and Partially Coherent Pathways in Multiply Enhanced Odd-Order Wave-Mixing Spectroscopy

Nuclear magnetic resonance spectroscopy relies on using multiple excitation pulses to create multiple quantum coherences that provide great specificity for chemical measurements. Coherent multidimensional spectroscopy (CMDS) is the optical analogue of NMR. Current CMDS methods use three excitation pulses and phase matching to create zero, single, and double quantum coherences. In order to create higher order multiple quantum coherences, the number of interactions must be increased by raising the excitation intensities high enough to create Rabi frequencies that are comparable to the dephasing rates of vibrational coherences. The higher Rabi frequencies create multiple, odd-order coherence pathways. The coherence pathways that involve intermediate populations are partially coherent and are sensitive to population relaxation effects. Pathways that are fully coherent involve only coherences and measure the direct coupling between excited quantum states. The fully coherent pathways are related to the multiple quantum coherences created in multiple pulse NMR methods such as heteronuclear multiple quantum coherence (HMQC) spectroscopy with the important difference that HMQC NMR methods have a defined number of interactions and avoid dynamic Stark effects whereas the multiply enhanced odd-order wave-mixing pathways do not. The difference arises because CMDS methods use phase matching to define the interactions and at high intensities, multiple pathways obey the same phase matching conditions. The multiple pathways correspond to the pathways created by dynamic Stark effects. This paper uses rhodium dicarbonyl chelate (RDC) as a model to demonstrate the characteristics of multiply enhanced odd-order wave-mixing (MEOW) methods. Dynamic Stark effects excite vibrational ladders on the symmetric and asymmetric CO stretch modes and create a series of multiple quantum coherences and populations using partially and fully coherent pathways. Vibrational quantum states up to v = 6 are excited. A series of spectra provides different two-dimensional cross sections through the multidimensional parameter space involving two excitation frequencies, the frequency of the output coherence, and the excitation pulse time delays. The spectra allow the identification of 18 different overtone and combination band states. Comparison with a local mode model with two anharmonic Morse oscillators with interbond coupling shows excellent agreement.

Microstructure determination of methyl methacrylate and n‐butyl acrylate copolymers synthesized by atom transfer radical polymerization with two‐dimensional NMR spectroscopy

AbstractCopolymers of methyl methacrylate (MMA) and n‐butyl acrylate (n‐BA) were synthesized under atom transfer radical polymerization (ATRP) conditions. The molar infeed ratio was varied to obtain copolymers with different compositions. Methyl 2‐bromo propionate was used as the initiator with CuBr/Cu(0)/N,N,N′,N″,N″‐pentamethyldiethylenetriamine as the catalyst at 60 °C. Molecular weight distribution was determined by gel permeation chromatography (GPC). Copolymer compositions (FM) were calculated from 1H NMR spectra. Reactivity ratios calculated with the Mao–Huglin terminal model at a high conversion were found to be rM = 2.17 and rB = 0.47. The polymerization mechanism was studied with the α‐methyl region of MMA. The backbone methylene and carbonyl carbons of both MMA and n‐BA units were found to be compositionally as well as configurationally sensitive. Complete spectral assignments were performed with the help of heteronuclear single quantum coherence (HSQC) spectroscopy along with total correlated spectroscopy (TOCSY). Further, the assignments of the carbonyl region were made with the help of heteronuclear multiple quantum coherence (HMBC) spectroscopy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1100–1118, 2005

Biochemical characterization of muscle tissue of limb girdle muscular dystrophy: an 1H and 13C NMR study.

The metabolic differences between the muscle biopsies of patients with limb girdle muscular dystrophy (LGMD) and normal controls were characterized using high-resolution 1H and 13C NMR spectroscopy. In all, 44 metabolites were unambiguously assigned in the perchloric acid extracts of skeletal muscle tissue, using 2D double quantum filtered (DQF COSY), total correlation (TOCSY), and 1H/13C heteronuclear multiple quantum coherence (HMQC) spectroscopy. The concentrations of glycolytic substrate, glucose (p=0.03), gluconeogenic amino acids, glutamine (p=0.02) and alanine (p=0.009) together with glycolytic product, lactate (p=0.04), were found to be significantly lowered in LGMD patients as compared with controls. The reduction in the concentration of glucose may be attributed to the decrease in the concentration of gluconeogenic amino acids in the degenerated muscle. Reduction in the rate of anaerobic glycolysis and lowered substrate concentration appear to be the possible reasons for the decrease in the concentration of lactate. A significant reduction in the concentration of choline in LGMD patients was also observed compared with controls. Lower concentration of choline may be the result of decreased rate of membrane turnover in LGMD patients. The data presented here provide an insight into the potentials of in-vitro NMR spectroscopy in the study of muscle metabolism.

Transients from a mixture of [(R(O)Sn)2C(CH3)2]2 and (RCl2Sn)2C(CH3)2 [R = (SiMe3)2CH]: an identification in situ by 1D 119Sn and 2D 1H119Sn HMQC NMR spectroscopy and electrospray mass spectrometry

AbstractThe reaction of the 2,2‐bis(organodichlorostannyl)propane [(Me3Si)2CH(Cl2)Sn]2CMe2 (A) with the corresponding organotin oxide {[(Me3Si)2CH(O)Sn]2CMe2}2 (B) does not provide the corresponding normally expected tetraorganodistannoxane {[(Me3Si)2CH(Cl)SnCMe2Sn(Cl)CH(SiMe3)2]O}n but a complex reaction mixture. One major product, namely the 2,4,6,8‐tetraorgano‐2,6‐dichloro‐1,5,9‐trioxa‐2,4,6,8‐tetrastannabicyclo[3.3.1]nonane derivative [(Me3Si)2CHSnCMe2Sn(Cl)CH(SiMe3)2]2O3 (C) was identified in situ by 2D 1H119Sn and 1H13C heteronuclear multiple quantum coherence and heteronuclear multiple bond correlation NMR spectroscopy as well as electrospray mass spectrometry. Compound C is proposed to be in equilibrium with an ionic species C′, the cation of which has an adamantane‐type structure. Copyright © 2003 John Wiley & Sons, Ltd.

A novel method for the determination of stereochemistry in six-membered chairlike rings using residual dipolar couplings.

A novel method for the determination of the relative stereochemistry of six-membered chairlike ring molecules by residual dipolar couplings is presented. C-H residual dipolar couplings were used to investigate the relative stereochemistry of 4,6-O-ethylidene-d-glucopyranose. For this and similar systems it is not necessary to acquire redundant dipolar couplings and to calculate the orientation order tensor. The presented methodology is a paradigmatic leap for the determination of the relative stereochemistry or remote stereochemistry in this kind of fused ring system. Residual dipolar coupling data were collected by 1D and 2D direct-measurement heteronuclear multiple quantum coherence (HMQC) spectroscopy. It was demonstrated that direct measurement of HMQC was quick and accurate for small molecules at natural abundance.

Studies of Allyl Alcohol Radical Polymerization by PFG-HMQC and HMBC NMR at 750 MHz

The structures of poly(allyl alcohol) were characterized by one- and two-dimensional gradient-enhanced heteronuclear multiple quantum coherence (gHMQC) and gradient-enhanced heteronuclear multiple-bond connectivity (gHMBC) NMR spectroscopy. Main-chain structures and chain-end structures were identified from the spectra. The polymerization of allyl alcohol can be described by degradative chain transfer to allyl alcohol monomers, which results in distinctive chain ends as well as low molecular weight polymers. After the allylic hydrogen abstraction by initiator radicals, allyl radicals produce chain ends with vinyl groups and aldehyde groups. The chain-end structures were identified by the correlation peaks in gHMQC and gHMBC spectra.

Structural elucidation and complete assignment of a novel class of sulfonamides: bridgehead tricyclic sultams

AbstractEndocyclic sulfonamide templates bearing both an exocyclic ketone function and an internal olefin underwent reaction with a variety of hydroxylamines to effect an intramolecular nitrone–olefin cycloaddition to afford a new class of compounds suitable for derivatization by high‐throughput medicinal chemistry. Structural elucidation via complete assignment of the 1H and 13C NMR spectra of this new class of compounds was achieved using gradient‐COSY, gradient heteronuclear multiple quantum‐coherence spectroscopy and gradient heteronuclear multiple bond correlation spectroscopy. Additionally, double pulsed field gradient spin echo–nuclear Overhauser effect experiments were carried out in order to study the spatial conformation of this new type of molecule and assess the stereo‐ and regio‐selectivity of the chemical transformation. The unequivocal molecular framework and structural conformation was confirmed by X‐ray diffraction. Copyright © 2002 John Wiley & Sons, Ltd.