1H NMR spectra and electronic structure of 3-arylmethyl-idenephthalide and 3-arylthiomethylidenephthalide derivatives

The ¹H NMR spectra of trans-3-phenylmethylidenephthalide and trans-3-phenylthiomethylidenephthalide derivatives were investigated. After applying a correction for the anisotropy of substituents and/or for changes of ring current in the substituted aromatic ring, linear correlations were obtained between the chemical shifts of protons of the substituted phenyl group and the methine group and s? constants of substituents. The influence of the bridge heteroatom on the transfer of electronic effects of substituents through the molecules under study is discussed.     

Direct and indirect substituent effects on 1J(CH) in vinyl derivatives and related compounds

The variation in the one–bond couplings ¹J(CH) in vinyl derivatives with substituent has been examined. For the geminal proton ¹J correlates very badly with substituent electronegativity but extremely well with σ_I, if conjugating substituents are excluded. In the case of halogen substituents the marked stereospecificity of ¹J(CH) for the cis and trans protons can be rationalised in terms of an intrinsic dependence of π_CH on the dihedral angle between the coupling atoms and the perturbing substituent, with an additional positive increment to the cis coupling due to direct interaction of the substituent non-bonding electrons or to orbital circulation of the substituent electrons. The intrinsic specificity of β-substituent effects on ¹J(CH) is also found in analogous compounds containing C?N and C?O bonds.     

13C NMR shifts and conformations of substituted indans

¹³C NMR spectra of indan derivatives bearing substituents in the 1, 2, 5 and 6 positions are reported and assigned by LIS measurements and other techniques. Epimeric indanes bearing vicinal oxygen and phenyl or benzyl substituents show ring carbon shielding in the cis relative to the trans isomers, which is compared with corresponding cyclopentane shifts, and indicates the predominance of envelope conformations with pseudoaxial oxygen substituents for the cis isomers. Acetylation shifts show consistently larger shielding at C-β for the trans compounds. Introduction of oxygen at C-5 leads to asymmetric shielding effects at the ortho carbon atoms as soon as there is a substituent in the para position which can participate in mesomeric forms.     

1,1-Dialkyl-2-acyl-3-hydroxypyrazolidinium and 2,2-dialkyl-5-hydroxyisoxazolidinium salts

Salts of 1,1-dimethyl-2-acylhydrazines and 1,1-dialkylhydroxylamines add quantitatively to the double bond of oxo compounds with an unsubstituted vinyl substituent. The structure of the products depends on the nature of the substituent at the carbonyl group.¹H and¹³C NMR spectroscopy indicated that acrolein derivatives have the cyclic structure of 1,1-dialkyl-2-acyl-3-hydroxypyrazolidinium and 2,2-dialkyl-5-hydroxyisoxazolidinium salts, while derivatives of phenyl vinyl ketone and hydrazide salts are the corresponding linear, hydrazinium salts. Ring-chain tautomerism was found for several derivatives of methyl vinyl ketone in solution.Military Medical Academy, 194175 St. Petersburg. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1199–1203, September, 1998.     

Structural variations and electronic substituent effects in phenylcubane derivatives: a quantum chemical study

Electronic substituent effects in 4-substituted 1-phenylcubane derivatives, Ph–C₈H₆–X, have been investigated from the structural changes caused by the substituent X. The molecular structures of 34 derivatives with charged or dipolar substituents have been determined from quantum chemical calculations at the HF/6-31G* and B3LYP/6-311++G** levels of theory. Geometrical variations caused by substitution appear both in the cubane framework and in the benzene ring, but the two kinds of changes show no correlation. The rather small changes in the benzene ring geometry are caused by long-range polar effects (field effects), while the larger changes in the cubane cage are controlled primarily by electronegativity effects. A structural parameter measuring the long-range polar effect of the substituent, S _F^CUB, has been derived from the geometry of the phenyl group acting as a probe. This parameter correlates well with the calculated gas-phase acidities of 4-substituted cubane-1-carboxylic acids, HOOC–C₈H₆–X, and with other indicators of long-range polar effects obtained from bicyclo[2.2.2]octane derivatives. The correlations can further be improved by introducing a resonance parameter as an additional explanatory variable. This indicates that the electron delocalization resulting from hyperconjugative interactions between substituent and cage modifies the long-range polar effect of the substituent. Strong hyperconjugative interactions between some charged substituents and the cubane cage result in remarkable variations in the cage geometry, superimposed onto those ascribed to electronegativity effects.     

1H NMR spectra of oxiranes. cis-Arylmethyl oxiranes substituted in the phenyl ring

The ¹H NMR parameters for a number of cis-arylmethyl oxiranes are reported and discussed in comparison with those of trans derivatives and styrene oxides substituted in the phenyl ring. While the macroscopic behaviour of the results is in agreement with a perturbative mechanism through the oxirane ring that is mainly electrostatic in character, a small contribution due to conjugative interaction is not excluded. It seems likely that the effect of substituents in the phenyl ring is mainly transmitted through bonds rather than through space, and that the different polarisation of the C? H bonds in the oxirane ring is mainly responsible for the different behaviour of the protons in cis- and trans- arylmethyl oxiranes towards the effect of substituents.     

1H NMR Investigation of Si-alkylsubstituted 1,3,5-Trisilacyclohexanes

Alkylsubstituted derivatives of 1,3,5-trisilacyclohexane have been prepared and their ¹H NMR spectra recorded and analyzed. For the compound series 1-mono-, cis-1,3-di- and cis-cis-1,3,5-tri-alkylated derivatives (alkyl = Me, Et, i-Pr and t-Bu) it is found that the conformational preference for an equatorial position of the substituents in the chair form is considerably less than for cyclohexane derivatives. In the compound series trans-1,3-di- and cis-trans-1,3,5-tri-alkylated derivatives the t-butyl group is found to behave uniqually by forcing the ring to escape into the twist-boat form. Each kind of substituent is found to have a characteristic effect on the chemical shift values of the ring protons.     

1H and13C NMR spectra of 2-substituted 5-nitrofurans and conformation of chemotherapeutic preparations of the 5-nitrofuran series

The¹H and¹³NMR spectra of t-nitrofuran and 17 2-substituted 5-nitrofurans were investigated. The Δ¹H and Δ¹³C substituent increments [Δ = δ(2-X-5-nitrofuran) δ(5-nitrofuran)] in the spectra of these compounds were analyzed by comparison with the analogous 5-methylfuran and furan derivatives, and the change in the sensitivity of the chemical shifts of the ring protons and the carbon atoms to the effects of substituents X as a function of the electronic character of substituent R was also analyzed. The chemical shifts and the spin-spin coupling constants were used to determine the preferred orientation of the substituents relative to the furan ring. It was found that medicinal preparations of the 5-nitrofuran series (5-nitrofurfurylidenehydrazones) exist in the form of s-trans conformers in solutions in dimethyl sulfoxide and water, whereas furagin has primarily the structure of the E s-trans form. Translated from Khimiya Geterotsiklichesklkh Soedinenii, No. 2, pp. 167–176, February, 1980. The authors thank N. O. Saldabol, M. A. Trushule, and K. K. Venter for providing us with samples of the compounds, the synthesis of which has been described in the literature.     

Nitrogen Bridgehead Compounds. Part 81. Synthesis of 9-(benzylidenehydrazono)-6-methyl-4-oxo-6,7,8,9-tetrahydro- and 9-(benzylidenehydrazine)-6-methyl-4-oxo-6,7-dihydro-4H-pyrido[1,2-a]-pyrimidine-3-carboxylates

Reaction of ethyl 9-hydrazono-6-methyl-4-oxo-6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrimidine-3-carboxylate and benzaldehyde and its derivatives give a tautomeric mixture of 9-arylidenehydrazono-6,7,8,9-tetrahydro- and 9-arylidenehydrazine-6,7-dihydropyrido[1,2-a]pyrimidine derivatives. In the same case the enhydrazine and hydrazone tautomers were separated. The structure of the products were characterised by uv, ir, ¹H and ¹³C nmr. The equilibrium of the tautomers was affected by the substituent of the phenyl ring. A fair linear correlation exists between the logarithms of the equilibrium constants and Hammett σ_m and σ^? constants of the substituents present on the phenyl ring.     

13C NMR study of some polychloro-isobutane and -isobutene compounds

The ¹³C chemical shifts and the carbon–proton coupling constants have been determined for some chlorinated isobutane and isobutene compounds. The one-bond coupling constants in isobutane derivatives showed a regular increase with an increasing number of γ-chlorine substituents. The three-bond coupling constant of the methyl carbon decreased from 4.2 to 2.0 Hz as the number of chlorine substituents in the γ-position increased. In the isobutene compounds, the vicinal coupling of C-1 was larger to protons in a group that is trans with respect to a chlorine substituent on C-1 than to those in the corresponding group cis to the chlorine. The vicinal coupling constants between atoms in geminal groups (on C-2) seem to be affected by the orientation of the chlorine substituent on C-1.     

Carbon-13 nuclear magnetic resonance spectra of some methyl and phenyl substituted 2H-azirines

Carbon-13 n.m.r. spectra have been obtained for some methyl and phenyl substituted 2H-azirines. The higher field resonance of C-2 than that of the corresponding aziridine carbon is interpreted in terms of ring strain. Substituent effects on the chemical shifts of the azirine ring carbons are discussed. A set of additivity parameters for the methyl and phenyl groups are obtained which can be used for the calculation of the chemical shifts of the azirine ring carbons. The substituent effect of an azirine ring on the chemical shift of benzene is also discussed in comparison with those of some other substituents. A high degree of s character (48.5%) in the exocyclic orbital of C-3 is indicated by a large J(¹³C-3,H) value (242.5 Hz).     

NMR spectra of pyrimidines

The chemical shifts of the protons in the even positions of the pyrimidine ring in 2- and 4-substituted pyrimidines in dimethyl sulfoxide solutions were determined. The correlation equations that link the relative chemical shifts (with allowance for corrections for the magnetic anisotropy of the substituents and the ring) with the F and R substituent constants were calculated. The ratios obtained were analyzed by comparison with the corresponding correlation equations for monosubstituted benzenes. The reasons for the significant increase in the transmission of the conjugation effects of the substituents to the even positions of the pyrimidine ring as compared with the meta positions of the benzene ring and the appreciable weakening of the conductivity of their inductive effects when the heteroring nitrogen atom is situated between a resonating proton and the substituent are discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 673–677, May, 1978.     

Rebek Imide Platforms as Model Systems for the Investigation of Weak Intermolecular Interactions

A Rebek imide receptor with an acetylene‐linked phenyl ring complexes 2,6‐di(isobutyramido)pyridine in (CDCl₂)₂ via triple H‐bonding and π–π‐stacking interactions, and the influence of para‐substituents on both rings was investigated by ¹H NMR binding titrations. When the phenyl ring was extended to biphenyl and the C(4)‐pyridine substituent varied, interaction energies increased in the order CH₃CH₂???phenyl<CH₃S???phenyl<phenyl???phenyl?N‐methylcarboxamide???phenyl, highlighting the energetic gain from π stacking on amide fragments. The predicted preference of amide–π stacking for an antiparallel alignment of the local dipoles could not be confirmed with the studied system. Different substituents were introduced in the para position of the phenyl ring and their interaction with bound 2,6‐di(isobutyramido)pyridine was investigated. Theoretical predictions that the mere introduction of a substituent has a stabilizing effect on π–π stacking, regardless of its electronic nature, were experimentally confirmed.     

How do the substituents affect and regulate the relative retention times of polychlorinated biphenyls during gas chromatography?

The effects and regulatory actions of the polychlorinated biphenyls (PCBs) substituent characteristics on their relative retention times (RRTs) during gas chromatography were analyzed based on known experimental RRTs of 209 PCB congeners and biphenyl; the substituent characteristics used for this analysis included the total amount of substituents, the similarity between two phenyl rings in a single PCB congener, the substituents distribution in single phenyl ring, the main/second‐order interactions effects at each position, and the combined effect of two phenyl rings. At last, the universality of regulation was validated on other experimental conditions. Among them, the full factorial experimental design included 10 factors correlated with each substituent position and two levels (0, 1) were initially applied to the domains of the substituent characteristics. The obtained results have revealed that increasing the total amount of substituents can increase the RRTs of PCBs linearly, but similarities between the two rings cannot control the RRTs effectively. Meanwhile, the more compact the substituent distributions on a single phenyl ring are, the bigger the RRTs of PCBs are. Based on a full factorial experimental design, the overall important trend for each position is as follows: para > meta > ortho and the main regulatory substituents for the second‐order interaction effects are distributed in the same phenyl ring in the following sequence: N_o > N_m > N_p. The congener with two perpendicular phenyl rings exhibits a milder combined effect on RRTs and smaller RRT relatively. The regulation has a good universality among different experimental conditions, revealing the dominant effect of substituent characteristics on RRTs of PCBs. Copyright © 2015 John Wiley & Sons, Ltd.     

13C NMR spectra of p- and m-substituted phenyl N-methyl- and phenyl N,N-dimethyl-carbamates

¹³C NMR spectra of p- and m-substituted phenyl N-methylcarbamates, phenyl N,N-dimethylcarbamates and p- and m-substituted phenyl propionates were recorded, and their para ¹³C SCS (substituent chemical shifts) were analysed by DSP (dual substituent parameters) and DSP-NLR (non-linear resonance) equations. It was found that the fixed substituent Y, ? OCONHCH₃, ? OCON(CH₃)₂ and ? OCOC₂H₅, were all mild in the sense that DSP analysis gave a good correlation, leaving little room for improvement by the DSP-NLR treatment. Further, the three series of compounds gave similar ρ_I and ρ_R values (para derivatives, 3.2–3.3 and 17.7–18.0; meta derivatives, 5.1–5.2 and 21.8–22.0). Examination of the corresponding analyses of similar compounds indicated that the ρ_I and ρ_R values and, hence, their ratio ρ_R/ρ_R = λ, depended primarily on the nature of the atom through which the fixed substituent Y (e.g. α-C, α-N and α-O) was bonded to the aromatic ring when the Y substituents are mild. The extent of this tendency for compounds with active fixed substituents is also discussed.     

Electrophilic substitution in a number of N-exo-carbamoyl derivatives of sydnoneimines

Depending on the character of the substituents and the reaction conditions, the bromination of N-exo-carbamoyl derivatives of sydnoneimines may proceed in the heterocyclic ring and (or) in the phenyl ring of the exocyclic substituent. Nitration proceeds only in the phenyl rings of the substituents.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1198–1203, September, 1975.     

Effets de substituants et conformation de stilbenes

Simultaneous study of para nitrostilbenes by X-ray diffraction and ¹³C nuclear magnetic resonance shows a quantitative relationship between the effect of a para nitro substituent on the chemical shift of ethylenic carbon not adjacent to the substituted phenyl ring and the dihedral angle between this phenyl ring and the central double bond. The alternative introduction of substituents in each phenyl ring discloses at the position of carbon β a certain π-polarization which extends to the double bond and to an unsaturated group carried by carbon α.     

SUBSTITUENT EFFECTS OF PHOSPHORUS-CONTAINING GROUPS. THE ELECTRONIC EFFECTS IN ANILIDES AND PHENYL ESTERS

Abstract

¹³C NMR shielding parameters have been determined for the N-phosphorylated aniline and O-phosphorylated phenol derivatives, Ph–Y–P(O)Z₂ (Y=NH, O), and for their complexes with titanium tetrachloride. Inductive and resonance substituent constants were calculated using the dsp approach for the neutral and charged substituents. The results are compared with those for the corresponding neutral and charged acetyl derivatives. Shielding effects and substituent constants are discussed in terms of the interactions of the lone pair at Y with the aromatic ring and with the acyl center. It is concluded that no significant p _π-d _π back-donation from Y to the phosphorus atom operates in the systems studied.     

B环对位取代异黄酮化合物的核磁共振研究

对14个合成的B环对位取代异黄酮化合物核磁共振氢谱进行了研究.利用超导核磁共振归属了B环无取代异黄酮质子的化学位移,根据取代基化学位移的变化影响规律考察了取代基对分子的影响方式.研究结果表明,2'(6'),3'(5')位质子共振迁移分别与取代基参数σ_p和S_o线性相关,说明4'位取代基主要通过电子效应影响其间位质子,其磁各向异性仅影响邻位质子,该取代基对A环质子影响不大,而对C环尤其是对2-H影响较明显.