MTBE (methyl tert-butyl ether), a widely used gasoline additive, is recently being scrutinized for potential environmental damage in groundwater and in the atmosphere. This study is a first-level investigation of the basic structure and properties of MTBE and various analogues, as well as an analogous class of amines, as a first step toward understanding the reactions of such species in the environment. The gas-phase structures and properties have been calculated using a variety of ab initio methods, including correlated Hartree−Fock and hybrid density functional theory methodologies. Results are discussed in light of known experimental and environmental phenomena. Accurate fundamental results are projected to aid experimental studies and provide insight into potential mechanisms of action, the latter of which will be the second level of investigation by this group. Eventual proposals of more effective gasoline additives are targeted.

This and the companion paper are dedicated to Professor Duilio Arigoni on the occasion of his 75th birthday.His steadfast work focused on the structure and biosynthesis of natural products, and mechanisms and stereochemistry of related biochemical processes, foreshadows important insights in our own investigations presented here.In this work, we present algorithmic modifications and extensions to our quantum-mechanical approach for the inclusion of solvent effects by means of molecule-shaped cavities. The theory of conductor-like screening, modified and extended for quantum-mechanical techniques, serves as the basis for our solvation methodology. The modified method is being referred to as COSab-GAMESS and is available within the GAMESS package. Our previous work has emphasized the implementation of this model by way of a distributed multipole approach for handling the effects of outlying charge. The method has been enabled within the framework of open-and closed-shell RHF and MP2. In the present work, we present a) a second method to handle outlying charge effects, b) algorithmic extensions to open-and closed-shell density-functional theory, second-derivative analysis, and reaction-path following, and c) enhancements to improve performance, convergence, and predictability. The method is now surtable for large molecular systems. New features of the enhanced continuum model are highlighted by means of a set of neutral and charged species. Computations on a series of structures with roughly the same molecular shape and volume provides an evaluation of cavitation effects.Introduction. ± In the development and refinement of continuum-solvation models (CSMs), highly accurate continuum-dielectric models are a desirable endpoint [1 ± 6]. Noncoupled iterative solute-specific shell approaches, including those of higher-order quantum-mechanical methods, such as coupled cluster [7] [8], M˘llerÀPlesset [9 ± 11], and multiconfigurational theories [12 ± 14], are now applied in this pursuit. Nonetheless, it is instructive to focus on some fine details of continuum-model implementations relevant for accurate predictions of chemical and biochemical systems, as well as in the efficiency and extensibility of CSMs. Particularly pertinent to our −COSab× model, are details that include methods to incorporate outlying-charge effects (which are mostly lost in the evaluation of E diel ) [15], nonelectrostatic components of the total solvation energy (e.g., cavitation), and self-consistency and convergence properties. As well, we have now implemented the ability to carry out open-and closed-shell densityfunctional-theory (DFT) computations, second-derivative analysis, and reaction-pathfollowing studies, which provide substantial upgrades to our model capabilities.

This and the companion paper are dedicated to Professor Duilio Arigoni on the occasion of his 75th birthday.His work on the structures of natural products and the mechanisms and stereochemistry of biochemical processes strongly influences our course of study. Non scholae sed vitae discumus.(Hydroxymethyl)acylfulvene (HMAF, irofulven; 4), a third-generation derivative of a natural product extracted from the mushroom Omphalotus illudens, is selectively toxic towards certain forms of malignant tumors. Conversion of HMAF and cognates to stable aromatic derivatives is triggered by thiol attack in vitro and in vivo. Quantum-chemical methods predict well the structure for several functionalized derivatives of irofulven as compared to known X-ray crystallographic structures. Computational reaction profiles for thiol attack and aromatic rearrangement of irofulven and illudin S, a toxin from which irofulven is derived, provide insight into HMAF×s selectivity and toxicity. Methods used include hybrid density-functional theory (HDFT), HartreeÀFock (HF), and M˘llerÀPlesset second-order perturbation theory (MP2). Solvent effects have been explored by means of the new continuum-solvation method, COSab, presented in an accompanying paper.