Outcome-changing effect of polarity reversal in hydrogen-atom-abstraction reactions

We have examined hydrogen-atom-abstraction reactions for combinations of electrophilic/nucleophilic radicals with electrophilic/nucleophilic substrates. We find that reaction between an electrophilic radical and a nucleophilic substrate is relatively favorable, and vice versa, but the reactions between a radical and a substrate that are both electrophilic or both nucleophilic are relatively unfavorable, consistent with the literature reports of Roberts. As a result, the regioselectivity for the abstraction from a polar substrate can be reversed by reversing the polarity of the attacking radical. Our calculations support Roberts' polarity-reversal-catalysis concept and suggest that addition of a catalyst of appropriate electrophilicity/nucleophilicity can lead to an enhancement of the reaction rate of approximately 5 orders of magnitude. By exploiting the control over regioselectivity associated with the polar nature of the radical and the substrate, we demonstrate the possibility of directing the regioselectivity of hydrogen abstraction from amino acid derivatives and simultaneously providing a significant rate acceleration.

Gas-phase structure and reactivity of the keto tautomer of the deoxyguanosine radical cation

Gas-phase IR spectroscopy, ion–molecule reactions, collision-induced dissociation and computational chemistry in combination form a powerful tool to gain insights into the structure of one-electron oxidised guanine in DNA and its resultant chemistry.

Hydrogen from formic acid through its selective disproportionation over sodium germanate--a non-transition-metal catalysis system

A robust catalyst for the selective dehydrogenation of formic acid to liberate hydrogen gas has been designed computationally, and also successfully demonstrated experimentally. This is the first such catalyst not based on transition metals, and it exhibits very encouraging performance. It represents an important step towards the use of renewable formic acid as a hydrogen-storage and transport vector in fuel and energy applications.

W3X: A Cost-Effective Post-CCSD(T) Composite Procedure

We have formulated the W3X procedure by incorporating cost-effective post-CCSD(T) components (up to the CCSDT(Q) level) into the W1X-1 protocol, the latter representing a recently reported economical yet accurate approximation to CCSD(T)/CBS. For medium-sized systems, W3X is moderately more computationally demanding than W1X-1, but it is significantly less costly than the W3.2lite and (especially) W3.2 procedures. Because of the use of the cost-effective W1X-1 method as the underlying CCSD(T) component, W3X is also less expensive than the W2.2 protocol, which does not incorporate post-CCSD(T) excitations. We find that, for single-reference systems (the G2/97 set and most of the W4-11 set), W3X is comparable in accuracy to the underlying W1X-1 protocol, as might have been expected. For the more challenging cases of the multireference systems within the W4-11 set, the dissociation of F2 and the automerization of cyclobutadiene, W3X provides improved performance compared with the CCSD(T)-based procedures (W1X-1 and W2.2). Highly multireference chromium oxides CrO, CrO2, and CrO3 are still somewhat challenging for W3X (and even for the higher-level W3.2lite and W3.2 procedures), but the inclusion of the economical post-CCSD(T) terms in W3X already leads to a significant improvement over W1X-1. Thus, W3X provides a cost-effective means for treating systems with significant (but perhaps not excessive) multireference character that are otherwise not well-described by CCSD(T)-based methods.