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

The matrix reactions of alkali metal chloride salts and HCl and DCl have been investigated in argon matrices, as well as the reaction of lithium metal with HCl and DCl. From each reaction product a single intense band was observed which has been assigned to the antisymmetric stretch ν3 of the HCl2− and DCl2− anions in the M+HCl2− and M+DCl2− ion pairs. Comparisons to literature spectra, in conjunction with quartic deuterium shifts, indicate that the anion has a linear, centrosymmetric geometry in the isolated ion pair. A rough estimate for the bond strength of the hydrogen bond in this anion is 18±2 kcal/mole. Further, comparison to the spectra of earlier workers indicates that bands previously asigned to the HCl2 radical are best reassigned to the isolated HCl2− anion.

Matrix reactions of alkali metal chloride salts and HCl and DCl: Infrared spectra of the M+HCl2− and M+DCl2− ion pairs

Infrared matrix isolation study of the reaction of diborane with the methylamines

Photolysis of 3-methyl-2-phenyl-2H-azirine (1a) in argon-saturated acetonitrile does not yield any new products, whereas photolysis in oxygen-saturated acetonitrile yields benzaldehyde (2) by interception of vinylnitrene 5 with oxygen. Similarly, photolysis of 1a in the presence of bromoform allows the trapping of vinylnitrene 5, leading to the formation of 1-bromo-1-phenylpropan-2-one (4). Laser flash photolysis of 1a in argon-saturated acetonitrile (λ = 308 nm) results in a transient absorption with λmax at ∼440 nm due to the formation of triplet vinylnitrene 5. Likewise, irradiation of 1a in cryogenic argon matrixes through a Pyrex filter results in the formation of ketene imine 11, presumably through vinylnitrene 5. In contrast, photolysis of 2-methyl-3-phenyl-2H-azirine (1b) in acetonitrile yields heterocycles 6 and 7. Laser flash photolysis of 1b in acetonitrile shows a transient absorption with a maximum at 320 nm due to the formation of ylide 8, which has a lifetime on the order of several millise...

Comparison of the Photochemistry of 3-Methyl-2-phenyl-2H-azirine and 2-Methyl-3-phenyl-2H-azirine

Absorption and emission spectra of argon matrix‐isolated XeF and KrF

Matrix isolation infrared spectroscopy has been combined with MP2/6-31+G(d,p) and MP2/aug‘-cc-pVTZ calculations to characterize the 1:1 hydrogen-bonded complexes between H2O2 and bases containing phosphorus and sulfur as electron pair donor atoms. Most obvious from the spectra of the complexes HOOH:PH3, HOOH:P(CH3)3, HOOH:SH2, and HOOH:S(CH3)2 and their deuterated analogues is the shift to lower frequency of the hydrogen-bonded O−H or O−D stretching bands (νs) relative to isolated H2O2 and D2O2. The experimental shifts are in good agreement with the computed shifts. Shifted modes of both H2O2 and base subunits have been observed, along with the band for the intermolecular librational mode of each complex. Comparisons are made between the structures and spectral properties of these complexes and related complexes formed between H2O2 and corresponding N and O bases.

Bruce S. Ault

Papers

Matrix reactions of alkali metal chloride salts and HCl and DCl: Infrared spectra of the M+HCl2− and M+DCl2− ion pairs

Infrared matrix isolation study of the reaction of diborane with the methylamines

Comparison of the Photochemistry of 3-Methyl-2-phenyl-2H-azirine and 2-Methyl-3-phenyl-2H-azirine

Absorption and emission spectra of argon matrix‐isolated XeF and KrF

Matrix Isolation and ab Initio Study of 1:1 Hydrogen-Bonded Complexes of H2O2 with Phosphorus and Sulfur Bases