A scheme that reduces the calculations of ground-state properties of systems of interacting particles exactly to the solution of single-particle Hartree-type equations has obvious advantages. It is not surprising, then, that the density functional formalism, which provides a way of doing this, has received much attention in the past two decades. The quality of the energy surfaces calculated using a simple local-density approximation for exchange and correlation exceeds by far the original expectations. In this work, the authors survey the formalism and some of its applications (in particular to atoms and small molecules) and discuss the reasons for the successes and failures of the local-density approximation and some of its modifications.

The density functional formalism, its applications and prospects

N-Heterocyclic Carbenes in Late Transition Metal Catalysis

The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

The Halogen Bond

Since the discovery of organic azides by Peter Griess more than 140 years ago, numerous syntheses of these energy-rich molecules have been developed. In more recent times in particular, completely new perspectives have been developed for their use in peptide chemistry, combinatorial chemistry, and heterocyclic synthesis. Organic azides have assumed an important position at the interface between chemistry, biology, medicine, and materials science. In this Review, the fundamental characteristics of azide chemistry and current developments are presented. The focus will be placed on cycloadditions (Huisgen reaction), aza ylide chemistry, and the synthesis of heterocycles. Further reactions such as the aza-Wittig reaction, the Sundberg rearrangement, the Staudinger ligation, the Boyer and Boyer-Aube rearrangements, the Curtius rearrangement, the Schmidt rearrangement, and the Hemetsberger rearrangement bear witness to the versatility of modern azide chemistry.

Organic Azides: An Exploding Diversity of a Unique Class of Compounds

The review covers the knowledge on photoremovable protecting
groups and includes all relevant chromophores studied in the
time period of 2000–2012; the most relevant earlier works are
also discussed.

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Photoremovable Protecting Groups in Chemistry and Biology: Reaction Mechanisms and Efficacy

Infrared matrix-isolation investigation of the mono- and dithiocarbonate anions

Matrix isolation study of the photochemical reaction of cyclohexane and cyclohexene with CrCl2O2

The matrix isolation technique with twin-jet deposition has been coupled with infrared spectroscopy for the isolation, identification, and characterization of the 1:1 complexes of TiF4 with NH3 and (CH3)3N. For each of these complexes, two perturbed Ti−F stretching modes were observed to be red-shifted 40−90 cm-1 from the triply degenerate parent TiF4 mode at 792 cm-1, indicating a reduction of symmetry in the complex to at least C3v. In addition, the symmetric deformation mode of the NH3 subunit shifted 228 cm-1 to higher energy, indicating that TiF4 is a moderate strength Lewis acid. Merged jet deposition of these reagents led to no observed product in the matrix and no parent TiF4, suggesting that a reaction to form a nonvolatile product in the merged or reaction region had occurred, probably forming the very stable 1:2 complex.

Matrix Isolation Spectroscopic Study of the 1:1 Complexes of TiF4 with NH3 and (CH3)3N

Organosulfates formed from heterogeneous reactions of organic-derived oxidation products with sulfate ions can account for >15% of secondary organic aerosol (SOA) mass, primarily in submicron particles with long atmospheric lifetimes. However, fundamental understanding of organosulfate molecular structures is limited, particularly at atmospherically relevant acidities (pH = 0-6). Herein, for 2-methyltetrol sulfates (2-MTSs), an important group of isoprene-derived organosulfates, protonation state and vibrational modes were studied using Raman and infrared spectroscopy, as well as density functional theory (DFT) calculations of vibrational spectra for neutral (RO-SO3H) and anionic/deprotonated (RO-SO3-) structures. The calculated sulfate group vibrations differ for the two protonation states due to their different sulfur-oxygen bond orders (1 or 2 versus 12/3 for the neutral and deprotonated forms, respectively). Only vibrations at 1060 and 1041 cm-1, which are associated with symmetric S-O stretches of the 2-MTS anion, were observed experimentally with Raman, while sulfate group vibrations for the neutral form (∼900, 1200, and 1400 cm-1) were not observed. Additional calculations of organosulfates formed from other SOA-precursor gases (α-pinene, β-caryophyllene, and toluene) identified similar symmetric vibrations between 1000 and 1100 cm-1 for RO-SO3-, consistent with corresponding organosulfates formed during laboratory experiments. These results suggest that organosulfates are primarily deprotonated at atmospheric pH values, which have further implications for aerosol acidity, heterogeneous reactions, and continuing chemistry in atmospheric aerosols.

Acidity-Dependent Atmospheric Organosulfate Structures and Spectra: Exploration of Protonation State Effects via Raman and Infrared Spectroscopies Combined with Density Functional Theory.

Bruce S. Ault

Papers

Infrared matrix-isolation investigation of the mono- and dithiocarbonate anions

Matrix isolation study of the photochemical reaction of cyclohexane and cyclohexene with CrCl2O2

Matrix Isolation Spectroscopic Study of the 1:1 Complexes of TiF4 with NH3 and (CH3)3N

Acidity-Dependent Atmospheric Organosulfate Structures and Spectra: Exploration of Protonation State Effects via Raman and Infrared Spectroscopies Combined with Density Functional Theory.

Matrix isolation and theoretical investigation of the photochemical reaction of CrCl2O2 with benzenes substituted with electron withdrawing groups