Deuterium bromide addition

According to Cram 88a>, the stereochemical course of several polar addition and substitution reactions at the bridge position of the [2.2]-paracyclophane system is best explained on the basis of a species similar to 96 Reaction of [2.2]paracyclophane-l-ene (32) with bromine or deuterium bromide is postulated to lead exclusively to the cis-addition products 97 and 99, which retain configuration on acetolysis. The reaction of cis-l,2-dibromo[2.2]paracyclophane (cis- 97) with lithium bromide in... 

Cabaleiro and Johnson (1967) report that the addition of chlorine to -methyl cinnamate in chloroform or acetic acid is syn-selective, SS 0-75, in chloroform and acetic acid acetoxychloro derivatives are produced as well. Again, Dewar and Fahey (1964) argue that the normal course of addition of hydrogen halides onto olefins is a polar electrophilic process involving classical carbonium ions as intermediates and leading mostly but not exclusively to cis-adducts. A syn-preference was found in the additions of deuterium bromide to acenaphthylene, indene, and cis- and fraws-phenylpropene. In the case of indene, phenylpropene and methyl cinnamate, which are styrene analogs, concerted syn addition is symmetry-allowed (see bottom of p. 273). 

The additions of HCl or HBr to norbornene are interesting cases because such factors as the stability and facile rearrangement of the norbornyl cation come into consideration. (See Section 4.4.5 to review the properties of the 2-norbornyl cation.) Addition of deuterium bromide to norbornene gives ejco-norbornyl bromide. Degradation to locate the deuterium atom shows that about half of the product is formed via the bridged norbornyl cation, which leads to deuterium at both the 3- and 7-positions. ° The exo orientation of the bromine atom and the redistribution of the deuterium indicate the involvement of the bridged ion. 

Deuterium bromide is obtained from D20 and thionyl bromide15 in the same way (for preparation of liquid DBr from the elements see Kalinatchenko et al.16). Its addition to carbon-carbon multiple bonds has been used mainly for the preparation of various deuterium-labeled halogeno-ethanes and -ethyl-enes,4a 17,18 for not only is the DBr readily added but also the bromine can be removed selectively from the products e.g. ... 

The addition of deuterium bromide to both cis- and tra s-2-butene proceeds in a stereospecific trans manner at low temperature. The dx-olefin yields three while the trans gives the eryihro bromide. Similarly, the addition of HBr to isomeric 2-bromo-2-butenes is stereospecific at low temperature and in excess of HBr. The stereospecificity decreases as the temperature of the reaction is increased. At room temperature, both olefins yield the same mixture of products. Goering and Larsen first suggested that two different conformations are involved as intermediates from ds- and trons-olefins. The lifetime of these two conformations is so short that they cannot interconvert prior to the chain transfer step, which takes place from the less hindered side. At room temperature, however, these can obtain equilibrium rapidly because of easy C-C bond rotation, which results in the same mixture of meso- and d,l-2,3-dibromobutanes. Another reason may be that the addition of bromine radical (Br ) to noncyclic olefins is often reversible and may lead to nonstereospecific products. The second mechanism assumes a tr-complex formation between olefin and HBr. A bromine atom then collides with the complex leading to its attachment and simultaneous breaking of the HBr bond, which explains the decrease in stereospecificity with rising temperature (Scheme 4.53). 

Attempted Grignard reaction of cyclohexanone with test-butylmagnesiu 1 n bromide gives only about 1% yield of the expected addition product along with 99% tin reacted cyclohexanone. If D30+ is added to the reaction mix l ure after a suitable period, however, the "un reacted" cyclohexanone is found to have one deuterium atom incorporated into it. Explain. 

As shown in Section 25A, the components of infrared instruments differ considerably in detail from those in ultraviolet and visible instruments. Thus, infrared sources are heated solids rather than deuterium or tungsten lamps, infrared gratings are much coarser than those required for ultraviolet/visible radiation, and infrared detectors respond to heat rather than photons. In addition, the optical components of infrared instruments are constructed from polished solids, such as sodium chloride or potassium bromide. 

When dibenzotricyclo[3.3.0.0 ]octadiene (47) was reacted with hydrogen bromide in di-chloromethane, the C2-C8 bond was cleaved. This addition across the cyclopropyl bond occurred in a cis orientation as shown in an experiment with a deuterium-labeled starting material. 

The effect of deuterium in The species, which is reduced in the catalytic cycle described above, need not be an alkyl halide, but may just as well be an easily reduced carbonyl compound like benzophenonc. Kharasch showed in 1941 [91] that though nicthylmagnesium bromide normally adds to benzophenone producing methylbenzhydrol in high yield, the addition of a few per cent of ferric chloride led to the production of henzopinacol instead of the addition product ... 

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