BITS Faculty Publications
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Item Local Softness and Hardness Based Reactivity Descriptors for Predicting Intra- and Intermolecular Reactivity Sequences: Carbonyl Compounds(ACS, 1998) Roy, Ram KinkarThe DFT-based reactivity descriptors “local softness” and “local hardness” are used as reactivity indices to predict the reactivity sequences (both intramolecular and intermolecular) of carbonyl compounds toward nucleophilic attack on them. The finite difference approximation is used to calculate local softness, whereas local hardness is approximated by −Vel/2N, where Vel is the electronic part of the molecular electrostatic potential. Both aldehydes and ketones, aliphatic and aromatic, have been selected as systems. Critical cases, e.g., C6H5CHCHCHO, CH3CHCHCHO, and CH2CHCHO, where a CC double bond is in conjugation with the CO group, are also considered. Two new reactivity descriptors are proposed, “relative electrophilicity” (sk+/sk-) and “relative nucleophilicity” (sk-/sk+), which will help to locate the preferable reactive sites. Our results show that local hardness can be used as a guiding parameter when constructing intermolecular reactivity sequences.Item A Simple Model to Predict Preferable Aldol Products from Unsymmetrical Ketones Using Local Hard−Soft Acid−Base Concept(ACS, 2001) Roy, Ram KinkarUnsymmetrical ketones produce two types of enolate intermediates upon deprotonation, which are known as “less substituted” and “more substituted” ones. The major final aldol product will depend on which one of these two enolate intermediates is more reactive toward the incoming reactant (i.e., aldehyde in the case of aldol condensation reaction) in the next stage of the reaction. As here the active sites belong to two different chemical systems, “local hardness” values are reported to be more reliable (Langenaeker et al. J. Phys. Chem. 1995, 99, 6424, and Roy et al. J. Phys. Chem. 1998, 102, 3746) to predict the intermolecular reactivity order of these two intermediates. But in this article we have proposed a very simple model which simultaneously represents both kinds of enolate intermediates. So the present study can be considered as a first one in which an intermolecular problem has been recasted as an intramolecular one, and thus “local softness” and related reactivity descriptors have been used, instead of the “local hardness”, to predict the intermolecular reactivity orders. The generated results show that the model works at satisfactory level.Item A Simple Model to Predict Preferable Aldol Products from Unsymmetrical Ketones Using Local Hard−Soft Acid−Base Concept(ACS, 2001) Roy, Ram KinkarUnsymmetrical ketones produce two types of enolate intermediates upon deprotonation, which are known as “less substituted” and “more substituted” ones. The major final aldol product will depend on which one of these two enolate intermediates is more reactive toward the incoming reactant (i.e., aldehyde in the case of aldol condensation reaction) in the next stage of the reaction. As here the active sites belong to two different chemical systems, “local hardness” values are reported to be more reliable (Langenaeker et al. J. Phys. Chem. 1995, 99, 6424, and Roy et al. J. Phys. Chem. 1998, 102, 3746) to predict the intermolecular reactivity order of these two intermediates. But in this article we have proposed a very simple model which simultaneously represents both kinds of enolate intermediates. So the present study can be considered as a first one in which an intermolecular problem has been recasted as an intramolecular one, and thus “local softness” and related reactivity descriptors have been used, instead of the “local hardness”, to predict the intermolecular reactivity orders. The generated results show that the model works at satisfactory level.