Carbon-13 n.m.r. spectra of 2,3-dimethylenebicyclo[2.2.1]heptanes and 2,3-dimethylene-7-oxabicyclo[2.2.1]heptanes

The ¹³C n.m.r. spectra of 11 derivatives of 2,3-dimethylenenorbornane, 1–11, of 5 derivatives of 2,3-dimethylene-7-oxanorbornane, 12–16, and of 2,3,5,6-tetramethylene-7-oxanorbornane (17) have been measured and the chemical shifts have been assigned. The effects of 1-methyl, 5-hydroxy, 5-acetoxy, 5-para-bromobenzenesulphonyloxy and 5-keto substituents on the olefinic carbons of the s-cis-butadiene group are compared with the same substituent effects reported for model compounds. Apparent linear correlations between the reciprocals of the V←N transition energies of the butadiene chromophores and the differences of the chemical shifts ΔδC between the quaternary and methylene olefinic carbons are found for the dienes 1–3, 12–14, butadiene and 2,3-dimethylbutadiene. The ΔδC of the olefinic carbons of the tetraene 17 also falls on the correlation line if the average of the two absorption hands at 250 and 228 nm is taken for the V←N transition energy of this compound. The chemical shift of the carbon of the methano bridge H₂C-7 is almost insensitive to the presence of one or two methylene groups at C-2,3, in contrast with the downfield shift of 10–14 ppm observed when an endocyclic double bond is introduced into the norbornane skeleton.     

Linear free energy relationships for carbon-13 NMR chemical shifts of substituted benzoic acids1

In order to examine ¹³C-SCS of substituted benzoic acids, chemical shifts of the acid form (I) and the dissociated form (II) have been obtained separately. Single substituent parameters, σ⁰ or σ⁺ are correlated with the shifts for the carboxyl (δ_co) or ipso carbons (δ_ipso), respectively. Among the available five equations which are developed for the analysis with dual (or divided) substituent parameters (DSP), the Swain-Lupton equation (eqn 3) and the Taft-Swain-Lupton equation (eqn 4) give much better correlations, not only for δ_co and δ_ipso but also for the results for ring carbons (C(2), C(5), C(6)), except for those attached to or neighboured by substituents. It is concluded that the SCS of aromatic compounds are best analyzed with substituent parameters derived from reactions or equilibria on the basis of linear free energy relationships.     

A Study of the 13C NMR Shifts in Two Tetradehydrocyclodecabiphenylenes and Related Aryl and Biphenylenylacetylenes

The ¹³C spectra of 5,6,9,10-tetradehydrocyclodeca[1,2,3,4-def]-benzo [7,8]biphenylene, 1, and 5,6,9,10-tetradehydrocyclodeca [1,2,3,4-def]-naphtho [2,3-7,8]biphenylene, 2, are reported as are those of a number of simpler acetylenic hydrocarbons used as spectral references. Most of the shifts can be assigned unambiguously. The acetylenic shift assignments were verified by ortho-proton, sp-carbon (¹H(1)-¹³C_sp(3)) decoupling experiments. A simple additive shift correlation is found for the hydrocarbons containing unstrained acetylenic groups. However, significant discrepencies are found for the ¹³C shifts for the strained hydrocarbons 1, 2, 1,2-bis(phenylethynyl)-benzene, 12, and 2,3-bis(phenylethynyl)-naphthalene, 13. The discrepencies are particularily large for carbons near the triple bonds and are attributed to a combination of strain, rehybridization, and other proximity effects related to the interaction between the ortho-substituted acetylenic carbons.     

Electrophilic reactions of chlorin derivatives and a comprehensive collection of 13c data of these products and closely related compounds

Vilsmeier-formylation of the copper(II) complex of chlorin-e₆ trimethyl ester (2), under mild conditions, gives selective substitution in the 3-vinyl group. In contrast chlorination of 2 is shown to lead to selective substitution at position 20 of the macrocycle. A similar result is found for [3-ethyl]-isochlorin-e₄ dimethyl ester (17) although further reaction leads to more highly chlorinated products which have been isolated and identified. ¹³C NMR data for some of these compounds and several related chlorin derivatives are reported. In particular, after correction of the literature, many of the quaternary carbon signals of the macrocycle are assigned and substituent effects assessed. Consideration of the shifts of the α-pyrrolic carbons confirms that chlorin and its derivatives exist in a tautomeric form with the two inner H atoms on diagonally opposite pyrrole rings A and C. Such a form allows a satisfactory explanation of the substituent chemical shifts of the formyl group at positions 15 and 20 to be made.     

The stereochemistry of 2,4-disubstituted γ-butyrolactones and 2,4,6-trisubstituted-5,6-dihydro-4H-1, 3-oxazines

2,4-Disubstituted butyrolactones and 2,4,6-trisubstituted-5,6 dihydro-4H-1,3-oxazines show similar features in their ¹H and ¹³C- NMR spectra. Two geminal ring hydrogens of cis isomers give rise to a complex ABXY spectra when the substituent is alkyl or aryl. In spectra of trans isomers these patterns are degenerated. When R is OMe(in 4) or OCOMe (in 6) the difference in chemical shifts of geminal protons and vicinal coupling constants cannot be used for diagnosis. In ¹³C spectra ring carbons C-2 and C-3 in lactones and C-4 and C-5 in oxazine of trans isomers show a small but consistent shift to higher fields.     

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.     

1H, 13C and 77Se NMR spectra of substituted selenoanisoles

The ¹H, ¹³C and ⁷⁷Se chemical shifts and the ¹J[C(Me)H(Me)], ^1.2J(SeC) and ²J(SeH) coupling constants in 14 para- or meta-substituted selenoanisoles, R? C₆H₄? Se? CH₃, have been measured and the dependence of these parameters on the electronic effects of the substituent R is discussed. A significant (up to 6 ppm) deviation from additivity of the substituent influence on the shielding of the ¹³C ring carbons has been found.     

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.     

Carbon-13 NMR spectra of some 4-substituted phenacyl bromides

The ¹³C NMR signals for some 4- substituted phenacyl bromides were assigned. The experimental chemical shifts of the aromatic ring carbons are in close agreement with those calculated using substituent chemical shifts. Both the carbonyl and the α-methylene carbons exhibit upfield shifts compared with those of the corresponding 4-substituted acetophenones.     

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.     

Dual substituent parameter analysis of the ethyl and ipso 13C n.m.r. chemical shifts of some ring-substituted ethylbenzenes and ethylnaphthalenes

The natural abundance ¹³C n.m.r. spectra of a series of para-substituted ethylbenzenes, 4-substituted-1-ethylnaphthalenes and a limited series of 6-substituted-2-ethylnaphthalenes have been examined at low dilution in deuterochloroform solvent. The ethyl carbons and C_ipso in the phenyl series (i.e. have been assigned, and substituent chemical shifts for these carbons calculated and analysed by the Dual Substituent Parameter treatment. (Chemical shifts of all ring carbons have been obtained, but not assigned). Generally speaking, electron-withdrawing substituents lead to positive (i.e. downfield) substituent chemical shifts for CH ₂ and negative substituent chemical shifts for C H₃, i.e. ‘normal’ and ‘inverse’ behaviour respectively. C_ipso in the phenyl series exhibits a ‘normal’ dependence. The dependences of the various substituent chemical shifts on inductive and resonance parameters are discussed, and compared with the behaviour of side chain carbons in other substituted benzene systems.     

Temperature-dependent racemic compound-conglomerate crystallization of 2,3:6,7-dibenzobicyclo[3.3.1]nona-2,6-diene-4,8-dione

2,3:6,7-dibenzobicyclo[3.3.1]nona-2,6-diene-4,8-dione 1 is a new example of a compound capable of temperature-dependent racemate-conglomerate crystallization: at temperatures below 90°C crystals of the racemic compound (space group P1̄, Z=4) can be obtained, whereas above 100°C a conglomerate of (+)- and (−)-homochiral crystals (space group P2₁2₁2₁, Z=4) forms and therefore it undergoes spontaneous resolution upon crystallization. Enantioselective analytical gas chromatography on a single crystal has been proposed as a simple method for detection of conglomerate formation. The ¹H and ¹³C NMR spectra of 1 are analyzed in detail and the crystal structures of both species (racemic compound and single enantiomer) have been solved by X-ray structural analysis.     

Enthalpy and entropy of activation and the heat effect of the ene reaction between 4-phenyl-1,2,4-triazoline-3,5-dione and 2,3-dimethyl-2-butene in solution

The rate of the fastest ene reaction between 4-phenyl-1,2,4-triazoline-3,5-dione (1) and 2,3-dimethyl-2-butene (2) is studied by means of stopped flow in solutions of benzene (k ₂ = 55.6 ± 0.5 and 90.5 ± 1.3 L mol^?1 s^?1 at 23.3 and 40°C) and 1,2-dichloroethane (335 ± 9 L mol^?1 s^?1 at 23.5°C). The enthalpy of reaction (?139.2 ± 0.6 kJ/mol in toluene and ?150.2 ± 1.4 kJ/mol in 1,2-dichloroethane) and the enthalpy (20.0 ± 0.5 kJ/mol) and entropy (144 ± 2 J mol^?1 K^?1) of activation are determined. A clear correlation is observed between the reaction rate and ionization potential in a series of ene reactions of 4-phenyl-1,2,4-tri-azoline-3,5-dione with acyclic alkenes.     

NMR study of orgnasilicon compounds : X. The transmission of substituent effects in phenoxysilanes as studied by 29Si and 13C NMR

²⁹Si and ¹³C NMR chemical shifts for a series of meta and para substituted phenoxytrimethylsilanes are given and compared with those in phenyltrimethylsilanes using the formal single and dual substituent parameter analysis of substituent effects.The silicon chemical shift is found to be about twice as sensitive to substituent effects in phenoxytrimethylsilanes as in phenyltrimethylsilanes. The chemical shift sensitivity to substituent effects, ?, is considered to be a product of two factors, ?^el and ?^shield, which describe the sensitivity of the electron density to substituent effects and the sensitivity of the shielding to the electron density, respectively.Using ¹³C chemical shifts and CNDO/2 net atomic charges, it is shown that the substituent effects propagate within XC₆H₄ fragment of phenoxysilanes no better than in phenylsilanes. The ¹³C chemical shifts of the terminal methyl groups are affected by the substituents in the former series of compounds much less than in the latter. An increase in the relative basicity of oxygen is accompanied by an increase in silicon shielding in phenoxytrimethylsilanes.According to CNDO/2 calculations, the substituents cause larger changes in net atomic charges on the silicon atom if it is bonded directly to the benzen ring rather than via the oxygen bridge. In spite of the fact that the possibility of a dative O·→Si interaction, not reflected by the CNDO/2 calculations, cannot be completely excluded, the results that the increased silicon shift sensitivity to substituent effects in phenoxysilanes is due to higher sensitivity of silicon shielding (?^shield) to electron density in these compounds rather than to a bettr transmission of electronic effects (?^el). The existing theory of silicon shielding must be improved or refined if it has to accomodate the increased sensitivity in the phenoxysilanes.     

13C NMR study of ortho-, meta- and para- substituted phenyldiphenylamines: Substituent effect correlations

The ¹³C chemical shifts of 11 substituted triphenylamines have been determined and the assignment of these resonances made using intensities, ¹H and ¹⁹F couplings and predictions from bond additivity relationships. ¹³C chemical shifts at carbons bearing the substituent and at carbons ortho to the substituent correlated reasonably well with the Q parameter. A multiple regression analysis of chemical shifts with the field and resonance parameters of Swain and Lupton and the Q parameter produced significantly better correlations than those obtained when Q was omitted for these positions. ¹³C chemical shift correlations for carbons meta and para to the substituent were not significantly better than when Q was omitted. Significant correlations were obtained between field and resonance parameters and ¹³C chemical shifts of C-o and C-p, and C-i, C-o, C-m and C-p of the non-substituent bearing phenyl rings in ortho- and para-substituted phenyldiphenylamines, respectively.     

Decyclization of 5-Aryl-4-methyl-2,3-dihydrofuran-2,3-diones by the Action of Nucleophiles

Ring cleavage in 4-methyl-5-phenyl-2,3-dihydrofuran-2,3-dione by the action of methanol and in 5-aryl-4-methyl-2,3-dihydrofuran-2,3-diones by the action of aniline and N-methylaniline results in formation of, respectively, methyl 3-methyl-4-phenyl-2,4-dioxobutanoate and 4-aryl-3-methyl-2,4-dioxobutananilides. The reaction mechanism was studied by ¹H NMR spectroscopy.     

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.     

13C NMR STUDY OF SUBSTITUENT EFFECTS IN 1,2,4-OXADIAZOLE AND 1,2,4-THIADIAZOLE DERIVATIVES

¹³C chemical shifts of C═N, C═O and C═S carbons of 3,4-disubstituted-1,2,4-oxadiazole-5-ones(thiones) and 3,4-disubstituted-1,2,4-thiadiazole-5-ones have been determined in CDCl₃ solution. Exceptionally good Hammett correlations of ¹³C NMR chemical shifts of these carbons with σ were obtained. The negative ρ values observed (inverse substituent effects) indicate π-polarization of the C═N, C═O and C═S bonds. As expected, the long distance C═O and C═S ¹³C chemical shifts were found less susceptible to substituent-induced electronic changes.     

Evidence for an important 13C NMR shielding effect for carbon atoms bearing a heavy chalcogen substituent

An important ¹³C NMR shielding effect on carbons bearing a heavy chalcogen is demonstrated. This effect is parallel to that induced by iodine, but to a lesser extent. For acyclic compounds and for partially saturated heterocycles, there is an excellent linear correlation between the ¹³C chemical shifts of carbons bearing a chalcogen and carbons bearing a halogen atom in the corresponding compound. The linearity of the relationship is less satisfactory with heteroaromatic compounds.     

Carbon-13 nuclear magnetic resonance spectra: III—2-heteroadamantanes

The ¹³C n.m.r. spectra of some 2-heteroadamantanes and 1-substituted 2-heteroadamantanes are reported. The influences of the heteroatoms in the adamantane framework, and those of the substituents attached to it, on the ¹³C chemical shifts of the adamantane carbons are investigated and compared with related compounds such as the corresponding heterocyclohexane derivatives and 2-mono- and 2,2-disubstituted adamantanes. The nonadditivity of the substituent effects for 1-substituted 2-heteroadamantanes, especially for the geminally substituted carbons, is substantially confirmed. In addition, the influences of a missing CH₂ group and of NCH₃ carbons upon the ¹³C chemical shifts of the carbons in the adamantane system are described.