Synthese von [1,2,4]Triazolo [1,5-a]chinazolinen. Ableitung der Konformation von Substituenten mit Hilfe der 13C-NMR.-Spektroskopie

Synthesis of [1,2,4]Triazolo[1,5-a]quinazolines. Assignment of the Conformation of Substituents with the Aid of ¹³C-NMR. Spectroscopy The synthesis of [1,2,4]triazolo[1,5-a]quinazolines by condensation of 2-hydrazinobenzoic acid with N-cyano-imidates is reported. The preferred conformation of substituents at C (5), e.g. N (CH₃)₂, N (CH₃)NH₂, N (CH₃)OH, relative to the aromatic system is deduced with the aid of ¹³C-NMR. chemical shifts and proton nuclear Overhauser effect experiments.     

Conformations and 13C NMR shifts in tetralins

Force field (MM2) calculations, ¹³C NMR substituent-induced shifts (SIS) and epimeric shift differences (ESD) indicate a preference for equatorial substituents in the 2-position, but equal eq/ax populations in the 1-position of tetralines. Similar conclusions are reached from Yb(fod)₃-induced shifts, which are also used for signal assignments, e.g. in 1-tetralone. Configurational assignments are possible for 1,2- and 1,3-epimers (ESD up to 4 ppm) but, in line with the non-discriminating eq/ax conformations at C-I, not for 1,4-epimers (ESD<0.5 ppm). More than 50 compounds were measured, including functional derivatives which show regular SIS for substituents in the aromatic moiety only for m- and p-carbon atoms. OMe, but not OH or OAc substituents, induce o-carbon SIS varying from ?11 to ?19 ppm. Conversion of 1-hydroxytetralin to esters induces shielding variations at the aromatic carbon atoms which indicate the electrostatic origin of derivatization shifts.     

13C-NMR-spektren von bicyclo[n.1.0]alkenen

The ¹³C-NMR spectra of some bicyclo[3.1.0]hex-3-en-2-ols and of some bicyclo[3.1.0]hex-3-en-2-ones are described. The bond parameters of bicyclo[3.1.0]hex-3-en-2-one are derived from a structure determination of endo-6-methoxy-1,3,6-triphenylbicyclo[3.1.0]hex-3-en-2-one. The electron density is calculated by the EHT method, and correlated with the ¹³C NMR shifts. For comparison the ¹³C NMR spectrum of a bicyclo[4.1.0]hepta-1,5-dione derivative is analysed. The influence of a cyclopropane system attached to a five-membered and to a six-membered ring is elucidated. Whereas the five-membered ring shows conjugation between the carbonyl group and the cyclopropane system, the same effect is not observed in the six-membered ring analogue. This is explained by the highly rigid structure of the five-membered ring.     

Über Polygermane. XIX [1]. Empirische Regelin Zur Abschätzung von 13C-NMR chemischen Verschiebungen in phenylieryten Polygermanen

On Polygermanes. XIX. Empirical rules for estimating ¹³C-NMR Chemical shifts in Phenylated polygermanes ¹³C-NMR chemical shifts are given for 85 phenyl groups independently bonded to Ge in 52 acyclic and 23 cyclic Ge compounds. ¹³C-NMR phenyl signals can be estimated from basic values for perorgano substituted homonuclear chains of Ge nd from increments for substitution at the Ge atoms.     

13C-NMR-spektren von spiro[2.4]hepta-(1,4,6)-trienen und -(4.6)-dienen

The ¹³C NMR spectra of [1.2]-spirenes 2 and spiro[2.4]hepta-(4.6)-dienes 5 are described and the effects of substituents are discussed. A bonding model of the [1.2]-spirenes 2 is derived on the basis of C-H coupling constants and calculated charge densities. The ¹³C NMR shifts of 1-aryl-spiro[2.4]hepta-(4.6)-dienes 6 show a good correlation with the Hammett σp constants of the substituents in p-position of the phenyl ring. Conclusions on spiroconjugation in [1.2]-spirenes 2 are drawn from comparing the ¹³C shifts of similar substituted [1.2]-spirenes and spiro[2.4]hepta-(4.6)-dienes. The spiroconjugation in [1.2]-, [2.2]- and [2.3]-spirenes 2, 3 and 4 is discussed comparing the calculated charge densities with the δ (¹³C) values, as well as the UV and p.e. spectra.     

Strukturbestimmung von O-Methylazafrinmethylester durch 13C-NMR.-Spektroskopie

Structure Determination of Azafrin Methyl Ester 5-O-Monomethyl Ether by ¹³C-NMR.-Specta. The structure of the monomethyl ether ( 2 ) of azafrin methyl ester ( 1 ) was determined by a partial analysis of the ¹³C-NMR.-spectra. Assignments of quaternary carbon atoms and methyl groups in the cyclohexane ring were achieved using vicinal ¹³C-, ¹H-spin coupling. Substituent effects on methyl and methylene carbon atoms in 2 are discussed with respect to the conformation of the methoxy group. The spectra prove C(5)? OH as the site of methylation. Therefore C(5)? OH is less hindered than C(6)? OH.     

9-Alkenylcarbazoles. 10. 13C NMR spectra of 9-vinyl- and cis- and trans-9-propenylcarbazoles

The ¹³C NMR spectra of a number of ring-substituted 9-vinylcarbazoles and cis- and trans-9-propenylcarbazoles were studied. It was found that the C_B chemical shifts of the vinyl atoms of these compounds correlate satisfactorily with the constants of the substituents in the 3 and 6 position of the carbazolyl rings; the slopes of the straight lines increase in the order 5.84, 7.68, 9.56. The inductive and conjugation components of the effect of the substituents on the chemical shifts of the C_B atoms were evaluated. It follows from the results obtained that the effects of p- conjugation are realized not only in the relatively planar isomers but also in the nonplanar cis isomers of 9-alkenylcarbazoles.See [1] for Communication 9.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1640–1644, December, 1982.     

Cyclopropanation of 2-arylmethylidenemalononitriles,alkyl 3-aryl-2-cyanoprop-2-enoates,and N-substituted 3-aryl-2-cyanoprop-2-enamides with bromine-containing zinc enolates

Zinc enolates derived from 2,2-dibromoindan-1-one and 2,2-dibromo-1,2,3,4-tetrahydronaphthalen-1-one reacted with 2-arylmethylidenemalononitriles, alkyl 3-aryl-2-cyanoprop-2-enoates, and N-substituted 3-aryl-2-cyanoprop-2-enamides to give, respectively, 3-aryl-1′-oxo-1′,3′-dihydrospiro[cyclopropane-1,2′-indene]-2-2-dicarbonitriles, 3-aryl-1′-oxo-3′,4′-dihydro-1′H-spiro[cyclopropane-1,2′-naphthalene]-2,2-dicarbonitriles, alkyl 3-aryl-2-cyano-1′-oxo-1′,3′-dihydrospiro[cyclopropane-1,2′-indene]-2-carboxylates, alkyl 3-aryl-2-cyano-1′-oxo-3′,4′-dihydro-1′H-spiro[cyclopropane-1,2′-naphthalene]-2-carboxylates, and N-substituted 3-aryl-2-cyanol-1′-oxo-3′,4′-dihydro-1′H-spiro[cyclopropane-1,2′-naphthalene]-2-carboxamides as a single diastereoisomer. The stereoconfiguration of the products was determined by ¹H and ¹³C NMR spectroscopy.     

Zur Verwendbarkeit von 13C-Substituenteninkrementen bei 1,4-Benzo- und 1,4-Naphthochinonen

About the Availability of ¹³C-NMR Substituent Increments in 1,4-Benzo- and 1,4-Naphthoquinones The ¹³C-NMR spectra of a number of substituted 1,4-benzo- and 1,4-naphthoquinones have been obtained and assigned. Effects of CH₃-, O-alkyl-, Cl-, NH₂- and N₃- substituents have been deduced for the quinoid part of the molecules and used for the calculation of ¹³C-chemical shifts.     

Über Pterinchemie 51. Mitteilung [1] CNDO-Rechnungen an Pterin, 6,7-Dimethyl-7,8-dihydropterin und 5-Formyl-6, 7-dimethyl-5,6,7,8-tetrahydropterin

The ¹³C-NMR.-spectra of 7,8-dihydropterines and 5,6,7,8-tetrahydropterines show a large difference in the chemical shifts of the 4a- and 8a-sp²-carbon atoms. From the CNDO calculations it is apparent that there is a considerable difference in electron density at C(4a) and C(8a) atoms, which leads to a strong polarity of the C? C-Bond. The electron distribution in the highest occupied molecular orbital (HOMO) is discussed.     

Zur Kenntnis des Chinoiden Zustandes—XX: 13CMR-Untersuchungen an Cyclohexadienonen

The ¹³C-NMR-chemical shifts of 19 para- and 5 ortho-cyclohexadienones are determined by ¹³C-Fourier-transformation spectroscopy and assigned. The effect of substituents on the chemical shift of the ring carbon atoms is discussed. The mutual dependence of the shifts of the olefinic ring carbons and the allylic carbon atom in the para-quinolid ring system is shown by computing regression lines. A frequently observed correlation between ¹³C-NMR and ¹H-NMR is examined in the case of cyclohexadienones.     

13C-NMR.-Spektren N-acylierter Indoline. Einfluss der Orientierung der Carbonylgruppe auf die chemische Verschiebung

¹³C-NMR. spectra of N-acylated indolines. Effect of the orientation of the carbonyl group on the chemical shift Large downfield shifts are observed in the ¹³C-NMR. spectra of indolines and related compounds induced by electric field effects of carbonyl and oxime groups.     

The structural dependence of 13C, 13C coupling constants in cyclopropanes

The smallest one-bond carbon—carbon coupling constants of cyclopropane derivatives have been measured for [1-¹³C]cyclopropane-1,1-dicarboxylic acid and cyclopropanecarboxylic acid. The ¹³C, ¹³C coupling constants of cyclopropylcarbinol have also been determined. The dependence of ¹J(CC) of the three-membered ring on different substituents and hybridization effects is evaluated. The carbon—carbon coupling constant of the unsubstituted cyclopropane is discussed on the basis of self-consistent perturbation theory (SCPT) and s character calculations (localized bond orbitals), and the results are compared with the experimental finding. It is shown that the ¹J (CC) can be interpreted by assuming a dual-pathway coupling mechanism.     

13C-NMR.-Spektren von Dicyanhydrochinonen und Dicyan-p-benzochinonen

¹³C-NMR. Spectra of Dicyanohydroquinones and Dicyano-p-benzoquinones The ¹³C-NMR. spectra of 12 dicyanohydroquinones and fully substituted dicyano- and diazido-p-benzoquinones have been measured and assigned by comparison with related benzene and p-benzoquinone derivatives. For p-benzoquinones the influence of the cyano and azido substituents on the chemical shift of the CO-, α- and β-C-atoms has been investigated.     

13C n.m.r. spectra of some polychloroalkenes

¹³C n.m.r. spectra have been measured for thirty-two polychloroalkenes including (i) monosubstituted compounds CH₂?CHCCl_nH_2?nX, where ? X stands for ? H, ? Cl, alkyl, and trisubstituted alkenes CCl₂?CHAlk, none of which form geometric isomers; (ii) disubstituted compounds RCH?CHR′; (iii) and (iv) trisubstituted compounds of the types RCCl?CHR′ and CHCl?CClR, respectively. Compounds (ii) to (iv) represent either individual isomers or mixtures of the Z and E forms. In the case of compounds (ii) and (iii), the ordering of chemical shifts is δ_E > δ_Z for the sp²-carbon atoms and δ_E < δ_z for the adjacent tetrahedral ones. On the contrary, the signals of the sp²-carbon atoms of compounds (iv) obey the rule δ_E < δ_z. The effect of vinyl and allyl groups as substituents on the ¹³C chemical shifts of chlorine-containing groups is discussed. The dependence of the sp²-carbon spin–spin coupling constants J(¹³C? ¹H) on the number of chlorinated substituents in the molecule is also considered.     

Der ‘Push-Pull’-Effekt von ‘Push-Pull’-Oligoacetylenen. Eine 13C-NMR-Untersuchung

The ‘Push-Poll’ Effect of ‘Push-Pull’ Oligoacetylenes. A ¹³C-NMR Investigation According to ¹³C-chemicaI shifts of ‘push-pull’ oligoacetylenes 1 – 4 , the ‘push-pull’ effect (i.e. π delocalization induced by ‘push-pull’ substituents) rapidly decays in this series. To correct for other than π -charge-density effects, Δδ values of symmetrically placed C-atoms of the oligoacetylene chain are discussed. Stereoelectronic resteffects (SER) of the substituents on terminal C-atoms of PP-ketones 1a – 3a and PP -esters 1b – 4b are estimated from the residual Δδ of the asymptotes of Fig. 3. Fig. 4 convincingly shows that Δδ values are dramatically decreasing with increasing number n of acetylene units between the push and pull substituents. Assignment problems of ‘push-pull’ triacetylenes 3 have been solved by ¹³C labelling of the CO group of 3a .     

13C FT-NMR spectra of alkyl substituted furans. A study of the influence of steric interactions

The ¹³C FT-NMR spectra of thirteen furans, monodi- or trisubstituted with methyl and/or t-butyl groups, were studied in detail. Substituent effects of methyl and t-butyl groups on the chemical shifts of ring carbon atoms are additive in nonsterically hindered furans. Steric shifts for the ring carbon atoms are found in furans with bulky neighbouring substituents, but the hybridisation of the carbon atoms in these hindered furans is not changed. The chemical shifts of the substituents are calculated according to the Grant-Cheney formula. No simple relationship between steric shift and steric hindrance can be ascertained.     

13C NMR spectra of adamantane derivatives

The carbon-13 chemical shifts of mono- and 1,3-disubstituted adamantanes are reported. The effects caused by the substituents are compared with those met in aliphatic and alicyclic compounds. It is shown that the 1,4-interactions have only minor importance in l-substituted adamantanes. The influence of polar groups on the chemical shifts of γ- and δ-carbon atoms is a typical ‘through-the-bonds’ interaction and correlates with inductive parameters of the substituents.     

Nuclear magnetic resonance studies of boron compounds : XVI. Carbon-13 studies of organoboranes: Phenylboranes and boron-substituted aromatic heterocycles

¹³C and ¹¹B NMR data of 29 phenylboranes and 9 boron-substituted aromatic heterocycles (thiophene, N-methylpyrrole and furan) are discussed. The observed ¹³C chemical shifts of the para-carbon atoms in phenylboranes and the corresponding carbon atoms in the aromatic heterocycles are consistent with mesomeric interactions of the boryl group with the aromatic system. The trend of δ(¹³C(para)) in phenylboranes corresponds to that observed for isoelectronic phenylcarbocations. Low temperature ¹³C NMR and/or ¹³C {¹¹B, ¹H} heterocuclear triple resonance experiments were employed to obtain the ¹³C chemical shifts of the boron-bonded carbon atoms.     

13C-NMR-Spektroskopische und stereochemische untersuchungen—XIV: Sessel- und bootkonformationen bei bicyclo[3.3.1]nonanverbindungen

Syntheses and ¹³C-NMR spectra of bicyclo[3.3.1]nonanes bearing substituents at C-1 (X = F, Cl, Br, J, OR) and C-3 (X = exo Cl, Br, OR; X = endo COOR, CH₃, OR) are described. The functional C_α shifts are found to show the known dependence on the electron withdrawing effect of heterosubstituents, including the 1-jodo compound; there is, however, no weakening attenuation effect with tertiary compounds, as often implied, but rather substituent effects which are up to 25 ppm higher than observed with the corresponding secondary derivatives The β carbon shieldings of all compounds can be represented as a function of the square electric field effect; the flattening of the cyclohexane rings in the 1- and 3-exo-compounds however are resulting in a change of the linear electric field effects at C_α, and even more at C_γ. The deshielding of _γ carbons in antipenplanar X-C_α-C_β-C_γ conformations is not restricted to structures bearing X on a bridgehead, it can be rationalized on the basis of through space bond polarization by the C_α-X dipoles (linear field effects). The very small upfield shifts generated by 3-exo-hetero-substituents at the C-7 position put an upper limit for pure through space long range shielding effects in ¹³C-NMR spectroscopy.With the exception of the 3-endo compounds the ¹³C shifts (as well as ¹³C-¹⁹F couplings) of all compounds indicate a flattened double chair conformation CC The parameters found for the endo-3-derivatives establish the predominance of boat chair forms. Lanthanide induced shifts show the 3-endo substituent to rest at the boat part of the molecule. Although the shifts of the basic BC form for the unsubstituted hydrocarbon cannot be measured directly, they can be obtained by subtraction of corresponding substituent effects. Low temperature measurements establish the absence of higher populations of CC forms; the comparison of shift temperature gradients however indicates the partition of some CC conformer in the case of the endo-3-methoxy compound.