13C?C13 coupling constants in dimethyl phthalate and phthalic anhydride. Determination of signs—III

Relative signs of ¹³C? ¹³C coupling constants between ring carbons and carbonyl carbons in dimethyl phthalate and phthalic anhydride, ¹³C-labelled in both carbonyl groups, have been determined. The two-and three-bond coupling constants are shown to be positive, whereas four-bond coupling constants are negative. Substituent effects on carbon-carbon couplings due to a carboxyl group have been determined and effects of 5-membered ring formation in phthalic anhydride have been observed.     

13C Pulse fourier transform NMR of menthol stereoisomers and related compounds

¹³C NMR spectra of menthol stereoisomers have been determined. The correlations of chemical shifts of these ring carbons with those of stereoisomeric 2-isopropylcyclohexanols are examined. Observed chemical shifts of 1-Me carbons are compared with those predicted from the chemical shifts of stereoisomeric 1-methyl-4-t-butylcyclohexanes. ¹³C NMR spectra of menthyl acetates, and cis and trans p -menthanes have also been examined.     

13C n.m.r. spectra of quercetin and rutin

The noise-decoupled and gated-decoupled ¹³C n.m.r. spectra of quercetin and rutin are studied and assignments are proposed. The previous assignments of carbons 2 and 4′, carbons 5 and 9, carbons 6 and 8 have been reversed.     

Investigation of substituent effects of chalcones by 13C n.m.r. spectroscopy

¹³C chemical shifts for 23 para- and meta-substituted chalcones of the types 1 and 2 have been determined. The aromatic shieldings are compared with previous results for other aromatic derivatives. Correlations of the ¹³C chemical shifts of vinyl carbons and carbonyl carbons as well as ring carbons with Hammett σ parameters, π electron densities and the reactivity parameters of Swain and Lupton provide a consistent picture of electronic effects transmitted through the carbon framework of the compounds studied.     

Partially graphitized ordered mesoporous carbons for high-rate supercapacitors

Partially graphitized ordered mesoporous carbons have been prepared with a soft template method using low-molecular-weight phenolic resol as a carbon source, triblock copolymer F127 as a template, and ferric citrate as a graphitization catalyst. N₂ sorption and transmission electron microscopy analysis show that the ordered mesoporous carbons have been partially graphitized when the carbonization temperature is above 700 °C. The graphitic ordered mesoporous carbons exhibit better rate performance than amorphous ordered mesoporous carbons. The specific capacitance of the graphitic ordered mesoporous carbons (GOMCs) prepared at 700 °C reaches to 112 F g^?1 at a scan rate of up to 1,000 mV s^?1. Its capacitance retention ratio is 64 %, which is much higher than that of the amorphous ordered mesoporous carbons prepared at 600 °C (33 %). High electronic conductivity and ordered mesoporous structure lead to the high electrochemical performance of the partially graphitized ordered mesoporous carbons.     

13C and 1H chemical shifts in 2-benzylidene[3]ferrocenophane-1,3-diones. Elucidation of the substituent dependence of carbonyl chemical shifts in different carbonyl derivatives

The ¹³C and ¹H chemical shifts of the ferrocene moiety, as well as the carbonyl carbons and styrene moiety, of substituted 2-benzylidene[3]ferrocenophane-1,3-diones have been assigned. Correlations of ¹³C substituent chemical shifts of both carbonyl carbons with the Hammett constants have been found, and the effect of the transmission of substituent effects on these chemical shifts through the styrene moiety is discussed. An explanation is given for the different sensitivities of the carbonyl carbon chemical shifts to the electronic effect of substituents in mono- and dicarbonyl derivatives.     

Diastereotopic splitting in the 13C NMR spectra of sulfur homofullerenes and methanofullerenes with chiral fragments

Using gauge‐invariant atomic orbital PBE/3ζ quantum chemistry approach, ¹³C NMR chemical shifts and diastereotopic splittings of sp² fullerenyl carbons of a number of sulfur homofullerenes and methanofullerenes have been predicted and discussed. An anisochrony of fullerene carbons is caused by a chiral center of attached moieties. Clearly distinguishable diastereotopic pairs (from 8 to 11) of fullerenyl carbons of homofullerenes were observed. Unambiguous assignments of ¹³C NMR chemical shifts were performed, and diastereotopic splittings of methanofullerenes were observed for α, β and γ to a functionalization site. Copyright © 2013 John Wiley & Sons, Ltd.     

Electronic effects in the cyclopentadienyl ring. The 13C NMR spectraof monosubstituted ferrocenes

The chemical shifts of C(2,5) and C(3,4) carbons in the ¹³C NMR spectra of monosubstituted ferrocenes have been assigned using deuterium labelling. An analogy is observed between the shielding of C(2,5) and C(3,4) carbons of ferrocene derivatives and ortho- and para-carbons of benzene derivatives withthe same substituents. Electron-density distribution in the cyclopentadienyl ring is discussed on the basis of ¹³C NMR data.     

Influence of substituents on carbonyl carbon chemical shifts in 4-substituted bornane-2,3-diones and the preparation of bornane-2,3-dione

¹³C Chemical shifts of the 4-substituted boniane-2,3-dione(1–6) have been assigned. The shielding of the CO carbons brought about by electron withdrawing substituents is attributed to a field effect of the substituent which serves to increase the CO bond order. For the substituent bearing carbons C(4), enhanced shielding is noted and these carbons exhibit small substituent chemical shifts. A preparative method leading to borane-2,3-dione is described and briefly discussed.     

13C NMR spectra of benzo[b]thiophene and 1-(X-benzo[b]thienyl)ethyl acetate derivatives

Carbon-13 chemical shift assignments are reported for benzo[b]thiophene and 1-(X-benzo[b]thienyl)ethyl acetate derivatives, where X=? CH(OAc)CH₃ substituted at positions 2-7. Substituent chemical shift (SCS) effects for the ethyl acetate group are additive at all positions. A substantial upfield shift was observed at C-3, arising from the peri interaction of H-3 and the 4-ethyl acetate substituent. Carbon-13 relaxation times (T₁) and nuclear Overhauser enhancements (η) have been measured for benzo[b]thiophene and its derivatives, and the contributions of dipolar, T^DD₁, and spin rotation, T^SR₁, relaxation have been determined. Intramolecular dipole–dipole interactions are found to provide by far the most important spin-lattice relaxation mechanism whenever protons are bound directly to the carbons under investigation. Nonprotonated ring carbons are relaxed by both DD and SR mechanisms. Anisotropic motion has an easily observable effect on the DD contribution to T₁, and can form the basis for spectral assignments, as in 1-phenylethyl acetate. Long-range ¹³C? ¹H coupling constants were observed both between ring carbons and between ring carbons with ring side-chain hydrogens. These results have been used for the structure determination of the title compounds.     

Principal component analysis of the 13C NMR spectra of enamino ketones

The ¹³C NMR spectra of eleven 3-N,N-dialkylamino-5,5-dimethylcyclohex-2-en-1-ones have been determined. The chemical shifts of the three sp² carbons and of the two methylene carbons on the cyclohexenone moiety have been subjected to factor analysis. Two factors are necessary and sufficient to account for more than 93% of the total variance. The more important axis (79%) corresponds to a factor closely related to the inductive and steric effects of the alkyl nitrogen substituents. The second parameter is more difficult to interpret and could correspond to the ‘ipso effects’ of amino groups.     

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.     

Identification of halogen substituents in natural products by measurement of 13c spin-lattice relaxation times and integrated intensities

A method is proposed for differentiating brominated carbons from chlorinated carbons by means of natural-abundance ¹³C NMR spectroscopy. The basis of the method is that the spin-lattice relaxation behaviour of brominated carbons is influenced by carbon-bromine scalar interactions, which can lead to shortened ¹³C spin-lattice relaxation times and reduced values of the nuclear Overhauser enhancement. C-Cl scalar interactions make a negligible contribution to the spin-lattice relaxation of chlorinated carbons. These effects are illustrated by measurement of the ¹³C spin-lattice relaxation times and integrated intensities of chloro-, bromo and iodobenzene and chloro-, bromo- and iodocyclohexane. The method is then tested on four polyhalogenated marine natural products. The results indicate that ¹³C relaxation measurements can be used to distinguish brominated carbons from chlorinated carbons in the case of halogenated quaternary carbons, sp² hydridized methine carbons and some sp³ hydridized methine carbons, but not in the case of halogenated methylene carbons or gem-dihalo substituted methine carbons.     

13C-NMR-Spektren isomerer Diazaphenanthrene

The ¹³C chemical shifts of eleven isomeric diazaphenathrenes (1.5-? 1.10-, 2.7-, 4.5-? 4.7-, and 5.6-DAP) have been determined and iteratively assigned by means of comparison with suitable model compounds. The data obtained (132 points) were used to test the relationship between ¹³C chemical shifts and HMO charge densities. The best correlation with a standard deviation S(E) = 4.8 ppm was found for the chemical shifts, relative to phenanthrene, of tertiary carbons. The different slopes for correlations of tertiary and quarternary carbons (275–300 vs 540–550 ppm/electron) are most probably due to different ΔE values for both types of carbons.     

Carbon-13–fluorine-19 coupling constants in benzotrifluorides

The carbon–fluorine coupling constants in 33 different substituted benzotrifluorides (trifluoromethyl-benzenes) have been determined. The ³J(CF) to the ortho aromatic ring carbons varied between 1.7 and 5.6 Hz and, in a given molecule, were always larger than the ⁵J(CF) to the para carbon, which ranged between 0.7 and 1.7 Hz. Coupling to the meta carbons, ⁴J(CF), was not observed and is under 0.3 Hz.     

The carbon-13 chemical shifts and the analysis of the relaxation times T1 and long range 13C−1H coupling constants of quinoline and of 1-(X-quinolyl)ethyl acetate derivatives

The ¹³C chemical shifts and the ¹³C−¹H coupling constants of quinoline (1-(X-quinolyl)ethyl acetate derivatives (where X=−CH(OAc)CH₃ substituted at positions 2,4,5–8) are reported. Substituent chemical shift (SCS) effects for the ethyl acetate group are additive at all positions. A substantial upfield shift of 4.5 and 4.8 ppm was observed at C-4 and C-5, arising from the peri interaction of 5- and 4-ethyl acetate substituents respectively. A vicinal (peri) ³J CCCH coupling constant of approximately 5 Hz is observed between both C₅−H₄ and C₄−H₅. Carbon-13 relaxation times (T₁) and nuclear Overhauser enhancements (η) have been measured for quinoline and its derivatives, and the contributions of dipolar, T₁^DD, and spin rotation, T₁^SR, relaxation have been determined. Intramolecular dipole-dipole interactions are found to provide by far the most important spin-lattice relaxation mechanism whenever protons are bound directly to the carbons under investigation. Non-protonated ring carbons are relaxed by both DD and SR mechanisms. Anisotropic motion has an easily observable effect on the DD contribution to T₁, and can form the basis for spectral assignments, as in 1-phenylethyl acetate. Long-range ¹³C−¹H coupling constants were observed both between ring carbons and between ring carbons with ring side-chain hydrogens. These results have been used for the structure determination of the title compounds.     

13C n.m.r. studies of some phenanthrene and fluorene derivatives

The ¹H and ¹³C spectra of fluorene, fluorenone, phenanthrene and their 4-methyl and 4,5-dimethyl derivatives have been examined. To complete the analyses for fluorenone and 4-methylfluorenone, ¹H spectra were recorded at 270 MHz. The results from the ¹H spectra permitted unequivocal assignments for the protonated aryl carbons by selective proton decoupling. A consistent set of assignments for the quaternary carbons was obtained through consideration of the dominant relaxation processes operative at these centres. This series of compounds was examined to investigate the shielding effects produced by the close approach of methyl groups separated by five bonds for comparison with the contrasting trends found for methyl carbons separated by three and four bonds. The results indicate that the relative orientation of the methyl groups is an extremely critical factor governing their shieldings and those of neighboring centres.     

New carbon from low cost vegetal precursors: acorn and cypress cone

Thermal-treated carbons from acorn and cypress cone were prepared and characterized. The uptakes of heavy metal ions (Ag⁺, Cd²⁺ and Cr⁺³) and organics (phenol, methylene blue and sodium dodecylbenzenesulfonate) from aqueous solution have been studied. Effects of activation by HCl and HNO₃ acids on the sorption properties of these carbons were investigated by mass titration, sorption isotherms, IRS, SEM and XRS. The models of Langmuir and Freundlich do not represent our sorption data very well. An earlier proposed empirical correlation is applied successfully to carry out a parameter of comparison between the studied carbons. The acidic treatment changes the surface chemical properties of the two thermal-treated carbons lowering their sorption performances. The carbons show good capacities to uptake metals, phenol and methylene blue, but sodium dodecylbenzenesulfonate is removed from its solutions to minor extent. The up-taking properties are found similar to those of two worldwide used commercial grade carbons.      

Estimations of fold surface densities using space-filling models

The model of a tight-fold adjacent reentry fold surface for polyethylene single crystals has been questioned, because it has been speculated that a tight-fold surface should have a density approximating that of the unit cell (～1.00 g/cm³). This would lead to an overall lamella density of close to unity. In contrast, the majority of measured values are in the range 0.96 to 0.97⁺ g/cm³. These lower values have been taken as evidence to disprove a tight-fold–surface model. The present calculations made on space filling models of tight folds indicates a fold surface density on the order of 0.75 g/cm³. This produces no inconsistency between a tight-fold model and accepted lamella density values. Further, calculated values of the weight fraction crystallinity of lamella, as a function of the number of carbons in the fold, limits this number to approximately 9 to 11 carbons per fold.     

Carbon-13 NMR spectra of ferrocenes and ferrocenyl-alkylium ions

The proton-coupled and proton-decoupled pulsed Fourier-transform ¹³C NMR spectra of a series of neutral ferrocene derivatives and ferrocenylalkylium ions have been recorded and analysed. The influence of a substituent group upon the ¹³C shifts of the carbons of the ferrocene rings has been investigated. The spectra of the ferrocenylalkylium ions are discussed in relation to the distribution of positive charge and to the various structural models which have been proposed for such species.