A study of substituent effect on 1H and 13C NMR spectra of mono,di and poly substituted carbazoles

¹H and ¹³C NMR spectra of several substituted carbazoles (Series 1, 2, 3, 4 and 5) were measured. Substituent chemical shifts (SCS's) and Lynch correlations of ¹H and ¹³C nuclei were calculated and the substituent effect on the NMR phenomena was determined. Atomic charge densities for carbazoles of Series 1, 2, 3, 4 and 5 were calculated by using the semi empirical PM3 method. These values also show a linear correlation with the ¹³C chemical shifts.     

Furopyridines. XI. 13C NMR Spectra of 2- or 3-Substituted Furo[2,3-b]-, Furo[3,2-b]-, Furo[2,3-c]- and Furo[3,2-c]pyridine

The ¹³C nmr spectra of 2- or 3-monosubstituted furo[2,3-b]- 1a-1j , furo[3,2-b]- 2a-2j , furo[2,3-c]- 3a-3j and furo[3,2-c]pyridine derivatives 4a-4j are reported. Effects by change in annelation and substituent effects on ¹³C chemical shifts and carbon-proton coupling constants are discussed. The spectra of benzo[b]furan derivatives 5a-5j having the corresponding substituent are also reported for comparison.     

Structure analysis of some α‐(n‐methyl‐n‐formylaminomethyl)‐quinolines

The ¹H and ¹³C nmr spectra of the rotational isomers 3a and 3b of 6‐N‐methyl‐N‐formylaminomefhyl)‐thioquinanthrene were completely assigned with a combination of 1D and 2D nmr techniques. The key‐parts of this methodology were long‐range proton‐carbon correlations and NOE experiments with N‐methyl‐N‐formylaminomethyl substituent. The X‐ray study of 4‐methyl‐2‐N‐methyl‐N‐formylaminomethyl)quinoline 4a as well as ¹H and ¹³C nmr spectra show that N‐methyl‐N‐formylaminomethyl substituent in 4a and 4b has a different steric arrangement than the same substituent in 3a and 3b .     

Linear Free‐Energy Relationships Applied to the 13C NMR Chemical Shifts in 4‐Substituted N‐[1‐(Pyridine‐3‐ and ‐4‐yl)ethylidene]anilines

Two series of 4‐substituted N‐[1‐(pyridine‐3‐ and ‐4‐yl)ethylidene]anilines have been synthesized using different methods of conventional and microwave‐assisted synthesis, and linear free‐energy relationships have been applied to the ¹³C NMR chemical shifts of the carbon atoms of interest. The substituent‐induced chemical shifts have been analyzed using single substituent parameter and dual substituent parameter methods. The presented correlations describe satisfactorily the field and resonance substituent effects having similar contributions for C1 and the azomethine carbon, with exception of the carbon atom in para position to the substituent X. In both series, negative ρ values have been found for C1′ atom (reverse substituent effect). Quantum chemical calculations of the optimized geometries at MP2/6‐31G++(d,p) level, together with ¹³C NMR chemical shifts, give a better insight into the influence of the molecular conformation on the transmission of electronic substituent effects. The comparison of correlation results for different series of imines with phenyl, 4‐nitrophenyl, 2‐pyridyl, 3‐pyridyl, 4‐pyridyl group attached at the azomethine carbon with the results for 4‐substituted N‐[1‐(pyridine‐3‐ and ‐4‐yl)ethylidene]anilines for the same substituent set (X) indicates that a combination of the influences of electronic effects of the substituent X and the π₁‐unit can be described as a sensitive balance of different resonance structures.     

Acetal formation from formylthiophene-2-carboxylic acids and recalculation of σI and σR substituent constants of the acetal group by 13C NMR chemical shifts

A uv-visible, ¹H and ¹³C nmr study has been carried out to show that 4-, 1, and 5-formylthiophene-2-carboxylic acids, 2, give acetals in methanol. The ms data have confirmed the acetal formation, which has been studied kinetically by the uv technique. The substituent chemical shifts induced on the carboxy carbon atom and on the endocyclic carbon atoms in the acetals formed from 1 and 2 and in the corresponding anions have been used to recalculate σ_I and σ_R values by means of a dual substituent parameter treatment of data.     

The Substituent Effect of 1‐Arylazonaphthen‐2‐ols on Azo‐hydrazone Tautomerization According to NMR Analysis

The substituent effect on azo‐hydrazone tautomerization of 1‐arylazonaphthen‐ols is studied by means of NMR analysis. Among the ¹³C chemical shifts, the C(2) of this series compound is the most sensitive to the variation in the nature of substituent on the phenyl ring. Therefore, the variation in the chemical shifts of C(2) is used to probe the substituent effect by using the substituent chemical shifts and free energy vs. Hammett’s constant (χρ⁺). Both methods give a negative correlation slope, indicating the electron‐with‐ drawing groups favor the hydrazone tautomer form. The effect on the chemical shifts of C(2) of compound 8 in ten solvents can be classified as the solvent with a proton‐donor, proton‐acceptor and arenes system. The substituent with electron‐donating character is more sensitive to the nature of solvent and it favors the hydrazone form. Free energy obtained from the dynamic NMR technique indicates the tautomerization favors the hydrazone‐form for the substituent with electron‐withdrawing character.     

Multinuclear magnetic resonance studies of 2‐aryl‐1,3,4‐selenadiazoles

2‐Aryl‐1,3,4‐selenadiazoles were studied by ¹H, ¹³C, ¹⁵N and ⁷⁷Se NMR spectroscopy. The results (chemical shifts and coupling constants) were correlated with Hammett substituent parameters as well as calculated chemical shifts and bond lengths. Copyright © 2012 John Wiley & Sons, Ltd.     

Carbon‐13 Nuclear Magnetic Resonance Spectroscopic Analyses of 3‐Aryl‐3‐hydroxyl‐2,2,4,4‐tetramethylcyclobutanones and Related Compounds

A series of 2‐aryl‐2‐hydroxy‐1,1,3,3‐tetramethyl‐5,8‐dioxaspiro[3.4]octanes ( 1 ), 3‐aryl‐3‐hydyoxyl‐2,2,4,4‐tetyramethylcyclobutanones ( 2 ), and l‐aryl‐2,2,4‐trimethyl‐1,3‐pentadiones ( 3 ) were studied using ¹³C NMR analyses. The chemical shifts of C‐c are dependent on the substituent groups on the phenyl ring for compounds 1 (ρ =‐0.966, R² = 0.987) and 2 (ρ = ?1.378, R² = 0.998). The chemical shifts of C‐a follow a similar trend (ρ =?0.926, R² = 0.989). In the case of compounds 3 , C‐c yielded the opposite trend with very poor correlation coefficiency (ρ = 1.22, R² = 0.179). This result reveals the field effect of a polar bond and resonance‐induced changes in pi electron‐density at C‐1 on the cyclobutanering series.     

Methyl substituent effects for methyltryptophans in 13C nmr

The ¹³C and ¹H nmr spectra of methyltryptophans 2–5 in 0.1 N sodium deuteroxide methanol-d₄ were assigned based on 1-D and 2-D nmr techniques, including COSY, inverse-detected direct (HMQC) and long-range (HMBC) correlation. Methyl substituent effects in chemical shifts (SCS) for the indole ring of tryptophan were calculated and compared with those of indole. The correlations were linear except for 4-methyltryptophan, which suggest structural changes in the indole ring of 4-methyltryptophan and 4-methylindole. The results of molecular modeling and NOE experiments supported that suggestion.     

Azobilirubin and azomesobilirubin isomers. A carbon-13 nmr analysis

The ¹³C nmr chemical shifts of azobilirubin and azomesobilirubin isomers are reported. The signals are assigned on the basis of substituent effects and comparison with structurally related compounds.     

Carbon-13 nmr spectra of the tRNA “wobble” nucleosides 5-carboxymethyl-, 5-carbomethoxymethyl-, and 5-carbamoylmethyluridine

The ¹³C nmr chemical shifts have been measured for 5-carboxymethyluracil 2 , 5-carbo-methoxymethyluracil 3 , their 2-thio derivatives 4 and 5 , respectively, as well as of the three β-D-ribonucleosides, 5-carboxymethyluridine 7 , 5-carbomethoxymethyluridine 8 , and 5-carbamoyl-methyluridine 9 . In addition, the ¹³C-¹H coupling constants for 2 and 7 have, also been obtained.     

Stereodivergent Synthesis and Stereochemical Reassignment of the C79–C104 Fragment of Symbiodinolide

We have synthesized eight possible diastereoisomers 3 a – h of the C79–C97 fragment of symbiodinolide ( 1 ) in a stereodivergent manner by utilizing a dithiane addition to the aldehyde as a key step. Comparison of the ¹³C NMR chemical shifts of the natural product 1 and the synthetic products 3 a – h indicated that the relative stereostructure of this fragment in symbiodinolide ( 1 ) is that represented in 3 a or f . We have stereodivergently synthesized eight possible diastereoisomers of the C94–C104 fragment 4 a – h , and we have compared their ¹³C NMR chemical shifts with those of the natural product, which established the relative stereochemistry of this fragment to be that described in diastereoisomers 4 a or e . By combining the stereostructural outcomes of the C79–C97 and C94–C104 fragments, we have proposed four candidate compounds of the C79–C104 fragment 2 a – d . We also synthesized diastereoisomers 2 a and b ( 2 a in the preceding article; Chem. Eur. J. 2015 , DOI: 10.1002/chem.201503880) by a Julia–Kocienski olefination and diastereoisomers 2 c and d by a Wittig reaction. By comparing the ¹³C NMR chemical shifts of natural symbiodinolide ( 1 ) with those of the synthetic products 2 a – d , we have reassigned the stereostructure of the C79–C104 fragment of natural product 1 to be that depicted in diastereoisomer 2 b .     

Carbon-13 nuclear magnetic resonance spectra of 1,2,3,4-tetrahydroquinazoline and some 3-benzyl derivatives

The concerted use of the ¹H/¹³C shift correlation with full ¹H/¹H decoupling and the modified COLOC sequence for long-range X/H correlation 2D nmr spectroscopy allows the total assignment of the ¹³C nmr resonances of 1,2,3,4-tetrahydroquinazoline and 3-benzyl-1,2,3,4-tetrahydroquinazoline. From these data, the ¹³C nmr chemical shifts of a series of 3-benzylsubstituted-1,2,3,4-tetrahydroquinazolines are deduced.     

Synthesis and molecular structure of novel 4‐aryloctahydropyrido‐[1,2‐c]pyrimidine derivatives

A series of new 4‐aryloctahydropyrido[1,2‐c]pyrimidine‐1,3‐diones 6a,b,d‐h and j were synthesized by intramolecular cyclization of α‐aryl‐α‐(1‐ethoxycarbonyl‐2‐piperidyl)‐acetamide derivatives 5a,b,d‐h and j . The structures of compounds were determined by ¹H and ¹³C nmr spectroscopy. Nmr and X‐ray diffraction data indicate that the configuration at the C4, C4a stereocenters constitute RR and SS pair.     

Carbon-13 Nmr spectroscopy of methoxy- and acetoxyaurones

The ¹³C nmr chemical shifts of methoxy and acetoxyaurones are reported. The signals are assigned on the basis of substituent effects and comparison with structurally related compounds. Assignments are also verified by Sford.     

Synthesis and isolation of iodocarbazoles. Direct iodination of carbazoles by N‐iodosuccinimide and N‐iodosuccinimide‐silica gel system

Carbazole ( 1 ) undergoes electrophilic aromatic substitution with various iodinating reagents. Although, 3‐iodocarbazole ( 1b ) and 3,6‐diiodocarbazole ( 1d ) obtained by iodination of carbazole were isolated and characterized sometime ago, 1‐iodocarbazole ( 1a ), 1,6‐diiodocarbazole ( 1c ) and 1,3,6‐triiodocarbazole ( 1e ) had never been isolated from the reaction mixture. The preparation and subsequent isolation and characterization of 1a, 1b, 1c, 1d and 1e are reported (mp, t_r, R_f, ¹H‐nmr, ¹³C‐nmr and ms). As iodinating reagents, NaIO₄/I₂ and NaIO₄/KI mixtures in (i) ethanol doped with catalytical amount of sulfuric acid and in (ii) acetic acid, and N‐odosuccinimide and N‐iodosuccinimide‐silica gel in dichloromethane and in chloroform have been used and their uses have been compared. The iodination reaction of different carbazole derivatives such as 2‐acetoxycarbazole ( 2 ), 3‐bromocarbazole (3) and 3‐nitrocarbazole ( 4 ) was also studied and the corresponding iododerivatives, 2a, 2b, 2c, 3a, 3b, 4a and 4b , are described for the first time. Semiempirical PM3 calculations have been performed in order to predict reactivity of carbazole ( 1 ), substituted carbazoles (2‐4) and iodocarbazoles ( 1a‐1e, 2a‐2c, 3a‐3b, 4a and 4b ) (Scheme 1). Theoretical and experimental results are discussed briefly.     

Carbon‐13 NMR and PM3 Study on the Substituent Effect of 1‐Aryl‐3,3‐Difluoro‐2‐Halocyclopropenes

The substituent‐induced chemical shifts (SCS) of C2 and C3 on the ¹³C NMR spectra of 1‐aryl‐3,3‐difluoro‐2‐halocyclopropenes were studied. The correlation between SCS and Hammett constants shows that the tendency of effect by the substituents on the phenyl ring is BrC2(ρ = 4.66) > ClC2(ρ = 4.50) and ClC3(ρ = ?1.63) > BrC3(ρ = ?1.41). The DSP treatment further confirms the SCS of C2 and C3 are the main contribution of the resonance effect and field effect, respectively. Those results of the incremental shifts reveals that the gem‐difluorocyclopropenyl bearing the phenyl group possesses a triple bond character, which is also observed in IR spectra with high n?_C=C (1768–1945 cm^?1).     

Investigation of Substituent Effects on Proton and Carbon-13 Chemical Shifts of 4-Substituted Trans-Stilbenes

Proton and carbon-13 chemical shifts of para-substituted stilbenes have been measured. ¹H-¹H, ¹H-¹³C COSY spectra were obtained to analyze unambiguously the chemical shifts of protons and carbons. A long range coupling between 2-H and α-H was observed in a ¹H-¹H COSY spectrum. The observed chemical shifts have been correlated with Hammett substituent parameters. Among ethenyl protons and carbons, all but the chemical shifts of α-H show good correlation with both dual substituent parameters and single substituent parameters. In addition to this finding, the excellent linear correlations of C-l, and 4′-H of 4-substituted trans-stilbenes are also reported. Besides the correlations of chemical shifts with Hammett parameters, a good correlation between the chemical shifts and the calculated charges of position C-4′ are reported.     

Synthesis and antiosteoclast activity of Di(1‐oxo/thioxoperhydro‐1λ5‐[1,3,2] diazaphospholo [1,5‐a]pyridine‐1‐yl) (4‐substituted phenyl) boronates

A new family of di(1‐oxo/thioxoper‐hydro‐1λ⁵‐[1,3,2]diazaphospholo[1,5‐a]pyridine‐1‐yl)(4‐substituted phenyl) boronates ( 4a – j ) has been synthesized in a two‐step process. A reaction of (±)‐piperidin‐2‐yl‐methanamine ( 1 ) phosphoryl/phosphorothioyl chloride in the presence of triethylamine in dry tetrahydrofuran formed the intermediate monochloride ( 2 ), which on condensation with p‐substituted phenylboronic acids ( 3a – j ) afforded the titled compounds ( 4a – j ). They were characterized by elemental, IR, ¹H, ¹³C, ³¹P NMR, and mass spectral analyses. All these compounds showed moderate to high antiosteoclast and osteoblast activity. © 2012 Wiley Periodicals, Inc. Heteroatom Chem 23:247–253, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.21010     

Neue wasserlösliche Osmiumkomplexe des 5,10,15,20‐Tetrakis(4‐sulfonatophenyl)‐porphyrin‐Anions

Metal Complexes with Tetrapyrrole Ligands. LXXVI. New Water‐soluble Osmium Complexes of 5,10,15,20‐Tetrakis(4‐sulfonatophenyl)porphyrin‐Anion The new symmetrical osmium(II) porphyrinates [Os(tpps₄)L₂]^4– ( 1 b – g ) are formed from [OsO₂(tpps₄)]^4– ( 1 a ) by reduction in presence of the ligands L. 1 e – g react with 1‐methylimidazole to yield the unsymmetrical complexes [Os(tpps₄)LL′]^4– ( 1 h – j ). Except for 1 g – h the osmium(II) porphyrinates are not inert in presence of air and are oxidized to the osmium(III) porphyrinates [Os(tpps₄)L₂]^3– ( 2 b – f ) and [Os(tpps₄)LL′]^3– ( 2 i – j ). These anions are deposited as sodium salts.