Temperature-dependent 1H Research Articles

Dynamic Stereochemistry of Di(3-methyl-1-azulenyl)phenylmethyl Cation. Flip of One Azulene Ring as the Threshold Rotation Mechanism

Abstract Dynamic stereochemistry of di(3-methyl-1-azulenyl)phenylmethyl hexafluorophosphate (5) was studied by temperature dependent 1H NMR spectra. The low temperature NMR indicated that the compound (5) exists in three propeller conformations (C1 and two C2 symmetry), and at higher temperature the spectra reflect rapid isomerization, which were interpreted by the flip mechanism of one azulene ring. The processes have activation energies of 53.8 and 45.2 kJ mol−1.

Equilibria between Contact and Solvent-Separated Ion Pairs of 1,1-Diphenylethylene Dimer Dianion and Tetraphenylethylene Dianion

Abstract Temperature-dependent 1H NMR chemical shifts of the two title carbanions have been measured in three solvents and with three counter ions. The equilibria between two types of ion pairs of the carbanions have been discussed in terms of solvent, counter ion, and temperature.

The ring inversion of gaseous N-methylpiperazine. Pressure and temperature dependent 1H NMR studies

Pressure dependent gas phase ring inversion rate constants of N-methylpiperazine (MPZ) obtained from line-shape analysis of exchange broadened 1H NMR spectra can be adequately modeled using RRKM theory indicating that intramolecular vibrational redistribution in critically energiezed MPZ molecules is statistical or nearly so and that transition state theory is a useful approximation at high pressures for providing a framework for comparisons of rate data obtained for this and other similar molecules. Temperature dependent gas phase 1H NMR spectra of MPZ are consistent with the following activation parameters for the chair ⇌ chair ring inversion process: Δ G ‡ = 51.5(1.2) kJ mol −1, Δ H ‡ = 51.9(1.7) kJ mol −1, Δ S ‡ = 2.1(1.7) J mol −1 K −1, E act = 55.7(1.7) kJ mol −1 and A ∞ = 2.2(1.3) × 10 13 s −1. Δ H ‡ and E act for MPZ are slightly higher than values obtained for gaseous N-methylpiperidine, indicating that replacement of the CH 2 group at position four of the ring with an NH group increases the barrier to ring inversion. Δ G ‡ 247 in the gas phase is 3.3 kJ mol −1 higher than in a 20% solution of MPZ in CH 2Cl 2, and 2.5 kJ mol −1 higher than in a 20% solution of MPZ in CH 3OH, indicating that interactions with polar solvent molecules facilitate the ring inversion process.

Gas and solution phase NMR studies of N-ethylmorpholine intra- and intermolecular effects on ring inversion rate constants

Temperature dependent gas phase 1H NMR spectra of N-ethylmorpholine are consistent with the following activation parameters for the ring inversion process: Δ G Δ = 47.7(0.3) kJ mol −1, Δ H Δ = 47.1(2.3) kJ mol −1, Δ S Δ = −1.9(4.9) J mol −1 K −1, E act = 49.2(2.3) kJ mol −1 and A ∞ = 1.2(0.4) × 10 13s −1. Rate constants in the gas phase and in CDCl 3 solution are very similar while those obtained in CS 2 solutions are almost twice as large at corresponding temperatures. Rate constant obtained for a 1% solution of N-methylmorpholine in CDCl 3, obtained in the present study and those previously obtained in the gas phase and CS 2 solutions show a similar trend. The observed phase and solvent dependent rate constants do not agree with predictions based on simple steric or dielectric considerations and may indicate that complex static and dynamic solvent effects are important in the liquid solutions.

Specific molecular recognition by cage-type cyclophanes having a helically twisted and cylindrical internal cavity

Cage-type cyclophanes, which are constructed with two rigid 2,11,20-triaza[3.3.3]paracyclophane skeletons and three chiral bridging components, were prepared. Temperature-dependent 1H NMR measurements in (CD 3) 2SO indicate that the molecular framework of the cage-type cyclophane having a cylindrical internal cavity is more rigid than those of the corresponding non-cage hosts. The guest-binding behavior of the cage-type hosts toward various guests was examined by electronic absorption spectroscopy and electrospray ionization (ESI) mass spectrometry. The present hosts were found to bind anionic guests, such as 1-hydroxy-2,4-dinitronaphthalene-7-sulfonate, 2-hydroxy-1-(phenylazo)naphthalene-6,8-disulfonate, 2,7-bis[(4-methyl-2-sulfophenyl)azo]-1,8-dihydroxynaphthalene-3,6-disulfonate, 8-anilinonaphthalene-1-sulfonate, 6- p-toluidinonaphthalene-2-sulfonate, naphthalene-1-sulfonate, and 3,5-bis(methoxycarbonyl)benzene-1-sulfonate, to form host-guest complexes. The computer-aided molecular modeling study reveals that the three pyridinium moieties bound to the chiral l- and d-valine residues in the bridging segments undergo chiral twist in the same directions. However, the twisted direction in the host bearing l-valine residues is opposite to that evaluated for the host bearing d-valine residues so that the former and latter cage-type cyclophanes furnish M and P-helical cavities, respectively, as reflected in their circular dichroism (CD) spectra. The chirality-based molecular recognition of the cage-type hosts toward enantiomeric guests such as bilirubin-IXα and pamoic acid in aqueous media was investigated by CD spectroscopy.

Molecular recognition of alkylamines: conformational and binding properties of calix[6]arene-based ester ligands

A series of alkyl 15,35,55,75,95,115-hexa-tert-butyl-1,3,5,7,9,11-hexa[1,3]benzenacyclododecaphane esters have been prepared that selectively bind to alkylammonium cations. Ester ligands showed extraction efficiency toward alkylamines in the sequence of ammonium Pr > Pri > Bu > Bui≃ Bus > tert-butylammonium guests. Single and competitive transport experiments of butylamines also confirmed the binding properties obtained with extraction experiments and the transport selectivity for Bu/But pair exceeds 25. Conformational properties, such as Tc and ΔGc‡, of ester ligands were investigated by means of temperature-dependent 1H NMR spectroscopy. Conformational freedom was generally found to decrease as the size of substituent of ester side chain increased. 1H NMR complexation studies of ethyl ester 2 with caesium tetraphenylborate and butylammonium picrate guests suggest that the conformational reorganization into a cone conformation has provoked complex formation.

Contents of volume 27

A 500 MHz NMR study of the lariat RNA tetramer 1 and pentamer 2 mimcking the naturally occurring lariat RNA is reported. The conformational properties of 1 and 2 were compared with those of a linear branched RNA tetramer 3, which show that the conformational features of the two lariat RNAs, 1 and 2, are quite constrained and significantly different from those observed for the linear branched RNA tetramer 3. The conformation of all sugar residues forming the lariat rign in 1 and 2 are locked in a rigid South-type conformation. All residues in both lariat RNAs have a high population of γ+ (67–85%) and βt (95–100%) rotamers except guanosine where the γ+ population is low. The conformation around the glycosidic bond is anti for all residues except for guanosine where NOE data indicates an equilibrium of syn ⇄ anti. In both lariat RNAs, 1 and 2, the temperature dependent 1H and 31P chemical shifts as well as the oligomerization shifts, with repect to adenosine 2′,3′,5′-triethyl-phosphate (Sund et al., 1992, Tetrahedron 48, 695) suggests that the 3′ → 5′ linked U4 or C4 residue is stacked on guanosine. Subsequently, 1H-1H, 1H-31P and 13C-31P coupling constants derived torsional constraints were used for molecular dynamics study in water with counter sodium ions for a total of 226 ps. The MD simulations were first carried out with harmonic torsional constraints which were derived from J couplings (0–86 ps) and then completely without constrainst (96–226 ps). The lack of any major changes in the conformation of the two lariat-RNA structures upon releasing the NMR constraints indicate that the conformers generated in the MD simulation in water agree well with the structural features suggested by experimental observables. This means that the ensemble of conformers generated during the MD trajectory of 226 ps are not artificially held in these conformations due to the NMR constraints, suggesting that these conformers can be considered to be good representatives of the actual NMR observed solution structures.

Solution structure of lariat RNA by 500 MHz NMR spectroscopy and molecular dynamics studies in water

A 500 MHz NMR study of the lariat RNA tetramer 1 and pentamer 2 mimcking the naturally occurring lariat RNA is reported. The conformational properties of 1 and 2 were compared with those of a linear branched RNA tetramer 3, which show that the conformational features of the two lariat RNAs, 1 and 2, are quite constrained and significantly different from those observed for the linear branched RNA tetramer 3. The conformation of all sugar residues forming the lariat rign in 1 and 2 are locked in a rigid South-type conformation. All residues in both lariat RNAs have a high population of γ + (67–85%) and β t (95–100%) rotamers except guanosine where the γ + population is low. The conformation around the glycosidic bond is anti for all residues except for guanosine where NOE data indicates an equilibrium of syn ⇄ anti. In both lariat RNAs, 1 and 2, the temperature dependent 1H and 31P chemical shifts as well as the oligomerization shifts, with repect to adenosine 2′,3′,5′-triethyl-phosphate (Sund et al., 1992, Tetrahedron 48, 695) suggests that the 3′ → 5′ linked U 4 or C 4 residue is stacked on guanosine. Subsequently, 1H- 1H, 1H- 31P and 13C- 31P coupling constants derived torsional constraints were used for molecular dynamics study in water with counter sodium ions for a total of 226 ps. The MD simulations were first carried out with harmonic torsional constraints which were derived from J couplings (0–86 ps) and then completely without constrainst (96–226 ps). The lack of any major changes in the conformation of the two lariat-RNA structures upon releasing the NMR constraints indicate that the conformers generated in the MD simulation in water agree well with the structural features suggested by experimental observables. This means that the ensemble of conformers generated during the MD trajectory of 226 ps are not artificially held in these conformations due to the NMR constraints, suggesting that these conformers can be considered to be good representatives of the actual NMR observed solution structures.

1H NMR Study of Molecular Motions and Phase Transitions in Methyl Ammonium Hexabromo Selenate [(CH3NH3)2SeBr6

AbstractThe temperature dependence of 1H spin‐lattice relaxation time, T1, and that of the second moment, M2, are analysed in the temperature range 390 K to 77 K. A plot of T1 vs inverse temperature shows three phase transitions at 250 K, 167 K and 111 K. At 167 K, T1 displays a large jump while it shows changes in slope at 250 K and 111 K. In the high temperature phase (> 167 K), the correlated motion of CH3 and NH3 groups is found to cause the relaxation while their uncorrelated motion takes over in the low temperature phases (< 167 K). The unusual T1 behaviour in phase II (250 K‐167 K) is ascribed to the small angle torsion of the cation. A constant M2 value of ∼ 9.7 G2, throughout the range of temperature studied, indicates the presence of reorientation of CH3 and NH3 groups.

1H, 13C-NMR and 57Fe-Mössbauer spectroscopic studies of α,α-ferrocenylruthenocenylmethylium + ion

Ferrocenylruthenocenylmethane reacts with chloro- or bromoruthenocenium(IV) + PF 6 − salts, giving a deep-purple salt. The results of 57Fe-Mössbauer, 1H, and 13C NMR spectroscopic studies on the salt suggest the formula α,α-ferrocenylruthenocenylmethylium hexafluorophosphate salt; [Fe IICp(C 5H 4CH +C 5H 4)CpRu II]PF 6 − ( 1). The salt gives remarkably temperature dependent 1H and 13C NMR spectra, due to rotation about the exocyclic carbon atom (-CH +-). The energy barrier of the rotation is estimated on the basis of 1H NMR line simulation studies to be about 34.0 ± 0.6 kJ mol −1. On the other hand, ferrocenylruthenocenylmethane reacts with iodoruthenocenium(IV) +Y − (Y; BF 4, PF 6) salts, giving paramagnetic dicationic salts formulated from the results of 57 Fe-Mössbauer and NMR spectroscopic studies as [Fe IIICp(C 5H 4CH 2C 5H 4)CpRu IV I] 2+Y 2 −.

Synthesis and characterization of novel halogeno(+I) adduct complexes containing malononitrile and 1,3,5-triazine

The 1-halogeno-1,3,5-triazinium hexafluoroarsenate and hexafluoroantimonate compounds of the type [(HCN) 3X][MF 6] (MAs; XF, ( 1), Cl ( 2) and MSb; XBr ( 3)) have been synthesized by direct reaction of 1,3,5-triazine, (HCN) 3, with halogenomonofluorides, XF, in the presence of AsF 5 or SbF 5, respectively. The reactions of (HCN) 3 and malonitrile, CH 2(CN) 2, with [I 3][AsF 6 afforded the iodonium adduct species [{(HCN) 3} nI][AsF 6] ( n=1 ( 4), 2 ( 5)) and [{CH 2(CN) 2} nI][AsF 6] ( n=1 ( 6), 2 ( 7)). All compounds have been characterized by chemical analyses, proton NMR spectroscopy and vibrational spectral data (IR, Raman). Temperature dependent 1H NMR spectroscopy on SO 2 solutions of 1– 3 revealed functional behaviour at room temperature which was frozen down at −60 °C (two resonances, ratio 1:2). According to the NMR the scale the cations in 4 and 5 exist already in the slow exchange region at room temperature. Solution behaviour, IR and UV data of 6 (naples yellow reddish) and 7 (black) suggest 7 to be polymeric and 6 to be monomeric with strong intermolecular I···I interactions.

Racemization kinetics and spin states of four-coordinate nickel(II) complexes with bidentate NS ligands, [pyrR 2R 3(NR 1S)] 2Ni. A comparative study

Nine complexes of the type [pyrR 2R 3(NR 1S)] 2Ni (R 1iPr) were synthesized in order to investigate possible relations between the spin-spin equilibrium and racemization of four-coordinate nickel(II) complexes with bidentate NS ligands. An X-ray structure analysis of bis(1,3-dimethyl-5-thiolato-pyrazol-4-isopropylaldimino- N,S)nickel(II) shows it to be monoclinic, space group I2/ a, with 4 molecules in a cell of dimensions a=19.091(4), b=7.564(2), c=15.760(4) Å and β=101.818(14)°. The structure refined to a final R value of 0.040 for 1144 reflections. The molecule has two-fold symmetry, the coordination at Ni is close to tetrahedral with NiS=2.249(1) Å and NiN=1.989(3) Å. Every complex was almost totally high spin, but small differences in spin states were found by comparisons of isotropic shifts and extinction coefficients for a pure high spin transition. The racemization was studied for three complexes by temperature dependent 1H NMR spectroscopy. Rate constants, resulting in approximate values of Δ H # (11.1–34.6 kJ/mol) and Δ S # (−56.7 to −144 J/(K×mol)), were determined from the iPrMe shifts and linewidths. Solvent effects of the kinetics were examined for one compound: the simultaneous promotion of the low spin form and the racemization rate at low temperature in the most polar solvent indicated that the low spin form may be the racemizing species.

Struktur und reaktivität von ytterbiumbenzamidinaten

Abstract The ytterbium(II) benzamidinates [RC6H4C(NSiMe3)2]2Yb(THF)2 (1a: R  H, 1b: R  OMe) react with diaryl diselenides and ditellurides to give ytterbium(III) complexes of the type [RC6H4C(NSiMe3)2]2Yb(SeR′)(THF) (2: R  H, R′  Ph; 3: R  H, R′  Mes) and [RC6H4C-(NSiMe3)2]2Yb(TeR′)(THF) (4: R  OMe, R′  Mes), respectively. The molecular structure of [PhC(NSiMe3)2]2Yb(SeMes)(THF) (3) has been determined by X-ray crystallography (triclinic, space group P 1 , a 1064.9(3), b 1377.1(3), c 3690(3) pm, α 68.61(2), β 89.46(3), γ 72.82(1)°, Z = 4, 10531 observed reflexions, R = 0.045). Moreover the strongly temperature-dependent 1H NMR spectra of 2 and 3 are discussed and 171Yb NMR spectra of some ytterbium(II) chelate complexes are reported.

Nuclear magnetic relaxation studies of poly( p-phenylene sulphide) doped with sulphur trioxide

Temperature dependences of 1H n.m.r. spin-lattice relaxation times ( T 1) were measured for poly( p-phenylene sulphide) (PPS) heavily doped with sulphur trioxide (SO 3). A clearly non-exponential character of the magnetization recoveries was observed. The magnetization recovery is characterized by an exp[−( t T 1 ) 1 2 ] time dependence over a wide time interval and for the whole temperature range studied, indicating diffusionless relaxation of the nuclei to the paramagnetic centres. The temperature dependence of T 1 is weakly thermally activated. The annealing of doped PPS at 450 K changes the mechanism of the relaxation. In this sample the relaxation is related to the thermally activated motion of protons from phenylene rings and sulphuryl groups.

I.r. spectroscopy and 1H n.m.r. broad line studies of poly( p-phenylene sulphide) doped with sulphur trioxide

I.r. spectra and temperature dependences of 1H n.m.r. linewidths were measured for poly( p-phenylene sulphide) (PPS) heavily doped with sulphur trioxide (SO 3) in the form of vapour and liquid. X-ray diffraction studies confirmed the total destruction of the crystalline phase as a result of the doping process. I.r. spectra show that doping with SO 3 leads to irreversible chemical modifications of the polymer by sulphonation. A comparison of the experimental values of the n.m.r. second moment determined for a rigid structure of the doped PPS with the poly(benzothiophene) excludes the formation of the latter as a result of doping. Doping with SO 3 in the vapour form leads to structural changes in the polymer with its two-phase character preserved. Annealing of the doped sample at 450 K results in the removal of chemically unbonded SO 3. However, the annealed polymer still has a different structure from the pristine polymer. PPS doped with liquid SO 3 shows a monophase structure indicated by a liquid-like resonance line.

Sulfur containing cinnamides with antifungal activity from glycosmis cyanocarpa

Bioassay guided analysis of the methanolic leaf extract of Glycosmis cyanocarpa ( Rutaceae) led to the isolation of a new type of sulfur containing cinnamides with antifungal activity: sinharine (cinnamic acid methylsulfidoethylamide) ( 2) and the corresponding N-methyl derivative methylsinharine ( 4). In addition, the dominating furoquinoline kokusaginine ( 3) together with small amounts of skimmianine ( 5) and the carbazole glycozolidol ( 1) were also isolated. A series of quinolone and quinazolone alkaloids were detected as minor components by reversed phase HPLC. The structures of 2 and 4 were elucidated by means of spectroscopic methods (IR, UV, 1H NMR, 13C NMR, MS). Temperature dependent 1H NMR and lanthanide induced shifts (LIS) established the stereochemistry of the two conformers of 4.

Conformational studies by dynamic NMR. Part 48. Conformational preferences and stereomutational processes of the rotational enantiomers of hindered naphthylimines and imonium salts

A number of 1-naphthylimines (and some of the corresponding imonium chlorides), having the isopropyl group as a prochiral probe, have been synthesized and their configurations assigned by the combined use of NOE experiments and molecular mechanics calculations. This method also provides reliable information about the conformations adopted in solution. The existence of diastereotopic methyl groups in the isopropyl moiety indicates the presence of conformational enantiomers, due to the rotation about the naphthyl–imino bond in nonplanar conformers. The barriers for the stereomutation of such enantiomeric forms have been determined by line-shape analysis of the temperature-dependent 1H or 13C signals of the prochiral probe. Molecular mechanics calculations have also helped in suggesting which is the preferred stereomutation pathway and in predicting the existence of a derivative having configurationally stable enantiomers. Such a compound has been synthesized and is found to display the predicted property (atropisomerism), in that the two enantiomers can be separated.

REVERSIBILITY IN THE SULFONATION OF 3,5-DIMETHOXYPHENOL AND ITS METHANESULFONATE ESTER

Abstract The reactions of 3,5-dimethoxyphenol (1) and its methanesulfonate ester (3) with sulfur trioxide have been studied. On reaction with 0.9 equiv of SO3 in nitromethane, 1 gives a 65:35 mixture of its 2sulfonic acid (1-2-S) and 1-4-S, whereas with 4.0 equiv of SO3, exclusively 1-2,6-S2 is formed. 1-2,6-S2 is subsequently converted into its hydrogen sulfate (2-2,6-S2), which in turn rearranges to give the intramolecular anhydride 5,7-dimethoxy-8-sulfobenzo-1,3,2,4-dioxadithiin 2,2,4,4-tetraoxide (4). Reaction of 3 with SO, in nitromethane leads to a 85:15 mixture of 3-2-S and 3-4-S which, upon further reaction, yields initially 3-2,6-S2 and eventually 4. Temperature dependent 1H NMR evidence suggests that there exist for both 1 and 3 equilibria between the two monosulfonic acids and the substrate.

The sysnthesis and reactivity of N-bonded η 1-1-azaallyl type complexes of platinum(II) and palladium(II). Crystal structure of [ [formula omitted]} (PMe 2Ph) 2

Reaction of cis-[MCl 2L 2] (M = Pt, L = PPh 3, PMePh 2, PMe 2Ph, PBzPh 2, L 2 = Ph 2PPh 2 (dppm), Ph 2P{CH 2} 2PPh 2, Ph 2P{CH 2} 3PPh 2; or Ph 2P{CH 2} 4PPh 2; M = pd, L 2 = Ph 2 = Ph 2P{CH 2} 3PPh 2) with α-acetamidocinnamic acid and silver(I) oxide affords quantitative yields of the N-bonded η 1-1-azaalyl complexes [ M{N(COMe)C(C(O)O} L 2]; in contrast, the analogous reaction of cis-[MCl 2L 2] (L = PPh 3, PMePh 2, PMe 2Ph; L 2 = Ph 2P{CH 2} 4PPh 2) with 2-acetamidoacrylic acid leads to the isolation of the metallaoxacyclopentenone products [ M{CHC(NHCOMe)C(O)O} L 2], characterised by an X-ray study on the platinum complex where L = PMe 2Ph. The complex [ Pt{N(COMe)C(CHPh)C(O)O} (dppm)] exhibits a temperature-dependent 1H NMR spectrum.

Gehinderte Ligandbewegungen in Übergangsmetallkomplexen, XXXVIII [1]. [4+5]-Cycloaddition von 2,3-Dimethyl-1,3-butadien an Tricarbonyl- η5-2,4-pentadienyl-mangan und Tricarbonyl-η5-dimethyl-2,4-pentadienyl-mangan / Hindered Ligand Motions in Transition Metal Complexes, XXXVIII [1]. [4+5] Cycloaddition of 2,3-Dimethyl-1,3-butadiene to Tricarbonyl(η5 -2 ,4 -pentadienyl)manganese and Tricarbonyl(η5 -2 ,4 -dimethyl-2 ,4 -pentadienyl)manganese

Tricarbonyl(η5-2,4-pentadienyl)manganese (1) and tricarbonyl(η5-2,4-dimethyl-2,4-pentadienyl)manganese (2) photochemically add 2,3-dimethyl-1,3-butadiene (3). Mediated by manganese, 6,7-dimethyl-2,6-cyclononadiene-1-yl and 1,3,6,7-tetramethyl-2,6-cyclononadiene-1-yl complexes are formed. Η-shifts from the methyl groups of the substituted CC double bonds convert the primary products into tricarbonyl-η3:CH-l-methylene-2-methyl-6-cyclononen-2-ylmanganese (4), and tricarbonyl-η3:CH-1-methylene-2,5,7-trimethyl-6-cyclononen-2-yl-manganese (6), respectively. In addition tetracarbonyl-η3-1-methylene-2-methyl-6-cyclononen-2-yl-manganese (5), and tetracarbonyl-η3-1-methylene-2,5,7-trimethyl-6-cyclononen-2-ylmanganese (7) are obtained. The latter are also formed from 4 and 6 by addition of CO under ambient conditions. In the complexes 4 and 6 the hydrocarbon ligands are coordinated by enyl units, encompassing C 1, C2, and the exocyclic methylene group, and by a C-H-Mn 2-electron-3-center bond of the 2-methyl group to the manganese. They exhibit temperature dependent 1H NMR spectra due to a hindered rotation of the 2-methyl group with a barrier of activation of AG* = 40-43 kJ ·mol -1. There is evidence for an equilibrium of the complexes 4 and 6 with the isomers tricarbonyl-η3:CH-1-methylene-2-methyl-5-cyclononen-2-yl-manganese (4′), and tricarbonyl-η3:CH-1-methylene-2,5,7-trimethyl-5-cyclononen-2-yl-manganese (6′). At higher temperatures the isomers 4, 4′ and 6, 6′ are interconverted by a 1,4-H shift with a barrier of activation of AG* = 75 kJ · mol-1. The crystal and molecular structure of 4 was determined by X-ray structure analysis. The constitutions of the complexes 4-7 were deduced from IR and 1H NM R spectra.