Substituent and temperature controlled tautomerism: Multinuclear magnetic resonance, X-ray, and theoretical studies on 2-phenacylquinolines

Proton-transfer equilibria in chloroform solution of twelve 2-phenacylquinolines were studied by 1H, 13C and 15N NMR spectroscopies. The (Z)-enaminone form stabilized by an intramolecular hydrogen bond was found to prevail in all cases. Electron-donating substituents in the phenacyl part of the molecule lead to an increase of the ketimine form (to 33% for p-NMe2). Variable temperature 1H NMR measurements show that higher temperatures have the same effect. The negative logarithm values of the equilibrium constant, pKT, were found to be linearly dependent on Hammett σ substituent constants. The pKTvs. temperature correlation also has a linear character. In general, strong electron-withdrawing…

NMR studies of benzoannulation in lithium, sodium and potassium ortho-formylphenolates

Abstract Lithium, sodium and potassium derivatives of (benzo)salicylaldehydes have been prepared and characterized by 1 H and 13 C NMR in order to see how the metal cation and benzoannulation affect spectral parameters. There is no qualitative effect of the alkali metal atom in the compounds studied (from this point of view salicylaldehydes remind β-diketones). On the other hand, 1 H chemical shifts of the hydroxyl and formyl protons and 13 C chemical shifts of C2 (bearing OX, X = H, Li, Na or K) and of that the formyl carbon show the most significant variations being the best indicators of aromatic character of the six-membered quasi-ring of salicylaldehyde. In contrast, C1 (bearing formyl…

?-Phenylsulfonyl-N-arylacetamides (?-phenylsulfonylacetanilides):1H,13C and15N NMR spectral characterization

Two (E)-2-({[4-(dialkylamino)phenyl]imino}methyl)-4-nitrophenols.

The slow evaporation of analytical NMR samples resulted in the formation of crystals of (E)-2-({[4-(dimethylamino)phenyl]imino}methyl)-4-nitrophenol, C15H15N3O3, (I), and (E)-2-({[4-(diethylamino)phenyl]imino}methyl)-4-nitrophenol, C17H19N3O3, (II). Despite the small structural difference between these twoN-salicylideneaniline derivatives, they show different space groups and diverse molecular packing. The molecules of both compounds are close to being planar due to an intramolecular O—H...N hydrogen bond. The 4-alkylamino-substituted benzene ring is inclined at an angle of 13.44 (19)° in (I) and 2.57 (8)° in (II) with respect to the 4-nitro-substituted phenol ring. Only very weak intermole…

Multinuclear magnetic resonance and x-ray diffraction studies of aminonitropyridines

The 15N NMR spectra for 21 aminonitropyridines were measured and their chemical shifts assigned. The 1H and 13C NMR chemical shifts and spin–spin coupling constants were also determined for 16 compounds of this series. In order to relate the structural properties of nitramino groups and their 15N NMR chemical shifts in 2- and 4-nitramino-3-nitropyridines, which differ remarkably from all other amino groups studied, low-temperature 1H NMR, 17O NMR, comparative INEPT and IR spectroscopic studies were carried out. In addition, the x-ray crystal structure of 2-nitramino-3-nitropyridine was determined. Comparative spectroscopic studies showed that the nitramino derivatives exhibit different char…

NMR spectral and X-ray structural investigation of 1,3-bis(2-quinolyl)-2-(p-chlorophenyl)-2-propanol

Abstract 1,3-Bis(2-quinolyl)-2-(p-chlorophenyl)-2-propanol (BQCP) has been prepared and characterised by 1H, 13C, 15N NMR spectral and X-ray structural parameters. The methylene protons of BQCP are diastereotopic in solution (CDCl3) as revealed by 1H NMR. In crystalline state there exists an intramolecular hydrogen bond O–H⋯N with one of two nitrogen atoms in BQCP. Variable temperature 1H NMR and PFG 1H, 15N HMBC runs show that in solution BQCP shows C2v-symmetry (both CH2-2-quinolyl fragments are equivalent) in NMR-time scale due to a fast exchange of the hydrogen bond from one nitrogen to the other even at 223 K.

1H,13C and17O NMR study of substituted nitropyridines

1H, 13C and 17O NMR spectra for 22 substituted nitropyridines were measured and their 1H NMR spectra were analysed. The most significant variations in the NMR parameters are found for isomeric hydroxy derivatives, owing to the possibility of keto–enol tautomerism. The prevalence of the keto form is observed in 2- and 4-hydroxy derivatives, while the 3-hydroxy derivative exists in its enol form. Among the three nuclei studied, 17O seems to be the best nucleus for probing the keto–enol tautomerism. No correlation is observed between the torsion angle of the nitro group and its 17O NMR chemical shift. Molecular mechanics calculations were performed to clarify the torsional energetics of the ni…

GIAO/DFT 13C NMR Chemical Shifts of 1,3,4-Thiadiazoles

1 H, 13 C and 15 N NMR spectra of 2-acetylamino-1,3,4-thiadiazole and its 5-substituted derivatives have been measured and assigned based on reference data, as well as homo- and heteronuclear 2 D NMR experiments. In addition, the GIAO/DFT approach at the B3LYP level of theory using the 6-311G basis set was used to calculate the 13 C NMR chemical shifts. Although this method gives reliable results for 2-arylhydrazones of 1,3-diphenylpropanetrione, 2-phenacylpyridines, (Z)-2-(2-hydroxy-2-phenylvinyl)pyridines, 4-fluoroanilines, (1Z,3Z)-1,4-di(pyridin-2-yl)buta-1,3-dienediols and their tautomeric forms, the calculated chemical shifts for the 1,3,4-thiadiazoles studied are less satisfactory. Pr…

(1Z,3Z)-3-[Quinolin-2(1H)-ylidene]-1-(quinolin-2-yl)prop-1-en-2-ol: An unexpected most stable tautomer of 1,3-bis(quinolin-2-yl)acetone

Abstract 1 H, 13 C and 15 N NMR spectra reveal that CDCl 3 solution of 1,3-bis(quinolin-2-yl)acetone contains only ( 1Z , 3Z )-3-[quinolin-2(1 H )-ylidene]-1-(quinolin-2-yl)prop-1-en-2-ol. The proton transfer takes place between two basic centers of the molecule, which means that the process is an identity reaction by character. The situation is completely different from that detected in chloroform solution of 1,3-bis(pyridin-2-yl)acetone where three different tautomers are in equilibrium with each other. Although the proton transfers in both ( 1Z , 3Z )-3-[quinolin-2(1 H )-ylidene]-1-(quinolin-2-yl)prop-1-en-2-ol and ( 1Z , 3Z )-3-hydroxy-1-[quinolin-2(1 H )-ylidene-4-quinolin-2-yl]but-3-e…

Predominance of inductive over resonance substituent effect on33S NMR chemical shifts of 4-substituted phenyl-4′-methylphenacyl sulfones

33S NMR chemical shifts have been determined for the first time for a series of 10 substituted phenacyl sulfones. Electron-withdrawing and electron-releasing substituents in 4-substituted phenyl-4′-methylphenacyl sulfones, p-MeC6H4COCH2SO2C6H4R-p, cause a ‘reverse’ substituent effect on the 33S NMR resonance. Dual-substituent parameter (DSP) analysis of δ(33S) values revealed that the inductive effect of the substituent predominates over its resonance effect. This finding shows that the 33S NMR chemical shifts are of importance in estimating the electronic properties of sulfur-containing compounds. The 13C and 17O NMR chemical shifts of the title compounds are also discussed. Copyright © 19…

N-methyl-1,2-dihydro-2-benzoylmethylenequinolines: configurational dissimilarity with unmethylated congeners

Abstract Twelve 1-methyl-1,2-dihydro-2-benzoylmethylenequinolines have been synthesized and their structures elucidated by 1 H, 13 C and 15 N NMR, UV–Vis and X-ray methods. The results unambiguously show that these compounds and the corresponding 1,2-dihydro-2-benzoylmethylenequinolines both in crystalline and in solution state are the Z and E isomers, respectively. Comparison of the X-ray structures reveal that ( Z )-1,2-dihydro-2-benzoyl-methylenequinolines are less twisted as compared to their 1-methyl derivatives. This difference is caused by formation of the quasi-aromatic six-membered ring stabilized by an intramolecular hydrogen bond in unmethylated congeners, prevented by N -methyla…

Structure-based evaluation of the resonance interactions and effectiveness of the charge transfer in nitroamines

Structural data for five nitroamines of general formula Me2N–G–NO2 show effectiveness of the ground-state charge transfer to be most and least efficient in N,N-dimethylnitramine and in 4-N,N-dimethylamino-β-nitrostyrene, respectively. Electron-donor power of the amino nitrogen atom in the latter compound is less than that in 4-nitro-β-N,N-dimethylaminostyrene (these two compounds are isomers). Natural population analysis shows that the charge transfer from the amino to the nitro oxygen atoms is most effective in N,N-dimethylnitramine, Me2N–NO2. The nitro oxygen atoms are not the only acceptors of the negative charge lost by the amino nitrogen atom. The nitro group in two substituted nitrobe…

NMR Spectra of Anilines

1 Introduction 2 Ring and N-Substituted Anilines 3 Multinuclear NMR Studies of p-F-Aniline Derivatives 4 Dynamic NMR of Aniline Derivatives 5 Anilines with Other (Fused) Aromatic Rings 6 NMR Relaxation Studies of Aniline Derivatives 7 Solid State NMR Studies 8 Theoretical Calculations of Aniline NMR Parameters Keywords: aniline NMR spectra; aniline (aminobenzene, phenylamine); ring and N-substituted anilines; dual-substituent-parameter (DSP) analysis; cyclic amine structures; dynamic NMR of aniline derivatives; H NMR spectroscopy as measure of donor strengths; aniline derivative NMR relaxation studies

Predominance of 2-arylhydrazones of 1,3-diphenylpropane-1,2,3-trione over its proton-transfer products

2-Phenylhydrazones of 1,3-diphenyl-1,2,3-trione are the dominant tautomeric form detected in chloroform solution by 15N NMR chemical shifts. The substituent in the phenylhydrazone moiety does not affect this tautomeric preference. The substituent effect is transmitted effectively only to the hydrazone nitrogen and hydrogen atoms. Ab initio calculations show that the ketohydrazone tautomer is really very much favoured over its proton-transfer products in chloroform solution. The same tautomer was also detected in the crystal state by X-ray crystallography. Copyright © 2001 John Wiley & Sons, Ltd.

ChemInform Abstract: 4-Fluoroanilines: Synthesis and Decomposition.

Abstract Fourteen N- and/or 2-substituted 4-fluoroanilines were prepared (the series includes N–C2-bridged compounds). Some of them were found to be thermally unstable when dissolved in chloroform. Both 19 F NMR spectra and comparison of GIAO-DFT calculated and experimental 13 C chemical shifts were used to suggest decomposition products of 4-fluoroanilines.

N-(2-Benzoyl-4-chlorophenyl)-4-chlorobenzenesulfonamide

The title compound, C19H13Cl2NO3S, is an N-arylsulfonyl derivative of 2-amino-5-chlorobenzophenone. The compound is biologically active and shows potential to be utilized as an inhibitor of CCR2 and CCR9 receptor functions. In the crystal structure, there is an intramolecular N—H...O hydrogen bond between the amide and carbonyl groups. The benzoyl and 4-chlorophenyl groups form intramolecular and intermolecular face-to-face contacts, with a dihedral angle of 10.6 (1)° between their mean planes in both cases, and centroid–centroid separations of 4.00 (1) and 4.25 (1) Å for the intra- and intermolecular interactions, respectively.

ChemInform Abstract: The Tautomerism of Nitraminopyridines

1H, 13C and 15N NMR data for nitraminopyridines are discussed in terms of tautomeric equilibria in these compounds. The favoured tautomer is determined mainly from 15N NMR spectroscopy. The chemical shift of the nitrogen atom of the nitro group in nitraminopyridines and N-nitroanilines which cannot tautomerize vary from 28·0 to 35·4 ppm in DMSO solution. 3-Nitraminopyridine and 2-nitramino-3- and -5-nitropyridines behave similarly. In the 15N NMR spectra of nitrimino-1-methyldihydropyridines, used as models, an upfield shift of that atom, different from that observed for 2-nitraminopyridine, indicates the significance of the nitrimino tautomer. In contrast, a downfield shift of the ring nit…

(1Z,3Z)-1,4-Di(pyridin-2-yl)buta-1,3-diene-2,3-diol:  The Planar Highly Conjugated Symmetrical Enediol with Multiple Intramolecular Hydrogen Bonds

1H, (13)C, and (15)N NMR spectral data show that in chloroform solution (1Z,3Z)-1,4-di(pyridin-2-yl)buta-1,3-diene-2,3-diol, OO, is in ca. 9:1 equilibrium with (3Z)-3-hydroxy-1,4-di(pyridin-2-yl)but-3-en-2-one, OK, while no 1,4-di(pyridin-2-yl)-2,3-butanedione, KK, was detected. The species present in the tautomeric mixture were identified by comparing their experimental chemical shifts with those known for similar compounds as well as with the theoretically calculated (GIAO-HF/DFT) values. Ab initio calculations show that OK and especially the highly conjugated OO forms are preferred in the tautomeric mixtures both in vacuo and in chloroform solution. Comparison of experimental (Arrhenius)…

2-Methyl-4-phenyl-3,4-dihydro­quinazoline

The title compound, C15H14N2, was formed during the lithiation of 2-methylquinazoline with phenyllithium followed by hydrolysis of the intermediate lithium 2-methyl-4-phenyl-4H-quinazolin-3-ide. NMR spectra as well as single-crystal X-ray structural data indicate that the reaction product to have the same structure in chloroform solution as in the crystalline state. The phenyl substituent is twisted out of the plane of the 3,4-dihydroquinazoline ring system by 86.47 (7)°. In the crystal, intermolecular N—H...N interactions connect the molecules into infinite chains.

Tautomeric preferences of phthalones and related compounds

Abstract Multinuclear magnetic resonance and IR spectra prove that although 2-(diacylmethyl)pyridines and 2-(diacylmethyl)quinolines are β-diketones, their proton transfer product present in chloroform solution is not ketoenol but enaminone (earlier opinions were contradictory). Quinoline derivatives are less zwitterionic by character than the respective pyridyl congeners. The β-diketone form itself may also be rarely present in the solution. X-ray data show that 2-(2(1H)-pyridinylidene)-1H-indene-1,3(2H)-dione, i.e., enaminone tautomer of 2-(pyridin-2-yl)-2H-indene-1,3-dione, is also the only form present in crystal. Ab initio calculations show that the enaminone is usually more stable tha…

Predominance of resonance over polar effects on1H,13C and15N NMR substituent chemical shifts inN-arylglycines

NMR spectral assignment of substituted salicylaldoximes by inverse pulse techniques withz-gradient selection: correlation of NMR parameters with substituent constants

Effect of π-Electron Delocalization on Tautomeric Equilibria – Benzoannulated 2-Phenacylpyridines

Most benzoannulated 2-methylpyridines react with phenyllithium and substituted alkyl benzoates to give the corresponding 2-phenacylpyridines. 3-Methylisoquinoline is transformed into 2-benzoyl-3-methyl-1-phenyl-1,2-dihydroisoquinoline under these conditions, but replacement of phenyllithium with lithium isopropylcyclohexylamide is effective for production of 3-phenacylisoquinolines. Except in the cases of some substituted 6-phenacylphenanthridines, tautomeric mixtures of benzoannulated 2-phenacylpyridines in chloroform solution always contain the ketimine forms.(Z)-2-(2-Hydroxy-2-phenylvinyl)pyridine (enolimine) forms also contribute if the pyridine ring is not benzoannulated or if such ann…

Unequivocal determination of isomeric products of reaction between 3-methyl-1-phenyl-2-pyrazoline-4,5-dione and aromatic 1,2-diamines

Abstract Regioselectivity of condensation of 3-methyl-1-phenyl-2-pyrazoline-4,5-dione with aromatic 1,2-diamines is dependent on substituent present. Isomeric 3-methyl-1-phenyl-1H-pyrazolo-[3,4-b]-quinoxaline products are distinguished by comparison of their 2D z-gradient selected 1H, 15N HMBC (Heteronuclear Multiple Bond Correlation) spectra. Multiplicity of H5 signal, which is recognizable by the cross-peak for CH3(3)-N4 and H5-N4 interactions, indicates substitution in position 6 or 7. The applied method is expected to be useful for structure determinations in other positional isomers.

Nitramino, NRNO2 (R = H, CH3), as a substituent.13C and15N NMR spectroscopic study of nitraminobenzenes and -pyridines

In order to clarify the special properties of the aryl-bound nitramino substituent NRNO 2 (R=H, CH 3 ), 13 C and 15 N NMR spectra of six nitraminobenzenes and nine nitraminopyridines were measured in DMSO-d 6 and their chemical shifts assigned. 1 H NMr chemical shifts and spin-spin coupling constants of all the compounds were also determined. In contrast to the behaviour of nitropyridines or -benzenes studied previously, most of the present compounds gave very broad 17 O NMR lines even at elevated temperatures and their 17 O NMR data were not useful for any reliable conclusions

Self-Organization of 2-Acylaminopyridines in the Solid State and in Solution

Aggregation of 2-acylaminopyridines and their 6-methyl derivatives in chloroform solution was studied by (1)H, (13)C, and (15)N NMR spectroscopies. The results were compared with (13)C and (15)N CPMAS NMR and IR spectral as well as with X-ray structural data. Intermolecular interactions in solution and in solid state were found to have a similar nature. Relatively strong N(amide)-H···N(pyridine) intermolecular hydrogen bonds enable dimerization to take place. Steric interactions in N-pivaloyl- and N-1-adamantylcarbonyl as well as that caused by the 6-methyl group hinder formation of the dimeric aggregates stabilized by the N(amide)-H···N(pyridine) intermolecular hydrogen bonds. In general, …

Influence of Bond Fixation in Benzo-Annulated N-Salicylideneanilines and Their ortho-C(O)X Derivatives (X = CH3, NH2, OCH3) on Tautomeric Equilibria in Solution

1H, 13C, and 15N NMR spectra show that an ortho-C(=O)X group present in the molecules of N-salicylideneanthranilamide (X = NH2), methyl N-salicylideneanthranilate (X = OCH3), N-salicylidene-o-aminoacetophenone (X = CH3), and their benzo analogues have only a minor effect on the tautomeric OH/NH-equilibrium in solution. Only two of three possible tautomers were detected. Lability of the absent form was proved by theoretical calculations. Calculated energies show that the enolimino form (OH) is less stable than the enaminone (NH) form only for dibenzo-annulated N-salicylideneanilines. The population of each species in the tautomeric mixture was found to be inversely proportional to its energy…

Structural characterization of β-2′-pyridylaminocrotonoyl-2-pyridylamide by ESI-MS, NMR, single crystal X-ray analysis and ab initio methods

Abstract In contradiction with earlier reports 1H, 13C and 15N NMR spectra show that β-2′-pyridylaminocrotonoyl-2-pyridylamide is the only form present in chloroform solution. According to the X-ray data the same tautomer exists also in the crystal state. The studied amide has a dimeric form where the monomer molecules are held together by two intermolecular hydrogen bonds. The NMR spectral data show that there is also an intramolecular hydrogen bond in each monomer subunit. The dilution experiments and variable-temperature 1H NMR runs show that β-2′-pyridylaminocrotonoyl-2-pyridylamide tends to form the dimers also in chloroform solution at higher concentrations. The ESI-TOF MS measurement…

Synthesis and Structural Characterization of Substituted 2-Phenacylbenzoxazoles

1 H and 13C NMR spectra of eleven 2-phenacylbenzoxazoles (ketimine form) show that their CDCl3-solutions contains also (Z)-2-(benzo[d]oxazol-2-yl)-1-phenylethenols (enolimine form). Intramolecular hydrogen bonding in the latter tautomer was found to be significantly weaker than that one in respective (Z)-2-(2-hydroxy-2-phenylvinyl)pyridines. Integrals of the 1 H NMR signals were used to evaluate the molar ratio of the tautomers. Strong electron-donating substituents were found to stabilize the ketimine tautomer. pKT (negative logarithm of the equilibrium constant, KT = [ketimine]/[enolimine]) was found to be linearly dependent on the Hammett substituent constant σ. The results of the MP2 ab…

Long-range substituent and temperature effect on prototropic tautomerism in 2-(acylmethyl)quinolines

Tautomeric equilibria between 2-(cinnamoylmethyl)quinoline, (Z)-1,2-dihydro-2-(cinnamoylmethylene)quinoline and (Z)-4-phenyl-1-(2-quinolyl)-1,3-butadien-2-ol were studied by 1H, 13C and 15N NMR methods. The —CHCH— fragment conjugated with phenyl and a strong electron donor p-(1-pyrrolidine) substituent were found to favour the enolimine tautomer. This undergoes fast exchange (on the NMR time-scale) with the enaminone form. The amount of the latter tautomer was found to increase at low temperatures. Copyright © 2001 John Wiley & Sons, Ltd.

Transmission of electronic effects in 4-aryl-2,6-diphenylpyrylium perchlorates and related compounds

Identity Double-Proton Transfer in (3Z)-3-Hydroxy-1,4-di(quinolin-2-yl)but-3-en-2-one

Although there is a very fast (on the NMR timescale) double-proton transfer in (1Z,3Z)-3-hydroxy-4-quinolin-2-yl-1-quinolin-2(1H)-ylidenbut-3-en-2-one (the product of the condensation of ethyl oxalate with 2-lithiomethylquinoline), it is the only species present in chloroform solution. Comparison of the product of condensation of ethyl oxalate with 2-lithiomethyl derivatives of pyridine (recent studies) and quinoline (present studies) shows that benzoannulation considerably affects the tautomeric equilibrium. The observed changes are not only quantitative but also qualitative. Moreover, contrary to the proton transfer in the pyridine tautomers, this process is fast in the quinoline tautomer…

(Z)-Ethyl 2-oxo-3-(1,2-dihydroquinolin-2-ylidene)propanoate

Both independent molecules in the asymmetric unit of the tautomeric title compound, C14H13NO3, a synthetic product obtained from 2-lithiomethylquinoline and diethyl oxalate, crystallize in the enaminone form with a Z configuration around the double bond. Intramolecular N—H...O hydrogen bonds occur, generating an S(6) graph-set motif. In the crystal, weak intermolecular C—H...O and π–π stacking interactions [centroid–centroid distances = 3.7020 (14)–3.7429 (13)Å] define a three-dimensional supramolecular network.

NMR and quantum chemical studies on association of 2,6-bis(acylamino)pyridines with selected imides and 2,2′-dipyridylamine

Association constants of 2,6-bis(alkylcarbonylamino)pyridines (alkyl = methyl or ethyl) and their perfluoroalkyl analogues with succin- and maleimide as well as with 2,2′-dipyridylamine (complementary DAD and ADA hydrogen bonding motifs are responsible for formation of the associates) have been determined by NMR titrations and quantum chemical calculations. Interactions of 2,6-bis(alkylcarbonylamino)pyridines with imides differ by character from these of perfluoroalkyl analogues. Such large difference was not observed for the 2,2′-dipyridylamine associates. Since fluorine atoms cause carbonylamino groups to be stronger hydrogen bond donors, perfluorinated species of this type were found to …

Preparation, reactivity and tautomeric preferences of novel (1H-quinolin-2-ylidene)propan-2-ones

1,1-Difluoro-3-(1H-quinolin-2-ylidene)propan-2-one 1a, 1,1,1-trifluoro-3-(1H-quinolin-2-ylidene)propan-2-one 1b, 1,1,1-trifluoro-3-(4-chloro-1H-quinolin-2-ylidene)propan-2-one 1c and 1,3-dibromo-1,1-difluoro-3-(2-quinolyl)propan-2-one 2 are prepared and characterized by various spectroscopic techniques. The crystal structure of 1a is determined by X-ray diffraction. Furthermore, a series of previously known non-halogenated (1H-quinolin-2-ylidene)propan-2-ones 1d-1h are oxidized with AgBrO3 in the presence of AlCl3. In all cases, 2-(1-bromo-1-chloromethyl)quinoline 3 is obtained in high yield. The bromination order and sites of 1a are analyzed based on ab initio MP2 and DFT calculations for …

Two (E)-2-({[4-(dialkylamino)phenyl]- imino}methyl)-4-nitrophenols

The slow evaporation of analytical NMR samples resulted in the formation of crystals of (E)-2-({[4-(dimethyl­amino)­phenyl]­imino}­methyl)-4-nitro­phenol, C15H15N3O3, (I), and (E)-2-({[4-(diethyl­amino)­phenyl]­imino}­methyl)-4-nitrophenol, C17H19N3O3, (II). Despite the small structural difference between these two N-salicylidene­aniline derivatives, they show different space groups and diverse mol­ecular packing. The mol­ecules of both compounds are close to being planar due to an intra­molecular O-H...N hydrogen bond. The 4-alkyl­amino-substituted benzene ring is inclined at an angle of 13.44 (19)° in (I) and 2.57 (8)° in (II) with respect to the 4-nitro-substituted phenol ring. Only very…

GIAO/DFT calculated chemical shifts of tautomeric species. 2-Phenacylpyridines and (Z)-2-(2-hydroxy-2-phenylvinyl)pyridines

1H, 13C and 15N NMR chemical shifts for 28 substituted 2-phenacylpyridines (ketimine forms) and their enolimine tautomers, (Z)-2-(2-hydroxy-2-phenylvinyl)pyridines, were calculated via the GIAO/DFT approach. Among four tested methods at the B3LYP level of theory, the 6–311G, 6–311++G and 6–311G** basis sets gave acceptable result for 13C NMR chemical shifts whereas the 6–311++G** basis set was the minimum needed for reproduction of 15N NMR chemical shifts. Satisfactory reproduction of 13C and 15N NMR chemical shifts for different tautomers revealed that intramolecular hydrogen bonding could be modeled reliably by these calculations when the geometry optimizations were done with the HF/3–21G…

Substituent and temperature controlled tautomerism of 2-phenacylpyridine: the hydrogen bond as a configurational lock of (Z )-2-(2-hydroxy-2-phenylvinyl)pyridine

2-Phenacylpyridines substituted in the benzene ring are in equilibrium with (Z)-2-(2-hydroxy-2-phenylvinyl)pyridines when dissolved in chloroform. The substituent affects significantly the tautomeric equilibrium [the amount of the enolimine form stabilized by the intramolecular hydrogen bond is 1 and 92% for R = p-N(CH2)4 and p-NO2, respectively]. The negative logarithm of the tautomeric equilibrium constant, KT, is linearly dependent on the Hammett σ substituent constants. The dependence of KTvs. temperature is exponential in character: the more electron-withdrawing is the substituent, the more distinct is the influence of temperature. Unexpectedly, the tautomer present in the crystalline …

Complex tauto- and rotamerism of 2-(R-phenyl)-1,2,3,4-tetrahydroquinazolines

Detailed NMR spectral analysis of CDCl3 solutions of 2-(R-phenyl)-1,2,3,4-tetrahydroquinazolines reveals three or four tautomeric forms. Apart from 2-[(benzylideneamino)methyl]aniline, the other chain tautomeric forms are present only in minor quantities. In general, electron-donating substituents increase the contribution of all chain forms. Lowering the temperature of the CDCl3 solution of 2-(R-phenyl)-1,2,3,4-tetrahydroquinazolines decreases the content of the 2-[(benzylideneamino)methyl]aniline form. At the same time, the amount of the ring form increases. Opening of the tetrahydropyrimidine ring in 2-(R-phenyl)-1,2,3,4-tetrahydroquinazolines was found to be an endothermic process espec…

Multinuclear Magnetic Resonance Study of 2,4,6-Triarylpyridines, 1-Methyl-2,4,6-Triarylpyridinium, and 2,4,6-Triarylpyrylium Cations

Abstract The H, 13C, 15N, and 19F NMR spectra of 2,4,6-triarylpyridines, 1-methyl-2,4,6-triarylpyridinium and 2,4,6-triarylpyrylium perchlorates have been studied. The H NMR signals of protons 3(5) in the heteroaromatic ring are deshielded due to the polarization of C-H bonds caused by delocalization of the positive charge in pyridinium and pyrylium cations. Generally, conformational and structural variations affect the 13C NMR chemical shifts of all carbons in the heteroaromatic ring. Those of carbons 3(5) can best be related to the electron-donating or electron-accepting ability of substituents. However, both electronic character of substituents and charge of heteroatom itself are needed …

The tautomerism of nitraminopyridines

1H, 13C and 15N NMR data for nitraminopyridines are discussed in terms of tautomeric equilibria in these compounds. The favoured tautomer is determined mainly from 15N NMR spectroscopy. The chemical shift of the nitrogen atom of the nitro group in nitraminopyridines and N-nitroanilines which cannot tautomerize vary from 28·0 to 35·4 ppm in DMSO solution. 3-Nitraminopyridine and 2-nitramino-3- and -5-nitropyridines behave similarly. In the 15N NMR spectra of nitrimino-1-methyldihydropyridines, used as models, an upfield shift of that atom, different from that observed for 2-nitraminopyridine, indicates the significance of the nitrimino tautomer. In contrast, a downfield shift of the ring nit…

4-Fluoroanilines: synthesis and decomposition

Abstract Fourteen N- and/or 2-substituted 4-fluoroanilines were prepared (the series includes N–C2-bridged compounds). Some of them were found to be thermally unstable when dissolved in chloroform. Both 19 F NMR spectra and comparison of GIAO-DFT calculated and experimental 13 C chemical shifts were used to suggest decomposition products of 4-fluoroanilines.

13C-NMR Based Evaluation of the Electronic and Steric Interactions in Aromatic Amines

Abstract: Chemical shifts of the para carbon atoms, δ(13C-4), in a series of aromatic amines were used to calculate the Ãp, ÃR and ÃOR substituent constants for different amino groups. 1-Pyrrolidino, N,N-di-n-butylamino and N,N-diethylamino groups were found to be the most strong electron-donors. ortho-Substitution decreases the donor properties of the amino group. The amino groups in 2,6-di-i-propylaniline and N,N-2,6-tetramethylaniline have very weak electron-donor properties. The nitrogen atom in benzoquinuclidine and N,N-dimethyl-2,6-di-i-propylaniline have an electron-acceptor character. The calculated substituent constants of the amino groups studied are consistent with the s…

CCDC 922097: Experimental Crystal Structure Determination

Related Article: Agnieszka Skotnicka, Erkki Kolehmainen, Przemysław Czeleń, Arto Valkonen, Ryszard Gawinecki|2013|Int.J.Mol.Sci.|14|4444|doi:10.3390/ijms14034444

CCDC 922098: Experimental Crystal Structure Determination

Related Article: Agnieszka Skotnicka, Erkki Kolehmainen, Przemysław Czeleń, Arto Valkonen, Ryszard Gawinecki|2013|Int.J.Mol.Sci.|14|4444|doi:10.3390/ijms14034444

2-Methyl-4-phenyl-3,4-dihydroquinazoline

The title compound, C15H14N2, was formed during the lithiation of 2-methylquinazoline with phenyllithium followed by hydrolysis of the intermediate lithium 2-methyl-4-phenyl-4H-quinazolin-3-ide. NMR spectra as well as single-crystal X-ray structural data indicate that the reaction product to have the same structure in chloroform solution as in the crystalline state. The phenyl substituent is twisted out of the plane of the 3,4-dihydroquinazoline ring system by 86.47 (7)°. In the crystal, intermolecular N-HN interactions connect the molecules into infinite chains. peerReviewed