IR spectra of substituted pyrroles

The IR spectra of 52 substituted pyrroles, including 24 1-vinylpyrroles, were thoroughly analyzed. The principal analytical bands of the pyrrole ring and the vinyl group were isolated. Doublet character of the bands of the stretching vibrations of the double bond ( ^v C=C) and the C-H (CH₂=) out-of-plane deformation vibrations, which indicates the presence of rotational isomerism relative to the N-vinyl bond, was detected. The integral intensify of the principal component of the ^v C=C doublet was measured for 12 of the 1-vinylpyrroles, and it is shown that it is practically independent of the structure of the alkyl substituents in the ring. Proof for the existence of a nonplanar gauche conformation for the 1-vinylpyrroles was obtained.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 910–914, July, 1977.     

Infrared spectra of cyclic ethers and their derivatives

Data for the characteristic bands of cyclic ethers are reviewed. The infrared spectra of a number of 2-mono- and 2, 5-di-substituted derivatives of tetrahydrofuran are investigated. Absorption bands at about 900 cm⁻¹ are related to pulsation vibrations, and those at about 1200 cm⁻¹ to antisymmetric skeletal vibrations, of the tetrahydrofuran ring. It is shown that to confirm the presence of a tetrahydrofuran ring in a molecule, it is necessary to take into account not only the band of valence antisymmetric vibrations of the group C-O-C (ν _C-O-C ^as 1075 cm⁻¹), but also bands due to ring pulsation vibrations (ring symmetric valence vibrations ν _sk ^s ∼ 900 cm¹).     

Electronic spectra of 1- and 9-fluorenecarboxylic acids

The absorption and fluorescence spectra of 1-fluorenecarboxylic acid and its anion have indicated that charge transfer interaction between the COOH group and the fluorene ring is more than that of the COO⁻ group with the ring, both in the S₀ and S₁ states. This has been explained by the greater possible resonance interaction between the aromatic ring and the COOH group than with the COO⁻ group. The respective interactions between the COOH or the COO⁻ group and the fluorene ring in the case of 9-fluorenecarboxylic acid is virtually negligible, both in the S₀ and S₁ states. The COO⁻ group becomes coplanar with the ring when deprotonation takes place at position 9. Various proton transfer reactions have been studied and pK_a values in the S₀ and S₁ states have been determined and discussed. The behaviour of the acids is confirmed by undertaking a similar study with their respective esters.     

Diazepines—XXII : 13C NMR spectra of 2,3-dihydro-1,4-diazepinium salts

The ¹³C NMR spectra of a number of 2,3-dihdyro-1,4-diazepinium salts, like ¹H NMR spectra, confirm shape, and charge distribution for these compounds. The ring has a half-chair shape which is inverting rapidly at room temperature. The atoms in the conjugated portion of the ring show alternating polarity, and phenyl groups attached to these positions act, respectively, as electron-donors or electron-acceptors. A methyl substituent in the saturated portion of the ring shows equal preference for quasi-equatorial and quasi-axial conformations. Some comparisons are drawn between present results and similar results obtained with related benzene derivatives.     

The NMR spectra of the porphyrins: 24—The NMR spectra of some tetraarylchlorins

The synthesis and complete assignment of the ¹H NMR spectra of 5-(o-pivaloylaminophenyl)-10,15,20-triphenylporphyrin (PIVTPP) and its two chiral dihydro adducts 3,4-dihydro-(PIVPTPC-I)- and 7,8-dihydr- (PIVPTPC-II)-porphyrins are reported. The use of the zinc complexes of the chlorins as chiral shift reagents with optically active bases is discussed. Comparison of the observed shift differences between the chlorins and the parent porphyrin with those calculated by a ring current model shows that a decrease in the ring current occurs on chlorin formation, and also specific effects occur at the reduced pyrrole ring, presumably reflecting different steric constraints.     

13C and 15N NMR spectra of 2,3-substituted 2H-azirines

The ¹³C and ¹⁵N NMR spectra of a series of 2,3-substituted 2H-azirines have been studied. The ¹⁵N chemical shift for the nitrogen in the azirine ring is found at much higher field than in acyclic imines with a considerable electronic effect for the substituents on the double bond. Cooperative steric and electronic effects associated with substituents on the unsaturated carbon atom of the ring were found to influence the shielding of the ¹³C and ¹⁵N nuclei. Reaction constants have been calculated for 2-alkyl(aryl)-3-phenylazirines. It has been shown that the azirine ring has a powerful —I effect (when compared with the phenyl ring) that exceeds the analogous value for the cyano group.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1181–1183, September, 1986.     

Non-empirical calculations of the nuclear magnetic resonance spectra of imidazole and hydrated imidazole

The magnetic shielding constants of the ¹H, ¹³C and ¹⁵N nuclei of imidazole are calculated for the isolated and hydrated molecules. The results show that the hydrogen bonds produce not only large variations of the chemical shifts for the nitrogen nuclei and the NH proton which are directly involved in the intermolecular bonding, but also measurable shifts for the carbon nuclei. The calculated shielding constants and their variation with hydration are discussed in relation to experimental results concerning imidazole, the 5-membered ring of the purine bases and the imidazole ring of histidine. The calculated values of the spin-spin coupling constants confirm that it is possible to study the tautomeric equilibrium of the imidazole ring from the measurement of these coupling constants and that spin-spin coupling constants are not very sensitive to solvent effects.     

Vibrational spectra of cyclopropenes. I. IR spectra of 3,3-disubstituted cyclopropenes

The IR spectra were measured and the vibrational problem was solved for a series of 3,3-disubstituted cyclopropenes [R¹: CH₃; R²: C(CH₃)₃ (I), C₆H₅ (II), CC–C(CH₃)₃ (III), CCH (IV)]. It was shown that a number of vibrations of the cyclopropene ring [symmetrical vibration of the ring, stretching and deformational (planar and out-of-plane) vibrations of the vinyl C–H bonds] are characteristic in frequency and form. On the basis of an analysis of the influence of a substituent at the C³ atom on the force field and the frequencies of the characteristic vibrations, it was concluded that the effect of conjugation of the substituent with _Walsh of the MO of the ring on the distribution of electron density in the ring plays a determining role.St. Petersberg University. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 1, pp. 112–124, January–February, 1993.     

Microwave spectra of transient species — cyclopentadienone

The microwave spectrum of the main isotopic species of cyclopentadienone has been measured and assigned. The rotational constants imply an essentially planar geometry and that the ring is rather “fatter” than the analogous ring in fulvene.The dipole moment, derived from Stark-effect measurements, is 10.4 × 10^?30 C m (3.13 D). A vibrational satel- lite spectrum, which, from its inertial defect, corresponds to an out-of-plane vibration has also been assigned.The life time of cyclopentadienone under our spectroscopic conditions is approximately 15 sec.     

The NMR spectra of the carbanions of xanthene and thioxanthene. Evidence for paratropism

The proton NMR spectra of the carbanions of xanthene [XH]^? and thioxanthene [TxH]^? have been recorded and interpreted. Paratropism in the central rings of [XH]^? and [TxH]^? is inferred from a comparison of the chemical shifts with those of the carbanion of 9,10-dihydroanthracene [AH]^?. The contributions to the chemical shifts arising from n-electron excess charges, local dipoles and magnetic anisotropies are discussed. Numerical values for the various ring currents have been estimated by a least squares analysis of the observed chemical shifts after applying corrections for the excess charge effect. The results point to a strongly increasing paramagnetic ring current in the central ring in the order [AH]^?, [TxH]^?, [XH]^?.     

13C, 14N, 15N and 17O NMR spectra of nitropyrroles and nitroimidazoles

Carbon, nitrogen and oxygen NMR spectra of some nitro derivatives of pyrrole and imidazole have been investigated. The ¹³C chemical shifts of para-carbons and the ¹⁷O chemical shifts of the nitro group correlate qualitatively with the electron densities on these carbon and oxygen atoms, which in turn depend upon the degree of conjugation of the nitro groups with the heterocyclic ring. Conjugation of several nitro groups with the benzene ring is in most cases not impaired by mutual interactions and the ¹³C shifts show good additivity. Such additivity is much worse in pyrrole and imidazole derivatives. Taken together with the diamagnetic nature of these deviations from additivity, this leads to a possible conclusion about the less pronounced conjugation of the nitro groups with the heterocyclic ring in heterocyclic dinitro derivatives.     

Mass spectra of some alkyl- and phenyl-substituted thiazoles

The mass spectra of a number of alkyl- and methyl-phenyl-substituted thiazoles at various ionizing electron energies were studied. The predominant disintegration reactions are processes involving contraction of the starting ring to form charged sulfur-containing fragments and nitrogen-containing neutral particles. It was noted that the peaks of the (M-H)⁺and (M-CH₃)⁺ ions are of low intensity, that the probability of rearrangement processes with ring expansion is low, and that the position of the methyl groups has a pronounced effect on the disintegration of the molecules during electron impact.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1372–1377, October, 1971.     

Infrared spectra of cyclic ethers and their derivatives

The IR spectra of six monosubstituted and of four 2,6-disubstituted 1,4-dioxanes have been studied in the 650–1800cm^–1 region. The assignment of the bands due to the vibrations of the 1,4-dioxane ring and to the deformation vibrations of the methylene groups of the ring is given. The appearance of a whole series of new absorption bands on passing from unsubstituted 1,4-dioxane to its derivatives is explained by the change in the symmetry of the molecule and the removal of the prohibition from the vibrations previously inactive in the IR spectra connected with this reduction in symmetry. It is proposed to use, in order to confirm the presence of a 1,4-dioxane ring in a molecule from the results of IR spectroscopy, not only the 1126-cm^–1 band but the whole group of bands lying in the frequency ranges 800–950, 1000–1150, and 1200–1300 cm^–1.For part I, see [3].     

Vibrational spectra of cyclopropenes. II. IR spectra of 1,2-disubstituted cyclopropenes

The IR spectra were measured and the vibrational problem was solved for the 1,2-dimethyl-3-phenylcyclopropene (I) and 1,2-diphenylcyclopropene (II) molecules. The forms of the normal vibrations were determined, and the vibrations associated with vibrations of the exo- and endocyclic bonds of the ring were distinguished. It was shown that substitution at the double bond of cyclopropene leads to a change in the form of the symmetrical vibration of the ring in comparison with the vibration of unsubstituted cyclopropene. It was shown that a significant hypsochromic shift of the band of the symmetrical ring vibration in 1,2-disubstituted cyclopropenes in comparison with cyclopropenes that do not contain substituents at the C^1,2 atoms is due chiefly to the kinematic effect of the substituent. It was found that the introduction of substituents at the double bond of the ring leads to a decrease in the force constant of the double bonds.St. Petersberg University. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 1, pp. 125–132, January–February, 1993.     

Carbon-13 NMR spectra of some epoxides derived from dicyclopentadiene

The ¹³C NMR spectra of a series of epoxides derived from endo- and exo-dicyclopentadiene and their partially hydrogenated compounds were determined to examine the substituent effects arising from the introduction of the oxirane ring in comparison with those found in other ring systems. The ¹³C signals of some epoxides were assigned by using lanthanide shift reagents. Characteristic substituent effects exerted by an oxirane ring were demonstrated. Marked steric γ-effects of ?8—13 ppm were observed at the bridge carbon signal in the bicyclo[2.2.1]heptane skeleton. Differences were found in the substituent effects between endo- and exo-dicyclopentadiene epoxides, and have been discussed in relation to the molecular geometry.     

13C NMR spectra of 7-substituted 8-mercaptoquinolines

The¹³C NMR spectra of 7-substituted [7-CH₃, 2,7-(CH₃)₂, 7-Cl, 7-Br, and 7-SCH₃] 8-mercaptoquinolines and 8-methylmercaptoquinolines were examined. It is shown that the changes in the¹³C chemical shifts of the quinoline ring in the spectra of 7-substituted 8-mercaptoquinolines are in good agreement with the additive contribution of the increments of the substituents, i.e., their conjugation with the ring is not disrupted. The conjugation of the SCH₃ group with the quinoline ring in 7-substituted 8-methylmercaptoquinolines is disrupted as a consequence of steric hindrance, and this leads to a decrease in the increments of this group. The data obtained are compared with the results of a calculation within the CNDO/2 approximation. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 801–805, June, 1980.     

The NMR spectra of porphyrins—12: 13C and proton NMR spectra of the zinc(ii)coproporphyrin isomers2

The ¹³C and proton NMR spectra of the zinc(II) complexes of the tetramethyl esters of the four coproporphyrin type isomers are reported and assigned. Effects of aggregation phenomena on these shifts are discussed and a method involving addition of a slight excess of pyrrolidine is proposed for measurement of the spectra of the “monomeric” species; spectra obtained under these conditions are capable of simple, straight-forward interpretation and assignment in terms of molecular symmetry. Thus, a facile distinction between the type isomers is obtained.The “monomer” chemical shifts so derived allow consistent SCS parameters to be derived. The C_β-Me SCS are shown to be related to the bond order of the C_β-C_β bond in the porphyrin ring, and are thus quite different from the corresponding SCS in pyrroles.Aggregation shifts in the ¹³C and proton spectra are shown to be consistent with the presence of “stacked” aggregates with the ring current of one molecule affecting the other, together with an additional effect on the chemical shifts of the meso carbons, which is probably steric in origin.     

The NMR spectra of fluoroaromatics—IV: 1H and 19F spectra of some fluorinated benzofurans

The complete analyses of the ¹⁹F spectra of some fluorinated benzofurans are given. These provide an unambiguous determination of the substituent position in these compounds. Comparison of the ¹⁹F SCS and coupling constants in the benzofuran, benzothiophene and benzene series shows that ¹⁹F spectral parameters can be transposed from the benzene series with caution. A large increase in the para F? F coupling with ring closure of the hetero-ring is noteworthy. A long-range through-space ⁸J_H is reported which arises from the proximity of the 3 carboethoxy methyl group and the C₄ fluorine in these molecules.     

Mass spectra and structure in the gas phase of isomeric 2-aroylbenzamides

The electron-impact mass spectra of various derivatives of 2-aroylbenzamides were studied. The principal pathways of fragmentation of the open and ring isomeric forms were described on the basis of an analysis of the high-resolution spectra and the DADI spectra. It is shown that peaks of ions formed in the fragmentation of the ring form, the intensities of which decrease as the volume of the substituent increases, are observed in the spectra of compounds with substituents R¹ = H, CH₃, and C₂H₅. Thermal isomerization of the ring form was proved on the basis of a study of the temperature effect on the intensities of the peaks of ions due to fragmentation of the open and ring forms when the samples are introduced through an inlet cylinder.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 666–670, May, 1982.     

Synthesis and 1H NMR spectra of some 1-aryl-2,5-pyrrolidinediones

Three 1-aryl-2,5 pyrrolidinediones, two of which are novel, were prepared by reaction of the requisite primary aromatic amines with succinic anhydride, followed by treatment with acetic anhydride. The ¹H nmr spectra for the derivatives in which aryl is 1-naphthyl and 1-anthracenyl exhibit 32-line multiplets for the four aliphatic hydrogens, indicating that all four are in different environments. Examination of molecular models demonstrates that the pyrrolidinedione and aryl ring systems cannot be coplanar and that rotation about the nitrogen-aryl bond is restricted. Molecular mechanics calculations reveal that a dihedral angle of 50–65° for the two ring systems results in the minimum steric interaction energy.