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 Synthesis of Several Lateral Difluoro-substituted 4,4″-Dialkyl- and 4,4″-Alkoxyalkyl-Terphenyls and a Rationalisation of the Effect of Such Substitution on Mesophase Type and Transition Temperatures

Abstract: In recent years we have prepared a large number of mono-fluoro- and ortho-difluoro-substituted 4,4''-dialkyl- and 4,4''-alkoxyalkyl-terphenyls. The synthesis and transition temperatures of a variety of related difluoro compounds is presented here so that it is now possible to identify(i) broadening of the molecule, (ii) twisting about an inter-annular bond, and (iii) the presence of an inner (2-, 2'-, 3'- or 2'' substituent) or an outer (3- or 3''-substituent) fluorine, as being the major factors which influence the type and the thermal stability of the mesophases obtained

[dialkylcarbamoylmethyl] phosphine oxides on their extraction capacity and selectivity

Abstract: Extraction of Am ( III), Pu( IV), U( VI) from nitric acid solutions by dialkyl ( aryl) [ dialkylcarbamoylmethyl] phosphine oxides of different structures has been studied. The nature of substituents at phosphorus and nitrogen atoms and in methylene bridge affects extraction capacity, solubility and selectivity of reagents. The increase in extraction capacity of reagents with respect to Am, U, Pu and decrease in solubility and selectivity at consecutive replacement of alkyl-( or alkoxy-) radicals at phosphorus atom by phenyl ones was found. The advantage of reagents usage with two different radicals one of which is phenyl at phosphorus atom has been shown. The nature of substituent at nitrogen atom affect solubility but does not practically affect extraction capacity of reagent.

The Effect of Ring Nitrogen Atoms on the Homolytic Reactivity of Phenolic Compounds: Understanding the Radical‐Scavenging Ability of 5‐Pyrimidinols

Abstract: Six substituted 5-pyrimidinols were synthesized, and the thermochemistry and kinetics of their reactions with free radicals were studied and compared to those of equivalently substituted phenols. To assess their potential as hydrogen-atom donors to free radicals, we measured their O-H bond dissociation enthalpies (BDEs) using the radical equilibration electron paramagnetic resonance technique. This revealed that the O-H BDEs in 5-pyrimidinols are, on average, about 2.5 kcal mol(-1) higher than those in equivalently substituted phenols. The results are in good agreement with theoretical predictions, and confirm that substituent effects on the O-H BDE of 5-pyrimidinol are essentially the same as those on the Obond;H BDE in phenol. The kinetics of the reactions of these compounds with peroxyl radicals has been studied by their inhibition of the AIBN-initiated autoxidation of styrene, and with alkyl and alkoxyl radicals by competition kinetics. Despite their larger O-H BDEs, 5-pyrimidinols appear to transfer their phenolic hydrogen-atom to peroxyl radicals as quickly as equivalently substituted phenols, while their reactivity toward alkyl radicals far exceeds that of the corresponding phenols. We suggest that this rate enhancement, which is large in the case of alkyl radical reactions, small in the case of peroxyl radical reactions, and nonexistent in the case of alkoxyl radical reactions, is due to polar effects in the transition states of these atom-transfer reactions. This hypothesis is supported by additional experimental and theoretical results. Despite this higher reactivity of 5-pyrimidinols towards radicals compared to phenols, electrochemical measurements indicate that they are more stable to one-electron oxidation than equivalently substituted phenols. For example, the 5-pyrimidinol analogues of 2,4,6-trimethylphenol and butylated hydroxytoluene (BHT) were found to have oxidation potentials approximately 400 mV higher than their phenolic counterparts, but reacted roughly one order of magnitude faster with alkyl radicals and at about the same rate with peroxyl radicals. The 5-pyrimidinol structure should, therefore, serve as a useful template for the rational design of novel air-stable radical scavengers and chain-breaking antioxidants that are more effective than phenols.