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.

The Effect of Structure Upon the Reactions of Organic Compounds. Temperature and Solvent Influences

Abstract: The effect of a substituent upon the heat of ionization of an organic acid is far from identical with its effect upon the free energy of ionization In the case of benzoic acid derivatives the entropy of ionization varies with structure in a way which can be predicted from the temperature dependence of the dielectric constant of the solvent, and which is closely correlated with the effect of a change in the dielectric constant of the solvent upon the relative strengths of substituted and unsubstituted acids The behavior of aliphatic acids is more complicated, probably because of their less rigid structure Similar considerations apply to the effect of changes in structure of reactant upon other equilibria and upon reaction rates

Regioselectivity and network structure of difunctional alkyl-substituted aromatic amine-based polybenzoxazines

Abstract: The regioselectivity of the benzoxazine polymerization in aromatic amine-based polybenzoxazines is investigated through systematic manipulation of the monomer chemistry. The network structures of the cured materials are elucidated by FTIR and GC/MS. Selectively protecting or activating sites on the pendant aromatic ring toward electrophilic aromatic substitution with alkyl groups allows a series of materials to be developed which contain a varying amount of phenolic Mannich bridges, arylamine Mannich bridges, and methylene linkages. Activation of sites on the pendant rings by methyl substituent groups lowers the peak exotherm temperature by up to 45 °C. Temperature-modulated differential scanning calorimetry shows that in some of these materials the development of the glass transition temperature exceeds that of the curing temperature.

Synthesis and Conformational Study of Optically Active Poly(phenylacetylene) Derivatives Bearing a Bulky Substituent

Abstract: Three optically active phenylacetylenes having a chiral carbamoyloxy group at the para or meta position were synthesized, polymerized, and copolymerized with various optically inactive comonomers with transition metal catalysts such as [RhCl(NBD)] 2 (NBD : norbornadiene) in THF in order to explore the role of the bulkiness of side groups on the phenyl moieties during the formation of a helical conformation. [RhCl(NBD)] 2 produced high molecular weight polymers and copolymers in THF. The yields and molecular weight of the obtained copolymers were influenced by the bulkiness of the comonomers. All polymers showed broad electronic absorptions up to ca. 570 nm, and the 1 H NMR spectra indicated that the polymers had a cis-transoidal structure. The chiral homopolymers and copolymers showed an intense induced CD in the UV-visible region depending on the position of the substituents of the chiral residues and the bulkiness of the achiral comonomers. The polymers having chiral carbamoyloxy groups at the para position on the phenyl groups showed very intense induced CD bands in the UV-visible region with negative and positive Cotton effects. The main chain of the polymers seems to be chiral, probably based on a predominant one-handed helical sense. The magnitude of the CD of the copolymers increased with an increase in the bulkiness of the substituents of the comonomers. The polymers with a chiral substituent at the meta position showed a very weak induced CD in the UV-visible region. However, a copolymer with the phenylacetylene having a bulky tert-butyldiphenylsiloxy group at the para position exhibited a very intense induced CD which was almost a mirror image to those of the chiral homopolymers in the 300-450 nm wavelength range. These results suggest that the copolymer may possess a reversed helical structure. The sign and specific rotation at 780 nm of the para-substituted polymers and copolymers were also influenced by the bulkiness of the substituents of the comonomers ; the specific rotation of the copolymer of 1 or 2 with the phenylacetylene having bulky tert-butyldiphenylsiloxy groups at the para position showed a specific rotation about 2 times larger than that of the homopolymers. The steric effects of bulky side groups on helical conformation was discussed on the basis of molecular mechanics and molecular dynamics calculations of model polymers.

Effects of the substituents on the reactivity of carbonyl oxides. A theoretical study on the reaction of substituted carbonyl oxides with water.

Abstract: The reactions between fifteen carbonyl oxides and water have been investigated with the aim of contributing to a better understanding of the effects of the substituents in the reactivity of carbonyl oxides We have employed density functional theory and large scale ab initio methods (CCSD(T), CASSCF, and CASPT2), combined with transition state theory, to investigate the addition of water to carbonyl oxide and, for those carbonyl oxides having a methyl substituent in syn, the hydrogen transfer from the methyl group to the terminal oxygen of carbonyl oxide In this case, the water acts as a catalyst and this reaction can contribute to the atmospheric formation of a hydroxyl radical Carbonyl oxides with electron withdrawing substituents and zwitterionic character have low energy barriers and react fast, whereas carbonyl oxides with electron releasing substituents have high energy barriers and react slowly The position of the substituents plays also an important role and carbonyl oxides having a hydrogen atom substituent in syn react faster than carbonyl oxides having a hydrogen atom substituent in anti The differences in the reactivity of different substituted carbonyl oxides raise up to ten orders of magnitude and the branching ratios for the two different reactions investigated are also reported