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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.
Phenols
Published in Brian D. Fath, Sven E. Jørgensen, Megan Cole, Managing Global Resources and Universal Processes, 2020
Leszek Wachowski, Robert Pietrzak
This increased stability is a consequence of the mesomeric effect stabilizing the phenate ion owing to the delocalization of the negative charge on the aromatic ring of phenol.[1,2]
Dielectric and electro-optical properties of nematic liquid crystal p-methoxybenzylidene p-decylaniline dispersed with oil palm leaf based porous carbon quantum dots
Published in Journal of Dispersion Science and Technology, 2023
Ayushi Rastogi, Pankaj Kumar Tripathi, Tarsh Manohar, Rajiv Manohar
As demonstrated by SEM, TEM, XRD, and FTIR results presented in Rastogi and Pandey's study,[3] OPL QDs include amino group and sp2 hybridized carbon network or graphitic carbon. The inclusion of amino and nitrogen groups in OPL QDs and pure MBDA LC causes a positive mesomeric effect in the benzene ring system which results in increased electron density and enhanced PL observed for composite 5. The PL enhancement can be used in display devices that need more luminescence and, UV to visible light conversion systems.[8] The quenching in PL for composites 1 to 4 has been related to non radiative recombination of electron and hole in photo excited LCs molecules. High quenching has been observed for composite 1, whereas as the concentration of OPL QDs in MBDA increases from composites 2 to 5 the quenching in PL intensity gets reduced. Consequently, composite 5 yield high luminescence.
Steric effect of di-lateral methyl substituent on the mesophase behavior of four-ring azo/ester/azo homologues
Published in Liquid Crystals, 2022
Abdelgawad A. Fahmi, Gamal R. Saad, Mohamed H. Ali, Nagwa H.S. Ahmed
In order to assure that the lateral methyl group exerts a steric effect, we are going to compare the derivatives of the present series, In, with that of the corresponding mono-laterally methyl substituted (IIn) and laterally un-substituted (IIIn) analogues. For comparison, the terminally un-substituent homologue (X = H) was chosen to neglect the contribution of the mesomeric effect of terminal polar substituent on the mesophase thermal stability and their temperature ranges. Figure 6 displays the influence of introduction of mono- and di-lateral methyl groups into laterally neat analogues on clearing temperatures and mesophase ranges. It is clear that the introduction of lateral methyl group lowers remarkably the Tc and ΔTc. Compared with neat laterally substituted analogues, the introduction of mono- methyl lateral group decreases the Tc by about 39.4 − 17.0°C and ΔTc by 28.2 − 65.3°C and two methyl lateral groups by 58.3–87.4°C and 54.9 − 81.8°C. These observations indicate that increase of number of lateral methyl substituent leads to increase of inter-ring twist angles between the planes of the middle phenyl rings due to a steric effect and consequently to reduce π–π interaction/conjugation, thereby disrupt the packing in the crystal lattice and therefore lowers the mesophase transition temperatures and their ranges. The molecular geometry and excluded volume also affect nematic–isotropic transition temperatures of liquid crystals [58]. The reduction in Tc and ΔTc as the result of introducing mono and di-lateral methyl groups may be related to an increase of free volume.
Water Modulated Framework Flexibility in NH2-MIL-125: Highlights from 13C Nuclear Magnetic Resonance
Published in Heat Transfer Engineering, 2022
Silvia Pizzanelli, Angelo Freni, Larisa G. Gordeeva, Claudia Forte
Furthermore, the spectra show changes in the position of the signals upon water loading, the chemical shift also depending on the water loading level. The chemical shift values for each signal and for the different samples are reported in Table 2. The variation in chemical shift provides insights into the homogeneity of water distribution in the matrix and on the most hydrophylic centers. In particular, the chemical shifts gradually changed, with no contribution from the dry sample persisting at the higher hydration degrees. This indicates that water was homogeneously distributed in all the crystallites. The chemical shift of the C-2 carbon atom, which is bound to the amino group, was the most sensitive to filling level, with an upfield shift of more than 3 ppm upon complete hydration, whereas C-1, C-3 and C-5 experienced a 2 ppm downfield shift. These trends can be interpreted considering that water competes with the carboxylic oxygen for hydrogen bonding with the aminic group. Consequently, the nitrogen lone-pair is less available for conjugation with the aromatic ring and hence reduces electron density in the ortho and para positions (C-1, C-3 and C-5) according to a mesomeric effect, causing a downfield shift of the corresponding signals. On the other hand, the opposite trend of the C-2 signal is determined by an inductive effect. For the remaining signals the shift was negligible. In addition, the changes of the mentioned chemical shifts were more pronounced at low loadings and tended to level off upon increasing the hydration level. This indicates that at low fillings water molecules preferentially bind to the hydrophylic NH2 groups and thus significantly perturb their magnetic environment. Additional water molecules induce a smaller perturbation on the amino environment because they are located farther from the NH2 groups in comparison with the pre-adsorbed water molecules, with which they probably form hydrogen bonds. This pore filling mechanism was suggested to explain the S-shaped isotherms of this material [32].