Ring-chain tautomerism of aldehyde n-methylated semicarbazones

Ring-chain tautomerism of thirty-six aldehyde semicarbazones was studied by nmr spectro-scopy. The 2,4-dimethylsemicarbazones of benzaldehyde, p-tolualdehyde, p-anisaldehyde, and P-chlorobenzaldehyde exist as chain forms in DMSO-d₆, but as both ring and chain forms in deuteriotriiluoroacetic acid. Unlike these semicarbazones, the aldehyde semicarbazones of N-unsubstituted semicarbazide, 2-methylsemicarbazide, and 4-methylsemicarbazide did not cyclo-isomerize in either DMSO-d₆ or deuteriotrifluoroacetic acid. These results indicate that protona-tion of the C=N nitrogen atom and steric hindrance of the 2-methyl group with an aromatic group at the C=N carbon atom in the chain form cause cycloisomerization to ring isomers.     

1H NMR study of cyclo-L-Thr-L-Thr and cyclo-L-Thr-L-His conformations

Cyclodipeptides containing L -Thr and L -His residues have been studied by ¹H NMR in D₂O and DMSO-d₆. In the neutral form in D₂O as in DMSO-d₆, the folded form of the L -His residue is not unique. The diketopiperazine ring seems to be not strictly planar.     

Structure of aldose condensation products with 2-hydroxyand 2-sulfanylbenzohydrazides

The structure of the condensation products of 2-hydroxy- and 2-sulfanylbenzohydrazides with a series of aldoses (L-arabinose, D-ribose, L-ramnose, D-galactose, D-glucose, D-mannose) was studied by ¹H and ¹³C NMR spectroscopy. The condensation products of monosaccharides with 2-hydroxybenzohydrazide in DMSO-d ₆ solution exist as equilibrium mixtures of linear hydrazone and cyclic pyranose and furanose forms, the cyclic tautomers being represented by two stereoisomers (α- and β-anomers). The aldose condensation products with 2-sulfanylbenzohydrazide in the crystalline state have cyclic 1,3,4-benzothiadiazepine structure, while in DMSO-d ₆ solution they undergo complete or partial isomerization into cyclic pyranose tautomer.     

Determination of the erythro and threo configuration of the two diastereoisomeric 2-amino-3-mercaptobutyric acids by NMR spectroscopy of derived thiazolidines

A study of the ¹H and ¹³C NMR spectra of the N-formyl-2,2,5-trimethyl-4-carboxythiazolidines and the N-formyl-4-carboxy-5-methylthiazolidines derived from the two diastereoisomeric 2-amino-3-mercapto-DL-butyric acids, permits unambiguous assignment of the erythro and threo configuration of these amino acids. The spectra of the N-formylthiazolidines, recorded in DMSO-d₆ solution, reveal the presence of two conformational isomers with a low rate of interconversion. The geometry around the carbon–nitrogen bond and correlated conformations of the 5-membered ring in both forms are discussed.     

13C-NMR study of 4H-1,3,4-thiadiazino[5,6-b]quinoxalines. A proof for the N5-deuteration in deuteriotrifluoroacetic acid

The carbon signals of the 2-acylamino-4H-1,3,4-thiadiazino[5,6-b]quinoxalines 1a,b , 2-acylamino-4H-1,3,4-thiadiazino[5,6-b]quinoxaline 1,1-dioxides 2a,b , and 2-amino-4H-1,3,4-thiadiazino[5,6-b]quinoxaline 3 in deuteriodimethyl sulfoxide and in deuteriotrifluoroacetic acid were assigned by the nmr (HMBC, HMQC) spectroscopy. The comparison of the carbon chemical shifts in deuteriodimethyl sulfoxide with those in deuteriotrifluoroacetic acid clarified that compounds 1a, 1b , and 3 were deuterized at the N₅-position in deuteriotrifluoroacetic acid, while the 1,1-dioxides 2a,b did not undergo the N₅-deuteration in deuteriotrifluoroacetic acid.     

13C and 1H NMR spectral studies of N-alkylmethylquinolinium salts

¹³C and ¹H chemical shifts of fourteen N-alkylmethylquinolinium salts in DMSO-d₆ are reported, and compared with those of the eleven corresponding methylquinoline bases. The influence of ring substitution by methyl groups in the salts and substitution at the nitrogen atom and the effect of the anion are discussed.     

13C-NMR study on the tautomerism of 3-(arylhydrazono)methyl-2-oxo-1,2-dihydroquinoxalines between the hydrazone imine and diazenylenamine forms

The ¹³C-nmr study was carried out for the tautomerism of the 3-(arylhydrazono)methyl-2-oxo-1,2-dihy-droquinoxalines 1a-g and 2a-e between the hydrazone imine A and diazenylenamine B forms, providing the carbon chemical shifts for the tautomers A and B of compounds 1a-g and 2a-e. The comparison of the carbon chemical shifts for the tautomer B of compounds 1d, 1f , and 2b in deuteriodimethyl sulfoxide with those in deuteriotrifluoroacetic acid showed that the C_4a, C₅, and diazenyl carbons were considerably shielded presumably due to the azo N-deuteration in deuteriotrifluoroacetic acid.     

Carbon-13 nuclear magnetic resonance studies of some 9-alkoxy- and 9-alkylthio-acridines

Carbon-13 NMR parameters were determined for some 9-alkoxy- and 9-alkylthio-acridines as solutes in DMSO-d₆ or D₂O.     

1H, 13C, 15N NMR and IR Spectroscopic Studies of a Rh(II) Complex of Thiourea

A rhodium(II) complex of thiourea (Tu), Rh₂(OAc)₄Tu₂, has been prepared from Rh₂(OAc)₄(H₂O)₂ and characterized. A shift of the ν(N?H) vibration towards higher frequencies in the IR spectrum is consistent with sulfur coordination to rhodium(II). ¹³C NMR spectra recorded in DMSO-d ₆ reveal that thiourea is replaced by DMSO-d ₆ solvent, followed by replacement of acetate ions by free thiourea. ¹⁵N NMR indicates some nitrogen involvement in coordination to form an S?N chelate.     

Synthesis of 2-(1-Alkoxyvinyl)oxazolidines by Condensation of 2-Alkoxypropenals with 2-Aminoalkanols and Ring-Chain Tautomerism of the Products

Reactions of 2-alkoxypropenals with 2-aminoalkanols afforded tautomeric mixtures of previously unknown 2-(1-alkoxyvinyl)oxazolidines and imino alcohols. The condensation takes 2 h at room temperature (89-100%) or 1-5 min under microwave irradiation. The tautomeric equilibrium shifts toward the open-chain structure with increase in the solvent polarity (CDCl₃, CD₂OD, DMSO-d ₆, D₂O) and temperature. The presence of substituents in the oxazolidine ring raises the stability of the cyclic tautomer.     

The proton magnetic resonance spectra of d-aldosterone and its acetylated derivatives

PMR spectra of d-aldosterone, its acetylated derivatives and related compounds were studied using 60 and 100 MHz spectrometers at various temperatures, in CDCI₃, DMSO-d₆, CD₃OD and D₂O. The aldehyde form ( 1 ) was not found. The solutions of d-aldosterone and aldosterone-21 acetate contain a mixture of the cyclic forms with one (11–18) hemi-ketal bridge ( 2 ) and two (11–18, 18–20) hemi-ketal bridges ( 3 ). Preliminary results concerning modifications of the relative concentration of 2 and 3 obtained by varying solvents and temperature are given. Aldosterone-diacetate exists in only one form, most likely form 2 . There is restricted rotation of the group at C-21 in d-aldosterone and in form 3 of aldosterone 21-acetate. One molecule of water is probably bound to d-aldosterone.     

Unusual structural isomerization of monopropiophenone thiocarbonohydrazone

Monopropiophenone thiocarbonohydrazone has been isolated in both linear and cyclic isomeric forms. Each form has been shown to isomerize and exist in equilibrium with the other in DMSO-d₆ solution by ¹H and ¹³C NMR spectroscopy. The kinetics of this transformation show attainment of equilibrium in approximately 6 h, with a linear to cyclic configuration ratio of 40:60.     

Assignment and solvent dependence of the carbon-13 nuclear magnetic resonance spectrum of nicotine

The ¹³C nmr spectrum of nicotine is assigned in Acetone-d₆, DMSO-d₆, Pyridine-d₅, and deuterium oxide (pD 10.7, 5.4, < 1). Attention is focused on assignment of the closely-spaced C(2) and C(6) resonances, using selective decoupling, population transfer, and long-range coupling constant measurements. C(2) resonates at lower field in the organic solvents hut at higher field in deuterium oxide at all pD values investigated.     

The NMR spectra of the porphyrins: 23—Metalloporphyrins as diamagnetic shift reagents,chemical applications

Some applications illustrating the use of zinc (II) meso-tetraphenylporphyrin (ZnTPP) as a diamagnetic shift reagent are described. The complexation shifts (ΔP) in a series of substituted pyridines are shown to be determined by both the basicity of the coordinating nitrogen atom and steric effects of ortho-substituents. The selectivity of ZnTPP (N»O) in the simplification of the spectra of multifunctional ligands is demonstrated. Addition of the reagent neither affects the rotamer populations of the Inderal side-chain nor produces any distortion of the 2-benzylmorpholine ring. In addition, the substrate-reagent solution may be shaken with D₂O to identify exchangeable protons. The application of ZnTPP in structural problems involving substituted imidazo[2,1-b]thiazoles and 2-benzyl-1,3-dioxopyrrolo[3,4-c]pyridines allows unambiguous identification of the possible structural isomers. To overcome the solvent limitations of ZnTPP, the more soluble Co(III)TPPBr can be used successfully as a shift reagent in DMSO-d₆, CD₃OD and acetone-d₆ solutions.     

Synthesis of Mono- and Disaccharide 4-[(ω-Sulfanylalkyl)oxy]benzoylhydrazones as Potential Glycoligands for Noble Metal Nanoparticles

A procedure has been developed for the synthesis of previously unknown aldose 4-[(ω-sulfanylalkyl) oxy]benzoylhydrazones (where alkyl is hexyl or decyl and aldoses are D-glucose, D-galactose, D-maltose, and D-lactose) that a repromising glycoligands for noble metal nanoparticles. According to the ¹H and ¹³C NMR data, 4-[(ω-sulfanylalkyl)oxy]benzoylhydrazones derived from D-glucose, D-maltose, and D-lactose in crystal and in DMSO-d₆ solution have exclusively the cyclic pyranose structure (α- and β-anomers). D-Galactose 4-[(ω-sulfanylalkyl)oxy]benzoylhydrazones in DMSO-d₆ solution exist as tautomeric mixtures of cyclic pyranose and open-chain acylhydrazone structures.

     

Hydrogen and carbon NMR data for aminoquinolines and aminoisoquinolines

Hydrogen and carbon chemical shifts and H? H and C? H couplings are reported for six aminoquinolines and six aminoisoquinolines in DMSO-d₆.     

Isolation of the saddle and crown conformers of cyclotriveratrylene (CTV) oxime

The oxime of cyclotriveratrylene (CTV) has been prepared and the individual crown and saddle conformers were isolated and characterized. The equilibrium constant was measured in CDCl₃ and in DMSO-d₆ and was shown to favor the crown conformer by an order of magnitude in DMSO-d₆, relative to an approximately equal mixture at equilibrium in CDCl₃. The time course for interconversion of the saddle to the crown was measured by ¹H NMR and the t_1/2 of the saddle was determined to be 2.45 h in CDCl₃ at 25 °C, and 3.71 h in DMSO-d₆.     

Carbon-13 nuclear magnetic resonance studies of leonurine hydrochloride and its analogues

The ¹³C NMR spectra of leonurine hydrochloride and thirteen of its analogues in DMSO-d₆ have been analyzed. Changes in the aromatic substituents have no significant effect on the chemical shifts of the side chain methylene carbons indicating that they do not influence the conformation of the latter. Observed deviations from additivity of substituent effects for the methylene carbon chemical shifts suggest that the methylene side chains of these compounds may be more tightly coiled than are the corresponding n-alkanes. In representative cases no change in conformation is evident in 50% aqueous DMSO-d₆ solutions, indicating that similar considerations may apply in aqueous media.     

NMR studies on aromatic compounds: VI—13C NMR spectra of some mono- and disulphonato-substituted hydroxynaphthoic acids in DMSO-d6–water solution

Carbon-13 NMR spectra of sulphonatosubstituted hydroxynaphthoic acids were recorded with and without proton noise decoupling in DMSO-d₆–water (2:1 v/v). The ¹³C chemical shifts were assigned by using substituted naphthalenes as reference compounds. The additivity law of the substituent effects is discussed for the naphthalenesulphonic acids studied.     

Substituent effects on carbon-13 NMR chemical shifts of side chain carbonyl carbons of 4-substituted 1-naphthamides

Substituent induced¹³C NMR chemical shifts of side chain carbonyl carbons of several 4-substituted 1-naphthamides have been measured in DMSO-d ₆ solvent. Analysis of the substituent induced chemical shifts by the DSP equation gave the regression equation. Both {ie207-1} and {ie207-2} values were negative. The negative sign on {ie207-3} term indicates the operation of a reverse substituent effect and that π-polarisation is the important mechanism for the transmission of substituent effects by inductive effect. Theperi-hydrogen interaction in naphthamides forces the amide group out of the plane of the naphthalene ring.