China
Africa
Explore chapters and articles related to this topic
A DFT investigation of the influence of α,β unsaturation in chemical reactivity of coumarin and some hydroxy coumarins
Published in Tanmoy Chakraborty, Prabhat Ranjan, Anand Pandey, Computational Chemistry Methodology in Structural Biology and Materials Sciences, 2017
M. A. Jaseela, T. M. Suhara, K. Muraleedharan
The other electronic effect is conjugative effect, also known as resonance or mesomeric effect. The present system deals with the electronic distributions occur in unsaturated, especially in conjugated, systems via their π orbitals. It has been observed for almost all cases, along with mesomeric effect there will also be an inductive effect with much smaller in amount than mesomeric effect as σ electrons are much less polarizable and hence less readily shifted than π electrons. The difference between this transmission of electrons via a conjugated system and the inductive effect in a saturated system is that the mesomeric effect suffers much less diminution by its transmission, and the polarity at adjacent carbon atoms alternates. The mesomeric, like inductive, the effects are permanent polarizations in the ground state of a molecule and so reflect in their physical properties.
Polyurethane Adhesives
Published in A. Pizzi, K. L. Mittal, Handbook of Adhesive Technology, 2017
Dennis G. Lay, Paul Cranley, Antonio Pizzi
Commercial catalysts consist of two main classes: organometallics and tertiary amines. Both classes have features in common, in that the catalytic activity can be described as a combination of electronic and steric effects. Electronic effects arise as the result of the molecule’s ability to donate or accept electrons. For example, in the tertiary amines, the stronger the Lewis base, generally the stronger the polyurethane catalyst. Empty electronic orbitals in transition metals allow reactants to coordinate to the metal center, activating bonds and placing the reactants in close proximity to one another.
Carboxylic Acids, Carboxylic Acid Derivatives, and Acyl Substitution Reactions
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
Bond polarization of σ-bonds leads to a so-called inductive effect, an electronic effect that is typically due to a difference in electronegativity between the atoms of that bond. What are through-bond inductive effects?
Synthesis, crystal structure, electrochemical properties, and photophysical characterization of ruthenium(II) 4,4′-dimethoxy-2,2′-bipyridine polypyridine complexes
Published in Journal of Coordination Chemistry, 2022
David A. Santos, An T. Vu, William W. Brennessel, Carly R. Reed, Robert N. Garner
The systematic optimization of complexes for increased stability in the dark and maximum ligand dissociation upon irradiation holds considerable promise for light-activated drug delivery [6, 8]. For example, the ligand dissociation quantum yield of the py (py = pyridine) ligand in [Ru(tpy)(bpy)(py)]2+ (1), where bpy = 2,2′-bipyridine, in CH3CN when irradiated with λirr. = 500 nm, is <10−4. When 6,6′-dimethyl-2,2′-bipyridine (Me2bpy) is substituted for bpy to form [Ru(tpy)(Me2bpy)(py)]2+, the ligand dissociation quantum yield increases by >1000 fold to 0.16. Here, the increased efficiency is attributed to increased steric strain caused by the methyl groups rather than the electronic effect of donating electron density [12]. Additionally, substituting electron-withdrawing groups, such as acetyl or trifluoromethyl, in the para position of the py ligand also increases the efficiency of photoinduced ligand dissociation in those complexes as compared to [Ru(tpy)(bpy)(py)]2+ [11]. The rate of photoinduced ligand dissociation of [Ru(tpy)(bpy)(4-trifluoromethypyridine)]2+ in CH3CN at λirr. = 450 nm increases 15-fold relative to [Ru(tpy)(bpy)(py)]2+ under similar conditions [11].
Therapeutical potential of metal complexes of quinoxaline derivatives: a review
Published in Journal of Coordination Chemistry, 2022
Chrisant William Kayogolo, Maheswara Rao Vegi, Bajarang Bali Lal Srivastava, Mtabazi Geofrey Sahini
The effects of Pd(II) and Cu(II) complexation of 3-aminoquinoxaline-2-carbonitrile N1,N4-dioxides on anti Trypanosoma cruz activity have been investigated by Benitez et al. [64]. The results showed complexation modifies the activity of the ligand. Excluding 107 (Figure 35), complexation with Pd (104‒106 and 108) improved the trypanosomicidal activity of the ligand 20 to 80 times. The higher anti T. cruz activity of Pd(II) complexes was ascribed to the role of electronic effect of the substituents in which the ability of negative inductive effect enhanced the bioactivity of the investigated compounds. Complexation to copper also modified the activity of the ligand, however, for some complexes (109‒111) it was increased, and for some complexes (112 and 113), it was decreased. The decrease in the activity of the copper complexes was ascribed to substituent groups playing the opposite role to that of Pd complexes [64].
Investigation of Aviation Lubricant Aging under Engine Representative Conditions
Published in Tribology Transactions, 2021
Abdolkarim Sheikhansari, Ehsan Alborzi, Christopher Parks, Spiridon Siouris, Simon Blakey
To understand the nature of the observed differences in reactivity, we next probed the steric and electronic properties of the antioxidant molecules. As can be seen in the space-filling structures in Fig. 13, the steric environment around the N-H hydrogen is very similar in both antioxidants. The hydrogen is pointing out into an open face and the approach of the radical oil species should not be impeded in either structure. The marginal difference in reactivity must therefore be attributed to an electronic effect. The radical that is forming on the nitrogen atom is immediately bound to two aryl rings. The difference arises in the DODPA structure, which has an octyl group on each ring in a para position relative to the nitrogen atom. Alkyl groups are electron donating and their presence will act to stabilize the generated nitrogen radical.