Evidence for conformational isomerism. II. Synthesis of 1-alkyl-2-carboazetidines using organolithium reagents

Treatment of 1-alkylazetidine-2-carboxylic acids with several organolithium reagents leads to the corresponding 1-alkyl-2-carboazetidines in near quantitative yield. Additional evidence is presented for conformational isomerism in the title compounds on the basis of infrared carbonyl stretching frequencies.     

Conformational isomerism in 1,2-di-o-tolylnaphthalenes: selective rotation of the 2-aryl ring

Two derivatives (X=Cl, CN) of 1,2-ditolylnaphthalene were prepared as models to investigate their conformational behavior that could involve rotation of either of the tolyl rings. The existence of anti and syn atropisomers was evident from their ¹H NMR spectra at room temperature indicating two pairs of well-resolved singlets for the methyl protons. Dynamic ¹H NMR studies estimated the rotation barrier to be about 76-82 kJ mol⁻¹, a value consistent with selective rotation of the 2-tolyl ring in the conformation inter-conversion.     

Carbon-13 NMR spectra of 3-aryl-2-thioxo-4-imidazolidinones. Conformational isomerism and substituent effects

A ¹³C NMR study of a series of 3-aryl-2-thioxo-4-imidazolidinones, which are capable of existing as enantiomeric or diastereomeric rotational isomers about the aryl C? N bond, shows that rates of internal rotation are slow at the probe temperature. The effects of hetero- and aryl-ring substituents on hetero-ring carbon atoms have been established.     

Carbon-13 NMR studies of 1-aryl-3-phenyl-2-thioxo-4-imidazolidinones. Conformational isomerism and substituent effects

Characteristic ^13C chemical shift ranges and substituent shifts of heterocyclic ring carbon atoms have been identified for a number of 1-aryl-3-phenyl-2-thioxo-4-imidazolidinones. ¹³CNMR spectra may be used to detect slow internal rotation about the aryl C? N-1 bond in compounds with diastereomeric rotational isomers; many corresponding carbon atoms in the rotamers have distinctly different chemical shifts. The δ-effects originating from aryl ortho substituents are both electronic and steric in origin.     

CIS-Trans isomerism of a,2-bistrichlorosilylethylene

Summary The existence of cis and trans isomers of 1,2-bis-rrichlorosilylethylene was detected spectrographically. It was noted that the frequencies of the double bonds of the cis and trans isomers of 1,2-bistrichlorosilyethylene, are unusually far apart as compared with the frequencies found for the cis and trans isomers of other compounds.     

Conformational isomerism of 1-butene secondary ozonide as studied by means of matrix isolation infrared absorption spectroscopy

Theoretical calculations of structures, stability and vibrational spectra of 1-butene secondary ozonide (SOZ) conformers were performed using DFT method B3LYP with a 6-311++G(3df, 3pd) basis set. The calculations predict six staggered structures of 1-butene SOZ. The FTIR spectra of 1-butene SOZ isolated in Ar, N₂ and Xe matrices were recorded. It was found that nitrogen is the best suited for the matrix isolation of 1-butene SOZ. The bandwidth of the spectral bands of the ozonide isolated in nitrogen was as narrow as 2 cm⁻¹. For the first time the existence of five conformers of 1-butene SOZ were confirmed experimentally by means of matrix isolation infrared absorption spectroscopy. The equatorial gauche (∠OCCC=−66.1°) conformer was proved theoretically and experimentally to be the most stable. It was found that due to high potential barriers of the conformational transitions annealing of the matrix is useless for the assignment of spectral bands to various conformers of 1-butene SOZ. Using the hot nozzle technique the van’t Hoff experimental plots were made for three additional conformers of 1-butene SOZ and experimental ΔH values for these additional conformers were established. The crystallization problems of 1-butene SOZ are discussed which accounts for the rich conformational diversity of the ozonide as well as high conformational barriers for axial-equatorial transitions.      

Ring-chain isomerism of imines of N-monosubstituted 2-benzoylbenzenesulfonamides

Imines of N-monosubstituted 2-benzoylbenzenesulfonamides or their ring isomers, viz., 3-amino-3-phenylbenzoisothiazoline 1,1-dioxides, were synthesized by condensation of the dilithium derivatives of N-monosubstituted benzenesulfonamides with benzonitrile. Interconversions of the isomers were realized for the N-phenyl derivative. The introduction of bulky isopropyl or tert-butyl substituents at the sulfonamide nitrogen atoms stabilizes the open structure. The ring isomers of the N-acylimines, viz., 3-acylamino-3-phenylbenzoisothiazoline 1,1-dioxides, are formed exclusively in the acylation of both the open and ring isomers.Communication 6 from the series Ring-Chain Transformations with the Participation of a C=N Group. See [1] for Communication 5.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1209–1213, September, 1981.     

Geometrical isomerism of 2′-piperidinomethyl-5-arylidenecreatinines

The aminomethylation of 5-arylidenecreatinines with paraformaldehyde and piperidine in benzene leads to 2-piperidinomethyl-5-arylidenecreatinines, in which the geometrical isomerism in relation to the C(₂) = N(₂) and C(₅) = C bonds was observed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1401–1404, October, 1989.The authors thank A. V. Dogadina for the taking of the PMR spectra.     

Ring — Chain isomerism of N-monosubstituted 2-cyanobenzenesulfonamides

A number of N-monosubstituted 2-cyanobenzenesulfonamides (A) and their chain isomers — 2-substituted 3-iminobenzothiazoline 1,1-dioxides (B), which are formed as a result of intramolecular nucleophilic addition of the sulfonamido group to the CN bond - were synthesized by acylation of primary amines with 2-cyanobenzenesulfonyl chloride. The inter conversions of the isomers -A B under alkaline-catalysis conditions and BA under thermal conditions — were accomplished for the first time. The influence of the electronic and steric effects of the substituent attached to the nitrogen atom on the relative stabilities of the open and chain isomers was ascertained. The AB equilibrium constants in solutions in a mixture of dioxane and triethylamine were determined by IR spectroscopy.Communication III of the series Ring-Chain Transformations with the Participation of the CN Group. See [1] for communication II.Translated from Khimiya Geteroistklicheskikh Soedinenii, No. 12, pp. 1632–1635, December, 1978.     

Conformational isomerism of 1,2-diformyl-, diacetyl-, and di(trifluoroacetyl) hydrazines and their methyl analogs

Conclusion The PMR method was used to determine the conformations of the 1,2-diformyl-, diacetyl-, and di(trifluoroacetyl)hydrazines and their 1-methyl and 1,2-dimethyl analogs. The effect of the structure and the medium, on the population of the conformers was discussed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1428–1430, June, 1982.     

Conformational preferences of 2-methoxy-acetophenone

On the basis of the presence or absence of long-range spin–spin coupling constants between side–chain and ring nuclei in 2-methoxyacetophenone, some literature ambiguities about the conformational preferences of the side-chains in this compound can be resolved. The long-range coupling between the methoxy protons and the ring proton ortho to the methoxy group, ⁵J(H, CH₃)o, is (?)0.28 ± 0.02 Hz, as expected for a conformation in which the methoxy group lies in the benzene plane and cis to H-3. The methyl protons of the acetyl group do not couple to H-6, implying that this methyl group does not approach H-6 closely. However, the ¹³C nucleus of this methyl group couples by +0.4 Hz to H-5 and not to H-3. This stereospecific five-bond coupling implies that the acetyl group predominantly prefers an arrangement in which the carbonyl group lies trans to the other substituent, as would be expected electrostatically. Large twists out of the ring plane are not consistent with the observed couplings.     

Rotational isomerism and conformational energies in 2-haloethanols

The Raman spectra of 2-fluoroethanol have been obtained as a function of temperature in the liquid and in the solid phases. The results of these experiments have provided substantial evidence for the existence of trans conformers in the liquid phase. The above study, coupled with analysis of the temperature dependence of the C-X stretching vibrations of the other haloethanols in the pure liquid, has permitted, for the first time, a determination of ΔH for all four members of the series. An interpretation is offered to explain the observed trends in the conformational energy differences.     

Pmr spectra and cis-trans isomerism of 2-methylenepyrrolidine and 2-methylenetetrahydrofuran derivatives

A number of secondary enamines and cyclic enol ethers (2-methylenetetrahydrofuran derivatives) were synthesized by the reaction of O-methylbutyrolactim and 2,2-diethoxytetrahydrofuran, respectively, with compounds that have an active methylene link. The absence of reversible cis-trans isomerization was established in a study of the PMR spectra of these compounds. The configuration of the secondary enamines is determined by the possibility of the formation of a strong intramolecular hydrogen bond between the carbonyl-containing substituent and the NH group. In the case of the cyclic enol ethers it was shown that the energy barrier to cis-trans isomerization is greater than 25 kcal/mole and that, as a consequence of this, the geometrical isomers can be separated preparatively.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 914–918, July, 1982.     

Conformational isomerism of chlorophenylthioureas and intramolecular N---H … Cl hydrogen bonds: IR spectra of N---H stretching vibrations

The vN---H regions of the IR spectra of thioureas with chlorophenyl (ClPh) groups and those with halophenyl groups were measured in dilute CCl₄ solution. The observed vN---H bands were classified into eight groups according to the wavenumbers and the two substituent groups. The suggested conformational states and the formation of intramolecular N---H … Cl hydrogen bonds in these compounds were discussed in comparison with those of the urea analogs. It was found that these thiourea derivatives are more stable in the cis form than the urea analogs and that thioureas with o-ClPh groups form fewer intramolecular N---H … Cl hydrogen bonds than do the urea analogs.