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Greener Methods for Halogenation of Aromatic Compounds
Published in Ahindra Nag, Greener Synthesis of Organic Compounds, Drugs and Natural Products, 2022
Paola Acosta-Guzmán, Diego Gamba-Sánchez
As we mentioned before, the classic bromination of aromatics is an old known reaction, it is typically accomplished using bromine and a Lewis acid, and the major problems are the same for all EASs, leading to problems of regioselectivity of secondary brominations or brominations of substituted aromatics. In addition, when the substituent is an electron-withdrawing group (EWG), the reaction time is increased substantially or requires very harsh conditions, making it incompatible with highly functionalized molecules; a good example is the method described by Saiganesh and co-workers in 2007.14 They used a mixture of N-bromosuccinimide (NBS) and concentrated H2SO4 and were able to accomplish the bromination of deactivated aromatics at a relatively low temperature (60°C); unfortunately, this method is clearly useful for simple aromatics (Scheme 3.2), but unsuitable for complex polyfunctionalized molecules since the use of concentrated sulfuric acid will cause undesired side reactions. However, it has some green chemistry advantages since it is used as a Brønsted acid, and consequently, the residues are water soluble salts, and the succinimide can be isolated or separated from the final product.
Atomic and Molecular Origins of Color
Published in Mary Anne White, Physical Properties of Materials, 2018
The color of organic materials can be changed substantially by the presence of electron-withdrawing and/or electron-donating functional groups, as this changes the electronic energy levels. These are called auxochromes (“color enhancers”).
“Liquid crystalline compounds containing lateral thiol group: synthesis, characterisation, its mesomorphic properties and DFT studies”
Published in Liquid Crystals, 2023
Mahima Rabari, Vaibhavee Patel, A. K. Prajapati
Additionally, the even number of carbon atoms in the alkoxy tail of LSH-n (n = 4, 6, 8,10, 12, 14, and 16) seems to play a role in increasing the dipole moment of the compounds, compared to those with odd number of carbon atoms. Overall, these findings provide insights into the molecular properties of LC Schiff bases and their potential applications in the development of new mesogenic materials. The electronic properties of the molecule can also affect its polarizability [57]. For example, the presence of electron-donating or electron-withdrawing groups can alter the distribution of electrons within the molecule, leading to changes in its polarizability. Understanding the factors that influence molecular polarizability is important for predicting and interpreting the behaviour of molecules in various contexts.
Ozone treatment process for the removal of pharmaceuticals and personal care products in wastewater
Published in Ozone: Science & Engineering, 2019
N. Evelin Paucar, Ilho Kim, Hiroaki Tanaka, Chikashi Sato
The PPCPs that are poorly removed by ozonation generally contain electron-withdrawing functional groups, such as fluoro, nitro, chloro, amide, and carboxyl group (Hey et al. 2012; Hollender et al. 2009; Nakada et al. 2007). Electron withdrawing groups reduce e− density from the organic structure inhibiting electrophilic substitution reactions. Moreover, the electronegative groups are less likely to react with O3 and cause a shielding effect (Antoniou et al. 2013). Some of the easily degradable PPCPs such as diclofenac and carbamazepine also contain electron-withdrawing functional groups (amide in carbamazepine, chloro and carboxylic acid in diclofenac) but remain O3-reactive, inferring the presence of the high e− density functional groups, such as an aromatic amine (diclofenac) and C=C double bond (carbamazepine) (Nakada et al. 2007). Direct oxidation by O3 is a selective reaction in which O3 preferentially reacts with the ionized and dissociated form of organic compounds; whereas, O3 is less effective to oxidize the neutral form of compounds (Deng and Zhao 2015). Moreover, O3 reacts selectively with unsaturated bonds, aromatic systems, and amino groups (Broséus et al. 2009). Ozonation can alter the molecular structure of refractory organic compounds, turning them into compounds that are easily assimilated biologically (Bila et al. 2005).