Bromine addition to olefins in aqueous solution (original) (raw)
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Reaction of bromine with hindered olefinic bonds
The Journal of Organic Chemistry, 1968
NOTES 1243 excess cyclopentadiene in 600 ml of n-hexane a t-78" for 52 hr gave 60 mg of colorless leaflets. This product was identified pound was proved to he V by the following spectral data and elemental analysis. The infrared spectrum (KBr pellet)
2003
quent reactions (formation of a bromonium ion and the backside attack of Br-) are hampered, as in sterically hindered,I21 cage,r31 and strainedF4] olefins. In the reaction of bromine with cy~lohexene[~~ and with (E)-2,2,3,4,5,5-he~amethylhex-3-ene[~1 in 1,2-dichIoroethane (DCE), however, the intermediacy of a second bromine-alkene z complex with a 2: 1 stoichiometry was inferred on the basis of thermodynamic evidence. There are indications that the 2: 1 complex has to be interposed between the 1 : 1 complex and the bromonium ion as an additional intermediate in electrophilic bromination (Scheme 1). Recently G. Maier and S. Senger found evidence that such a 2: 1 complex is also formed by cocondensation of ethylene with an excess of bromine in an argon matrix at 10-20 K.IS1 We now report the first direct UV-spectroscopic detection of a 2: 1 bromine-olefin complex. Theoretical investigations reveal the structure of the so far elusive species. Suitable candidates for our studies are hig...
Journal of the American Chemical Society, 1990
Abstrae The early stages of electrophilic bromination of a hindered olefin, tetraisobutylethylene (TIBE, 2), have been investigated with an aim to determining the formation constant (Kr) for the 1:l charge-transfer complex and information about the reversible formation of the corresponding bromonium ion. In dichloroethane and acetic acid at 25 OC, the respective Kr values are 9.71 (0.19) and 1.72 (0.2) M-I, while in methanol, the value can be no larger than -2.5 M-I. On the basis of the values of Kr in dichloroethane at 6, 25, and 50 OC, the thermodynamic parameters for CTC formation from TIBE + Br2 are AH = -4.07 (0.35) kcal/mol and A S = -9.20 (0.1 1) eu. TIBE reacts with bromine in acetic acid to form a double bond rearranged allylic bromide. The reaction is not consistent with a free radical process and is more consistent with one proceeding via an ionic bromonium ion intermediate. The kinetics of bromination in acetic acid at 25 OC of TIBE (2-H8) and d,-TIBE (2-D8), in which the eight allylic positions are deuterated, reveal a substantial kinetic isotope effect (KIE) of 2.3 (0.1). This value is too large for any imaginable 8-secondary KIE on the bromonium ion formation and is most consistent with a primary effect in which a CH or CD (CL) bond is removed in a rate limiting or partially rate limiting step. This step is suggested to be deprotonation of the bromonium ion which leads to formation of double-bond rearranged allylic bromide. The KIE data provide the first kinetic isotope evidence for the reversible formation of a bromonium ion. (2) (a) Brown, R. S.; Gedye, R.; Slebocka-Tilk, H.; Buschek, J.; Kopecky, K. Wieringa, J. H.; Wynberg, H. J . Chem. SOC., Chem. Commun. 1969,907-908. (b) Slebocka-Tilk, H.; Ball, R. G.; Brown, R. S. J. Am. Chem. SOC. 1985, 107, 4504-4508. ( 5 ) Bellucci. G.; Bianchini, R.; Chiappe, C.; Marioni, F.; Ambrosetti, R.; Brown, R. S.; Slebocka-Tilk, H.
The ultraviolet-visible absorption spectrum of bromine between room temperature and 440°
The Journal of Physical Chemistry, 1967
ULTRAVIOLET-VISIBLE ABSORPTION SPECTRUM OF BROMINE 937 quinones, they made no attempt to prove that the faint Health Service (Grant No. GM-10499) is most grateabsorption bands which they observed were not due to fully acknowledged. The assistance of Mr. Jess some reaction products. Long in some of the temperature-dependence studies is also acknowledged with thanks,
The Journal of Physical Chemistry A, 1999
Cavity ring-down spectroscopy (CRDS), end-product analysis, and ab initio calculations have determined absorption cross sections, rate coefficients, reaction mechanisms, and thermochemistry relevant to the addition of halogen atoms to propargyl chloride and propargyl bromide. Halogen atoms were produced by laser photolysis, and the addition reaction products were probed at a variable delay by CRDS using a second laser pulse. We report the continuum spectra of C 3 H 3 Cl 2 (1,2-dichloroallyl), C 3 H 3 ClBr (1-chloro-2-bromoallyl), and C 3 H 3 Br 2 (1,2-dibromoallyl) radicals between 238 and 252 nm and the absorption cross sections, σ 240 (C 3 H 3 -Cl 2 ) ) (4.20 ( 1.05) × 10 -17 cm 2 molecule -1 and σ 242 (C 3 H 3 Br 2 ) ) (1.04 ( 0.31) × 10 -17 cm 2 molecule -1 . When the observed data are fit to complex reaction schemes, the 298 K rate coefficients for formation of 1,2-dihaloallyl radicals at 665 Pa were found to be k(Cl + C 3 H 3 Cl) ) (1.2 ( 0.2) × 10 -10 cm 3 molecule -1 s -1 and k(Br + C 3 H 3 Br) ) (2 ( 1) × 10 -12 cm 3 molecule -1 s -1 . At 298 K and 665 Pa the self-reaction rate coefficients of these radicals were found to be k(C 3 H 3 Cl 2 + C 3 H 3 Cl 2 ) ) (3.4 ( 0.9) × 10 -11 cm 3 molecule -1 s -1 and k(C 3 H 3 Br 2 + C 3 H 3 Br 2 ) ) (1.7 ( 1.1) × 10 -11 cm 3 molecule -1 s -1 . The listed uncertainties are twice the standard deviation of individual determinations, and those for rate coefficients include the uncertainty of the appropriate absorption cross section. † NIST/NRC Postdoctoral Associate 1995-1997.
A quantum chemical investigation of electrophilic addition reaction of bromine to benzonorbornadiene
Journal of Molecular Structure-theochem, 1999
Full geometric optimization of bicyclo[3.2.2lnona-6,8-diene (BND) has been done by semiempirical and ab initio methods and the structure of the molecule has also been investigated. The double bond (I) situated in the opposite direction of methylene group in END molecule is more exo pyramidalized than the other double bond (II). The electron density (qj,HOMO) of the double bond(l) in HOMO of the molecule is more than that of the (II) double bond. Exo and endo faces of exo pyramidalized double bonds of the molecule are not equal and electron density is higher in elldo faces. The molecular complexes of BND with bromine have been investigated by AM 1 method and their stable configurations determined. The reason for endo molecular complexes being more stable than exo is that the stability is caused by electronic and steric factors. Because of electronic factors, BND ... Br2(endo I) complex is more stable than BND. .. Br2 (elldo 2). The endo-bridged bromonium cation(I) is relatively more stable than the elldo-bridged cation(IV). Endo-facial stereoselectiv ity and regioselectivity should be observed in the addition of bromine to BND molecule. Endo-facial stereoselectivity is caused by electronic and steric effects, regioselectivity by electronic effects. The rearranged bromocarbonium cation(V) is the most stable among the cationic intermediates and the ionic addition reaction occurs via this cation.
Journal of Molecular Modeling, 2015
The present work provides sets of correction factors to adjust the calculated vibrational frequencies of a series of α, ω-diamines hydrochloride salts to account for the intermolecular interactions with the counterion. The study was performed using different theory levels for predicting the vibrational data of isolated dicationic α,ω-diamines and their hydrochloride forms, with and without the explicit account of the interactions with the chloride counterions. Different sets of correction factors were determined for each theory level considering the four smallest elements for the α,ω-diamines series, while their transferability and reliability was evaluated considering the larger elements of the series. The theory level simplification was also evaluated and was found to neither compromise the vibrational frequencies estimates nor the magnitude and accuracy of the pre-defined scaling factors. This suggests that transferability of the correction factors is possible not only for different diamines but also between different levels of theory with the averaged group correction factor, ζ g a , being the best choice to account for the effects of the N-H•••Cl interactions. The possibility of simplifying the theory level without compromising efficiency and accuracy is additionally of utmost importance. This computational approach can constitute a valuable tool in the future for studying the hydrochloride forms of larger and more complex diamine systems.
ChemInform Abstract: Use of Bromine and Bromo-Organic Compounds in Organic Synthesis
ChemInform, 2016
Bromination is one of the most important transformations in organic synthesis and can be carried out using bromine and many other bromo compounds. Use of molecular bromine in organic synthesis is well-known. However, due to the hazardous nature of bromine, enormous growth has been witnessed in the past several decades for the development of solid bromine carriers. This review outlines the use of bromine and different bromo-organic compounds in organic synthesis. The applications of bromine, a total of 107 bromo-organic compounds, 11 other brominating agents, and a few natural bromine sources were incorporated. The scope of these reagents for various organic transformations such as bromination, cohalogenation, oxidation, cyclization, ringopening reactions, substitution, rearrangement, hydrolysis, catalysis, etc. has been described briefly to highlight important aspects of the bromo-organic compounds in organic synthesis.