Chemical Arguments Research Articles

A 13C‐NMR assignment study of a series of 2,3,4,5‐tetrahydro‐1‐methyl‐1H‐1,5‐benzodiazepine‐2,4‐diones

AbstractThe natural abundance 13C‐nmr spectra of a series of 2,3,4,5‐tetrahydro‐1‐methyl‐1H‐1,5‐benzodiazepine‐2,4‐diones have been recorded: two of these compounds, clobazam and triflubazam, are clinically used as psychotherapeutic agents. The assignments of the various resonances have been made by chemical shift arguments, by the analysis of the fine splittings caused by one bond and long range couplings, and also by comparison with model compounds.

Carbon-13 Nuclear Magnetic Resonance of Some New β-Blockers. - Part I

Abstract The assignment of the Carbon - 13NMR resonances of Penbutolol, Timolol, Pindolol and Nadolol, new and non-cardioselective β-adrenergic blockers, in deuterated chloroform or deuterated dimethylsulfoxide has been made. The assignments were made using model compounds, chemical shift arguments, peak intensities and signal multiplicities observe d in the single-frequency off-resonance decoupled (SFORD) spectra. From the 13C-NMR chemical shifts it can be concluded that the aromatic ring systems in these compounds have negligible effects on the 2-propanol side-chain which is essential for the biological activity of β-adrenergic blockers.

Computerunterst�tzte Zuordnung von13C-NMR-Spektren

A computer program for the assignment of13C resonances to the respective carbons of a known structure is presented. The algorithm is based on the prediction of chemical shift ranges from a data base containing carbon-centered substructural environments and their corresponding chemical shifts. The method permits a stepwise solution of the assignment problem using chemical shift arguments up to a five-bond radius.

13C NMR studies on dibenz[b,f]azepines

AbstractThe assignment of the 13C nmr resonances of six dibenz[b,f]azepines (1‐6) in dimethylsulfoxide‐d6 was made using chemical shift arguments, coupling to a fluorine substituent, selective proton decoupling, and fully coupled spectra. Exchange of the heterocyclic N‐H with deuterium simplified and clarified the coupled spectrum of 1.

Abkömmlinge der 3‐Chinolincarbonsäure mit Sauerstoffsubstitution in Stellung 4, 5 and 8: Synthese, Reaktionen, NMR.‐Studien

Derivatives of 3‐Quinolinecarboxylic Acid with Oxygen Substitution in Positions 4, 5 and 8: Synthesis, Reactions, NMR. StudiesStarting from either 1, 4‐dibenzyloxybenzene (7) or 2, 5‐dimethoxyaniline (16), synthetic routes have been developed to benzenoid and quinoid derivatives of 4‐oxo‐1, 4‐dihydro‐3‐quinolinecarboxylic acid with O‐bearing substituents in the positions 5 and 8 (compounds 12‐15, 19, 20, 23, and 24). With the 1‐ethyl‐4, 5, 8 trioxo acid 14 as a dienophile, a series of linear tricyclic diene adducts (29‐32) has been prepared, the structures of which were further modified by aromatization, reduction or dehydrogenation (compounds 33‐40). A series of benzenoid and quinoid compounds with an additional substituent in position 6 or 7 (Table 1) has been derived mainly from the quinone 14, primarily by addition of nucleophiles and eventually subsequent steps, and by aromatic electrophilic substitution of the 1‐ethyl‐5, 8‐dimethoxy acid 23. The substitution pattern of some of these compounds has been elucidated by detailed 13C‐NMR. studies (Table 2) and/or nuclear Overhauser‐effect studies (Table 3). Correlations, based essentially on chemical arguments, allowed to define the structures of most of the residual new compounds (Table 4).

Chemistry of the phenoxathiins and isosterically related heterocycles. XXIII . 1‐azathianthrene: First reported synthesis of a monoazathianthrene and the investigation of the 13C‐NMR spectrum using two‐dimensional NMR techniques

AbstractThe reaction of the dianion of 3‐mercaptopyridin‐2(1H)‐thione with 2‐chloronitrobenzene in N,N‐dimethylformamide leads to the formation of 1‐azathianthrene, the first reported mono‐aza analog of the thianthrene ring system. A partial assignment of the 13C‐nmr spectrum of the title compound is reported, the assignment based on chemical shift arguments, spin‐lattice (T1) relaxation times and 1H‐13C spin coupling constants. Amplitude modulated two‐dimensional Fourier transform (AM2DFT) techniques were employed for the acquisition of the heteronuclear spin‐coupling constants.

The utilization of chemical shift and spin‐lattice (T1) relaxation time data for the discrimination of isomeric indenoisoxazoles

AbstractTreatment of 2‐pivaloyl‐1,3‐indandione with hydroxylamine leads to the formation of a pair of isomeric indenoisoxazoles, the product formed dependent upon the cyclization conditions. Under acidic conditions, 8‐t‐butylindeno[1,2‐c]isoxazol‐7‐one (5) is formed while under neutral or basic conditions, an oxime, 2, is generated which may then be cyclized under acidic conditions to give 3‐t‐butylindeno[1,2‐c]isoxazol‐4‐one (4). Although these isomeric indenoisoxazoles may be discriminated by chemical means, we were interested in developing an unequivocal method for distinguishing these and potentially other isomeric pairs by spectroscopic means. A 13C‐nmr based method for the discrimination of these isomers which is based on the utilization of chemical shift arguments and spin‐lattice relaxation data is thus presented.

A carbon 13‐NMR assignment study of a series of oxetanes derived from carbonyl compounds and furan and thiophene derivatives

AbstractThe assignment of the carbon‐13 nmr resonances of a series of oxetanes derived from the photoaddition of benzophenone and 2‐naphthaldehyde to furan and some of its methyl derivatives and of benzophenone to 2,5‐dimethylthiophene has been made. The assignments were made by chemical shift arguments, by the use of C‐13 labelling when required and different decoupling techniques. This information may be useful in the identification of new compounds with analogous carbon skeleton.

Azo—hydrazone tautomerism in azo dyes. II. Raman, NMR and mass spectrometric investigations of 1-phenylazo-2-naphthylamine and 1-phenylazo-2-naphthol derivatives

In a comparative study 1-phenylazo-2-naphtylamines, 1(R) , and 1-phenylazo-2-naphthols, 2(R) , with R = MeO, CN and NO 2 have been investigated by means Raman, NMR and mass spectroscopy in order to elucidate their tautomeric structures. Based on Raman spectra obtained under resonance conditions, the trans azo structure has been inferred for 1(R) with all the substituents under scrutiny. From the naphthol derivatives the hydrazone predominance has been confirmed for 2(CN) and 2(NO 2 ) in agreement with previous reports using different techniques. No useful Raman spectrum could be obtained, however, for 2(MeO) due to the inherent fluorescence of this dye. Here nuclear magnetic resonance proved to be helpful, yielding a K T of 0·7 from both 13C and 1H chemical shift arguments. For the other five dyes the Raman results have been corroborated by the measurement of carbon and proton chemical shifts [δ(C-2), δ(H-3) and δ(H-8)] and the coupling coupling constants J(H-3, H-4). In the mass spectrometer all compounds behaved similarly irrespective of the tautomeric structures in solution or in the solid state with an 'azo-type' fragmentation pattern originating from a primary CN cleavage of the molecular ion. A theoretical discussion is provided to show that this decomposition pathway for the hydrazones is not contradictory to the results obtained above. An initial CN cleavage instead of the generally assumed NN cleavage of the hydrazone molecular ion can occur in certain cases, particularly with electron withdrawing R, thus leading to the observed azo type decomposition. From the present results it became obvious that mass spectrometry is not a generally applicable tool for azo-hydrazone structure discrimination.

A theoretical study of defects in amorphous group-V semiconductors

Clusters of about 55 atoms have been built to model possible bonding coordination defects (BCDs) in the amorphous group-V semiconductors (P, As, Sb). A tight-binding Hamiltonian is used to examine trends in the position and localisation of defect states due to the BCDs. Whereas similar studies have in the past included only nearest-neighbour interactions, the authors now explicitly consider longer-range effects. These are found to be crucial in determining the properties of certain of the defect states, especially these associated with overcoordinated atoms. They find that dangling bond states more closer to mid-gap as one goes down the group and that states due to the overcoordinated atom lie near mid-gap in all three elements. Both these results can be understood by chemical arguments and because they are in good agreement with experiment for As can be applied with confidence to amorphous P.

REE geochemistry and isotopic data of Archean silicic volcanics and granitoids from the Pilbara Block, Western Australia: implications for the early crustal evolution

Eighteen silicic volcanic rocks of the Warrawoona Group and ten associated plutonic rocks from the Pilbara Block, Western Australia, have been chosen for geochemical and isotopic studies. Silicic volcanics of the UNSB (Upper member of North Star Basalt) are dated at 3.56—3.57 ▪, by both the Rb-Sr and the Sm-Nd methods. The respective 1 (initial isotopic composition) values are 0.7005 ± 5 (Sr) and 0.50810 ± 39 (Nd). This age is consistent with the stratigraphic interpretation that the TalgaTalga Subgroup, in which the North Star Basalt occupies the lowermost position, is overlain by the Duffer Formation, whose age was earlier established at 3.45 ▪ by the zircon U-Pb method. The new Rb-Sr data on six silicic lava samples from the Duffer Formation yield an isochron of 3.23 ± 0.28 (2v). Though imprecise, this age agrees with the zircon age within error limits. Rb-Sr ages of 2.3–2.4.▪ obtained for the ‘Panorama’ rocks and the Wyman Formation do not correspond to their initial eruption ages. Chemical arguments suggest that these ages represent the time of metasomatism associated with the widespread thermal event in this region about 2.3–2.4 ▪ ago.Geochemically, most of these analyzed rocks (volcanic and plutonic) are of tonalite-trondhjemitegranodiorite (TTG) composition, a typical feature found in many other Archean terrains. They generally show fractionated REE patterns, except the Panorama Formation rocks. Furthermore, the Wyman Formation rhyolites and the post-tectonic adamellites show significant negative Eu anomalies, suggesting a similar mode of magma generation and a probable genetic link. Theoretical considerations suggest that most of these TTG rocks could have been generated by partial melting of amphibolitic or basaltic sources, followed by fractional crystallization.Although the Archean granitic gneisses often possess mantle-like Isr values, the trace element data indicate that they could not have been derived by direct melting of upper mantle materials. The immediate tectonic implication is that in any Archean terrain, the formation of Na-rich continental crust of TTG suite must be preceded by the presence of basaltic crust. The occurrence of this basaltic crust is a matter of controversy. Such crust might have been totally destroyed by repeated melting processes, or its remnants are now represented by some of the mafic-ultramafic enclaves within the tonalite-trondhjemite batholiths.

Passivation and interface state studies on n-GaAs

The surface preparation of GaAs with HCl solutions is shown to be very important in determining anodic oxidation characteristics as well as resulting interface state densities on oxidized samples. Auger data and chemical thermodynamic arguments are used to show that the HCl pretreatment selectively removes Ga while leaving elemental arsenic on the GaAs surface. Interface state densities are compared for various HCl pretreatment times. Growth of the anodic oxides in neutral electrolytes containing KF are beneficial for the interface state density.

Synthesis of spiro[isobenzofuran-1(3H),4'-piperidines] as potential central nervous system agents. 6. Synthesis, 13C NMR, and biological evaluation of cis- and trans-4-amino-3'-arylspiro[cyclohexane-1,1'(3'H)-isobenzofuran] derivatives.

4-(Dimethylamino)- and 4-(methylamino)-3'-arylspiro[cyclohexane-1,1'(3'H)-isobenzofuran] derivatives were prepared as analogues of previously reported 3-arylspiro[isobenzofuran-1(3H),4'-piperidines]. Metalation of benzanilide with n-butyllithium, addition of 4-(dimethylamino)cyclohexanone, and acidification afforded a mixture of cis- and trans-4-(dimethylamino)spiro[cyclohexane-1,1'(3'H)-isobenzofuran]-3'-ones (1a,b), which were separated by fractional crystallization. Addition of aryllithium or aryl Grignard reagents to 1a,b and formic acid reduction afforded cis- and trans-4-(dimethylamino)-3'-arylspiro[cyclohexane-1,1'(3'H)-isobenzofurans] 3a-f, which were converted to secondary amine analogues 5a-e. Tentative stereochemical assignments are based on chemical arguments and are supported by 13C NMR chemical shift data. Marked inhibition of tetrabenazine-induced ptosis is a property of most antidepressants, and significant antitetrabenazine activity is observed for several of these compounds. Optimal antitetrabenazine activity is associated with the cis-3'-phenyl series, and the cis secondary amine 5a is approximately twice as potent as the cis tertiary amine 3a. The various compounds are relatively weak with respect to potentiation of L-5-hydroxytryptophan-induced seizures.

ChemInform Abstract: SULFONATION OF STRYCHNINE AND SOME RELATED COMPOUNDS BY SULFUR DIOXIDE‐MANGANESE DIOXIDE (THE LEUCHS REACTION)

AbstractManganese Dioxide (the Leuchs Reaction).

A carbon‐13 Nmr assignment study of 3,5‐diarylisoxazoles

AbstractThe assignment of the carbon‐13 nmr resonances of 3‐(aryl)‐5‐phenylisoxazoles (I) and 3‐phenyl‐5‐(aryl)‐isoxazoles (II) in dimethylsulfoxide‐d6 has been made. The assignments were made by using model compounds, chemical shift arguments, coupling with fluorine substituents, and shifts resulting from quaternization of the isoxazole ring. A carbon‐13 nmr method for distinguishing between I and II which can be produced simultaneously by certain synthetic methods is presented.

Sulfonation of strychnine and some related compounds by sulfur dioxide – manganese dioxide (the Leuchs reaction)

On the basis of pK measurements, 13C nmr, and chemical arguments, the zwitterionic structures 3 and 4 have been assigned to the two minor products obtained by sulfonating strychnine or brucine in water with a mixture of sulfur dioxide and manganese dioxide. The same reagent sulfonates the quaternary salts of strychnine and brucine to give betaines, but fails to sulfonate many other strychnine derivatives as well as a number of other alkaloids examined.

Assignment of the 13C chemical shifts of ethidium bromide and analogs in D2O solution

AbstractThe 13C resonances of ethidum bromide (1), dimidium bromide (2) and 3,8‐diamino‐5‐methylphenanthridinium chloride (3) in D2O solution have been assigned. Assignments were made using fully coupled spectra, spectra obtained from a selected 180°‐τ‐90° pulse sequence in conjunction with gated irradiation to obtain NOE intensification, selective proton decoupling, chemical shift arguments and by noting the effect of pD on the 13C chemical shifts of 1 and 3.

Laboratory and Modeling Studies of Chemistry in Dense Molecular Clouds

A chemical evolutionary model with a large number of species and a large chemical library is used to examine the principal chemical processes in interstellar clouds. Simple chemical equilibrium arguments show the potential for synthesis of very complex organic species by ion-molecule radiative association reactions.

Structure and structure formation of viroids

The structure of viroids and the mechanism of structure formation were investigated by different methods. Results from gel analysis, partial degradation pattern, electron microscopy, dye binding, hydrodynamic studies, and temperature-jump kinetics were interpreted in a common structural and mechanistic scheme. Gel analysis, electron microscopy and kinetic investigations show that viroids may assume the native as well as metastable conformations under the same conditions. The native conformation is obtained by complete renaturation, i.e. slow cooling throughout the transition range (e.g. 52 to 48 ° C for potato spindle tuber viroid (PST viroid) in 0.01 m-sodium cacodylate, pH 6.8). In contrast, metastable conformations were trapped if viroids were redissolved in the cold from their ethanol precipitate or if they were denatured and cooled quickly. The native secondary structure of the recently sequenced PST viroid (Gross et al., 1978) was optimized for the free energy of base-pairing. The scheme agrees with that proposed by Gross et al. (1978), which was derived from chemical arguments. The extended structure does not undergo tertiary structure folding under a wide range of conditions, as was concluded from electron microscopy, sedimentation measurements and binding studies of ethidium bromide and a new dye specific for A · U pairs (2-(4′-aminophenyl)-5-(4′-methylpiperazin-1″yl)-benzirnidazol). Intermediate structures during viroid denaturation were analysed on theoretical and experimental grounds. The experimental data, in combination with the model calculations, show that all of the native base-pairs of viroids are dissociated in one highly co-operative main transition, and that during the same process very stable hairpins are formed that are not present in the native structure. The formation of stable hairpins induces a new type of long range cooperativity, which is responsible in part for the high co-operativity observed experimentally. This interpretation is in good agreement with kinetic results presented elsewhere (Henco et al., 1979). In order to understand the uniqueness of viroids, the structure and the conformational transitions of circular RNA molecules of the same base composition as PST viroids but with 359 nucleotides arranged randomly, were studied theoretically. Common viroid features, such as the number of base-pairs, the high co-operativity and the formation of very stable hairpins, are found to be improbable in such random sequences. It is concluded that various viroid species, although differing in nucleotide sequence, follow common principles of structure and structure formation.

The molecular beam electric resonance spectrum of OPF3

The molecular-beam electric resonance spectrum of phosphoryl fluoride (16OPF3) has been investigated. A hyperfine study of (K = 0) multiplets has been combined with earlier magnetic resonance data and chemical shift arguments to obtain four spin–rotation constants and two tensor spin–spin constants. The results (in kHz) are: [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], dFF = −2.3(9), and dFF = 4.1(9). A study of molecular magnetic effects has yielded the two molecular g-factors [Formula: see text] and [Formula: see text] as well as the anisotropy in the susceptibility [Formula: see text]. The molecular quadrupole moment has been calculated. From a study of the Stark effect, the electric dipole moment has been determined for the ground vibrational state and for the (ν5 = 1) and (ν6 = 1) fundamentals. The results are: μ = 1.86847(10) D, (μ5 − μ)/μ = −3.49(4) × 10−3, and (μ6 − μ)/μ = −0.65(4) × 10−3. For each of these two excited vibrational states, the l-doubling constants qt, and DqJ(t) (t = 5,6) have been obtained. This work demonstrates that the molecular beam electric resonance method can be applied to symmetric tops with relatively large room temperature rotational partition functions by reducing the rotational temperature to a few degrees kelvin with the seeded beam technique.