Synthesis,structural and conformational study of some amides derived from 3,7-dimethyl-9-amino-3,7-diazabicyclo[3.3.1]nonane-9-carboxamide

A series of 3,7-dimethyl-9-amino-3,7-diazabicyclo[3.3.1]nonane-9-carbonitrile and 3,7-dimethyl-9-amino-3,7-diazabicyclo[3.3.1]nonane-9-carboxamide N-substituted have been synthesized and studied by ¹ H and ¹³C nmr spectroscopy and the crystal structure of 3,7-dimethyl-9-benzylamino-3,7-diazabicyclo[3.3.1]nonane-9-carboxamide dihydrochloride ( IVb· 2HCl) has been determined by X-ray diffraction. The compounds studied display in deuteriochloroform, dimethyl sulfoxide-d₆ and methanol-d₄ the same preferred flattened chair-chair conformation with the methyl groups in equatorial position. The carboxamido group lies in a plane nearly perpendicular to the bispidine skeleton. The conformation and protonation sites of IVb· 2HCl in the crystal state and in deuterium oxide solution are discussed.     

Non-chair six-membered-ring conformations. Preference for a twist-boat (or skew) structure in α- -sorbopyranose derivatives

The conformational preferences for 2,3-O-isopropylidene-α- -sorbopyranose derivatives 3–6 were determined by using ¹H NMR data and empirical force field calculations. Proton NMR studies of 3–6 indicate that a twist-boat (or skew) conformation (³S₀) prevails over possible chair forms for each compound. Force-field calculations (MM2, MNDO, AM1) on a model 2,3-O-isopropylidene-α- -sorbopyranose system (18) indicate that the ³S₀ conformation is among the low-energy structures. X-Ray crystallographic analysis of α- -sorbopyranose sulfamate 3, a compound with potent anticonvulsant activity, demonstrates that the ³S₀ skew conformation is manifested in the solid state, as well.     

HeI photoelectron spectroscopic study of the electronic structure of SSF2 and FSSF compounds

HeI photoelectron (PE) spectra are re-recorded for SSF₂ and FSSF. The assignment of bands has been made with the aid of band shapes, band intensities and ab initio calculations. In the PE spectrum of SSF₂, two sharp peaks at 10.48 and 11.22 eV are considered to result from through-space interaction of lone-pair orbitals in the two S atoms and two sharp peaks at 12.50 and 12.90 eV from through-space interaction of lone-pair orbitals in the two F atoms. The larger splitting of the S atoms can be attributed to the larger 3p orbital of S. The lack of sharp peaks in the PE spectrum of FSSF shows that there is no orbital which embodies the character of a lone-pair. So the PE spectra of SSF₂ and FSSF are examples embodying through-space interaction of lone-pair orbitals.     

Synthesis,vibrational, and conformational properties of novel polyazadioxime chain molecules

Novel large polyazadioxime molecules 4,5,8,9-tetraaza-3,6,7,10-tetramethyl -3,5,7,9-dodecatetraene-2, 11-dione-2, 11-dioxime (H₂doxN₄) and 4,5,8,9,12, 13-hexaaza-3,6,7,10,11,14-hexamethyl-3, 5,7,9,11,13-hexadecahexane-2,15-dione-2, 15-dioxime (H₂doxN₆) were synthesized. The molecular geometries of these molecules as well as smaller dioxime molecules, H₂dox and H₂doxN₂ were optimized by using modified intermediate neglect of differential overlap (MNDO) calculations. The optimized conformations for all the molecules under study are close to the all-E, all-s trans conformation of C_2h symmetry group. However, the energy barriers of internal rotation around the N-N single bonds were found to be low. Therefore some distortions of the polyazabackbone through internal rotation the N-N bonds have been evidenced. By infrared and Raman spectroscopies in the solid state as well as in solution. From the MNDO calculations and vibrational spectroscopy, the polyaza chain molecules under study appear as a poorly conjugated system and can be represented as a sequence of single and double bond alternation.     

Crystal structures of two syn bent tetraalkylhydrazines,their radical cations,and a dication

The crystal structures of 2,7-diazatetracyclo[6.2.2.2^3,6.0^2.7]tetradec-4-ene, 2, its cation radical nitrate salt 2⁺, NO₃^-, 2,7-diazatetracyclo[6.2.2.2^3,6.0^3,7]tetradecane, 3, its dication dihexafluorophosphate salt 3²⁺(PF₆^-)₂, and a low quality structure of the monocation radical tosylate salt of 3 are reported and compared with MNDO calculations of these structures. Cations 2⁺ and 3⁺ are found to be significantly syn bent at nitrogen, and the dication 3²⁺ has a longer N-N distance than its azo analogue, 2,3-diazabicyclo [2.2.2]oct-2-ene (11).     

Intense shake-up satellites in the XPS spectra of planar and sterically hindered N-piperidyl-nitrobenzenes and -nitrothiophens

The shake-up satellites present in the O_1s and N_1s energy regions of the XPS spectra of the planar 4-N-piperidyl-nitrobenzene (1) and 2-N-piperidyl-5-nitrothiophen (3), and of the sterically hindered 2-N-piperidyl-nitrobenzene (2), 2-N-piperidyl-3-nitrothiophen (4) and 3-N-piperidyl-2-nitrothiophen (5) and, for comparison, of 2-bromo-3-nitrothiophen (6) have been analyzed with the help of CNDO/S CI calculations. The spectra of the planar derivatives closely resemble these of the related compounds previously analysed, the main satellites deriving from the transition between the highest occupied molecular orbital (HOMO, localized at the donor-ring moiety) towards the lowest unoccupied one (LUMO, localized at the nitro group). Calculations indicate that in the ortho derivatives new relaxation processes are allowed upon N_1s/NO₂ ionization. In 2, where the angle of rotation θ is closer to 90° than 60°, the NR ₂ lone-pair orbital relaxes through space towards the core-ionized N/NO₂ atom. In 4 and 5, where 45° ? θ ? 60°, both through-ring and through-space relaxations are present. The assignment of the main N_1s/NO₂ line in 1 is discussed.     

Chair-boat equilibria in bicyclo[3.3.1]nonane and some 3- and 3,7-substituted derivatives: Thermodynamic parameters and geometry of the conformers as obtained by molecular mechanics

ΔG-Values for conformational equilibria in 3,7-substituted bicyclo[3.3.1]nonanes have been obtained by means of epimerisation experiments (cc α bc) and by variable temperature ¹³C NMR (bc α bb). The results of these experiments fit well with those of molecular mechanics using the Schleyer force field. In bicyclo[3.3.1]nonane and 3β-substituted derivatives the cc conformation predominates; however, the bulky 3β-substituent t-butyl, is found to have a destabilizing effect. A 3α-substituent forces the substituted wing into the boat conformation. For the 3α,7α-substituted derivatives the conformational preferences depend on the size of the substituents: for 3α-methyl-7α-t-butylbicyclo[3.3.1]nonane the cb and t-bb conformers are of approximately equal enthalpy. The geometries, obtained by the calculations, show that the conformers of bicyclo[3.3.1]nonane (cc, bc and t-bb) are all distinctly flattened. The boat wings of bc conformers are not twisted to any extent. The t-bb is the most stable bb conformation. The influence of substitution at positions 3 or 7 is discussed in detail; in general, a bulky substituent such as t-butyl, affects the geometry of both wings of the ring system. The calculated geometries are in good agreement with the conclusions of previous ¹H NMR investigations.     

13α-Hydroxymethylenedeacetyllaurenobiolide, a New Germacranolide from Tanacetopsis mucronata

The new sesquiterpene lactone 13-hydroxymethylenedeacetyllaurenobiolide was isolated from the aerial part of Tanacetopsis mucronata S. Koval. (Asteraceae). Its structure was established using spectral data and X-ray structure analysis. The germacranolide macrocycle has the chair-chair conformation with the configuration ₁D¹⁴, ¹⁵D₅.     

A lanthanide induced shift (LIS) investigation of the conformation of cyclohexanones in solution

The solution conformations of cyclohexanone1 and 4-t-butyl cyclohexanone2 have been obtained by the use of the LIS given by Yb(fod)₃. A starting geometry for the substrates was obtained by molecular mechanics calculations. The use of a two-site model for lanthanide-substrate complexing, together with iteration on the¹H and¹³C induced shifts allowed the angle of pucker of the cyclohexanone rings to be determined. In contrast, a one-site model gave no acceptable solutions. The cyclohexanone ring is somewhat flatter at the carbonyl end than cyclohexane, the angle of pucker (α) being reduced from 51° to 49° i.e. the dihedral angle (ω₁₂) is reduced trom 56 to 51°. In 4-t-butyl-cyclohexanone the angle of pucker at the carbonyl end is further reduced. The solution conformation of1 agrees closely with that deduced by MM calculations; interestingly, the conformation of2 is essentially identical with the geometry found in the crystal.     

Application of DNMR,group theory and molecular mechanics in the elucidation of the inversion process in the flexible molecule perhydrotetra-azapyrene

The inversion process in cis-10b,10c-perhydro-1H,6H-3a,5a,8a,10a-tetraazapyrene (1) has been investigated by ¹H and ¹³C NMR. The free energy of activation is found to be 14.95 ± 0.2 kcal mole^?1 at 45°. Application of group theoretical techniques led to a graph representing the essential symmetry properties of the potential energy surface for conformational change. The energies of intermediates on this graph were then estimated using molecular mechanics calculations. This combined approach suggests that the total inversion proceeds via a conformation of C_2v symmetry with two non-chair piperazine rings, calculated to be 6.8 kcal mole^?1 less stable than the ground state conformation (C₂ symmetry).     

Force field and multinuclear nmr study of the conformational properties of thiolane-1-oxide and its mono and dimethyl derivatives

Force field calculations and ¹H, ¹³C and ¹⁷O NMR data are reported for thiolane S-oxide and several of its mono and dimethyl derivatives. For comparison carbon-13 and oxygen-17 chemical shifts of the corresponding S-dioxides are also reported. According to force field calculations and NMR data the conformation of S-oxides depends on the number and on the position of ring substituents. Oxygen-17 chemical shifts of thiolane S-oxides are apparently not very sensitive to ring substitution and to the configuration of the sulfinyl group. This is however the result of conformational changes which cannot be easily predicted. For 2-methyl derivatives δ₁₇₀ allows an easy identification of the cis and trans isomers.     

Nitrosolates and related compounds—IX: Coordination compounds of divalent copper,nickel and cobalt with nitroacetate(2−) ions as chelating ligands. Crystal and molecular structure of potassium bis[nitroacetato(2−)]cuprate(II)-water (1/1)

The syntheses of K₂[Cu(nac)₂]·H₂O (4), [Cu(nac)(N-N)(H₂O)]·H₂O (N-N = bpy, phen; 5,6) and [M(nac)(N-N)₂]·xH₂O (M = Ni, Co; 7–10) with nitroacetate(2?) ions (nac^2?) as chelating ligands are described.The structure of 4 has been determined by single crystal X-ray diffraction and contains square planar [Cu(nac)₂]^2? units in which the nitro and carboxyl groups of the two chelate ligands are in cis positions. Two of the units form a centrosymmetric dimer with a four-membered CuOCu“O”-ring, the dimers being connected by exo-oxygens of the ligands into two-dimensional layers. The water molecules and the potassium ions are arranged between the layers; there are two kinds of potassium ions with distorted (1+4+1) and (2+4+3) coordinations respectively.     

Über Arsen-haltige Heterocylen. V. Konformative Gleichgewichte in 8gliedrigen Heterocyclen des Arsens und Antimons

On Heterocyclic Systems Containing Arsenic. V. Conformational Equilibria in Eight-Membered Heterocycles of Arsenic and Antimony ¹H- and ¹³C-NMR spectra were measured at and below room temperature and analysed quantitatively for two arsocanes and two stibocanes. Chemical shifts and coupling constants could be assigned and correlated with torsion angles starting from the known conformations in the solid. There are equilibria in solution between a chair-chair conformation and the two enantiomers of a boat-chair conformation at room temperature. These transitions turn infrequent at lower temperature. The amount of the two conformations is different for the four compounds. Transition states are discussed.     

Cyclopericodiol and new chlorinated melleins isolated from Periconia macrospinosa KT3863

Cyclopericodiol (1) and two new chlorinated melleins (2 and 3) were isolated from Periconia macrospinosa KT3863. The results of density functional theory (DFT)-based calculations while estimating the values of the ¹³C chemical shifts and the spin coupling constants allowed to determine the relative configurations of 1 and 2. The absolute configurations of these compounds were established by comparing the experimental electronic circular dichroism (ECD) spectra with those obtained while performing time-dependent DFT calculations. Interestingly, the methyl and hydroxy groups at C3 and C4, respectively, of 2 assume an 1,2-anti-diaxial conformation due to absence of 1,3-diaxial repulsion. This conclusion was supported by the observation that 2 afforded an ECD spectrum that was almost the mirror image of that of 3. Furthermore, the theoretical spin coupling constants ³J_H-3/C1, ²J_H-3/C4, ³J_H-3/C4a, and ²J_H-3/C9 were in agreement with the heteronuclear multiple-bond correlation (HMBC) intensities of H-3 with C1, C4, C4a, and C9.     

Tautomeric equilibria of heterocyclic molecules. A test of the semiempirical AM1 and MNDO-PM3 methods

Tautomeric equilibria (mainly of the lactam-lactim type) for a rather large number of six-membered heterocyclic molecules are calculated by the semiempirical AM1, MNDO-PM3, and MNDO methods. Except for compounds with adjacent pyridine-like lone pairs both AM1 as well as MNDO-PM3 give rather reliable predictions for relative stabilities of the various tautomeric species–comparable to quite high level ab initio calculations. The known errors associated with MNDO in the treatment of heterocyclic tautomerism are thus largely corrected in AM1 as well as MNDO-PM3. For 2-hydroxypyridine-pyrid-2(1H)-one the effect of self-association is less satisfactorily described by MNDO-PM3 than by AM1. MNDO-PM3 calculated relative stabilities of methylated derivatives are, however, in considerably closer agreement with experimental values than those obtained by AM1. Ionization potentials, especially those for lone-pair orbitals, are overestimated by all three semiempirical methods. MNDO-PM3 results for nitrogen lone-pair orbital energies are slightly better than those obtained by the AM1 or MNDO method.     

The synthesis and fluxional behavior of the first [2.1.2.1] metacyclophane

8,15,23,30-Tetramethyl[2.1.2.1]metacyclophane,4, is synthesised. Variable temperature ¹Hmr and ¹³Cmr spectra indicate that 4e is the most likely conformation and that at temperatures above 50°C the molecule is fluxional (ΔG^≠₃₂₃ = 15.4 kcal/mole).     

An analysis of the through-bond interaction using the localized molecular orbitals with ab initio calculations—I : Lone-pair orbital interactions in cis- and trans-hydrazines

Ab initio SCF MO calculations using STO-3G basis set were performed on the cis- and trans- hydrazines. The cannonical MOs obtained by these calculations were then transformed into the localized MOs. With the use of the localized MOs thus obtained, the variation in the lone-pair orbital energies of the molecules were pursued in the light of the through-space and/or the through-bond interactions between the specified localized MOs. As a result of this analysis, it was found that ; (a) the effect of the inner shell orbitais, l s electrons of N atoms, is not negligibly small, (b) the effect of the through-bond interaction is not so larger than the through-space interaction, and (c) the large contribution of the through-space interaction is caused from the indirect as well as direct interactions between two lone-pairs.     

Conformational mobility of the six-membered ring in 5-oxo-1,3-cyclohexadiene and its derivatives

Molecular mechanics and MNDO calculations showed that the six-membered ring in the molecule of 5-oxo-1,3-cyclohexadiene possesses high conformational mobility. The transition from a planar equilibrium conformation to a distorted sofa conformation in which the C(sp²)-C(=O)-C(sp³)-C(sp²) torsion angle is equal to ±30° increases the energy of the molecule by less than 1 kcal mol^–1. The influence of steric (R = Me, Et, Prⁱ, Bu^t) and electronic (R = NH₂, NO₂) effects of substituents R on the equilibrium conformation and mobility of the carbocycle has been analyzed. Both types of substituents at unsaturated C atoms do not change the equlibrium conformation or flexibility of the six-membered ring. Substituents at saturated C atoms cause the transition of the carbocycle to the distorted sofa conformation and significantly restrict its mobility. The electronic structures of 5-oxo-1,3-cyclohexadiene and its amino and nitro derivatives have been analyzed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 849–854, May, 1995.     

Quantum chemical calculations and35Cl NQR study of the molecular structure of trichloroacetyl halides and trichloroacetaldehyde

An optimal geometry of CCl₃C(O) X molecules (X=H, F, Cl, Br, and I) is determined by the MNDO quantum chemical method. According to the results of calculations, the molecules in the free state have an eclipsed conformation with a syn-peri-planar position of the oxygen atom and one of the chlorine atoms of the trichloromethyl group. However, as follows from the³⁵Cl NQR spectra at different temperatures, in the crystal state of CCl₃C(O)X this conformation is distorted under the influence of intermolecular interactions due to the torsional rotation of the CCl₃ group around the C-C bond. Indicatory potentialities of the NQR method with respect to the structural features that are due to crystallographic effects are discussed. Perm State University. Translated fromZhurnal Strukturmoi Khimii, Vol. 37, No. 3, pp. 494–500, May-June, 1996.     

Spectroscopic study of 3-methyl-2,4-diphenyl-3-azabicyclo[3.3.1]nonan-9-α(β)-ols

3-Methyl-2,4-diphenyl-3-azabicyclo[3.3.1]nonan-9-α(β)-ols have been synthesized and studied by ir, ¹H and ¹³C nmr spectroscopy. In deuteriochloroform and perdeuteriobenzene solutions, these compounds adopt a flattened chair-chair conformation in which the cyclohexane ring is more flattened. From the ¹H and ¹³C nmr data, several stereoelectronic effects have been deduced. The complete and unambiguous assignment of all protons of the 3-azabicyclo[3.3.1]nonane system, not described up to date, has been carried out.