There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

The relatively small diffuse function-augmented basis set, 3-21+G, is shown to describe anion geometries and proton affinities adequately. The diffuse sp orbital exponents are recommended for general use to augment larger basis sets.

Efficient diffuse function‐augmented basis sets for anion calculations. III. The 3‐21+G basis set for first‐row elements, Li–F

A. Water Exchange 2326 B. Proton Exchange 2327 C. Electronic Relaxation 2327 D. Relaxivity 2331 E. Outerand Second-Sphere Relaxivity 2334 F. Methods of Improving Relaxivity 2336 V. Macromolecular Conjugates 2336 A. Introduction 2336 B. General Conjugation Methods 2336 C. Synthetic Linear Polymers 2336 D. Synthetic Dendrimer-Based Agents 2338 E. Naturally Occurring Polymers (Proteins, Polysaccharides, and Nucleic Acids) 2339

https://mriquestions.com/uploads/3/4/5/7/34572113/lauffer_1999_review.pdf

Gadolinium(III) Chelates as MRI Contrast Agents: Structure, Dynamics, and Applications

I. Introduction: Conceptual vs Fundamental andComputational Aspects of DFT1793II. Fundamental and Computational Aspects of DFT 1795A. The Basics of DFT: The Hohenberg−KohnTheorems1795B. DFT as a Tool for Calculating Atomic andMolecular Properties: The Kohn−ShamEquations1796C. Electronic Chemical Potential andElectronegativity: Bridging Computational andConceptual DFT1797III. DFT-Based Concepts and Principles 1798A. General Scheme: Nalewajski’s ChargeSensitivity Analysis1798B. Concepts and Their Calculation 18001. Electronegativity and the ElectronicChemical Potential18002. Global Hardness and Softness 18023. The Electronic Fukui Function, LocalSoftness, and Softness Kernel18074. Local Hardness and Hardness Kernel 18135. The Molecular Shape FunctionsSimilarity 18146. The Nuclear Fukui Function and ItsDerivatives18167. Spin-Polarized Generalizations 18198. Solvent Effects 18209. Time Evolution of Reactivity Indices 1821C. Principles 18221. Sanderson’s Electronegativity EqualizationPrinciple18222. Pearson’s Hard and Soft Acids andBases Principle18253. The Maximum Hardness Principle 1829IV. Applications 1833A. Atoms and Functional Groups 1833B. Molecular Properties 18381. Dipole Moment, Hardness, Softness, andRelated Properties18382. Conformation 18403. Aromaticity 1840C. Reactivity 18421. Introduction 18422. Comparison of Intramolecular ReactivitySequences18443. Comparison of Intermolecular ReactivitySequences18494. Excited States 1857D. Clusters and Catalysis 1858V. Conclusions 1860VI. Glossary of Most Important Symbols andAcronyms1860VII. Acknowledgments 1861VIII. Note Added in Proof 1862IX. References 1865

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Conceptual density functional theory.

Asymmetric enamine catalysis.

Geometrics of the radical anions of ethylene, fluoroethylene, 1,1-difluoroethylene, and tetrafluoroethylene

An entropic intermediate is defined as a free energy minimum that is not a potential energy minimum; the favorable entropy in this region of the potential surface is responsible for the increased lifetime of this species. Enabled by molecular dynamics simulations, entropic intermediates have been identified for several types of reactions, particularly pericyclic reactions. This review highlights recent advances in the mechanistic and dynamic investigations of organic and biosynthetic pericyclic reactions that involve entropic intermediates. We have proposed timing criteria to differentiate dynamically concerted from dynamically stepwise mechanisms. These criteria complement the usual definitions of concertedness based on energetics and bonding changes along the potential surface.

Mechanisms and Dynamics of Reactions Involving Entropic Intermediates

A modification of Allinger's MM2 force field has been developed to rationalize and predict the stereochemistries of intramolecular ene reactions. This force field reproduces the stereochemical trend observed for intramolecular ene reactions with unactivated enophiles, but gives poor results with activated enophiles. Ab initio molecular orbital calculations on the ene reaction of acrylonitrile with propene were performed to investigate the change in the transition structure caused by activating substituents

Force field modeling of transition structures of intramolecular ene reactions and ab initio transition structures for an activated enophile

A novel bridged [2.2.1] bicyclic phosphine oxide, devised to circumvent the waste generation and burdens of purification that are typical of reactions driven by the generation of phosphine oxides, has been prepared in three steps from commercially available cyclopent-3-ene-1-carboxylic acid. The performance of this novel phosphine oxide was superior to those of current best-in-class counterparts, as verified experimentally through kinetic analysis of its silane-mediated reduction. It has been applied successfully in halide-/base-free catalytic γ-umpolung addition-Wittig olefinations of allenoates and 2-amidobenzaldehydes to produce 1,2-dihydroquinolines with good efficiency. One of the 1,2-dihydroquinoline products was converted to known antitubercular furanoquinolines.

/pdf/bridged-2-2-1-bicyclic-phosphine-oxide-facilitates-catalytic-54aaf237t4.pdf

Bridged [2.2.1] bicyclic phosphine oxide facilitates catalytic γ-umpolung addition–Wittig olefination

Precise time trajectories and detailed reaction pathways of the Diels-Alder reaction were directly observed using accurate single-molecule detection on an in situ label-free single-molecule electrical detection platform. This study demonstrates the well-accepted concerted mechanism and clarifies the role of charge transfer complexes with endo or exo configurations on the reaction path. An unprecedented stepwise pathway was verified at high temperatures in a high-voltage electric field. Experiments and theoretical results revealed an electric field-catalyzed mechanism that shows the presence of a zwitterionic intermediate with one bond formation and variation of concerted and stepwise reactions by the strength of the electric field, thus establishing a previously unidentified approach for mechanistic control by electric field catalysis.

/pdf/electric-field-catalyzed-single-molecule-diels-alder-w12lbp70qw.pdf

K. N. Houk

Papers

Geometrics of the radical anions of ethylene, fluoroethylene, 1,1-difluoroethylene, and tetrafluoroethylene

Mechanisms and Dynamics of Reactions Involving Entropic Intermediates

Force field modeling of transition structures of intramolecular ene reactions and ab initio transition structures for an activated enophile

Bridged [2.2.1] bicyclic phosphine oxide facilitates catalytic γ-umpolung addition–Wittig olefination

Electric field-catalyzed single-molecule Diels-Alder reaction dynamics.