Scientific Research: Opportunities and Threats

In the first half of this talk, Dr. Ramu will present a few recent developments in chemistry, physics, and biology to set the stage for discussing the challenges and opportunities awaiting the next generation of scientists. In the second half of the talk, he will discuss some of the existential threats that we must understand and address in order to ensure that our future, both as inhabitants of this planet and as scientists engaged in fundamental research, is as secure as we can make it

Rearrangement Reactions of Lithiated Oxiranes

The first computational study of the rearrangement reactions of oxiranes initiated by lithium dialkylamides is presented. Aside from the well-known carbenoid insertion pathways, both β-elimination and α-lithiation have been suggested as the exclusive mechanism by which oxiranes react in the presence of organolithium bases. The products of the former are allyl alcohols (and, in some cases, dienes) and are ketones in the case of the latter. The computational studies reported in this work indicate that both mechanisms could be simultaneously operational. In particular, our work shows that the allyl alcohols from β-elimination are unlikely to undergo 1,3-hydrogen transfer to the vinyl alcohols and thus to the ketones, suggesting that ketones are formed through the opening of the oxirane ring after α-substitution. Elimination of LiOH from the lithiated allyl alcohol is found to result in the diene product. Low activation barriers for β-elimination are offered as the explanation for the few special cases where the allyl alcohol is the dominant or exclusive product. These findings are consistent with the product distributions observed in several experiments

Carbenoid Alkene Insertion Reactions of Oxiranyllithiums

The first computational investigations of the carbenoid reactions of α-lithiated dimethyl ether (methoxymethyllithium) and the intramolecular and intermolecular reactions of lithiated epoxides with the alkene double bond to yield cyclopropane rings are presented. These reactions represent the full spectrum of known carbenoid pathways to cyclopropanation. The reaction of Li–CH₂–O–CH₃ with ethylene proceeds exclusively through a two-step carbolithiation pathway, the intramolecular reaction of 1,2-epoxy-5-hexene follows either the carbometalation or a concerted methylene transfer pathway (the former is energetically more favorable), and the reaction of lithiated ethylene oxide (oxiranyllithium) with ethylene, the main focus of this paper, appears to proceed exclusively by the methylene transfer mechanism. In the case of these latter reactions, the free energy of activation for cyclopropanation tends to decrease with the higher aggregation states. Formation of tetramers or higher aggregates is favorable in nonpolar solvents, but in strongly coordinating solvents such as tetrahydrofuran (THF), steric factors appear to limit aggregate sizes to the dimer. In the case of 1,2-epoxy-5-hexene, consideration of competing reaction pathways provide an explanation for the observed product distribution

Structure and magnetic properties of Fe

The electronic, geometrical, and magnetic structures of iron clusters Fen substituted with a single Gd atom are studied using density functional theory with generalized gradient approximation for n = 12 − 19. An all electron basis set of a triple-ζ quality is chosen for the iron atoms whereas an effective core potential and the basis set of a triple-ζ quality are used for the Gd atom in optimizations of FenGd clusters. The lowest total energy state of a FenGd cluster was found to possess a geometrical structure where the Gd atom substitutes for a surface Fe atom of the Fen+1 cluster at given n. The total spin of a substituted cluster is larger than the total spin of the lowest total energy state of a unary iron cluster with the same number of atoms. The binding energy per atom in a substituted Fen−1Gd cluster is somewhat smaller than the binding energy per atom in a non-substituted Fen cluster. That is, the Gd substitution increases the total spin magnetic moment but destabilizes substituted iron clusters

Molecular Mechanisms for the Lithiation of Ruthenium Oxide Nanoplates as Lithium-Ion Battery Anode Materials: An Experimentally Motivated Computational Study

First-principles computational studies were used to calculate discharge curves for lithium in RuO₂ and to understand the molecular mechanism of lithium sorption into crystalline bulk RuO₂. These studies were complemented by experiments to provide new insights into the molecular mechanisms for the first and subsequent discharges of RuO₂ anodes in lithium ion batteries. RuO₂ nanoplates show slow fading of capacity over multiple cycles, retaining 76% of their original capacity after 20 cycles. The calculated discharge curves for lithium in RuO₂ lattice show qualitative agreement with experimental discharge curves for RuO₂ nanoplates. The molecular level analysis shows that an intercalation mechanism is operational until a 1:1 Li:Ru ratio is reached, which is followed by a conversion mechanism into Ru metal and Li₂O. Furthermore, in agreement with experiment, the computations predict superstoichiometric capacity of RuO₂, i.e., accommodation of lithium well beyond the stoichiometric limit of 4:1 Li:Ru ratio, and show that the additional lithium atoms reside at the interface of the Ru metal and Li₂O. This shows that the extra capacity can be explained without invoking electrolyte or solvent–electrolyte interface effects

Dissociation of Singly and Multiply Charged Nitromethane Cations: Femtosecond Laser Mass Spectrometry and Theoretical Modeling

Dissociation pathways of singly- and multiply charged gas-phase nitromethane cations were investigated with strong-field laser photoionization mass spectrometry and density functional theory computations. There are multiple isomers of the singly charged nitromethane radical cation, several of which can be accessed by rearrangement of the parent CH3–NO2 structure with low energy barriers. While direct cleavage of the C–N bond from the parent nitromethane cation produces NO2+ and CH3+, rearrangement prior to dissociation accounts for fragmentation products including NO+, CH2OH+, and CH2NO+. Extensive Coulomb explosion in fragment ions observed at high laser intensity indicates that rapid dissociation of multiply charged nitromethane cations produces additional species such as CH2+, H+, and NO22+.  On the basis of analysis of Coulomb explosion in the mass spectral signals and pathway calculations, sufficiently intense laser fields can remove four or more electrons from nitromethane