1H-NMR-Spektroskopische Untersuchungen an methylsubstituierten Cyclohexen-(4)-dicarbonsäure-(1,2)-anhydriden

Chemical shifts and coupling constants of methyl substituted 4-cyclohexene-1,2-dicarboxylic anhydrides were determined. The NMR data demonstrate the boat conformation of the cis-anhydrides. The orientation of the cis-anhydride ring relative to the cyclohexene boat depends on the constitution and configuration of the compounds, and can be deduced from coupling constants and δ-values of the H₁- and H₂-protons. Methyl groups in the neighbourhood of these protons shift the resonance frequencies dependent upon molecular conformation.     

Photochemical studies on η5-cyclopentadienyl(triphenylphosphine)nickelalkyl and -aryl compounds

Photo-induced degradation studies of a series of organonickel complexes of the type (η⁵-C₅H₅)(PPh₃)Ni(R) (R = CH₃, C₂H₅, C₆H₅ and C₆H₄CH₃-p) as well as certain deuterated analogs have been undertaken. Photolysis of the methyl compounds in benzene as well as benzene-d₆ gives methane as the major gaseous product, the photogenerated methyl group abstracting hydrogen from either the cyclopentadienyl ring, from the solvent, or from another methyl group. The photo-induced dealkylation of the ethyl compound gives both ethylene and ethane, and is explained by β-hydride elimination followed by subsequent reaction of the hydrido intermediate with additional ethyl compound. The photolysis of the phenyl and p-tolyl complexes in benzene solution leads to biaryl formation, both from the coupling of two coordinated aryl groups as well as interactions with the solvent. Triphenylphosphine is a product in all of these photo-decomposition studies.     

Observation and interpretation of HH coupling in 1H187Os satellite NMR spectra

The single hydride resonance observed for each of the compounds H₃Os₃(CO)₉CX (X = OMe, Br, H) has one set of ¹⁸⁷Os satellites which are further split into doublets by HH coupling. The implications of this observation for structural assignments based on ¹⁸⁷Os satellites are discussed.     

The NMR spectra of fluoroaromatics—IV: 1H and 19F spectra of some fluorinated benzofurans

The complete analyses of the ¹⁹F spectra of some fluorinated benzofurans are given. These provide an unambiguous determination of the substituent position in these compounds. Comparison of the ¹⁹F SCS and coupling constants in the benzofuran, benzothiophene and benzene series shows that ¹⁹F spectral parameters can be transposed from the benzene series with caution. A large increase in the para F? F coupling with ring closure of the hetero-ring is noteworthy. A long-range through-space ⁸J_H is reported which arises from the proximity of the 3 carboethoxy methyl group and the C₄ fluorine in these molecules.     

Synthesis and properties of new macrocyclic compounds: Utilization of bond character of hypervalent sulfur in tetraazathiapentalene derivatives

2,3‐Bis[(p‐isothiocyanatomethylphenyl)methyl]‐6,7‐dihydro‐5H‐2a‐thia(2a‐S_IV)‐2,3,4a,7a‐tetraaza‐cyclopent[cd]indene‐1,4(2H,3H)‐dithione ( 3 ), prepared by the reaction of 2,3‐dimethyl‐6,7‐dihydro‐5H‐2a‐thia(2a‐S^IV)‐2,3,4a,7a‐tetraazacyclopent‐[cd]indene‐1,4(2H,3H)‐dithione ( 1 ) with p‐xylylene diisothio‐cyanate, reacted with N,N′‐dialkyl substituted diamines to give macrocyclic compounds bearing hypervalent sulfur by a ring closure reaction in good yields. These macrocyclic compounds were converted into ring‐expanded macrocyclic compounds with release of the hypervalent sulfur by treating with NaBH₄ and CF₃COOH.     

Quantum chemical study of several monocyclic complex β‐lactam C‐3, C‐4, and N‐derivatives,and β‐ring model molecules

A quantum chemical study of several complex monocyclic 4‐benzoyl‐4‐phenyl‐β‐lactam derivatives was carried out using cyclobutane, azetidine, 2‐azetidinone, 1‐methyl‐2‐azetidinone, and 3‐methyl‐2‐azetidinone as model compounds. The optimum geometry was obtained for the different conformations. The planarity of the ring was discussed in terms of the influence of the substituents on the amide resonance. To better analyze the amide resonance and the activity of the β‐lactam ring, a vibrational study was also carried out. To examine the influence of solvent polarity on the carbonyl bands, the Fourier transform–infrared (FT‐IR) spectra of the β‐lactam monocyclic derivatives were recorded in CCl₄, C₆H₆, and CHCl₃ solutions. The normal vibrations of the β‐lactam ring in the model compounds were characterized and used in the analysis of the β‐ring of more complex derivatives. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Electron distribution in 3,4-dimethylanisole molecule according to quantum-chemical calculations

Calculations of two forms of 3,4-dimethylanisole molecule with full geometry optimization are performed by AM1, RHF/6-31G(d), and MP2/6-31G(d) methods. The form with cis location of H₃C-O and C¹–C⁶ bonds is somewhat more preferable energetically than that with the trans location. By the RHF/6-31G(d) method, this molecule is also calculated with fixed rotation angles of methoxy group around the C-O bond. It is shown that, in the first form, the negative charge on the C⁶ atom is considerably smaller than on C², while in the second form the charges are practically equal, which does not confirm the concerted effects of steric and electronic factors in reactions of 3,4-dimethylanisole with methyl isocyanate and isobutyraldehyde. The charge difference is due to the effect of methyl group in the 3-position of the aromatic ring and to the orientation of the methoxy group toward geminal C-C bonds of the ring.     

An 17O nuclear quadrupole double resonance study of several crystal hydrates

Using the technique of double resonance with coupled multiplets (DRCM), ¹⁷O double resonance signals were detected in natural abundance from the H₂O molecule in the hydrates BeSO₄ · 4H₂O, AlCl₃ · 6H₂O, CH₃COOLi · 2H₂O, LiClO₄ · 3H₂O, Sr(OH)₂ · H₂O, Ba(OH)₂ · 8H₂O, LiBr · 2H₂O and MgSO₄ · 7H₂O.Using the DRCM technique approximate values for the HOH bond angle and the OH bond length were determined from the dipolar structure present on the ¹⁷O double resonance signals. A Townes and Dailey analysis was used to examine the small differences in the ¹⁷O quadrupole coupling constants and asymmetry parameters between these samples.     

The oxidation and thermal transformations of macrooradicals in gamma irradiated cellulose

The secondary reactions of the oxidation and thermal transformations of gamma irradiated (at 77 K) and plasticized (with water) cellulose radicals were studied by 3 cm-and 2 mm-band EPR spectroscopy. The radiolysis of cotton cellulose was found to produce the H-C*=O formyl radical, and heating the irradiated samples to 190–200 K resulted in the formation of the ROO* peroxide radical. The EPR spectra of microcrystalline cellulose recorded at room temperature contained an individual triplet (α _β ^H = 2.5–2.7 mT) with an additional quadruplet structure (splitting 0.5–0.7 mT) from three γ-hydrogens. This triplet was interpreted as a signal of the primary radical at C4. The main direction of thermal transformations of primary radicals was synchronous reactions of the dehydration of the polycarbohydrate complex accompanied by the dissociation of the C-H, C-OH, and C-C bonds and elimination of H₂O, H₂, CO, and CO₂ with successive formation of allyl and then polyene radicals, which were a source of the growth of polyconjugated systems in macromolecules.     

Electron ionization mass spectrometric study of substituted alloxazine‐5‐oxides and iso‐alloxazine‐5‐oxide

The fragmentation pathways in electron ionization (EI) mass spectra of a series of new N(5)‐oxides of alloxazines and iso‐alloxazine are presented, and compared with those of substituted alloxazines and iso‐alloxazine. The EI mass spectra of these compounds showed characteristic fragmentation pathways A, B and C, started by the ejection of atomic oxygen, a HNCO molecule and an OH ^. radical, respectively. On the basis of B/E and B²/E spectra, the mechanism of elimination of the OH ^. radical is discussed. The influence of the methyl substituent in the benzene ring of alloxazine on the mass fragmentation pathways is described. Copyright © 2009 John Wiley & Sons, Ltd.     

17O, 13C, 1H NMR and IR spectroscopic investigations of (CH3)nC5H5–nRe(CO)3 analogues (n = 0–5)

¹³C, ¹H NMR investigation of the (CH_3nC₅H_5–nRe(CO)₃ Me_nCpReT) n = 0–5 analogous series showed that the signals of almost all magnetic nuclei shift upfield with increase n, which also occurs in (Me_nCp)₂M compounds (M = Fe²⁺, Co³⁺; n = 0–5). The smaller value of the C(CH₃) signal (1.5 ppm.) shifts upfield when a further methyl group is introduced into the vicinal position, this shift can be attributed to the absence of the second methyl cyclopentadienyl ring. It is noteworthy that methyl cyclopentadienyl ring coordination to the transition-metal atom results in the downfield shift of the substituted carbon atom (C_key) signal. One of the reasons for such a shift might be the reduction in screening effect of the central CpM bond π-electron current on C_key owing to nodal properties of Cp ring e-orbitals. The δ ¹³C(CO), δ ¹⁷O(CO), and v(CO) values reflect successive increases of Re → CO π-back donation with increase in n.     

Four related esters: two 4‐(aroylhydrazinyl)‐3‐nitrobenzoates and two 3‐aryl‐1,2,4‐benzotriazine‐6‐carboxylates

The molecules of both methyl 4‐[2‐(4‐chlorobenzoyl)hydrazinyl]‐3‐nitrobenzoate, C₁₅H₁₂ClN₃O₅, (I), and methyl 4‐[2‐(2‐fluorobenzoyl)hydrazinyl]‐3‐nitrobenzoate, C₁₅H₁₂FN₃O₅, (II), contain an intramolecular N—H...O hydrogen bond, and both show electronic polarization in the nitrated aryl ring. In both compounds, molecules are linked by a combination of N—H...O and C—H...O hydrogen bonds to form sheets, which are built from R₄³(18) rings in (I) and from R₄⁴(28) rings in (II). In each of methyl 3‐phenyl‐1,2,4‐benzotriazine‐6‐carboxylate, C₁₅H₁₁N₃O₂, (III), and methyl 3‐(4‐methylphenyl)‐1,2,4‐benzotriazine‐6‐carboxylate, C₁₆H₁₃N₃O₂, (IV), the benzotriazine unit shows naphthalene‐type delocalization. There are no hydrogen bonds in the structures of compounds (III) and (IV), but in both compounds, the molecules are linked into chains by π–π stacking interactions involving the benzotriazine units. The mechanism of chain formation is the same in both (III) and (IV), and the different orientations of the two chains can be related to the approximate relationship between the unit‐cell metrics for (III) and (IV).     

Study of molecular structures for arylidene derivatives of 3R‐methylcyclohexanone by 1H NMR and molecular simulation

Conformational states of the cyclohexanone ring were established for 3R‐methyl‐6‐(4‐phenylbenzylidene)cyclohexanone and several 2,6‐bis(4‐X‐benzylidene)‐3R‐methylcyclohexanones (X = Br, OCOCH₃ and C₆H₅) by ¹H NMR spectroscopy combined with molecular simulation using the semi‐empirical methods AM1 and PM3. The first compound studied contains only one arylidene group, and exists predominantly in a chair conformation of the cyclohexanone ring with an equatorial orientation of the methyl substituent in C₆D₆ and CDCl₃ solutions at room temperature (22–23 °C). In contrast, the 2,6‐bis(arylidene) derivatives of 3R‐methylcyclohexanone preferentially adopt conformations with an axially oriented methyl group. The extent of twisting of enone fragments was also characterized for the compounds studied based on simulation results and comparison of chemical shifts for the arylidene protons of appropriate model compounds. Copyright © 2003 John Wiley & Sons, Ltd.     

Synthesis of new thieno[3,2-b]pyridine derivatives by palladium-catalyzed couplings and intramolecular cyclizations

Two methyl 3-aminothieno[3,2-b]pyridine-2-carboxylates were prepared from 3-fluoro or 3-nitropicolinonitriles and methyl thioglycolate in DMF/KOH(aq). From the unsubstituted precursor in the pyridine ring, di(hetero)arylamines were obtained by C-N Buchwald-Hartwig coupling with bromonitrobenzenes and with 2-bromopyridine. In the latter case a tetracyclic compound was formed by intramolecular cyclization. Using a brominated derivative in the pyridine ring as a coupling component, it was possible to synthesize C-C (Suzuki and Sonogashira) and C-N (Buchwald-Hartwig) coupling products and a tetracyclic compound obtained by bifunctionalization of the thienopyridine system.     

The electronic structure and reactivity of small ring compounds—VII : The CMR spectra of 1-cyanobicyclo[1.1.0]butane

The 25·2 MHz CMR (FFT) spectra of 1-cyanobicyclo [1.1.0]butane are reported both with and without hydrogen decoupling. Chemical shifts are discussed in terms of dipolar resonance contributions to the ground state and the unsaturated nature of the bicyclobutane ring. The C-H coupling constants, including directly bonded and long range interactions, are reported. It is suggested that the large long range H_x′-C₂ coupling constant is a result of a favorable interaction between the H_x′-C₄ bond and C₂ bond and C₂ and that the H₃-cyano carbon coupling constant results from a 0° dihedral angle and to a small extent, if at all, from a favorable geometry. The C₁-C₂ (22 Hz) and C₁-C₃ (16 Hz) ¹³C-¹³C coupling constants are presented, compared with the calculated values, and discussed in terms of hybridization. The possibility of a negative value for the C₁-C₃ coupling constant is also considered. It is pointed out that using coupling constant-hybridization relationships and extrapolating from several known to an unknown hybridization around a carbon atom can, in many cases, lead to a sizeable error in calculated hybridization.     

2J(P,C) and 3J(P,C) Coupling Constants in Some New Phosphoramidates. Crystal Structures of CF3C(O)N(H)P(O)[N(CH3)(CH2C6H5)]2 and 4‐NO2‐C6H4N(H)P(O)[4‐CH3‐NC5H9]2

Some new phosphoramidates were synthesized and characterized by ¹H, ¹³C, ³¹P NMR, IR spectroscopy and elemental analysis. The structures of CF₃C(O)N(H)P(O)[N(CH₃)(CH₂C₆H₅)]₂ ( 1 ) and 4‐NO₂‐C₆H₄N(H)P(O)[4‐CH₃‐NC₅H₉]₂ ( 6 ) were confirmed by X‐ray single crystal determination. Compound 1 forms a centrosymmetric dimer and compound 6 forms a polymeric zigzag chain, both via ‐N‐H…O=P‐ intermolecular hydrogen bonds. Also, weak C‐H…F and C‐H…O hydrogen bonds were observed in compounds 1 and 6 , respectively. ¹³C NMR spectra were used for study of ²J(P,C) and ³J(P,C) coupling constants that were showed in the molecules containing N(C₂H₅)₂ and N(C₂H₅)(CH₂C₆H₅) moieties, ²J(P,C)>³J(P,C). A contrast result was obtained for the compounds involving a five‐membered ring aliphatic amine group, NC₄H₈. ²J(P,C) for N(C₂H₅)₂ moiety and in NC₄H₈ are nearly the same, but ³J(P, C) values are larger than those in molecules with a pyrrolidinyl ring. This comparison was done for compounds with six and seven‐membered ring amine groups. In compounds with formula XP(O)[N(CH₂R)(CH₂C₆H₅)]₂, ²J(P,CH₂)_benzylic>²J(P,CH₂)_aliphatic, in an agreement with our previous study.     

SYNTHESIS,CHARACTERIZATION, AND REACTIONS OF MONOMERIC TITANIUM COMPLEXES CONTAINING A CHELATING BIS(PHENOLATE) LIGAND [1, 2]

Abstract

The synthesis of Ti(iso)Cl₂ (iso = the dianion of 2, 2′-ethylidenebis(4, 6-di-rert-butylphenol)) is described. Metathesis reactions of this complex with Grignard reagents, as well as alkali metal salts, yielded Ti(iso)X₂ (X = CH₃, CH, Ph, CH₂SiMe₃, OCMe₃, or NMe₂). Reactions of the Ti-C bond in Ti(iso)(CH₃)₂ toward halogens, active hydrogen compounds, and acetone were studied. In addition. Ti(iso)(X)(Y) (X = CI or CH₃; Y = OC₆H₂-2, 6-^tBu₂-4-Me) could be prepared with the formation of only one coordination isomer. The new complexes have been thoroughly characterized by ¹H and ¹³C NMR spectroscopies. The solid state structure of Ti(iso)Cl₂ was determined via single crystal X-ray diffraction methods. The complex is monomeric, with approximately tetrahedral geometry about the titanium ion. The structure of Ti(iso)Cl₂ is compared to that of Ti(ultra)Cl₂ (ultra = the dianion of 2, 2′-mefhylenebis(6-tert-butyl-4-mefhylphenol)), which was redetermined to greater precision.     

Synthesis and Spectroscopic Study of Some New Phosphoramidates,Crystal Structures of N‐Benzoyl‐N′,N″‐bis(azetidinyl)phosphoric Triamide and N‐Benzoyl‐N′,N″‐bis(hexamethylenyl)phosphoric Triamide

Some new N‐carbonyl, phosphoramidates with formula C₆H₅C(O)N(H)P(O)R₂ (R = NC₃H₆ ( 1 ), NC₆H₁₂ ( 2 ), NHCH₂CH=CH₂ ( 3 ), N(C₃H₇)₂ ( 4 )) and CCl₃C(O)N(H)P(O)R′₂ (R′ = NC₃H₆ ( 5 ), NHCH₂CH=CH₂ ( 6 )) were synthesized and characterized by ¹H, ¹³C, ³¹P NMR and IR spectroscopy and elemental analysis. The structures were determined for compounds 1 and 2 . Compound 1 exists as two crystallographically independent molecules in crystal lattice. Both compounds 1 and 2 produced dimeric aggregates via intermolecular ‐P=O…H‐N‐ hydrogen bonds, which in compound 2 is a centrosymmetric dimer. In compounds with four‐membered ring amine groups, ³J(P,C)>²J(P,C), in agreement with our previous studies about five‐membered ring amine groups. Also, ³J(P,C) values in compounds 1 and 5 are greater than in compounds with five‐, six‐ and seven‐membered ring amine groups.     

Experimental and theoretical study of the intramolecular C–H···N and C–H···S hydrogen bonding effects in the 1H and 13C NMR spectra of the 2‐(alkylsulfanyl)‐5‐amino‐1‐vinylpyrroles: a particular state of amine nitrogen

In the ¹H NMR spectra of the 1‐vinylpyrroles with amino‐ and alkylsulfanyl groups in 5 and 2 positions, an extraordinarily large difference between resonance positions of the H_A and H_B terminal methylene protons of the vinyl group is discovered. Also, the one‐bond ¹J(C_β,H_B) coupling constant is surprisingly greater than the ¹J(C_β,H_A) coupling constant in pyrroles under investigation, while in all known cases, there was a reverse relationship between these coupling constants. These spectral anomalies are substantiated by quantum chemical calculations. The calculations show that the amine nitrogen lone pair is removed from the conjugation with the π‐system of the pyrrole ring so that it is directed toward the H_B hydrogen. These factors are favorable to the emergence of the intramolecular C–H_B???N hydrogen bonding in the s‐cis(N) conformation. On the other hand, the spatial proximity of the sulfur to the H_B hydrogen provides an opportunity of the intramolecular C–H_B???S hydrogen bonding in the s‐cis(S) conformation. Presence of the hydrogen bond critical points as well as ring critical point for corresponding chelate ring revealed by a quantum theory of atoms in molecules (QTAIM) approach confirms the existence of the weak intramolecular C–H???N and C–H???S hydrogen bonding. Therefore, an unusual high‐frequency shift of the H_B signal and the increase in the ¹J(C_β,H_B) coupling constant can be explained by the effects of hydrogen bonding. Copyright © 2013 John Wiley & Sons, Ltd.     

Electron spin resonance of gamma-irradiated (CH3)4NPF6 and (CH3)4NBF4 single crystals

The electron spin resonance spectra of γ-irradiated tetramethylammonium hexafluorophosphate and tetramethylammonium tetrafluoroborate single crystals and powders have been investigated between 120–350 K. The dominant species in both compounds have been attributed to (CH₃)₃N⁺ radical. All hyperfine coupling constants of the methyl protons and the nitrogen nucleus have been found to be temperature independent and determined. It is concluded that the motional behaviour of (CH₃)₃N⁺ does not differ in tetramethylammonium compounds. The outer lines of the main spectrum of (CH₃)₄NPF₆ have been attributed to PF^-₅ and FPO^-₂ radicals and the anisotropic behaviour of the hyperfine coupling constants has been presented.