Topic
Halogen
About: Halogen is a research topic. Over the lifetime, 6789 publications have been published within this topic receiving 110903 citations. The topic is also known as: group 17 elements & halogens.
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TL;DR: It is demonstrated that a halogen bond formed between a brominated uracil and phosphate oxygen can be engineered to direct the conformation of a biological molecule, in this case to define the conformational isomer of a four-stranded DNA junction when placed in direct competition against a classic hydrogen bond.
Abstract: The halogen bond, a noncovalent interaction involving polarizable chlorine, bromine, or iodine molecular substituents, is now being exploited to control the assembly of small molecules in the design of supramolecular complexes and new materials. We demonstrate that a halogen bond formed between a brominated uracil and phosphate oxygen can be engineered to direct the conformation of a biological molecule, in this case to define the conformational isomer of a four-stranded DNA junction when placed in direct competition against a classic hydrogen bond. As a result, this bromine interaction is estimated to be ≈2–5 kcal/mol stronger than the analogous hydrogen bond in this environment, depending on the geometry of the halogen bond. This study helps to establish halogen bonding as a potential tool for the rational design and construction of molecular materials with DNA and other biological macromolecules.
329 citations
TL;DR: Computational evidence is provided that fluorine does have the capability of forming halogen bonds, if R is sufficiently electron withdrawing, and it is shown how the computed electrostatic potentials can provide guidance in selecting appropriate halide/base pairs.
Abstract: In some halides RX, the halogen X has a region of positive electrostatic potential on its outermost portion, centered around the extension of the R−X bond. The electrostatic attraction between this positive region and a lone pair of a Lewis base is termed halogen bonding. The existence and magnitudes of such positive potentials on some covalently bonded halogens, and the characteristic directionality of the interaction, can be explained in terms of the degree of sp hybridization and polarizability of X and the electronegativity of R. Halogen bonding increases in strength in the order Cl < Br < I; fluorine is frequently said to not form halogen bonds, although a notable result of the present study is computational evidence that it does have the capability of doing so, if R is sufficiently electron withdrawing. An increasingly important application of halogen bonding is in the design of new materials (e.g., crystal engineering). In this paper, we present the calculated energies of a series of halogen-bonding interactions that could be the basis for forming linear chains, of types X----X----X---- or X----Y----X----Y----. We focus upon chlorides and bromides, and nitrogen bases. The B3PW91/6-311G(3df,2p) and MP2/6-311++G(3df,2p) procedures were used. We show how the computed electrostatic potentials (B3PW91/6-31G**) can provide guidance in selecting appropriate halide/base pairs.
325 citations
TL;DR: It was found that, depending on the nature of the Au catalyst used, either selective bromine migration or hydrogen shift occurs, leading to the formation of 3- or 2-bromofurans, respectively, in haloallenyl ketones.
Abstract: Selective 1,2-iodine, bromine, and chlorine migration in haloallenyl ketones in the presence of Au catalyst has been demonstrated. It was found that, depending on the nature of the Au catalyst used, either selective bromine migration or hydrogen shift occurs, leading to the formation of 3- or 2-bromofurans, respectively. Halirenium intermediate was proposed for the unusual 1,2-halogen migration. This cascade transformation allows for mild and efficient synthesis of various types of 3-halofurans.
315 citations
Patent•
15 Feb 2006
TL;DR: In this paper, the pyrazole carboxylic acid anilides of formula (I) were defined, in which the variables have the following meanings: n is zero or 2; m is 2 or 3; X 1 represents fluorine or chlorine; X 2 represents halogen; X 3 represents hydrogen, methyl or ethyl; W represents O or S; with the provision that if: a) W = O, R1 = methyl, and R3 represents hydrogen.
Abstract: The invention relates to pyrazole carboxylic acid anilides of formula (I), in which the variables have the following meanings: n is zero or 2; m is 2 or 3; X1 represents fluorine or chlorine; X2 represents halogen, Y represents CN, NO2, C1-C4 alkyl, C1-C4 alkyl halide, methoxy or methylthio; p is 0 or 1; R1 represents fluorine, chlorine, bromine, C1-C4 alkyl and C1-C4 alkyl halide; R2 represents hydrogen or halogen; R3 represents hydrogen, methyl or ethyl, and; W represents O or S; with the provision that if: a) W = O, R1 = methyl, and R3 represents hydrogen, R2 does not represent fluorine or; b) W = O, n = 0, m = 2, p = 0, and R2 and R3 represent hydrogen, R1 does not represent trifluoromethyl or difluoromethyl. The invention also relates to a method for producing these compounds, to agents containing them, and to a method for using them for controlling pathogenic fungi.
311 citations
TL;DR: In this article, the absorption spectrum of gaseous fluoride ion has been observed in shock-heated vapors of CsF, RbF, and KF and the electron affinity determined from the low-energy threshold is 3.448±0.005 eV.
Abstract: The absorption spectrum of gaseous fluoride ion has been observed in shock‐heated vapors of CsF, RbF, and KF. The spectrum is a continuum with two sharp thresholds at 3595 and 3542 A, similar to those of the other halide ions. The electron affinity determined from the low‐energy threshold is 3.448±0.005 eV. The cross‐section for photodetachment at 3565 A is about 2.5±2×10−18 cm2 and at 3525, about 3.3±2×10−18 cm2. The electron affinities of chlorine, bromine and iodine are revised, respectively, to 3.613, 3.363, and 3.063 eV, all with uncertainties of 0.003 eV.
297 citations