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.

Silicon octaphenoxyphthalocyanines: photostability and singlet oxygen quantum yields

Abstract: Photochemical properties of series of axially substituted silicon octaphenoxyphthalocyanines with aryloxy, siloxy, aminoalkoxy, esters of carboxylic acids and sulphonic acid esters residues as axial ligands were studied in dimethylsulfoxide (DMSO) solution. It was found, that under Q-band excitation axial ligands in compounds studied have the propensity to be changed by hydroxyl groups with quantum yields in the range 10 −5 to 10 −2 depending on the nature of the axial ligand. Axial substituent phototransformation was followed by slow photobleaching of dihydroxysilicon octaphenoxyphthalocyanine (photoproduct) in self-sensitized singlet oxygen mediated oxidation of the macrocycle. Singlet oxygen quantum yields were found to be in the range 0.15–0.20 for majority of the phthalocyanines (Pc) studied.

Polyfluoroalkyl, Polyethylene Glycol, 1,4-Bismethylenebenzene, or 1,4-Bismethylene-2,3,5,6-Tetrafluorobenzene Bridged Functionalized Dicationic Ionic Liquids: Synthesis and Properties as High Temperature Lubricants

Abstract: A new class of geminal dicationic ionic liquids was formed with a bridging moiety, such as a polyalkyl ether, polyfluoroalkyl, 1,4-bismethylenebenzene, or 1,4-bismethylene-2,3,5,6-tetrafluorobenzene link, between alkyl-substituted imidazolium rings. Their properties were modified by varying the linker chains and/or alkyl substituents on the imidazolium ring. The polyfluoroalkyl bridged dicationic ionic liquids exhibit the highest densities and viscosities. Although melting points are directly proportional to the length of the alkyl substituent, the densities decrease concomitantly. With 1,4-bismethylene-2,3,5,6-tetrafluorobenzene as the linking chain and with longer alkyl substituents on the imidazolium rings, the nonpolar character of the ionic liquid greatly increases, e.g., the solubilities in toluene of dicationic ionic liquids 36 and 37, where the ring substituents are C10H21 and C14H29, increase markedly. Some of the salts exhibit higher conductivities than an equimolar tetrabutylammonium iodide sol...

Substituent effects on the properties of the hemi-bonded complexes (XH2P···NH2Y)(+) (X, Y=H, F, Cl, Br, NH2, CH3, OH).

Abstract: Ab initio calculations have been performed to study the structures, binding energies, and bonding properties of the hemi-bonded binary complexes (XH2P···NH2Y)(+) with the substituents X and Y being H, F, Cl, Br, NH2, CH3, and OH. The P···N interactions in these open-shelled systems have typical pnicogen bond characteristics but much stronger than the usual pnicogen bonds in closed-shell systems. This P···N bond can be strengthened by an electron-withdrawing substituent X or an electron-donating substituent Y, the bonding energy varies from 17 kcal mol(-1) of (CH3H2P···NH2F)(+) to 54 kcal mol(-1) of (FH2P···NH2CH3)(+). A nearly linear X-P···N arrangement is required by the pnicogen bond P···N and results in a strong hyperconjugation and charge transfer from the N lone pair to the X-P σ* antibond orbital for α spin, the P···N interaction is described as a single-electron σ bond of β spin. The AIM and NBO analyses revealed that the P···N bonds in the majority of the hemi-bonded complexes are partly covalent in nature. Graphical Abstract The P···N interactions in the open-shelled systems (XH2P···NH2Y)(+) (X, Y=H, F, Cl, Br, NH2, CH3, OH) with bonding energy of 17~54 kcal mol(-1) have typical pnicogen bond characteristics but much stronger than the usual pnicogen bonds in closed-shell systems. This P···N bond can be strengthened by an electron-withdrawing substituent X or an electron-donating substituent Y.

A Computational Analysis of Substituent Effects on the O-H Bond Dissociation Energy in Phenols: Polar Versus Radical Effects

Abstract: O−H bond dissociation energies (BDEs) of phenol, p-aminophenol, and p-nitrophenol have been computed using ab initio and density functional theory (DFT) methods. The MP2 and MP4 methods consistently overestimate the absolute BDEs but provide reasonable relative BDEs. Spin projected MP2 and MP4 energies are not able to reproduce the substituent effects on the BDE. The BLYP and B3LYP DFT methods provide more reliable and economical approaches for prediction of phenol BDEs. B3LYP/6-31G** computed ΔBDEs for 10 substituted phenols have been compared with values determined by different experimental approaches. The computed values are in most cases within the uncertainty of the measurements. It is shown that the substituent effects on the BDEs can be interpreted in terms of polar and radical stabilization. The polar stabilization is found to be related to the ability of the substituent to delocalize the lone pair on the phenol oxygen. The radical stabilization is dependent on the degree of spin delocalization. A...