- Vibrational spectra of cis and trans but-2-enes: assignments, isolated CH stretching frequencies and CH bond lengtsh
-
Infrared and Raman spectra have been obtained from 11 isotopomers of cis and trans but-2-enes in various phases (c- and t-CH3CHCHCH3, CH3CHCDCH3, CD3CHCHCD3, CD3CHCDCD3, CD3CDCDCD3; c-CH3CDCDCH3).Nearly all the fundamentals are securely assigned.Isolated CH stretching frequencies νisCH are observed or deduced from the spectra and used to predict CH bond lenghts and dissociation energies.The olefinic CH and methyl CHs bonds are stronger in the cis compound than those in the trans, in keeping with substituent effects previously observed in propene, and with molecular mechanics predictions.Comparison of νisCH values with local mode fifth overtone spectra for cis-CH3-CH=CH-CH3 indicates that the part of the latter associated with the CHa bond cannot be readily interpreted.
- McKean, D. C.,MacKenzie, M. W.,Morrisson, A. R.,Lavalley,J. C.,Janin, A.,et al.
-
-
Read Online
- Electron-Transfer Reactions and Associated Conformational Changes. Electrochemical Reduction of Some Vicinal Dibromides
-
The effect of molecular conformation on the electrochemical reduction of derivatives of trans-1,2-dibromocyclohexane (1-4) and substituted 1,2-dibromoethanes (5-8) has been investigated by low-temperature cyclic voltammetry.Reduction via conformations with antiperiplanar bromine atoms is preffered and conformational interconversion prior to electron transfer was observed in trans-1,2-dibromocyclohexane (1), 1,1-dimethyl-trans-3,4-dibromocyclohexane (2), meso- and dl-1,2-dibromo-1,2-diphenylethane (meso-5 and dl-5), and 2,3-dibromo-2,3-dimethylbutane (8).Digital simulation of the low-temperature voltammetric data has provided thermodynamic and kinetic information on the conformational interconversion in 1, 2, 5, and 8.The energy barriers to conformational interconversion in meso- and dl-2,3-dibromobutane (meso-6 and dl-6) are quite small, and conformational effects in the electrochemical reduction of 6 could not be detected at temperatures as low as -135 deg C. 1-Methyl-cis-3,trans-4-dibromocyclohexane (3), 1-methyl-trans-3,cis-4-dibromocyclohexane (4), and meso- and dl-3,4-dibromo-2,5-dimethylhexane (meso-7 and dl-7) exist almost entirely in a single conformation.Voltammetric peak potentials of 3,4,meso-7, and dl-7 reflect the geometry of their principal conformation.
- O'Connell, Kathleen M.,Evans, Dennis H.
-
-
Read Online
- Induced Fitting and Polarization of a Bromine Molecule in an Electrophilic Inorganic Molecular Cavity and Its Bromination Reactivity
-
Dodecavanadate, [V12O32]4? (V12), possesses a 4.4 ? cavity entrance, and the cavity shows unique electrophilicity. Owing to the high polarizability, Br2 was inserted into V12, inducing the inversion of one of the VO5 square pyramids to form [V12O32(Br2)]4? (V12(Br2)). The inserted Br2 molecule was polarized and showed a peak at 185 cm?1 in the IR spectrum. The reaction of V12(Br2) and toluene yielded bromination of toluene at the ring, showing the electrophilicity of the inserted Br2 molecule. Compound V12(Br2) also reacted with propane, n-butane, and n-pentane to give brominated alkanes. Bromination with V12(Br2) showed high selectivity for 3-bromopentane (64 %) among the monobromopentane products and preferred threo isomer among 2-,3-dibromobutane and 2,3-dibromopenane. The unique inorganic cavity traps Br2 leading the polarization of the diatomic molecule. Owing to its new reaction field, the trapped Br2 shows selective functionalization of alkanes.
- Hayashi, Yoshihito,Inada, Yasuhiro,Katayama, Misaki,Kikukawa, Yuji,Kitajima, Hiromasa,Seto, Kensuke,Watanabe, Daiki,Yamashita, Shohei
-
supporting information
p. 14399 - 14403
(2020/07/13)
-
- Stereochemistry of Polymethylated β,β'-Dibromoethers Formed by Bromination of Alkene-Epoxide Mixtures
-
Examination of β,β'-dibromoethers formed when bromine is added to alkene-epoxide mixtures in pentane at -78 deg C revealed that opening of the bromonium ion and the epoxide occurs under high stereochemical control, whilst approach of the epoxide and the bromomonium ion is subject to lower or no stereochemical control.
- Neill, David,Thomas, Susan E.
-
p. 2620 - 2622
(2007/10/02)
-
- Efficient Conversion of Alkyl Chlorides into Bromides
-
The convenient and selective catalytic conversion of secondary and tertiary alkyl chlorides into bromides with hydrogen bromide in the presence of small amounts of anhydrous iron(III) bromide is described.
- Yoon, K. B.,Kochi, J. K.
-
p. 1013 - 1014
(2007/10/02)
-
- A reinvestigation of the vapor phase bromination of 2-bromobutane
-
The soltuion phase photobromination of 2-bromobutane yields 2,2-dibromobutane, meso-2,3-dibromobutane, dl-2,3-dibromo-dibromobutane, small amounts of 1,2-dibromobutane, and 2,2,3-tribromobutane.However, in the corresponding vapor phase bromination these products appear along with other polybrominated products.The yield of these polybromides increases with temperature.The increase in yield of the polyhalogenated materials is rationalized by considering the thermal instabilty of the β-bromoalkyl radical, which eliminates a bromine atom to form the corresponding alkene.It is demonstrated that in the vapor phase allylic bromination competes succesfully with bromine addition.Reaction schemes are suggested to explain the formation of polybromides.An explanation is also offered for the dicrepancy between these results and those of previously reported vapor phase work.
- Tanner, Dennis D.,Ruo, Tomoki C. S.,Kosugi, Yoshio,Potter, Alan
-
p. 2310 - 2316
(2007/10/02)
-
- Free Radical Substitution. Part 38. The Effect of Solvent on the Atomic Chlorination and Bromination of 2-Substituted Butanes and the Importance of Steric Effects
-
The relative selectivity of atomic halogenation of 2-substituted butanes is influenced by the phase and by solvents.There are solvents which increase the selectivity compared with the gas phase and solvents which decrease the relative selectivity.However the most striking feature of the halogenation (especially the bromination) of 2-substituted butanes is the high reactivity of the 2-position notwithstanding very unfavourable polar effects.This reactivity is attributed to the release of steric compression associated with the abstraction of the tertiary hydrogen atom.The halogenation of butan-2-ol esters is associated with some decomposition of 2-butyl radical (OCOR)CH3> and the chlorination of 2-phenylbutane with the formation of olefins 2-phenylbut -1-ene and 2-phenylbut-2-ene.
- Atto, Saeed Y.,Tedder, John M.,Walton, John C.
-
p. 629 - 634
(2007/10/02)
-
- Two channel competitive photodecomposition reaction of gaseous bromoethane at 193.1 nm
-
The vacuum ultraviolet photolysis of gas phase bromoethane at 193.1 nm (6.42 eV) was studied over the pressure range of 1.1-303.2 Torr at room temperature using a carbon atom lamp.The pressure effect with and without inert gas, i.e., He or N2, was investigated.A scavenger effect of the reaction was also observed by adding NO as a radical scavenger.The principal reaction products were C2H6, C2H4, 1,1-C2H4Br2, and N-C4H10.The quantum yields of C2H4 and C2H6 were found to increase slightly with the reactant pressure.When the pressure of He or N2 was varied at a constant pressure of C2H5Br, however, the quantum yields of C2H4 and C2H6 were found to be pressure independent.Addition of NO completely suppressed the formation of C2H6, C2H4Br2, and C4H10, and partially reduced that of C2H4.These results were interpreted in terms of two channel competition between the molecular elimination and the formation of radicals.Two different decomposition modes were 82percent radical reaction and 18percent molecular elimination.
- Jung, Kyung-Hoon,Lee, Chong Mok,Yoo, Hee Soo
-
p. 2486 - 2489
(2007/10/02)
-
- Infrared absorption spectra of 2,2-dibromobutane
-
The possible existence of geometrically isomeric forms of the title compound, CH3CBr2-CH2CH3, has been investigated by i.r. spectroscopy.It was found that the general features of the spectra can be interpreted reasonably in terms of only one conformation of the molecules in the liquid state.Further confirmation of this view, based on a brief comparison of the liquid phase spectra of CH3CBr2-CH2CH3 and CH3CHBr-CHBrCH3 is given.Vibrational assignments have been made for most of the fundamental bands assuming Cs molecular symmetry.
- Diallo, A. O.
-
p. 687 - 690
(2007/10/02)
-
- Copper(I)-Mediated Synthesis of cis-Isoprenoids. Models for Natural Rubber
-
Two copper(I)-mediated routes for the preparation of all-cis-2,6,10-trimethyl-2,6,10-dodecatriene are investigated.Reaction of the Grignard reagent derived from 1-bromo-4-methylpent-3-ene with CuBr, and then with excess propyne, gave a vinylcopper intermediate which could be alkylated with 1-iodo-3-methylpent-3-ene, to afford the required triene stereospecifically cis- in 28percent yield.Iodination of the same intermediate and subsequent conversion to 1-bromo-4,8-dimethyl-3,7-nonadiene is shown to occur with retention of configuration, so allowing the iterative construction of cis-isoprenoids.This vinylcopper-based route is shown to be also applicable to the synthesis of larger cis-isoprenoids.In contrast, the CuI-modified coupling reaction of the Grignard reagent from 1-chloro-2-methylbut-2-ene with neryl chloride gave a mixture of triene isomers.
- Parr, William J. E.
-
p. 4101 - 4130
(2007/10/02)
-
- Gas-Phase Acid-Induced Nucleophilic Displacement Reactions. 4. A Stereochemical Probe for the Existence and the Relative Stability of Cyclic Halonium Ions in the Gas Phase
-
A comprehensive investigation on the existence and the relative stability of gaseous three-membered cyclic butene halonium ions was carried out by establishing the stereochemistry of the acid-induced displacement by nucleophilic such as H2O, H2S, etc., on a number of positively charged intermediates.The latter were obtained in the gas phase from the reaction of radiolytic formed Broensted (CH5+ and C2H5+) and Lewis (C2H5+ and CH3FCH3+) acids with 2,3-dihalobutanes.The stereoisomeric distribution of the neutral 3-halobutan-2-ols (or thiols) formed in these processes strongly implies the intermediacy of cyclic 2,3-butene halonium ions, whose stability in the gas phase depends on the nature of the halogen involved, increasing in passing from Cl to Br.No evidence for the occurrence of stable cyclic 2,3-butene fluoronium ions was obtained by the same procedure.Other factors, namely the strength of the radiolytic gaseous acid "catalysts" and the configuration of the starting dihalobutane, were found to play a role in determining the stereochemistry of the substitution processes investigated.A close correspondence does exist between the present results and those from strictly related mass spectrometric and condensed phase investigation.
- Angelini, Giancarlo,Speranza, Maurizio
-
p. 3792 - 3799
(2007/10/02)
-
- Gas-Phase Acid-Induced Nucleophilic Displacement Reactions. 5. Quantitative Evaluation of Neighboring-Group Participation in Bifunctional Compounds
-
A previous radiolytic study on the stereochemistry of gas-phase nuclephilic displacement on several classes of positively charged intermediates, formed from the attack of gaseous acids (CH5+, C2H5+, CH3FCH3+, etc.) on suitable substrates, is now completed with the assessment of the detailed mechanism and the relative extent of the other major reaction pathways accompanying them.The analysis of the stereoisomeric distribution of the neutral end products allows a quantitative evaluation of the gas-phase neighboring-group participation in such systems.A participating-group ability trend of OH >> Br >/= Cl is found, which is appreciably dependent on the nature of the leaving group and the configuration of the starting substrate.The evaluation of the adjacent-group "effective concentration" in these gaseous systems provides the first direct evidence for a gas-phase anchimerically assisted ionic reaction, involving a three-membered ring formation.The results obtained in the gas phase differ significantly from those concerning related solvolytic processes.
- Angelini, Giancarlo,Speranza, Maurizio
-
p. 3800 - 3806
(2007/10/02)
-
- Direct and Regioselective Transformation of α-Chloro Carbonyl Compounds into Alkenes and Deuterioalkenes
-
The successive treatment ethyl chloroacetate or chloroacetyl chloride with Grignard reagents and lithium powder leads to symmetrical terminal olefins in a regioselective manner.The best results are obtained with acid chlorides.The influence of the temperature and the reaction time on overall yield of the process are studied; in general, yields are increased by working at low temperature (-60 deg C).Internally substituted olefins are obtained from α-chloro acid chlorides through a similar process.The treatment of α-chloro aldehydes, ketones and carboxylic acid derivatives (esters or acid chlorides) with lithium aluminium hydride or lithium aluminium hydride/aluminium chloride and lithium powder at low temperature (-60 deg C) leads in a regioselective manner to olefins with the same carbon skeleton as the starting carbonyl compound.Reactions with lithium aluminium deuteride lead to incorporation of deuterium at predetermined positions in the alkene.
- Barluenga, Jose,Yus, Miguel,Concellon, Jose M.,Bernad, Pablo
-
p. 2721 - 2726
(2007/10/02)
-