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.

Substituent effects on the oxidation and reduction potentials of phenylthiyl radicals in acetonitrile.

Abstract: Oxidation ( ) and reduction potentials ( ) of a series of para-substituted phenylthiyl radicals XC6H4S• generated from the pertinent disulfides or thiophenols have been measured by means of photomodulated voltammetry in acetonitrile. The values of are of particular interest as they give access to the hitherto unknown thermochemistry of short-lived phenylsulfenium cations in solution. Both and decrease as the electron-donating power of the substituent raises, resulting in linear correlations with the Hammett substituent coefficient σ+ with slopes ρ+ of 4.7 and 6.4, respectively. The finding of a larger substituent effect on than is a consequence of a corresponding development in the electron affinities and ionization potentials of XC6H4S• as revealed by quantum-chemical calculations. Solvation energies extracted for XC6H4S+ and XC6H4S- from thermochemical cycles show the expected substituent dependency; i.e., the absolute values of the solvation energies decrease as the charge becomes more delocalized in t...

Substituent effects in halogen bonding complexes between aromatic donors and acceptors: a comprehensive ab initio study

Abstract: Substituent effects in halogen bonding complexes involving aromatic rings are investigated. We have analyzed how the interaction energy (the RI-MP2/aug-cc-pVDZ level of theory) is affected by the substitution in both halogen bond donor and acceptor aromatic moieties. In addition, we have used two different aromatic electron donor molecules pyridine and cyanobenzene, which allow us to study the effect of having the electron donor nitrogen atom forming part of the ring or outside the ring (–CN). Interestingly, the effect of the substituents on the interaction energies is similar in both cases. We have obtained the Hammett's plots for four combinations of aromatic donors and acceptors and in all cases we have obtained good regression plots (interaction energies vs. Hammett's σ parameter). We have also studied and compared bifurcated halogen bonds using both possible combinations, that is two donors and one acceptor and vice versa. In addition, we have analyzed the effect of the solvent on the interaction energies using COSMO. Finally, we have used Bader's theory of “atoms-in-molecules” to demonstrate that the electron density computed at the bond critical point that emerges upon complexation can be used as a measure of bond order in this noncovalent interaction.

Fluorescence Enhancement from Self-Assembled Aggregates: Substituent Effects on Self-Assembly of Azobenzenes

Abstract: We have found for the first time significant substituent effects on the light-driven self-assembly of para-substituted azobenzene derivatives and the resulting fluorescence enhancement. The unusual fluorescence enhancement is attributed to the light-driven self-assembly of cis-azobenzenes showing (1) sufficient lifetime and (2) a larger dipole moment.

The reaction of porphyrins with organolithium reagents.

Abstract: Porphyrins react readily with organolithium reagents, preferentially in the meso positions. The overall reaction is a nucleophilic substitution and proceeds via initial reaction of the organic nucleophile with a meso carbon yielding an anionic species which is hydrolyzed to a porphodimethene (5,15-dihydroporphyrin), formally constituting an addition reaction to two Cm positions. Subsequent oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) yields meso-substituted porphyrins. The reaction is highly versatile as it is accomplished in high, often quantitative yields with various alkyl or aryl lithium reagents. In addition, LiR can be used for reaction with a variety of metal complexes (best with NiII, but also with ZnII, CuII, and CoII) and most useful with free base porphyrins. Similarly beneficial this reaction can be used in sequence for the introduction of 1, 2, 3, or 4 (different) meso substituents giving for the first time an entry into any desired meso-substituted porphyrin. If meso-substituted porphyrins are used, reaction with LiR can be used for either the preparation of phlorins (already known reaction), porphodimethenes (5,15-dihydroporphyrins, including those with exocyclic double bonds, for example, 51,52-didehydroporphyrins) or chlorins (2,3-dihydroporphyrins) depending on the substituent type in the reactant porphyrins. Thus, this reaction presents a generally applicable method for the facile and versatile functionalization of porphyrins.