16519-97-4Relevant articles and documents
Smith, D. W.,Andrews, L.
, p. 5295 - 5303 (1971)
Kinetics and mechanism of the reaction of F atoms with CH3Br
Sehested, Jens,Bilde, Merete,Mogelberg, Trine,Wellington, Timothy J.,Nielsen, Ole John
, p. 10989 - 10998 (1996)
The reaction of F atoms with CH3Br at 296 K was studied using a pulse radiolysis/transient UV absorption spectroscopy absolute technique and a FTIR relative rate technique. The rate constant for this reaction was determined to be (4.46 ± 0.22) × 10-11. The reaction proceeds via two channels, 69 ± 5%, via hydrogen abstraction giving CH2Br radicals and HF, and 31 ± 5%, to give the adduct CH3Br-F. In the FTIR system the observed rate constant was 69 ± 8% of that measured using the pulse radiolysis system because the CH3Br-F adduct falls apart to re-form the reactants. The CH3Br-F adduct reacts with NO, with a rate constant of (2.25 ± 0.14) × 10-11 cm3 molecule-1 s-1, giving FNO as a product. There was no discernible reaction of the CH3Br-F adduct with O2 and an upper limit of 6 × 10-15 cm3 molecule-1 s-1 was derived for this reaction. The CH3Br-F adduct absorbs strongly at 260-340 nm. The absorption cross section at 280 nm of the CH3Br-F adduct was (2.06 ± 0.31) × 10-17 cm2 molecule-1. A lower limit for the equilibrium constant was [CH3Br-F]/([CH3Br][F]) > 5 × 10-16 cm3 molecule-1 at 296 K. A lower limit of 12 kcal mol-1 is estimated for the binding energy of the F atom in the CH3Br-F adduct. The UV absorption spectrum of the CH2BrO2 radical was determined; at 250 nm σ = (3.4 ± 0.9) × 10-18 cm2 molecule-1.
Halogen abstraction reaction between aminoalkyl radicals and alkyl halides: Unusual high rate constants
Lalevée,Allonas,Fouassier
, p. 415 - 418 (2008)
The very high reactivity of aminoalkyl radicals toward the halogen abstraction reaction is reported for the first time. Reaction rate constants with CCl4 and CBr4 are close to the diffusion limit: they are about 4-5 orders of magnitude higher than those previously determined for typical alkyl radicals. A better understanding of this unusual behavior is obtained using molecular orbitals (MO) calculations. The participation of polar effects is directly evidenced. This approach can be useful for the design of new reducing agents.
Femtosecond photolysis of CH2Br2 in acetonitrile: Capturing the bromomethyl radical and bromine-atom charge transfer complex through deep-to-near UV probing
Pal, Suman K.,Mereshchenko, Andrey S.,El-Khoury, Patrick Z.,Tarnovsky, Alexander N.
, p. 69 - 73 (2011)
Dibromomethane (CH2Br2) in acetonitrile is a suitable precursor to characterize the absorption signatures of the CH 2Br· radical and solvent ·Br charge-transfer complexes. Following irradiation of CH2Br2 at 255 nm, the iso-H2CBrBr isomer product rapidly converts back to the parent species, and transient absorption spectra reveal the bands of solvent-separated radical species, the CH2Br· radical peaking at 235 nm, as well as the CH3CN·Br complex at 272 nm. The absorption of CH2Br· exhibits minor solvatochromic shifts upon going from acetonitrile to cyclohexane, and the molecular decadic extinction coefficient of CH3CN·Br is estimated to be 1470 M-1 cm-1.
Chemical Ionization Mass Spectrometry of Halomethanes with Tetramethylsilane as Reagent Gas
Chizhov, Oleg S.,Kadentsev, Valentin I.,Stomakhin, Andrei A.
, p. 699 - 701 (1992)
Chemical ionization mass spectra of halomethanes measured using tetramethylsilane as reagent gas exhibit three major peaks corresponding to (1+), (1+) and (MeSi)2X(1+) ions (X = Cl, Br or I).Dihalomethanes CH2X2 form the most stable silylated molecular ions, whereas in the mass spectra of tetrahalomethanes (CX4) these ions have not been detected and the ions CX3(1+) are the most abundant.Production of bistrimethylsilylhalonium ions is the most pronounced process for haloforms (CHX3).
Absolute rate constants for the reactions of Cl atoms with CH3Br, CH2Br2, and CHBr3
Kambanis,Lazarou,Papagiannakopoulos
, p. 8496 - 8502 (2007/10/03)
The rate constants for the reactions of chlorine atoms with the complete series of the three bromomethanes CH3Br (1), CH2Br2 (2), and CHBr3 (3) were measured in a very low pressure reactor, employing a microwave discharge for the generation of Cl atoms with mass spectrometric detection of reactants and products. The experiments were performed in the temperature range 273-363 K and at total pressures approximately 1 m Torr. The reactions proceed via hydrogen atom transfer leading to HCl product and the corresponding bromomethyl radicals. Their rate constant expressions are (in cm3 molecule-1 s-1): k1 = (1.66±0.14)×10-11 exp(-1072±46/T), k2 = (0.84±0.15)×10-11 exp(-911±101/T), and k3 = (0.43±0.11)×10-11 exp(-809±142/T). The activation energy of the reaction decreases with additional bromine substitution, which is attributed to the gradual weakening of the corresponding C-H bond strength. Ab initio theoretical calculations performed at the MP2/6-31++G(2d,2p) level of theory suggest C-H bond strengths for CH3Br, CH2Br2, and CHBr3 of 416.58, 407.03, and 396.60 kJ mol-1, respectively.
