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.

/pdf/photoremovable-protecting-groups-in-chemistry-and-biology-2n33qs6p7b.pdf

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

Matrix isolation infrared spectroscopy has been combined with MP2/aug‘-cc-pVDZ calculations to characterize the 1:1 hydrogen-bonded complexes between H2O2 and the hydrogen halides HF, HCl, and HBr....

Matrix Isolation and ab Initio Study of 1:1 Hydrogen-Bonded Complexes of H2O2 with HF, HCl, and HBr

The matrix isolation technique has been combined with theoretical calculations to identify and characterize the photoproducts in the reaction of PH3 with OVCl3 and CrCl2O2. In contrast to previous studies, HCl elimination from an initial complex is not observed. Instead, a number of product bands, some quite intense, were observed and have been assigned to phosphine oxide, H3PO, through the direct O atom transfer from the transition metal oxo compound. This identification was supported by extensive isotopic labeling, and by comparison to theoretical calculations. H3PO formed in this manner is cage-paired and interacts with the transition metal fragment (VCl3 or Cl2CrO), leading to a 113 cm-1 red-shift of the PO stretching mode relative to isolated monomeric H3PO.

Matrix isolation and theoretical study of the photochemical reaction of PH3 with OVCl3 and CrCl2O2

Chemical vapor deposition (CVD) is a widely used technique for the production of thin semiconductor films such as gallium arsenide (GaAs) and related III-V compounds. These films have applications in such diverse areas as solar energy conversion and microelectronics. The first definitive identification and infrared spectroscopic characterization of the 1:1 molecular complex of (CH{sub 3}){sub 3}Ga with AsH{sub 3} is reported. Matrix isolation is well suited to the study of transient intermediates, particularly weakly bound or reactive molecular complexes. Preliminary photochemical studies of the dissociation/rearrangement of this complex by an excimer laser operating at 193 nm are also reported.

Matrix isolation studies of chemical vapor deposition: Isolation and characterization of the trimethylgallium-arsine adduct

The matrix isolation technique combined with infrared spectroscopy has been employed to isolate and characterize hydrogen-bonded complexes between a series of substituted alkynes and several oxygen and nitrogen bases. Distinct evidence for hydrogen bond formation was observed in each case, with a characteristic red shift of the hydrogen stretching motion {nu}{sub r}. Shifts between 100 and 300 cm{sup {minus}1} were observed, the largest being for the complex of CF{sub 3}CCH with (CH{sub 3}){sub 3}N. The perturbed carbon-carbon triple bond stretching vibration was observed for most complexes, as was the alkynic hydrogen bending motion. Attempts were made to correlate the magnitude of the red shift of {nu}{sub s} with substituent constants for the different substituted alkynes; a roughly linear correlation was found with the Hammett {sigma} parameter. Lack of correlation {Delta}{nu}{sub s} with either {sigma}{sub 1} or {sigma}{sub R} alone suggests that both inductive and resonance contributions to the strength of the hydrogen-bonding interaction are important.

Infrared matrix isolation study of hydrogen bonds involving C-H bonds: Substituent effects

The 1:1 molecular complexes between SO/sub 3/ and NH/sub 3/, pyridine, and the methylamines have been isolated and characterized in nitrogen matrices. All complexes are characterized by a red shift of the SO/sub 3/ antisymmetric stretching vibration typified by the 1354-cm/sup -1/ absorption of the SO/sub 3/.NH/sub 3/ complex. In addition, the perturbed symmetric and antisymmetric deformation modes of the coordinated NH/sub 3/ were observed, and assignment was confirmed by /sup 15/N labeling. The magnitude of the red shift of nu/sub 3/ of SO/sub 3/ increased with increasing basicity of the amine from 44 cm/sup -1/ for NH/sub 3/ to 68 cm/sup -1/ for trimethylamine. In addition, the activation of the SO/sub 3/ symmetric stretching mode was observed via lowering in symmetry. While the NH/sub 3/.SO/sub 3/ complex was very sensitive to annealing, the remaining complex studies were quite stable. 31 references, 2 figures, 3 tables.

Bruce S. Ault

Papers

Matrix Isolation and ab Initio Study of 1:1 Hydrogen-Bonded Complexes of H2O2 with HF, HCl, and HBr

Matrix isolation and theoretical study of the photochemical reaction of PH3 with OVCl3 and CrCl2O2

Matrix isolation studies of chemical vapor deposition: Isolation and characterization of the trimethylgallium-arsine adduct

Infrared matrix isolation study of hydrogen bonds involving C-H bonds: Substituent effects

Infrared spectra and structure of the matrix-isolated 1:1 complexes of sulfur trioxide with ammonia and the methylamines