Cis- and trans-3-hexene: infrared spectrum in liquid argon solution, ab initio calculations of equilibrium geometry, normal coordinate analysis, and vibrational assignments

The infrared spectra of cis-3-hexene and trans-3-hexene dissolved in liquid argon have been obtained at temperatures from 93 to 120 K. The absorptions were observed with a low-temperature cell and a Fourier transform infrared spectrophotometer. Ab initio molecular orbital calculations were performed to obtain the equilibrium geometry, vibrational frequencies, force fields, and infrared intensities. The calculations were done at the Hartree-Fock level using 6-31G basis set. The Cartesian force fields from ab initio calculations have been converted to the force field in symmetry coordinates. The scale factors of ab initio calculated force fields were determined. Normal coordinate calculations were performed using a scaled quantum mechanical (SQM) force field. Vibrational normal modes calculated for the lowest energy rotamers of cis- and trans-3-hexene have been assigned to infrared absorption bands observed in liquid argon solution. The assignments were based on calculated frequencies and potential energy distributions. The equilibrium geometries of the two lowest energy rotamers (symmetry C₂ and C_s) of cis-3-hexene and of the three lowest energy rotamers (symmetry C_i, C₂, and C₁) of trans-3-hexene were calculated. Variable temperature studies of the infrared spectrum of cis- and trans-3-hexenes dissolved in liquid argon were done to obtain the ΔH of conversion between the rotamers C₂ and C_s of cis-3-hexene and between the rotamers C_i, C₂, and C₁ of trans-3-hexene.     

Zur Komplexierung von enantiomerenreinen cis- und trans-3-Diphenylphosphino-4-hydroxy-tetrahydrofuranen mit [Rh(COD)2]BF4

The complexation behaviour of cis- und trans-3-diphenylphosphino-4-hydroxyl-tetrahydrofurans with [Rh(COD)₂]BF₄ is studied with the help of NMR and IR spectroscopy. In dependence of the spatial arrangement of hydroxyl and phosphino group the formation of different intra- and intermolecular bridged O-P complexes has been observed.

Zusammenfassung

Das Komplexierungsverhalten von cis- und trans-3-Diphenylphosphino-4-hydroxy-tetrahydrofuranen mit [Rh(COD)₂]BF₄ wird mit Hilfe von NMR- und IR-Spektroskopie studiert. In Abhängigkeit von der räumlichen Anordnung von Hydroxy- und Phosphinogruppe zueinander wird die Bildung von intra- bzw. intermolekular verbrückten O-P-Komplexen beobachtet.     

Tautomeric equilibrium of ketonic and cis- and trans-enolic forms of β-dicarbonyl compounds in solution

In this paper the tautomeric equilibrium of ketonic and cis- and trans-enolic forms of β-dicarbonyl compounds is considered as an acid-base protolytic one. The application of the Brønsted-Izmaylov theory has enabled to suggest a general equation K_TS = for keto-enol equilibrium constant, depending on the solvent, the well known Meyer's equation being included in it as a particular case. Equilibrium constants have been bromometrically determined in a number of solvents of keto-enols of three types, i.e. “cis-fixed”, “trans-fixed” and that involving both stereo-isomeric forms. A method for quantitative determination of cis-trans-enol equilibrium had been proposed.     

Studies in the pinacol rearrangement—V The rearrangements of cis- and trans-1,2-diphenyl-1,2-ditolylethylene oxides

The intermediate formation of the two epoxides was observed in the perchloric acid-catalysed rearrangement of meso-2,2′-dimethylbenzpinacol (P_meso) to 2-methylbenzoyl tolyl diphenyl methane (K) Two kinds of epoxides were separated with preparative TLC and the configuration (cis and trans) of these epoxides was inferred in the light of UV, NMR and IR spectra, dipole moment and kinetic data. The rearrangement rates of these epoxides were measured in HClO₄-anhydrous acetic acid. Linear correlations of logarithm of the rate constants (log k) with the Hammett acidity function of the medium (H₀) were obtained, which supports the A-1 mechanism, together with the large positive values of the entropy of activation. It is shown that the perchloric acid-catalysed rearrangement of meso-2,2′-dimethylbenzpinacol (P_meso) occurs via such many kinetically distinguishable routes as the following where C and T are cis- and trans-epoxide respectively. The mechanisms of the rearrangements were discussed from the data of kinetics.     

Studies in stereochemistry—I Stereospecific routes to trans- anti- and cis- syn-Δ-dodecahydrophenanthrenes

Reduction of trans-1-oxo-7-methoxy-1,2,3,4,9,10,11,12-octahydrophenanthrene (XI) by lithium tri-t-butoxyaluminohydride gave trans-1β-hydroxy-7-methoxy-1,2,3,4,9,10,11,12-octahydrophenanthrene (XII) which on lithium—liquid ammonia reduction gave trans-anti-1β-hydroxy-7-oxo-Δ⁸⁽¹⁴⁾-dodecahydrophenanthrene (XIII). Reduction of cis-1-oxo-7-methoxy-1,2,3,4,9,10,11,12-octahydrophenanthrene (XV) by sodium borohydride gave cis-1-hydroxy-7-methoxy-1,2,3,4,9,10,11,12-octahydrophenanthrene (XVI) which on lithium—liquid ammonia reduction gave cis-syn-1-hydroxy-7-oxo-Δ⁸⁽¹⁴⁾-dodecahydrophenanthrene (XVII).     

Reactivity of ruthenium complexes with uninegative (X,S)-donor ligands (X = S,P)—II. Phosphine substitution in [Ru(S,S)2(PR3)2] derivatives. Crystal structure of trans-bis(O-ethyldithiocarbonate)bis(dimethylphenylphosphine)-ruthenium(II)

The complexes [Ru(S,S)₂(PPh₃)₂] [S,S = EtCOCS₂⁻, (CH₂)₄NCS₂⁻] react with a variety of tertiary phosphines with the substitution of triphenylphosphine and the formation of [Ru(S,S)₂(PR₃)₂]. The reaction occurs with the formation ofthe cis isomer, except for the complex with PMe₂Ph that gives rise to the trans isomer as the crystal structure shows. The effect of the different phosphines on the ruthenium complex is analysed in terms of the spectroscopic and electrochemical properties of the isolated compounds. The cyclic voltammetric studies of the cis complexes show that isomerization to the trans isomer occurs on oxidation. This isomerization is not observed in the trans-[Ru(S,S)₂(PMe₂Ph)₂] complexes that give rise to stable trans-ruthenium(II)/ruthenium(III) couples. In a similar way the diphosphine complexes afford a quasi-reversible cis-ruthenium(II)/ruthenium(III) process.     

The use of trans-2,3-divinyl epoxides as precursors to carbonyl ylides

trans-2,3-Divinyl epoxides have been found to be good substrates for the generation of carbonyl ylides in CCl₄ and 145 °C. These ylides, to a limited extent, undergo isomerization to cis-2,3-divinyl epoxides, leading to the isolation of 4,5-dihydrooxepins. Of greater potential usefulness is the finding that these ylides can be efficiently trapped in an intermolecular sense by a dipolarophile, leading to dihydrofurans.     

The manifestation of non-bonded attraction in the physical properties of cis and trans olefins

Non-bonded attraction is suggested to account for a host of differences in the physical properties of cis and trans olefins of the type XHC=CHX. The main predictions are: (i) The cis isomer is more stable than the trans isomer; (ii) The C=C bond is longer and the C-X bonds are shorter for the cis isomer; (iii) The π MO's orbital energies of the two isomers differ such that the trans isomer is a better electron donor and electron acceptor than the cis isomer. Ab initio calculations at the STO-3G and the 4-31G levels in support of the model are presented. The photoelectron spectra of cis and trans difluoro, dichloro and dibromoethylene are discussed, and found to be in accord with our qualitative model.     

The absolute configuration of trans-1,2-dimethylcyclopropane

By application of the newly discovered fact that 1° alkyl chlorides with γ-hydrogen form cyclopropanes on treatment with sodium metal, (−)-trans-1,2-dimethylcyclopropane has been prepared from (+)-1-chloro-2-methylbutane. Rigorous assignment of configuration to the isomeric cis- and trans-dimethylcyclopropanes is thereby achieved. The absolute configuration, (1R : 2R) trans-1,2-dimethylcyclopropane, can be assigned to the (−) enantiomer by several lines of argument and agrees with that calculated by Fitts.     

The stereochemistry of Ei reaction of N-p-toluenesulphonyl sulphilimines

The stereochemistry of the pyrolysis of S-alkyl-N-p-tosylsulphilimines was investigated with both the erythro and threo isomers of S-phenyl-S-1-phenyl-2, 2-phenylmethoxy-1-ethyl-N-benzene-sulphonylsulphilimine I_E and I_T. Pyrolyses revealed that I_E gives only trans-1-methoxystilbene V_T in nearly quantitative yield while a mixture of 5·5% trans-V_T and 94·5% cis-V_C are formed from I_T. The kinetics of the reactions of both I_E and I_T obey a good 1st order rate equation. Pyrolysis is considered to proceed via a concerted cis elimination involving a five membered cyclic transition state.     

Synthesis of mer-[RuCl3(DMSO)(bpy)], reactivity and electrochemistry of mer-[RuCl3(DMSO)(bpy)] and mer-[RuCl3(TMSO)(bpy)] complexes

[H(DMSO)₂][trans-RuCl₄(DMSO)₂] (1) reacts with 2,2′-bipyridine in ethanol at room temperature resulting in the formation of a major compound, mer-[RuCl₃(DMSO)(bpy)] (bpy = 2,2′-bipyridine) 3 and a known minor compound, cis-[RuCl₂(DMSO)₄] (4). The compounds 3 and 4 are formed via an anticipated intermediate mer-[RuCl₃(DMSO)₃] (2). The reaction of 3 and mer-[RuCl₃(TMSO)(bpy)] (5) with small molecules like imidazole, carbon monoxide and KSCN yield, mer-[RuCl₃(bpy)(im)] · 2DMSO (im = imidazole) (6) and cis-[RuCl₂(TMSO)(CO)(bpy)] (7), cis-[RuCl₂(DMSO)(CO)(bpy)] (8) and K[RuCl₃(bpy)(SCN)] (9), respectively. The formations of 3, 6 and 7 have been authenticated by single crystal structure determinations. Compound 6 is formed by the substitution of DMSO or TMSO from 3 and 5, respectively, whereas 7 and 8 are formed by unprecedented one-electron reductions of 5 and 3. The reactions of 3 and 5 with KSCN resulted in the same compound, K[RuCl₃(NCS)(bpy)] (9). DFT calculations were performed to distinguish whether the thiocyanate ligand is bound to ruthenium through S or N. In the ruthenium bipyridine systems, the HOMO contains ruthenium d-orbitals and the LUMO is typically π^*-orbitals of the bipyridine ring. Complexes 3, 6 and 7 are redox active in acetone and DMSO solvent showing prominent a reduction peak and corresponding oxidation peak.     

Use of ab initio computational results and experimental frequencies to construct the internal rotational potential function for acrolein

Ab initio optimizations of the complete acrolein molecular geometry accomplished using analytical gradient methods at the 6-31G* SCF level at ten points during rotation from the planar trans- to the planar cis-form (rotation about the single C---C bond) are used to calculate the values of the Pitzer function F(φ), the coefficients of its Fourier expansion, and the coefficients in the potential energy expansion. The theoretical potential expansion coefficients are then adjusted using the experimental torsional frequencies and their overtones for the trans- and cis-forms of CH₂=CH---CH=O and CH₂=CH---CD=O. For the cis-conformer two different sets of experimental frequencies are employed. The dependence of the slope of the acrolein potential energy curve on the experimental frequency set used for the cis-rotamer is discussed.     

Multidimensional anharmonic calculation of the vibrational frequencies and intensities for the trans and cis isomers of HONO with the use of normal coordinates

The equilibrium geometry and the potential energy and dipole moment surfaces have been determined for the cis and trans isomers of the HONO molecule by an ab initio Moller–Plesset (MP2) calculation with a wide set of atomic orbitals. The multidimensional anharmonic vibrational Schrodinger equations are solved using the variational method with the Hamiltonian and wave functions written in the normal coordinates of cis and trans isomers. All one- and two-dimensional and a number of three-dimensional vibrational problems are solved to obtain the energy levels and vibrational eigenfunctions. The frequencies and intensities for the fundamental, overtone and some combination bands are determined in good agreement with the available experimental results. The calculation shows the strength of coupling between different vibrational modes and reveals the presence of strong resonances between the (v₁, v₃, v₆) and (v₁, v₃−1, v₆+2) states of cis-HONO. This fact may be important for understanding the energy redistribution between the intermolecular degrees of freedom. The magnitude and direction of vibrationally averaged ground-state dipole moment of both isomers, as well as the direction of transition dipole moments, are in good agreement with the experimental findings. The changes in the values of dipole moment and some geometrical parameters of cis- and trans-HONO on vibrational excitation are also computed.     

Fluorocyclohexanes-II Cis- and trans- 1H:3H- and 1H:4H-decafluorocyclohexanes

An extension of the methods employed in the isolation of (trans) 1H/2H-decafluorocyclohexane,¹ (I) from the polyfluorocyclohexane mixture obtained by the vapour phase fluorination of benzene with cobaltic fluoride at about 150°, has afforded the four remaining members of the series of decafluorocyclohexanes [the cis- and trans-1H:3H- and 1H:4H-isomers (1H:3H/-(IV), 1H/3H-(III), 1H:4H/-(VII), and 1H/4H-(VIII), respectively)] and also the cis-1H:2H-decafluorocyclohexane (II), obtained previously^1,2 by the lithium aluminium hydride reduction of 1:2-dichlorodecafluorocyclohexane. The structures of the 1H:3H- and 1H:4H-decafluorides have been established by dehydrofluorination studies. The six decafluorocyclohexanes have been related to two new nonafluorocyclohexanes³ (IX and X) by further fluorination of the latter. 2H-Heptafluoroadipic acid has been obtained from 3H-nonafluorocyclohex-1-ene (V), one of the dehydrofluorination products of the 1H:3H-decafluorides.     

Potential constants and Coriolis coupling constants of perhalogenated ethylenes: Part 3. trans-ClFC=CFCl, trans-ClBrC=CBrCl and trans-FBrC=CBrF

Based on vibrational frequencies a calculation of a general quadratic force field has been carried out for trans-ClFC=CFCl, trans-ClBrC=CBrCl and trans-FBrC=CBrF via an iterative method. The resulting transformation L matrices were used to evaluate the Coriolis coupling constants and these were used to calculate inertial defects. The calculated values of the inertial defects are lower than those of the respective cis-ethylene-type molecules.     

Stereochemical studies of optically active 2-hydroxy-5-alkyl-δ-valerolactone derivatives as chiral dopant for ferroelectric liquid crystals

Both (2S, 5R)- and (2R, 5R)-2-hydroxy-5-alkyl-δ-valerolactone derivatives, cis and trans, respectively, show almost the same magnitude of spontaneous polarization (P_s) when added to a non-chiral smectic C mixture. The stereochemistry of these chiral dopants was studied using ¹H NMR. Trans derivatives seem to have a half-chair conformation with the 2, 5-diequatorial substituents and the cis derivatives have rather a flat conformation in solution. However in the liquid-crystalline phase, the cis and trans derivatives appear to change their conformation or the distribution of their conformations as the alkyl chain length is varied. The difference in the effect as a chiral dopant depends upon lateral interactions between chiral molecules through the solvent liquid crystal phase.     

Vibrational spectra of some tetraalkylammonium acid salts of acetic acids. Hydrogen bonding in solids and solutions

Infrared and Raman spectra are reported of several hydrogen dicarboxylates of the composition MH(D)X₂ (M = tetramethyl or tetrabutylammonium, X = CH₃COO, CF₃COO, CCl₃COO) as solids and solutions in nonaqueous solvents. It is shown that very strong hydrogen bonding persists in solution although in some cases the high symmetry observed in the solid is lost by dissolution of melting. The hydrogen diacetate anion appears to have different conformations in the solid and solution. Calculations in the ab-initio scheme (STO-3G) for the trans and cis forms of this ion, without and with countercharges, demonstrate that the cis conformation is more stable in the latter case whereas the trans conformation is preferred without charges.     

Synthesis, characterisation and reactivity of trans-[Ru(L)(PPh3)Br2]; L=2-pyridyl-N-(2′-methylthiophenyl)methyleneimine: Crystal structure of trans-[Ru(L)(PPh3)Br2]

Reaction of Ru(PPh₃)₂Br₂ with the NNS chelating tridentate ligand 2-pyridyl-N-(2′-methylthiophenyl)methyleneimine (L) led to the isolation of the ruthenium(II) complex [Ru(L)(PPh₃)Br₂]. Reactivity of this complex with different bidentate chelating ligands revealed that the products are quite different from those obtained by reacting Ru(L)(PPh₃)Cl₂ (the corresponding cis dichloro complex) with the same ligands under comparable conditions. The mixed chelates were isolated and characterised by elemental analysis, magnetic moment measurement and by different spectroscopic methods along with their precursor. Electrochemistry of the complexes was examined by cyclic voltammetry using a platinum working electrode and a Ag/AgCl electrode as reference. The crystal structure of [Ru(L)(PPh₃)Br₂] disclosed that, unlike Ru(L)(PPh₃)Cl₂, the two bromo ligands are in trans position and this explained the difference in its reactivity pattern from the corresponding chloro complex.     

X-ray study of the hetero ring flexibility in trans-5,6- trimethylene- and tetramethylene-5,6-dihydro 2-phenyl-[4H]-1,3-thiazines

The structures to two 1,3-thiazine derivatives differing only in the number of CH₂ groups in their trans fused hydrocarbon ring (_n = 3 for I and n = 4 for II) have been established by X-ray crystallography from diffractometer data. Crystals of I (trans-5,6- trimethylene-5,6-dihydro-2-phenyl-[4H] - 1,3-thiazine) are triclinic, space group P with a = 7.661(1), b = 8.282(1), c = 9.566(2) Å, = 91.75(1), β = 100.72(1), γ = 105.45(1)° Z = 2, D_c = 1.260 g cm^-3. Crystals of II (trans-5,6-tetramethylene-5,6-dihydro-2-phenyl [4H]-1,3-thiazine) are monoclinic, space group P2₁/c with a = 7.914(2), b = 19.362(13), c = 8.440(1) Å, β = 109.16(2)°C Z = 4, D_c = 1.258 g cm^-3. The structures determined by Patterson (I) and direct (II) methods were refined to R = 0.050 for 1330 reflections of I and R = 0.082 for 1012 reflections of II. The proper treatment of the positional disorder of the carbon atoms (C(5) and C(6)) forming the trans ring junction in I discovered two discrete conformations with a ratio of 1:2. The opposite chirality of atoms C(51) and C(52), and C(61) and C(62), indicates a simultaneous configurational disorder with a pattern of total disorder: A A . The puckering parameters of the hetero rings in the same enantiomers of molecules IA, IB and II indicate a connection between the conformers: ⁵E(II)→⁵H₆(IB)→E₆IA) via pseudorotation. Their relationship is discussed and compared with the conformational freedom of the analogous 1,3-oxazine derivatives.     

Molecular determinants for drug-receptors : Part 11. The preferred conformation of N-(p-anisoyl)pyrrolidin-2-one (“Aniracetam”) in the solid and solution states as indicated by X-ray crystal structure analysis, dipole moment and theoretical calculations

N-(p-anisoyl)pyrrolidin-2-one in the crystalline state exhibites a cis—rans conrotatory conformation with N---CO and CO---C_ar rotational angles of 33.5° and 38.5° respectively, and the p-methoxy group situated cis to the central carbonyl bond, as shown by X-ray structure analysis. As suggested by dipole moment analysis and MMP2 molecular mechanics calculations, in solution similar conrotatory models hold for both c- and t-subconformers having the p-methoxy group cis or trans to the central carbonyl bond. INDO calculations were also carried out, indicating that both subconformers are equally stable.