The molecular dynamics of poly(1, 4-Trans-butadiene) in the amorphous state and in an inclusion complex

The molecular dynamics of poly(1, 4-trans-butadiene) in the amorphous state at bulk density and in its inclusion complex with perhydrotriphenylene are compared here. The internal motions differ in the two systems, due to the occupation of gauche states at CH₂-CH₂ of the amorphous polymer, but the exclusion of gauche states at these bonds in the inclusion complex. This difference in conformational preferences at CH₂-CH₂ has consequences for the decay rates for the orientation autocorrelation functions.     

Isomerization reactions of RSNO (R=H,C<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>H<Subscript>2<Emphasis Type="Italic">n</Emphasis>+1</Subscript><Emphasis Type="Italic">n</Emphasis>≤ 4)

We have applied various theoretical methods to gain detailed insights into the isomers as well as the transition states (TSs) along the corresponding reaction pathways for RSNO (R=H, C _n H_2n+1 n ≤ 4). On the basis of G2 and G2MP2 results, the relative order of stability for R=H is estimated to be trans-HSNO > cis-HSNO > HNSO > cis-HONS trans-HONS, while it is cis-CH₃SNO trans-CH₃SNO > CH₃NSO > trans-CH₃ONS > cis-CH₃ONS for R=CH₃. A similar trend is also obtained from the B3P86 method with considerably less computing effort if the nearly isoenergetic isomers cis-HONS and trans-HONS are ignored. Based on the results of B3P86, cis-RSNO is more stable than trans-RSNO when R=H is replaced by alkyl groups except for R=t-Bu. Natural bond orbital analyses allow us to explore whether the high reactivity of S-nitrosothiols is due to the strong negative hyperconjugation (). The mesomeric effect of S-nitrosothiols, although non-negligible, does not cause the breakage of N–O bond due to the compensation of columbic attraction between N and O.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Synthesis of Titanatranes Containing Bis(aryloxo)-(alkoxo)amines and their Use in Catalysis for Ethylene Polymerization

Syntheses of titanatranes containing [(O-2,4-Me₂C₆H₂-6-CH₂)₂-{O(CH₂)_nCH₂}]N³⁻ (n = 1,2) have been explored. Catalytic activity for ethylene polymerization by Ti₂(OⁱPr)₂{[(O-2,4-Me₂C₆H₂-6-CH₂)₂(µ₂-OCH₂-CH₂)]N}₂ ( 1a ) - MAO catalyst increased at high temperature; the activity also increased upon addition of AlMe₃. Ti(O- 2,6-ⁱPr₂C₆H₃){[(O-2,4-Me₂C₆H₂-6-CH₂)₂(OCH₂CH₂)]N} ( 1c ) showed higher activity than 1a under the same conditions. Ti{[(O-2,4-Me₂C₆H₂-6-CH₂)₂(HOCH₂CH₂CH₂)]N}₂ was isolated from the reaction of Ti(OⁱPr)₄ with bis(2-hydroxy-3,5-dimethylbenzyl)-propanolamine; the structure was determined by X-ray crystallography.     

Synthesis and Characterization of O,O′ Dialkyl and Alkylene Dithiophosphates of Lanthanum(III) and their Adducts with Nitrogen and Phosphorus Donor Bases

Lanthanum(III) tris(dithiophosphates), [La{S₂P(OR)₂}₃] (where R=-CH₂CH₂CH₃ or -C₆H₅) and [La{S₂PO₂G}₃] [where G=-C(CH₃)₂CH₂CH(CH₃)-, -CH₂C(CH₃)₂CH_2-, -C(CH₃)₂C(CH₃)_2- and -CH₂CH₂CH(CH₃)-] were prepared in methanolic solutions of anhydrous LaCl₃ and ammonium dithiophosphates. Addition complexes of the type [La{S₂P(OR)₂}₃·nL] and [La{S₂PO₂G}₃·nL] [where n = 1, L = N₂C₁₀H₈ or N₂C₁₂H₈ and n = 2, L = P(C₆H₅)₃] were prepared by reaction of lanthanum(III) tris(dithiophosphates) and nitrogen or phosphorus donor bases in benzene. These newly synthesized derivatives have been characterized by elemental analyses, molecular weights, IR, ¹H and ³¹P NMR spectral measurements. Coordination numbers of six and eight are suggested for lanthanum(III) in these derivatives.     

Researches on the reactivity of mannich bases part VIII synthesis of N-methyl(vinylaryl)quinolinium salts and their photosensitivity

Described in this communication is a new synthesis of N-methyl-4-(vinylaryl)quinolinium salts by cyclization of the aminoketones, Ar-CH=CH-CO-CH₂-CH₂-N(CH₃)-C₆H₄-X. The aminoketones were obtained by replacement of the alkyiamino group of the ketoarylidene Mannich bases with various N-methylarylamines. The U.V. spectra of the compounds were obtained. The photosensitivity characteristics in solution are reported. These data show the possibility of dimerization and probable trans → cis isomerization on exposure to visible and ultraviolet light.     

rac‐9‐Ethyl‐12a‐hydroxytetradecahydrotriphenylene‐1,5(2H,4bH)‐dione: stabilization of a new isomer of a functionalized perhydrotriphenylene through a tandem Michael addition–aldol reaction

The title compound, C₂₀H₃₀O₃, is a new functionalized perhydrotriphenylene derivative formed via a tandem Michael addition–aldol reaction. The structural study reveals that the system of fused rings approximates a C₂ point symmetry, with trans–cis–cis ring junctions, while highly symmetric all‐trans perhydrotriphenylene, previously characterized, approximates a D₃ symmetry. The perhydrotriphenylene nucleus of the title compound corresponds to the third stable stereoisomer isolated for this polycyclic system. Considering that the C_s isomer was obtained recently through a similar tandem reaction, a general strategy is proposed which may help to obtain other stable stereoisomers of perhydrotriphenylene.     

Ab-Initio studies on π-nonbonded and through-bonds interactions in n-alkanes,n-alkyl radicals,and polymethylene diradicals

Ab-initio studies were conducted on quantitative aspects of π-nonbonded, σ–σ*, n–σ*, and throughbond interactions in R₁CH₂(CH₂)_N–1 CH₂ R₂, where R₁ and R₂ are H and/or nonbonding AO , n, and N = 2, 3, and 4. Geometrical preferences were found to depend both on π-nonbonding and bond–antibonding interactions, the latter being more important. Level orderings and energy splittings involved in the through-bond interactions of diradicals can be qualitatively predicted by examining the signs of the overlap between the n orbitals and a common vicinal σ* bond orbital, using simple orbital patterns and paying special attention to the “backside” tails of bond orbitals.     

Carbon-13 NMR spectra of all-trans-N-retinylidene-n-butylamine as an analogue of the Schiff's base linkage-compound in visual pigment

Carbon-13 NMR spectra have been obtained for all-trans-N-retinylidene-n-butylamine as an analogue of the Schiff's base linkage compound in visual pigment. The chemical shift changes on going from all-trans-retinal₁ to all-trans-N-retinylidene-n-butylamine are observed. These changes indicate the collapse of the bond alternation in conjugated polyene carbons, whereas N-protonation in all-trans-N-retinylidene-n-butylamine does not affect the bond alternation.     

Theoretical study of the force field and vibrational assignments of acetamide and deuterated analogues

The complete harmonic force constants of acetamide have been evaluated by ab initio calculations at the Hartree-Fock level with the 4–31G(d) basis set. The force field was scaled to compensate for the systematic overestimations of the Hartree-Fock-level force constants by empirical factors using the matrix isolation IR spectra of CH₃CONH₂ and CD₃CONH₂. A normal coordinate treatment has been carried out with the scaled force field to analyze the vibrational spectra of CH₃CONH₂. A normal coordinate treatment has been carried out with the scaled force field to analyze the vibrational spectra of CH₃COND₂, cis-CH₃CONHD and trans-CH₃CONHD. The effect of cis/trans isomerism of CH₃CONHD on the fundamental bands was well reproduced by the calculations. The fundamental vibrations were also predicted for CD₃COND₂, cis-CD₃CONHD and trans-CD₃CONHD.     

The relaxation processes of several long-chain aliphatic ketones and amines in glassy media

The dielectric absorption of 2-alkanones (CH₃(CH₂)_nCOCH₃) (where n = 4, 5, 6, 7, 8, 10, 12, 14 and 16) and 1-aminoalkanes (CH₃(CH₂)_nNH₂) (where n = 2, 3, 5, 7, 8, 9, 10 and 11) has been studied in a polystyrene matrix between 80 and 300 K in the frequency range 10–10⁵ Hz. 2-alkanone with n = 8 has also been examined in polyphenylether, glassy o-terphenyl and a polypropylene matrix. For both series two sets of absorption peaks were obtained, one around 80–150 K and the other in approximately the 170–300 K region. The lower-temperature absorption can be accounted for by a model involving segmental motion about the CC bonds with consequent displacement of the polar end group. The enthalpy of activation for this intramolecular motion is independent of whether the polar end group is -CH₂Br, -COCH₃, or -CH₂NH₂. The higher-temperature absorption may be ascribed to a molecular relaxation process.     

Tandem mass spectrometry for the structural determination of backbone-modified peptides

A variety of backbone-modified peptides were desorbed by fast atom bombardment and collisionally activated. These peptide modifications involve the replacement of a normal [CONH] peptide linkage with such groups as thiomethylene ether (CH₂S), thioamide (CSNH), methyleneamine (CH₂NH), and thiomethylene sulfoxide (CH₂SO) moieties. Modified linear peptides decompose to give fragmentations characteristic of the modifications as well as typical peptide bond fragments. The presence of a replacement group in cyclic peptides can induce new fragmentations. The presence of other functional groups, such as an exocyclic N-terminal residue, however, can dominate the observed fragmentations. Upon collisional activation, unmodified linear peptides fragment to give N-terminal ions as the most abundant daughter ions. In comparison, ψ[CH₂NH] and ψ[CH₂S ] modified linear peptides decompose to give prominent C-terminal sequence ions. The ψ[CH₂SO] modified linear peptides, however, fragment into both N- and C-terminal ions of high relative abundance. Depending on the modification, daughter ions or internal fragment ions are observed that are characteristic of the amide bond replacement. Useful structural information can therefore be obtained.     

Synthesis of pyridine N-imine complexes of methylcobaloxime and reactions of bis(dimethylglyoximato)methyl(Pyridine N-imine)cobalt with acid anyhydrides and acetylenedicarboxylic acid dimethyl ester

Pyridine N-imine complexes of methylcobaloxime, CH₃Co(Hdmg)₂(R¹— C₅H_nN⁺N^?H) (n = 4; R¹ = H, 2-CH₃, 3-CH₃, 4-CH₃: n = 3; R¹ = 2,6-CH₃), have been synthesized by the reaction of CH₃Co(Hdmg)₂S(CH₃)₂ with a pyridine N-imine which is generated from a pyridine, hydroxylamine-O-sulfonic acid and K₂CO₃. The reactions of CH₃Co(Hdmg)₂(C₅H₅N⁺N^?H) with acid anhydrides form new methylcobaloxime complexes with N-substituted pyridine N-imines, CH₃Co(Hdmg)₂(C₅H₅N⁺N^?R²) R² = COPh, COMe, COEt). With maleic anhydride, (pyridine N-acryloylimine)carboxylic acid is formed. With acetylenedicarboxylic acid dimethyl ester, 1,3-dipolar cycloaddition of the ligand gives pyrazolo[1,5-a]pyridine-2,3-dicarboxylic acid dimethyl ester.     

Aminosilylgermylenes: (E)-Digermene versus Germylene Crystallization [1]

The diaminosilylene tBuNCH₂CH₂NtBuSi: reacted with the diaminogermylenes RNCH₂CH₂NRGe: R = 2,6-Me₂C₆H₃, iPr, by silylene insertion into one of the Ge–N bonds to furnish the aminosilylgermylenes 8 , R = 2,6-Me₂C₆H₃, and 9 , R = iPr. The X-ray structure analyses of these compounds revealed that 8 remains monomeric in the crystal with weak Ge … Ge interactions to the germanium atom of a neighbouring germylene molecule, whereas 9 dimerizes to give the strongly twisted (E)-1,2-diamino-1,2-disilyldigermene (E)- 10 with a long Ge–Ge double bond of 246 pm and a large trans-bent angle of 47.3°.     

Polymerization of 2‐pentene with Ni(II) α‐diimine complex/M‐MAO catalyst and structure of the polymer

Polymerization of 2‐pentene with [ArN?C(An)C(An)·NAr)NiBr₂ (Ar?2,6‐iPr₂C₆H₃)] ( 1‐Ni) /M‐MAO catalyst was investigated. A reactivity between trans‐2‐pentene and cis‐2‐pentene on the polymerization was quite different, and trans‐2‐pentene polymerized with 1‐Ni /M‐MAO catalyst to give a high molecular weight polymer. On the other hand, the polymerization of cis‐2‐butene with 1‐Ni /M‐MAO catalyst did not give any polymeric products. In the polymerization of mixture of trans‐ and cis‐2‐pentene with 1‐Ni /M‐MAO catalyst, the M_n of the polymer increased with an increase of the polymer yields. However, the relationship between polymer yield and the M_n of the polymer did not give a strict straight line, and the M_w/M_n also increased with increasing polymer yield. This suggests that side reactions were induced during the polymerization. The structures of the polymer obtained from the polymerization of 2‐ pentene with 1‐Ni /M‐MAO catalyst consists of ? CH₂? CH₂? CH(CH₂CH₃)? , ? CH₂? CH₂? CH₂? CH(CH₃)? , ? CH₂? CH(CH₂CH₂CH₃)? , and methylene sequence ? (CH₂)_n? (n ≥ 5) units, which is related to the chain walking mechanism. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2858–2863, 2008     

N.m.r. characterization of functional groups: 5—on the nature of olefinic end groups in polyisobutylenes

Proton n.m.r. signals for two types of olefinic end groups, -CH₂C(CH₃)?CH₂ (δ4.68 and δ4.87) and -CH?C(CH₃)₂ (δ5.21), have been observed in high molecular weight polyisobutylenes. Comparable amounts of both these end groups exist in commercial and laboratory prepared samples of polyisobutylenes contrary to previous reports that the former group is by far predominant. That different catalysts produce different relative concentrations of these end groups is demonstrated. Evidence for the presence of a third type of unsaturation from the -CH₂C(CH₂)?CH₂- structure is discussed.     

Preparation and Properties of Molybdenum and Tungsten Dinitrogen Complexes. 30.1 Syntheses of Zero-Valent Molybdenum Complexes with the DMF Ligand: The Crystal Structure of Trans-[Mo(CO)(DMF)(Ph2PCH2CH2PPh2)2]

Abstract

Treatment of trans-[Mo(N₂)₂(dpe)(dpm)] (dpe = Ph₂PCH₂CH₂PPh₂, dpm = Ph₂PCH₂PPh₂) or trans-[Mo(N₂)₂(dpe)(dpp)] (dpp = Ph₂PCH₂CH₂CH₂PPh₂) with excess DMF in benzene at reflux under Ar resulted in the formation of trans-[Mo(CO)(DMF)(dpe)(dpm)] or trans-[Mo(CO)(DMF)(dpe)(dpp)]. X-ray structural analysis of trans-[Mo(CO)(DMF)(dpe)₂] was performed using single crystals isolated as the minor product from the reaction mixture of trans-[Mo(N₂)₂(dpe)(dpp)] and DMF. Crystal data: C₅₆H₅₅O₂NP₄Mo, monoclinic, space group P2₁, a = 11.145(4), b = 23.425(5), c = 10.516(3) Å, β = 117.17(2)° V = 2442.6(13) ų, D _calcd = 1.35 g/cm³ for Z = 2. This disclosed the relatively long C O bond distance of the carbonyl ligand and the significantly short C=O bond length in the DMF ligand. When recrystallized from benzene/hexane under N₂, trans-[Mo(CO)(DMF)(dpe)(dpm)] was converted into trans-[Mo(CO)(N₂)(dpe)(dpm)].     

Molecular and electronic structure of B10H12L2 compounds,where L is a lewis base

The geometrical characteristics of the B₁₀H₁₂L₂ complexes of the borane nido-cluster |B₁₀H₁₂| with Lewis base molecules L=NH₃, CH₃CN, Me₂S, Py, which are typical electron pair donors, are analyzed. The complexes are calculated by the MNDO quantum chemical method. Chemical bonding between |B₁₀H₁₂| and L is characterized using, the fragment analysis of molecular orbitals (MOs). It is shown that both occupied and unoccupied MOs of the |B₁₀H₁₂| fragment make important contributions to the bonding. The higher MOs of the system as well as its lower MOs with orbital energies up to 20 eV and higher involve the unoccupied orbitals of the cluster. The electron density is transferred from one L orbital to two unoccupied MOs of |B₁₀H₁₂|, 9a₁ and 6b₂. There is a large group of HOMOs defined as lone electron pairs of |B₁₀H₁₂| (boron AOs), whose energies change almost symbatically due to bonding to L. The localization of the electron paris by an ab initio calculation in the STO-3G basis set revealed ten three-center bonds and one four-center bond, B(1)-B(2)-B(3)-B(4). The charge transferred from L to |B₁₀H₁₂| is localized mainly on the B(6) and B(9) atoms. The B-L bond is of σ type; a significant θ component is observed for L=CH₃CN and Py. It is shown that the simplest two-orbital model of a donor-acceptor bond is inapplicable in the case of the B₁₀H₁₂L₂ compounds. Deceased. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 4, pp. 652–663, July–August, 1996. Translated by I. Izvekova     

Molecular geometry of benzosemiquinone radicals: Radicals from resorcinol and its derivatives

The observed proton hyperfine coupling constants of radicals from resorcinol and 2-carboxylic, 5-carboxylic, and 5-methyl resorcinols in acidic and alkaline solution were reproduced by means of the INDO (intermediate neglect of differential overlap) with molecular geometry adjusting method. The bond lengths of C? O were longer in acidic solution than in alkaline solution and the total energies were lower in acidic solution than in alkaline solution. The assignments of the coupling constants of the radicals from resorcinols were |A₂| > |A₅| in alkaline oxidation and |A₂| < |A₅| in acidic oxidation.     

A pipecolic acid (Pip)‐containing dipeptide,Boc‐d‐Ala‐l‐Pip‐NHiPr

The title dipeptide, 1‐(tert‐butoxy­carbonyl‐d ‐alanyl)‐N‐iso­propyl‐l ‐pipecol­amide or Boc‐d ‐Ala‐l ‐Pip‐NHⁱPr (H‐Pip‐OH is pipecolic acid or piperidine‐2‐carboxylic acid), C₁₇H₃₁N₃­O₄, with a d –l heterochiral sequence, adopts a type II′β‐­turn conformation, with all‐trans amide functions, where the C‐terminal amide NH group interacts with the Boc carbonyl O atom to form a classical i+3 i intramolecular hydrogen bond. The C^α substituent takes an axial position [H^α (Pip) equatorial] and the trans pipecolamide function is nearly planar.     

Carbon-13 NMR spectra of monosulphones and disulphones: Substitution rules and conformational effects

Carbon-13 NMR spectra have been obtained for 27 aliphatic monosulphones and 13 aliphatic disulphones. Substitution rules have been formulated which allow the prediction of chemical shifts when a CH₂ group in a hydrocarbon is replaced by an SO₂ group, or when an H atom in a sulphone is replaced by an alkyl group. Carbon atoms β to a sulphone group show a marked upfield shift effect which is sensitive to the conformation about the C? S bond; atoms in the trans position experience an upfield shift (?9.39±1.64 ppm) compared with those in the gauche position. An assignment of the meso (m) and racemic (r) β-carbon peaks in di-sec-butyl sulphone was made by synthesis of the optically active compound. |δ_m–δL_r| decreases with increasing temperature for both β–carbon atoms; this effect was interpreted in terms of two available conformers for each of the m and r compounds, those for the m form having the same energy and entropy, and those for the r form having ΔS=0.6 J K^?1 mol^?1 and ΔH=0.8 kJ mol^?1. Observed chemical shifts for the disulphones were compared with those estimated by the application of the first set of substitution rules.