Substituent

About: Substituent is a research topic. Over the lifetime, 42877 publications have been published within this topic receiving 516716 citations. The topic is also known as: side chain & side group.

Directed Homogeneous Hydrogenation [New Synthetic Methods (65)]

Abstract: Stereochemical control is a major concern in the application of homogeneous catalysis to organic chemistry. In this context, the directed hydrogenation of olefins employing cationic rhodium or iridium catalysts has considerable potential, for very high selectivity can be attained under mild reaction conditions. The only requirement is a polar functional group in proximity to the double-bond which remains bound to the metal during the catalytic cycle and thereby controls the Stereochemical course of hydrogen delivery through the constraints of chelation. The substituent is most frequently a hydroxy group OH but can also be an ester, amide or carbamate group; other groups remain to be scrutinized. In cyclic compounds, directed hydrogenation can lead to face-selectivity, and the polar substituent may be in the β-, γ-, or δ-position to the double-bond. Acyclic stereoselection ensues with β- or γ-substituents in appropriate compounds, and the configuration of reduced product is predictable on the basis of simple rules. The application of optically active rhodium complexes leads to useful kinetic resolution procedures.

Rapid Solution and Solid Phase Syntheses of Oligo(1,4-phenylene ethynylene)s with Thioester Termini: Molecular Scale Wires with Alligator Clips. Derivation of Iterative Reaction Efficiencies on a Polymer Support

Abstract: The syntheses of soluble oligo(2-alkyl-1,4-phenylene ethynylene)s via an iterative divergent/convergent approach starting from 1-(diethyltriazyl)-3-alkyl-4-[(trimethylsilyl)ethynyl]benzenes are described. When the solublizing alkyl group is an ethyl substituent, the monomer, dimer, tetramer, and octamer can be synthesized. The octamer, however, is only minimally soluble. When the alkyl substituent is 3-ethylheptyl or dodecyl, the compounds are easily dissolved even at the 16-mer stage. The 16-mer is 128 A long in its near-linear extended conformation. At each stage in the iteration, the length of the framework doubles. Only three sets of reaction conditions are needed for the entire iterative synthetic sequence: an iodination, a protodesilylation, and a Pd/Cu-catalyzed cross coupling. Synthesis of the dodecyl-containing 16-mer was also achieved on Merrifield's resin using the iterative divergent/convergent approach. The oligomers were characterized spectroscopically and by mass spectrometry. The optical ...

Gas phase basicities and relative proton affinities of compounds between water and ammonia from pulsed ion cyclotron resonance thermal equilibriums measurements

Abstract: The pulsed ion cyclotron resonance method for precise determinations of proton transfer equilibrium constants has been applied to 46 carbon, nitrogen, oxygen, phosphorus, sulfur, arsenic, and selenium bases, with duplicating overlapping sequences, to obtain the relative proton affinities of water and ammonia. Where comparison is possible, the results are in generally good accord with those obtained by high-pressure mass spectroscopy. The results provide important new insights into the intrinsic effects of molecular structure on base strengths. Applications of these results to derive other gaseous ion thermochemical data are illustrated. In particular, methyl substituent effects on proton affinities have been extensively evaluated and interpretations are made of the comparisons with corresponding effects of homolytic bond dissociation energies of the conjugate acids of n-bases and with the hydride affinities of substituted methyl cations. Comparisons of the effects of n-alkyl substituents on the proton affinities of water and alcohols with carboxylic acids and their esters indicate that protonation is thermodynamically favored in the gas phase at the carbonyl oxygen of the latter. Large effects of polar electronegative substituents have been observed for various oxygen and nitrogen bases. An evaluation of entropy effects in gas phase proton transfer equilibria shows such effects to bemore » generally small for simple bases and approximately equal to entropy effects expected for changes in molecular rotational symmetry numbers. Finally, the present result provides the basis for evaluations of absolute proton affinities and of relative ion solvation energies.« less

Precursors for depositing silicon-containing films and methods for making and using same

Abstract: Aminosilane precursors for depositing silicon-containing films, and methods for depositing silicon-containing films from these aminosilane precursors, are described herein. In one embodiment, there is provided an aminosilane precursor for depositing silicon-containing film comprising the following formula (I): (R 1 R 2 N) n SiR 3 4-n (I) wherein substituents R 1 and R 2 are each independently chosen from an alkyl group comprising from 1 to 20 carbon atoms and an aryl group comprising from 6 to 30 carbon atoms, at least one of substituents R 1 and R 2 comprises at least one electron withdrawing substituent chosen from F, Cl, Br, I, CN, NO 2 , PO(OR) 2 , OR, SO, SO 2 , SO 2 R and wherein R in the at least one electron withdrawing substituent is chosen from an alkyl group or an aryl group, R 3 is chosen from H, an alkyl group, or an aryl group, and n is a number ranging from 1 to 4.

C13 Splittings in Proton Magnetic Resonance Spectra. II. Bonding in Substituted Methanes

Abstract: We have measured indirect spin‐spin couplings between protons and C13 nuclei in a variety of substituted methanes As found earlier for hydrocarbons, the coupling constants, JC–H, appear to be linearly related both to the percent s character of the carbon atomic orbital participating in the C–H bond and to the bond length On the basis of the large variations of the JC–H values and of the C–H bond lengths in these compounds we conclude that the state of hybridization of the carbon atom cannot be reliably inferred from the observed, essentially tetrahedral valence angles This means that the bonds must in many cases be considered as somewhat bentWe investigated the dependence of the C–H bond hybridization in compounds of type CH3X upon the properties of the substituent group The results can be correlated on the assumption that the effective electronegativity and the size of the atom directly attached to the methyl carbon primarily determine the hybridization