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.

How does the addition of steric hindrance to a typical N-heterocyclic carbene ligand affect catalytic activity in olefin metathesis?

Abstract: Density functional theory (DFT) calculations were used to predict and rationalize the effect of the modification of the structure of the prototype 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) N-heterocyclic carbene (NHC) ligand. The modification consists in the substitution of the methyl groups of ortho isopropyl substituent with phenyl groups, and here we plan to describe how such significant changes affect the metal environment and therefore the related catalytic behaviour. Bearing in mind that there is a significant structural difference between both ligands in different olefin metathesis reactions, here by means of DFT we characterize where the NHC ligand plays a more active role and where it is a simple spectator, or at least its modification does not significantly change its catalytic role/performance.

Unusual aryl-porphyrin rotational barriers in peripherally crowded porphyrins.

Abstract: Previous studies of 5,10,15,20-tetraarylporphyrins have shown that the barrier for meso aryl−porphyrin rotation (ΔG‡ROT) varies as a function of the core substituent M and is lower for a small metal (M = Ni) compared to a large metal (M = Zn) and for a dication (M = 4H2+) versus a free base porphyrin (M = 2H). This has been attributed to changes in the nonplanar distortion of the porphyrin ring and the deformability of the macrocycle caused by the core substituent. In the present work, X-ray crystallography, molecular mechanics (MM) calculations, and variable temperature (VT) 1H NMR spectroscopy are used to examine the relationship between the aryl−porphyrin rotational barrier and the core substituent M in some novel 2,3,5,7,8,10,12,13,15,17,18,20-dodecaarylporphyrins (DArPs), and specifically in some 5,10,15,20-tetraaryl-2,3,7,8,12,13,17,18-octaphenylporphyrins (TArOPPs), where steric crowding of the peripheral groups always results in a very nonplanar macrocycle. X-ray structures of DArPs indicate diffe...

Comparative theoretical studies of energetic substituted carbon- and nitrogen-bridged difurazans.

Abstract: Density functional theory method was used to study the heats of formation (HOFs), electronic structure, energetic properties, and thermal stability for a series of bridged difurazan derivatives with different linkages and substituent groups. The results show that the −N3 group and azo bridge (−N═N−) play a very important role in increasing the HOF values of the difurazan derivatives. The effects of the substituents on the HOMO−LUMO gap are combined with those of the bridge groups. The calculated energetic properties indicate that the −ONO2, −NO2, −NF2, −N═N−, or −N(O)═N− group is an effective structural unit for enhancing the detonation performance for the derivatives. An analysis of the bond dissociation energies for several relatively weak bonds suggests that the N−O bond in the ring is the weakest one and the ring cleavage is possible to happen in thermal decomposition. On the whole, the −NH−NH−, −N═N−, or −N(O)═N− group is an effective bridge for enhancing the thermal stability of the derivatives. Con...

Electroluminescent device containing organometallic compound with tridentate ligand

Abstract: Disclosed is an electroluminescent device comprising a cathode, an anode, and, located there between, a light emitting layer (LEL) containing a light emitting material that contains an organometallic complex comprising Pt or Pd metal and a tridentate (NNC) ligand, wherein the tridentate (NNC) ligand represents a ligand that coordinates to the metal through a nitrogen donor bond, a second nitrogen donor bond, and a carbon-metal bond, in that order, wherein at least one of the nitrogen donors is part of an aromatic ring or an imine group, and wherein the Pt or Pd atom also forms a bond to an anionic ligand group L, wherein L represents alkyl, alkenyl, aryl, or a cyano carbon, or halogen, or RX, wherein X represents a substituent that forms a bond to the Pt or Pd atom and wherein X represents N, O, S, or Se, and R represents a substituent. Such a device provides useful light emissions.