Vibrational spectroscopic studies of conformation of poly(oxyethylene). II. Conformation–spectrum correlations

Detailed normal-coordinate analysis has been carried out on a large number of conformers of model molecules of poly(oxyethylene); the model molecules treated are CH₃(OCH₂CH₂)_nOCH₃ with n = 2,3, and 6. The systematic treatment provides well-defined correlations between conformation and vibrational spectra of poly(oxyethylene). The vibrations in the region 1050–800 cm^?1, which are associated with the C? O and C? C stretching and CH₂ rocking modes, are highly dependent on the conformation of the polymer chain. On the basis of these correlations, the infrared and Raman spectra of the molten state and of the aqueous solution are interpreted in terms of the conformational states. The analysis indicates that the following conformational fragments are present in these phases: GT-TG (T: trans; G: gauche), TT-TG, GT-GG, TT-TT, and TT-GG for the CH₂? CH₂? O? CH₂? CH₂ group, and TGT and TGG for the O? CH₂? CH₂? O group. Conformational fragments GT-TG′ and GT-G′G′ are also possible in the analogy to GT-TG and GT-GG.     

Über Chalkogenolate. 180. Methoxythiocarbonyl-methylsulfane CH3O?CS?Sx?CH3 mit x = 1, 2 und Methylthiothiocarbonyl-methylsufane CH3S?CS?Sx?CH3 mit x = 1, 2

On Chalcogenolates. 180. Methoxythiocarbonyl Methyl Sulfanes CH₃O? CS? S_x? CH₃ with x = 1, 2 and Methylthiothiocarbonyl Methyl Sulfanes CH₃S? CS? S_x? CH₃ with x = 1, 2 The monosulfanes have been prepared by known procedures. For the first time the disulfanes have been synthesized by reaction of K[S₂C? OCH₃] and K[S₂C? SCH₃] with the S-methyl ester of methanethiosulfonic acid CH₃? SO₂? SCH₃. The sulfanes CH₃O? CS? S_x? CH₃ and CH₃S? CS? S_x? CH₃, where x = 1 and 2, have been characterized by means of electron absorption, infrared, nuclear magnetic resonance, and mass spectra.     

Proton magnetic resonance studies of compounds with bridgehead nitrogen atoms—XX: The NMR spectra and stereochemistry of some hexahydropyrido[2, 1-c] [1, 4] oxazin-3(4H)-ones and related compounds

A series of substituted hexahydropyrido [2,1-c] [1,4] oxazin-3(4H)-ones has been synthesised, and the configurations of these bicyclic lactones assigned utilising chemical and spectral data. All the compounds adopt trans-fused conformations and the conformation of the lactone ring is discussed with reference to the magnitude of the geminal coupling constant of the N? CH₂? C(O)? O protons, and the vicinal couplings between the angular proton and the methylene protons adjacent to the ring oxygen atom. The lactone ring conformation is shown to differ slightly from the half chair conformation described for some monocyclic δ -lactones. The synthesis and NMR spectra of some related compounds possessing the bridgehead N? CH₂? C(O)? O system are discussed and these compounds are also shown to adopt a trans-fused ring conformation.     

Conformational Flexibility of the Methoxyphenyl Group Studied by Statistical Analysis of Crystal Structure Data

In a large sample of observed methoxyphenyl groups, the twist angle τ about the MeO-C_Ph bond measuring internal rotation of the MeO group shows a continuous distribution with maxima at (0°) (coplanar conformation) and (～90°) (perpendicular conformation). The preferred conformation of methoxyphenyl depends on the nature of the ortho--substituents: In general, it is coplanar in the case of one or two ortho-hydrogens, and perpendicular in the case of two substituents. The internal rotation of the MeO group is accompained by systematic variations in bond angles and bond distances: 1 if MeO is twisted out of plane, the bond angle CH₃? O? C_Ph decreases from 117.7°, until it reaches a minimum of 114.9° at τ = ±90°. The O? C? C angle which is syn to CH₃ for τ = 0° decreases from 124.6° to a minimum of 115.4° at τ = ±180°. These angles changes keep the nonbonded distance CH₃ …? ortho substituent maximal during internal rotation of MeO and tend to minimize the corresponding strain energy. (2) In the perpendicular conformation, the O-atom is ～ 0. 06 Å displaced from the Ph plane, O and CH₃ and being on opposite sides of this plane. In addition, small but systematic increases of bond lengths MeO? C_Ph and CH₃? O are observed. These variations indicate a decrease in conjugation with increasing twist angle. Their interdependence during twisting and the magnitudes of the changes are close values obtained by ab initio calculations.     

Metal ion distribution and solubility of Mn1−xCux(HCOO)2 · 2 H2O Mixed Crystals [1–5]

The metal ion distribution on the two metal sites of monoclinic Mn_1?xCu_x(HCOO)₂ · 2(H,D)₂O mixed crystals are studied by infrared and Raman spectroscopic methods. The spectral regions 3 200–3 400 cm^?1 (v_OH), 2 875–2 990 cm^?1 (v_CH), 2 330–2 500 cm^?1 (v_OD of matrix isolated HDO molecules), 1 350–1 400 cm^?1 (symmetric CO₂ stretching modes), 570–950 cm^?1 (H₂O librations), and 490 cm^?1 (M? O lattice modes) are mostly sensitive to the metal ions present. The frequency shifts of these bands with increasing content of copper show that Cu²⁺ prefers the M(1) site, coordinated by HCOO^? only. The strengths of the hydrogen bonds increase on going from manganese to copper formate, due to the increased synergetic effect of Cu²⁺. Solubility and X-ray data of the mixed crystals are included. Irrespective of the same crystal structure, two series of mixed crystals are formed: eutonic area at 0.65 ≥ x ≥ 0.5.     

IR spectra of long-chain α,ω-alkanediols: 1,22-docosanediol and 1,44-tetratetracontanediol

The IR absorption spectra of α,ω-alkanediols with different chain lengths, HO(CH₂)₂₂OH and HO(CH₂)₄₄OH, in the spectral range of 400–5000 cm^?1 are analyzed. The assignment of numerous absorption bands to vibration modes in short methylene sequences and terminal hydroxyl groups is suggested. The splitting of IR absorption bands into doublets at 720–730 cm^?1 (rocking vibrations of CH₂ groups) and 1463–1473 cm^?1 (bending vibrations of CH₂ groups) testifies that the crystal unit subcells in the lamellae of alkanediols are orthorhombic with parameters typical of normal hydrocarbons. The specific features of absorption bands due to O-H stretching and C-O-H bending vibrations have been analyzed. These bands appear during formation of lengthy associates from hydrogen bonds formed by hydroxyl groups on the surface of elementary lamellae. A sharp increase in the intensity of the absorption bands in progression of C-C stretching and CH₂ wagging vibrations due to the anharmonic Fermi resonance with the stretching vibrations of C-O groups in the terminal hydroxyl groups has been detected.     

Random-Coil configurations of the polymormals [CH2?O?(CH2)y?O?]. II. Dipole moments of poly(1,3–dioxepane) [CH2?O?(CH2)4?O?;]

Dielectric constant measurements were carried out on a sample of poly(1,3–dioxepane) [CH₂? O? (CH₂)₄? O? ], in benzene over the range 25—60°C. This chain molecule was found to be very similar to poly(1,3–dioxolane) [CH₂? O? (CH₂)₂? O? ] in having a relatively small dipole moment, which increases markedly with increasing temperature. Rotational isomeric-state calculations show that these two characteristics are due to very strong preferences for gauche states in the two central bonds in the sequence CH₂? O? CH₂? O? CH₂. Such pairs of gauche states, necessarily of the same sign, place neighboring-group dipoles in essentially antiparallel orientations. The resulting attenuation of dipole vectors is the origin of the small dipole moment, and the disruption of these preferred conformations with increasing temperature gives rise to the large positive temperature coefficient of the dipole moment.     

Étude des spectres infrarouges de divers dialcoyl-diméthoxy-stannanes

The infrared absorption spectra of some dialkyldimethoxystannanes have been investigated in the 400–1500 cm^?1 region. The bands associated with v_s(SnC₂) and v_s(SnO₂) vibrations have been found at 510–521 cm^?1 and 466–475 cm^?1. The group of bands between 560 and 620 cm^?1 is assigned jointly to v_a(SnC₂) and v_a(SnO₂) vibrations. v(C? O) of the methoxy groups linked to tin appears at 1064–1068 cm^?1.     

Molecular vibrations of irregular chains. I. Analysis of infrared spectra and structures of polymethylene chains consisting of CH2, CHD,and CD2 groups

Various samples of irregularly deuterated polyethylene were prepared and their infrared spectra were studied. The results support the previously proposed view that poly-trans-CHD?CHD or -cis-CHD?CHD obtained with Al(i-Bu)₃–TiCl₄ is an irregularly deuterated chain consisting of the CH₂, CHD, and CD₂ groups. A simplified calculation of the CHD scissors and CDH rocking vibration frequencies has been made for various model chains. The assignments of the CDH rocking vibration bands in the region of 700–500 cm.^?1 have been given on this basis.     

Molecular vibrations of irregular chains. II. Configurations of polydideuteroethylene

A simplified calculation of the CHD scissors vibration frequencies has been made for ? (CHD)_n? of various configurations. The correlation between the CHD scissors frequency and the local configuration has been established. On this basis the infrared absorption bands of poly-trans-CHD? CHD and poly-cis-CHD?CHD appearing in the region of 1350–1280 cm.^?1 have been interpreted in greater detail.     

New interpretation of progression bands observed in infrared spectra of nylon‐m/n

A series of progression bands observed in the infrared spectra of nylon‐m/n and their model compounds have been interpreted in a new manner on the basis of simply coupled oscillator models of zigzag alkyl chains. Nylon‐m/n possesses the methylene sequences of (CH₂)_m and (CH₂)_n?2, and so the effective models of m and n ? 2 coupled oscillators, respectively, had previously been assumed for the methylene rocking–twisting mode, for example. However, the spectral patterns of progression bands predicted by this previously proposed model have been found to be inconsistent with those observed for many kinds of nylon samples with various m and n values. It is rather reasonable to assume that the effective numbers of oscillators should be m ? 2 and n ? 4 for the methylene rocking, twisting, and wagging modes of the (CH₂)_m and (CH₂)_n?2 sequences, respectively. In other words, the infrared progression bands observed for methylene local modes of nylon‐m/n may be interpreted reasonably with the data of n‐alkane molecules with the chemical formulae CH₃(CH₂)_m?2CH₃ and CH₃(CH₂)_n?4CH₃. For the C? C stretching modes, the equivalent n‐alkanes are CH₃(CH₂)_m?1CH₃ and CH₃(CH₂)_n?3CH₃, respectively. In the simply coupled oscillator model, the vibrational mode of one methylene group is represented by an oscillator, for example. Our new concept is to isolate the terminal oscillator adjacent to the amide group from the other oscillators in the inner parts of the methylene zigzag sequence. This corresponds to a physical situation in which the methylene group adjacent to the amide group shows a different vibrational behavior of larger amplitude than those of the inner methylene sequence, as supported by broad‐line NMR data and molecular dynamics calculations reported in the literature. Another possibility is a difference in the electron structure of the methylene unit adjacent to the amide group from that of the inner methylene sequence, resulting in a difference in the force constant and giving a vibrational decoupling between these two types of methylene units. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1294–1307, 2003     

In situ infrared investigation of alkylation reaction of dianionic triruthenium ketenylidene cluster on magnesium oxide with methyl iodide

The reaction between [Ru_3(CO)_9(CCO)]~(2-) supported on magnesium oxide and alky-lating agent CH_3I was investigated in an attempt to understand its reactivity and mechanism byusing FT-IR technique. The IR spectra show that [Ru_3(CO)_9(CCO)]~(2-)/MgO reacts with CH_3Ito produce [Ru_3(CO)_9CC(O)CH_3]-/MgO, which exhibits bands at 2960, 2022, 1988, 1638, 1460and 1350 cm~(-1). The absorption at 2960, 1460 and 1350 cm~(-1) are attributed to -CH_3 group, whilebands at 2022, 1988 and 1952 cm~(-1) are assigned to the terminal CO groups attached to ruthenium.The band at 1638 cm~(-1) was assigned to acyl carbonyl. Isotopes labeled compounds CD3I, ~(13)COand [Ru_3(CO)_9(*C*CO)]~(2-) were used in investigation. The results demonstrate that β-carbon ofCCO ligand is attacked by CH_3~+ species and produces [Ru_3(CO)_9CC(O)CH_3]-/MgO.     

Ring-opening polymerization of ethylene organophosphorothioates: Stereoregular polymerization involving asymmetry at phosphorus

Stereoregular polymerization involving asymmetry at phosphorus has been obtained from ethylene methyl or phenyl phosphorothioate with R₂Mg? NH₃ catalysts, or, in some cases, with R₂Mg alone. The methyl ester gave two types of polymer: an amorphous rubber and a low-melting (75°C) crystalline polymer. The phenyl ester gave mainly a low-melting (68°C) crystalline polymer of 2.2 inherent viscosity. Proton and ³¹P NMR and infrared spectra of these polymers are in accord with the expected chain unit, ? CH₂CH₂? O? P(S)(OR)? O? . The polymerization mechanism probably involves an anionic ring-opening step with P? O cleavage. Ring opening with C? O cleavage appears to be largely excluded. This conclusion is based on the expectation that anionic ring opening with C? O cleavage should lead to a rearranged chain unit, ? CH₂CH₂? O? P(O)? (OR)? S? , because of the high nucleophilicity of sulfur as compared with oxygen. Proton and ³¹P NMR spectra give no evidence for the rearranged unit within the limit of detection (ca. 3%). However, on aging, the methyl ester polymer changes drastically to form up to 40% CH₂SP groups. Presumably, the polymer undergoes the well-known thiono-thiolo rearrangement characteristic of simple phosphorothioate esters to form ? CH₂CH₂? O? P(O)(SCH₃)? O? chain units. The phenyl ester polymer is stable under the same aging conditions.     

Preparation of (AB)n-type block copolymers by use of polyazoesters

Polyesters of the formula, [(OR)_n? O? CO? C(CH₃)₂? N?N? C(CH₃)₂? CO]_m, where (OR)_n are poly(ethylene oxide), Poly(propylene oxide), or PTHF units, were used to prepare block copolymers with styrene. Ester and ether groups were cleaved with HI, NaOCH₃, and diisobutylaluminum hydride. The resulting polystyrene is telechelic with two COOH and OH groups, respectively. The number of styrene blocks per polymer molecule is 3–4.     

The anomeric effect: Ab-initio studies on molecules of the type X?CH2?O?CH3

The anomeric effect of the functional groups X = C?N, C?CH, COOH, COO^?, O? CH₃, NH₂, and NH⁺₃ has been studied with ab initio techniques. Geometry effects upon rotation around the central C? O bond in X? CH₂? O? CH₃ have been compared in the various compounds. The energy differences between the conformers with a gauche and trans (X? C? O? C) arrangement were calculated at the 6-31G* level in the fully optimized 4-21G geometries. Energy differences calculated at the 4-21G level appeared not to be reliable, especially for the groups X that contain non-sp³ hybridized atoms. The 6-31G* energy differences indicate a normal anomeric effect for X = COO^?, O? CH₃, and NH₂(g⁺) (ca. 13 kJ/mol) and a small anomeric effect for X = COOH, C?N, and C?CH (ca. 6 kJ/mol). For X = NH₂(t) and NH⁺₃ a reverse anomeric effect occurs. These observations are in line with experimental results and evidence is given for a competition among various stereoelectronic interactions that occur at the same anomeric center. Geometry variations can be understood in terms of simple rules associated with anomeric orbital interactions. Trends followed when the group X is varied cannot be related in a straightforward way to the energy differences between the trans and the gauche forms in these compounds. Only the variation in the gauche torsion angle X? C? O? C follows roughly the same trend.     

Carbanion rearrangements. Collison induced dissociations of deprotonated alkyl acetoacetates

Deprotonation of methyl acetoacetate yields two enolate ions MeCOC?HCO₂Me (a) and C?H₂COCH₂CO₂Me (b). On collisional activation, ions a and b fragment differently. The major fragmentation of a is specific loss of MeOH through a four-centred transition state to form ^?O(Me)C?C?C?O. In contrast, ion b eliminates CH₂CO to give ^?CH₂CO₂Me. Some rearrangement of b to a is also noted. Rearrangement of a to b is very minor under single collision conditions but at high collision gas pressure rearrangement of a to b is strongly promoted. Similar effects are observed in the collisional activation spectra of MeCOC?(Me)CO₂Me (c) and ^?CH₂COC(Me)CO₂Me (d). The loss of MeOH from (c) proceeds via a six membered transition state to ^?CH₂? CO? C(Me)?C?O; this is a stepwise process in which the deprotonation (step two) is not rate determining. A number of other decompositions occur, these have also been studied by deuterium labelling.     

Hydrogen bonding effects on the skeletal optical and the longitudinal acoustical modes in long chain molecules and polymers

Raman spectra of stearyl alcohol (n-C₁₈H₃₇OH) indicate that vibrational bands in both the skeletal optical (1000-1200 cm^?1) and longitudinal acoustical (0–500 cm^?1) regions are considerably perturbed by intermolecular hydrogen bonding. The zone interior skeletal stretching mode reflecting phonon dispersion in the v₄ branch of the infinite polyethylene chain is found at 1105 cm^?1, approximately 20 cm^?1 higher than in the corresponding n-alkane. Similarly the single nodal longitudinal acoustical mode (LAM-1) is found shifted by 12 cm^?1 to higher frequency when the expected “mass effect” produced by the ? OH group is considered. This shift is further increased to 16 cm^?1 at ?100°C indicating a further perturbation on this accordion mode due to the increased strength of the hydrogen bond at the low temperatures. The positions of the higher multinodal vibrations, LAM-3 and LAM-5, are also perturbed by the hydrogen bond but by differing amounts. The observation of a low-frequency Raman-active LAM in polytetrahydrofuran [(? CH₂CH₂CH₂CH₂O? )_n] is discussed in conjunction with the expected effects of hydrogen bonding at the lamellar surface.     

Theoretical investigations on structure, electrostatics potentials and vibrational frequencies of Li+ - CH3- O- (CH2- CH2- O)n- CH3 (n=3-7) conformers

Electronic structure, charge distributions and vibrational characteristics of CH₃ O(CH₂ CH₂ O) _n CH₃ (n=3-7) have been derived using the ab initio Hartree Fock and density functional calculations. For tri- to hexaglymes the lowest energy conformers have trans- conformation around the C-C and C-O bonds of the backbone. For heptaglyme (n=7 in the series), however, gauche-conformation around the C-C bonds renders more stability to the conformer and turns out to be 10.1 kJ mol ⁻¹ lower in energy relative to the conformer having trans-orientation around the C-C and C-O bonds. The molecular electrostatic potential topographical investigations reveal deeper minima for the ether oxygen in conformers having the gauche conformation around the C-C bonds over those for the trans- conformers. A change from trans- to gauche-conformation around the C-C bonds of the lowest energy conformer of heptaglyme engenders a triplet of intense bands ∼1,150 cm ⁻¹ in the vibrational spectra. Theoretical calculations predict that Li ⁺ binds strongly to the heptaglyme conformer in the above series. The frequency shifts in the vibrational spectra of CH₃O(CH₂CH₂O) _n CH₃- Li⁺ (n=3-7) conformers have been discussed     

Etude de composés d'addition des acides de Lewis XXVIII. Constantes de Hammett et vibration carbonyle des composés formés par TiCl4 et SbCl5 avec des chlorures de benzoyle parasubstitués

The adducts of benzoyl chlorides p-substituted by CH₃O? , CH₃? , and H? with the electronic acceptors SbCl₅ and TiCl₄ have been prepared, and the IR. absorption spectra of the solid products studied.     

Far-infrared studies of ethanols and fluoroethanols trapped in low-temperature matrices

Ethanol, its deuterated derivatives (C₂H₅OD, C₂D₅OD) and fluoroethanols (CFH₂CH₂OH, CF₃CH₂OH) have been isolated in low temperature matrices and investigated in the far-infrared region. From the concentration dependency of the observed bands and from studies of the pure alcohols in the gaseous, liquid, and solid phase it was found that the hydrogen bond stretching frequencies ν_σ associated with the hydrogen bonded system OH?O appear in the 100 – 160 cm^?1 range. At higher M/A ratios the OD(OD) torsion modes τ_OH are dominating and were identified in the 200 – 300 cm^?1 region. The influence of various matrix materials like argon, krypton, xenon, nitrogen and methane on the low frequency spectra of ethanol have also been studied. It was found, that nitrogen and methane matrices produce significant changes in the far infrared spectra.