Prince Sebastian (St.Berchmans College, Changanacherry, India)
LinkedIn: @Prince Sebastian
Abstract: The stability and chemical reactivity of substituted benzene derivatives are largely determined by their aromatic nature. Using the Nucleus-Independent Chemical Shift at 1 Å above the ring center [NICS(1)] as an aromaticity probe, we examine how binary solvent mixtures affect the modulation of aromaticity in ortho, meta, and para-nitroaniline isomers. To simulate different solvation environments, binary mixtures comprising water, chloroform, dimethyl sulfoxide, acetonitrile, trifluroethanol, N,N-Dimethylformamide, dioxane, and tetrahydrofuran were employed. Less negative NICS(1) values in solvent combinations indicate that solvation reduces aromaticity for all three nitroaniline isomers, according to our computational analysis. Solvent-induced polarisation and hydrogen bonding effects, which affect electron delocalisation within the aromatic ring, are responsible for this decrease in aromaticity. Interestingly, the type of isomer and solvent composition affect the amount of aromaticity loss, with para-nitroaniline exhibiting the highest sensitivity to solvation effects. The reactivity and mechanism of chemical transformations involving nitroaniline derivatives may be influenced by solvent-dependent aromaticity, according to these findings, which also emphasise the critical role of solvent environment in modulating electronic properties.
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Hi Prince, great presentation. I have two questions.
1) From your data it seems like NICS(0) values in binary mixtures are often lower than the NICS(0) values for each solvent making up the mixture. Can you comment on this?
2) How are your calculated NICS values validated? Or is that the next step? -
Hi Blake,
1)Yes, our observations indicate that the NICS(0) values for binary mixtures are generally lower than those of the individual pure solvents. This suggests a decrease in aromaticity when two solvents are mixed. The possible reason for this decrease is the presence of specific intermolecular interactions, such as hydrogen bonding or other non-covalent interactions, that alter the electronic environment of the aromatic ring.
In particular, inter-hydrogen bonding appears to play a crucial role in modulating aromaticity within the mixtures. These interactions can lead to redistribution of electron density, thereby reducing the magnetic shielding experienced in the aromatic system, which manifests as a lower NICS(0) value. To further support this interpretation, we carried out AIM (Atoms in Molecules) analysis, which confirmed the presence and nature of these intermolecular interactions in the mixtures.
2)The calculated NICS values were validated by comparison with literature data, ensuring that the observed trends match previously reported results, and by verifying consistency across computational methods, confirming that variations in the computational approach did not significantly affect the trends.
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