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Methyl Substitution (methyl + substitution)
Selected AbstractsChemInform Abstract: Influence of ,-Methyl Substitution of Proline-Based Organocatalysts on the Asymmetric ,-Oxidation of Aldehydes.CHEMINFORM, Issue 41 2009Sok-Teng Tong Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Improved and Controlled Complexation of Paraquat Derivatives by the Formation of a Bis(m -phenylene)-26-Crown-8-Based Lariat EtherEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 29 2010Mingming Zhang Abstract A novel bis(m -phenylene)-26-crown-8-based lariat ether (i.e., 3b) was synthesized and characterized. It can bind paraquat derivatives more strongly than bis(m -phenylene)-26-crown-8 in solution. It forms pseudorotaxanes with two paraquat derivatives in the solid state. N -Methyl substitution was found to play an important role on the binding strength of lariat ether 3b. Furthermore, due to the introduction of two benzyloxy groups, its binding to paraquat derivatives can be switched off (and back on) by adding K+ (and then dibenzo-18-crown-6), and the disassociation percentage depends on the concentration of the added K+ ions. [source] Hyperbranched polymers from propargyloxysilanes: New types of acetylenic resinsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2001Yingxin Xiao Abstract New hyperbranched polymers (1P,3P) from propargyloxysilanes (1,3) are described. The propargyloxysilanes were prepared from readily available reagents in 53,61% yields. The polymerizations were clean, one-pot hydrosilylation processes catalyzed by Pt/C that were typically complete within 3 h. The polymers contained pendant acetylenic groups that underwent thermally induced crosslinking reactions. Heating the polymers to 1300 °C in flowing nitrogen resulted in weight losses ranging from 33 to 66%. Methyl substitution resulted in lower thermal stability. Further modification of the polymers was demonstrated by the reaction of 1P and 2P with phenylethynyldimethylsilane in the presence of a Pt catalyst. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3383,3391, 2001 [source] Planarity of acetamides, thioacetamides, and selenoacetamides: Crystal structure of N,N -dimethylselenoacetamideHETEROATOM CHEMISTRY, Issue 4 2002Shuqiang Niu The planarity of acetamides 1a,3a, thioacetamides 4a,6a, and selenoacetamides 7a,9a, R1R2NC(=E)CH3 where E = O, S, Se, and R1, R2 = H or CH3, was investigated using theoretical calculations at the density functional theory (DFT) level. The calculations showed that the methyl substitution on nitrogen and the change from the amide moiety (NCO) to NCS or NCSe group increased the double bond character of the NC bond. In other words, the planarity of these compounds (1a,9a) increases in the order NH2 < NHCH3 < N(CH3)2 and O < S < Se. The calculations of bending energy suggest that the planar geometry represents the lowest energy conformation for all compounds investigated in this work. N,N-Dimethyl-selenoacetamide (9a), (CH3)2NC(Se) CH3, has the largest bending energy of 10.37 kcal/mol, which suggests that it possesses the greatest planarity among the compounds 1a,9a. However, the solid phase molecular structure of 9a was found to be slightly nonplanar by X-ray crystallography. The slight nonplanarity observed experimentally is very likely the consequence of intermolecular interactions arising within the crystal packing. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:380,386, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10056 [source] Kinetics of the thermal isomerization of 1,1,2,2-tetramethylcyclopropaneINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2006David K. Lewis Reaction rates for the structural isomerization of 1,1,2,2-tetramethylcyclopropane to 2,4-dimethyl-2-pentene have been measured over a wide temperature range, 672,750 K in a static reactor and 1000,1120 K in a single-pulse shock tube. The combined data from the two temperature regions give Arrhenius parameters Ea=64.7 (±0.5) kcal/mol and log10(A, s,1) = 15.47 (±0.13). These values lie at the upper end of the ranges of Ea and log A values (62.2,64.7 kcal/mol and 14.82,15.55, respectively) obtained from three previous experimental studies, each of which covered a narrower temperature range. The previously noted trend toward lower Ea values for structural isomerization of methylcyclopropanes as methyl substitution increases extends only through the dimethylcyclopropanes (1,1- and 1,2-); Ea then appears to increase with further methyl substitution. In contrast, the pre-exponential factors for isomerization of cyclopropane and all of the methylcyclopropanes through tetramethylcyclopropane lie within ±0.3 of log10(A, s,1) = 15.2 and show no particular trend with increasing substitution. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 483,488, 2006 [source] Synthesis and biodistribution of novel 99mTc-nitrido methylpiperidine dithioformate derivatives as potential brain imaging agentsJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 6 2009Jie Lu Abstract Three dithioformate ligands with methyl substituted on the piperidine rings, potassium 1-(2-methylpiperidine-1-yl)-dithioformate (2-mp), potassium 1-(3-methylpiperidine-1-yl)-dithioformate (3-mp) and potassium 1-(4-methylpiperidine-1-yl)-dithioformate (4-mp) were synthesized. The corresponding 99mTc-nitrido complexes were prepared in high yield (>95%) through the [99mTcN] intermediate and characterized by thin layer chromatography and high-performance liquid chromatography. All the neutral 99mTc-nitrido complexes were stable under physiological conditions and lipophilic with log,P values between 1.40 and 1.58. In vivo biodistribution results showed that all the 99mTc-nitrido complexes displayed high brain uptakes and long retention times. Among them, 99mTcN-4mp, demonstrated the best properties for brain imaging with the brain uptake 3.40±0.24, 3.22±0.31, 2.72±0.28 and 2.22±0.18% ID/g at 5, 30, 60 and 120,min p.i., respectively. Moreover, the influence of stereochemistry of the 99mTcN complexes with methyl substitution on ortho, meta and para positions on piperidine ring on the biodistribution properties were investigated with B3LYP/6-31G*(LANL2DZ for Tc) method using the Gaussian 03 program package. Copyright © 2009 John Wiley & Sons, Ltd. [source] Magnesium and biological activity of oxytocin analogues modified on aromatic ring of amino acid in position 2JOURNAL OF PEPTIDE SCIENCE, Issue 8 2001ina Slaninová Abstract For the purpose of evaluating substitution effects in the ortho, meta or para positions of the aromatic ring of tyrosine or phenylalanine in position 2 of oxytocin on uterotonic activity in vitro in the presence and absence of magnesium ions, six new analogues of oxytocin ([,,- and ,,- m -methylphenylalanine2]oxytocin, [,,- and ,,- m -methoxyphenylalanine2]oxytocin and [,,- and ,,- o -methyltyrosine2]oxytocin) were synthesized and several previously described analogues resynthesized. For the phenylalanine series, it is found that, in the absence of magnesium ions, substitution of the ortho and meta positions leads to loss of intrinsic activity (the analogues are antagonists) in contrast to the para position. In the tyrosine series, only methyl substitution in the meta position has this effect (substitution of ortho position only attenuates the agonistic biological activity). Addition of Mg ions restores to a certain degree the agonistic activity in the case of the o -methylphenylalanine analogue and enhances the agonistic activity of o -methyltyrosine oxytocin. All other analogues keep the original qualities as in the absence of Mg. Molecular modelling calculations of the structure of the above analogues was carried out to help explain these findings of the molecular level. Copyright © 2001 European Peptide Society and John Wiley & Sons, Ltd. [source] Studies of ethylene,styrene copolymerization with dinuclear constrained geometry complexes with methyl substitution at the five-membered ring in indenyl of [Ti(,5:,1 -C9H5SiMe2NCMe3)]2 [CH2]nJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 7 2004Seok Kyun Noh Abstract The new dinuclear half-sandwich CGC (constrained geometry catalyst) with methyl substitution in indenyl, [Ti(,5:,1 -2-methylindenyl)SiMe2NCMe3]2 [(CH2)n] [n = 6 (10), n = 9 (11), n = 12 (12)], have been synthesized, and structure of these complexes has been characterized by 1H and 13C NMR. The most important feature is that two protons of methylene directly bonded to the indenyl ring become inequivalent to be shown as two separated resonances at 2.9 and 3.0 ppm, probably due to the formation of planar chirality caused by a titanium complex formation. It has been found that the dinuclear CGCs with methyl substitution at an indenyl ring were very active catalysts for ethylene and styrene copolymerization. The activity increases in the order of 10 < 11 < 12, which indicates that the presence of a longer bridge between two active sites contributes to facilitate the polymerization activity of the dinuclear CGC more effectively. This result might be understood by the implication that the steric factor rather than the electronic factor may play a major role to direct the polymerization behavior of the dinuclear CGC. It is found that the dinuclear catalysts are very efficient to incorporate styrene in the polyethylene backbone. The styrene contents in the formed copolymers ranged from 5 to 40% according to the polymerization conditions. One can observe strong signals at 29.7 ppm of the polyethylene sequences, and, in addition, peaks at 27.5, 36.9, and 46. 2ppm (S,,, S,,, and T,,, respectively) of sequences of EESEE. Weak peak at 25.3 ppm are attributed to S,,, which represents SES sequence. The absence of a signal for T,, at 41.3 ppm and for S,, at 43.6 ppm shows there is no styrene,styrene sequences in copolymers. This result indicates that the dinuclear CGC are very effective to generate well-distributed poly(ethylene- co -styrene)s. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1712,1723, 2004 [source] Systematic Evaluation of Substituted Cyclopentadienyl Ruthenium Complexes, [(,5 -C5MenH5,n)RuCl(cod)], for Catalytic Cycloadditions of DiynesCHEMISTRY - AN ASIAN JOURNAL, Issue 4 2010Yoshihiko Yamamoto Prof. Abstract A series of ,5 -cyclopentadienylruthenium complexes, [(,5 -C5MenH5,n)RuCl(cod)] (cod=1,5-cyclooctadiene), are evaluated as catalysts for the cycloaddition of 1,6-diynes with alkynes. As a result, we unexpectedly found that the complex bearing the 1,2,4-Me3Cp ligand is the most efficient catalyst in terms of turnover number (TON) for the cycloaddition of a bulky diiododiyne with acetylene, recording the highest TON of 970 with a catalyst loading of 0.1,mol,%. To obtain insight into this result, we evaluate the electron richness of all complexes by cyclic voltammetric analyses, which indicate that the electron density of the ruthenium center increases with an increase in methyl substitution on the Cp, ligands. The initial rate (up to 10,% conversion) of the cycloaddition was then measured using 1H,NMR spectroscopy. The initial rate is found to decrease as the number of methyl substituents increases. According to these results, we assumed that the optimum catalytic performance exhibited by the 1,2,4-trimethylcyclopentadienyl complex can be attributed to its robustness under the catalytic cycloaddition conditions. The steric and electronic effects of the Cp, ligands are also investigated in terms of the regioselectivity of the cycloaddition of an unsymmetrical diyne and in terms of the chemoselectivity in the cycloaddition of a 1,6-heptadiyne with norbornene. [source] | ||||||||||