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CH3 Groups (ch3 + groups)
Selected AbstractsMolecular Structures and NMR Studies of Lithium and Germanium(II) Complexes of a New Chelating Amido,Imino Ligand Obtained by Addition of nBuLi to 1,2-Bis(arylimino)acenaphthene,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2006Igor L. Fedushkin Abstract The reaction of 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (dpp-bian, 1) with 1 equiv. of nBuLi in diethyl ether or with 2 equiv. of nBuLi in hexane produces [{dpp-bian(nBu)}Li(Et2O)] (3) and [{dpp-bian(nBu)Li}nBuLi]2 (4), respectively. Complexes 3 and 4 are formed by the transfer of an nBu anion to one of the imine carbon atoms of the dpp-bian ligand. Treatment of 3 and 4 with H2O affords the C -alkylated N -protonated amino-imino compound dpp-bian(H)(nBu) (5). The reaction of 3 with GeCl2(dioxane) affords the three-coordinate germylene complex [{dpp-bian(nBu)}GeCl] (6). The molecular structures of 3,6 were determined by single-crystal X-ray structure analysis. The lack of symmetry in the alkylated bian system in 3,6 causes the non-equivalence of all protons except those of the CH3 groups of the iPr substituents. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Improved intermolecular force field for molecules containing H, C, N, and O atoms, with application to nucleoside and peptide crystalsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 11 2001Donald E. Williams Abstract A new intermolecular force field for nitrogen atoms in organic molecules was derived from a training dataset of 76 observed azahydrocarbon crystal structures and 11 observed heats of sublimation. The previously published W99 force field for hydrogen, carbon, and oxygen was thus extended to include nitrogen atoms. Nitrogen atoms were divided into four classes: N(1) for triply bonded nitrogen, N(2) for nitrogen with no bonded hydrogen (except the triple bonded case), N(3) for nitrogen with one bonded hydrogen, and N(4) for nitrogen with two or more bonded hydrogens. H(4) designated hydrogen bonded to nitrogen. Wavefunctions of 6-31g** quality were calculated for each molecule and the molecular electric potential (MEP) was modeled with net atomic and supplementary site charges. Lone pair electron charge sites were included for nitrogen atoms where appropriate, and methylene bisector charges were used for CH2 and CH3 groups when fitting the MEP. XH bond distances were set to standard values for the wave function calculation and then foreshortened by 0.1 Å for the MEP and force field fitting. Using the force field optimized to the training dataset, each azahydrocarbon crystal structure was relaxed by intermolecular energy minimization. Predicted maximum changes in unit cell edge lengths for each crystal were 3% or less. The complete force field for H, C, N, and O atoms was tested by intermolecular energy relaxation of nucleoside and peptide molecular crystals. Even though these molecules were not included in any of the training datasets for the force field, agreement with their observed crystal structures was very good, with predicted unit cell edge shifts usually less than 2%. These tests included crystal structures of representatives of all eight common nucleosides found in DNA and RNA, 15 dipeptides, four tripeptides, two tetrapeptides, and a pentapeptide with two molecules in the asymmetric unit. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1154,1166, 2001 [source] High-efficiency stimulated Raman scattering from alcohols: theory and experimentsJOURNAL OF RAMAN SPECTROSCOPY, Issue 5 2005Lorenzo Echevarrķa Abstract The coherent Raman emission from primary alcohols [CH3(CH2)nOH, n = 0,10], 2-propyl alcohol and tert -butyl alcohol was studied using a frequency-doubled Nd:YAG pump laser (532 nm). We show that increases in the chain length (CH2 groups) and the number of CH3 groups in the alcohols (CH3 > CH2) enhance the Raman emission efficiency. Theoretical density functional theory (DFT) calculations and frequency scaling allow one to associate the vibrational wavenumbers with the molecular fragment responsible for the vibration. We obtained good agreement between the observed phenomena and the predictions of the theory. Copyright © 2005 John Wiley & Sons, Ltd. [source] Improved multiplicity-editing of HMBC NMR spectraMAGNETIC RESONANCE IN CHEMISTRY, Issue 8 2006Andrew J. Benie Abstract A new improved multiplicity-edited HMBC experiment is introduced that leads to better J cross-talk suppression in the even (i.e. C + CH2 groups) and odd (i.e. CH + CH3 groups) subspectra. By combining data recorded with three different pulse sequences J cross-talk becomes a second-order effect in ,1J, i.e. the deviation of an actual 1J coupling constant from the value 1J0 used in setting delays , = (1J0),1/2, which is adequate for most applications. As for the original multiplicity-edited HMBC experiment, the improved experiment can be performed with a single excitation delay or implemented in a broadband version similar to broadband HMBC. Copyright © 2006 John Wiley & Sons, Ltd. [source] In Situ Characterization of Thermo-Responsive Poly(N -Isopropylacrylamide) Films with Sum-Frequency Generation SpectroscopyCHEMPHYSCHEM, Issue 7 2010Volker Kurz Abstract The thermo-responsive behaviour of thiol modified poly(N -isopropylacrylamide) (pNIPAM) films immobilized on gold are probed by in situ broadband sum-frequency generation (SFG) spectroscopy. The pNIPAM films were prepared by atom transfer radical polymerization (ATRP) using a nitro-biphenyl-thiol (NBT)-SAM on a polycrystalline gold surface as a substrate. Additionally, Raman and infrared reflection absorption spectroscopy (IRRAS) are applied to spin-coated pNIPAM films. Molecular groups involved in the reorientation and disordering of the polymer chains during the LCST (lower critical solution temperature) transition of pNIPAM are identified. The characteristic vibrations of the CH3 groups show a gradual reorientation of the isopropyl groups within the pNIPAM film and instantaneous reorientation of the outermost CH3 groups around 32,°C. [source] | ||||||||||