Benzenes bromination

As an example of Mulliken CT complexation, let us consider the benzene bromine complex, whose optimized structure and leading intermolecular NBO interaction are displayed in Fig. 5.41. NBO charge analysis of the C6H6- -B complex reveals the presence of slight CT (0.(X)21 e) from C6H6 to Br2, which is consistent with the Mulliken description. Both monomers are altered by complex formation, with the Br—Br bond NBO becoming noticeably polarized away from the benzene ring,... 

Picric acid in alcohol Benzoic acid in benzene Bromine in ether... 

Chemically, cyclooctatetraene behaves like an alkene not like benzene. Bromine, for example, does not form a substitution product but an addition product. There is something strange going on here—why is benzene so different from other alkenes and why is cyclooctatetraene so different from benzene The mystery deepens when we look at what happens when we treat cyclooctatetraene with powerful oxidizing or reducing agents. 

SPMD Anthracene, Benzene, Brominated diphenylether, Cio-13-chloroalkanes,... 

This mixing of such levels of property occurs consciously or sub-consciously even amongst teachers and professors. For example, an organic chemist might do the following as he or she explains the mechanism of an electrophilic substitution reaction, the bromination of benzene the bromine approaches the benzene (...) bromine attacks the benzene core (...) the electrons relocate and the bromine splits (...) bromobenzene results (...) a bromine has substituted a hydrogen . 

Bromo-4-methylbutyric acid 556 Isovaleric acid (8.6 moles dehydrated by azeotropic distillation with benzene), bromine (1500 g dried by shaking with 11 of concentrated H2S04), and PC13 (15 ml) are heated at 70-80° until the deep red color of bromine has disappeared from the condenser (10-20 h). More bromine (25 ml) is added and heating continued to disappearance of the red color, the oil bath temperature is raised slowly to 100-105° and kept there for 1.5-2 h, and the mixture is distilled in a vacuum. The fraction of b.p. 110-125°/ 15 mm (87.5-88.6%) is used for preparation of DL-valine. 

EXPLOSION and FIRE CONCERNS nonflammable gas, but strong oxidizer NFPA rating Health 4, Flammability 0, Reactivity 0 reacts explosively with acetylene, ether, turpentine, ammonia, fuel gas, hydrogen, and finely divided metals reacts violently with many alcohols explodes on contact with molten aluminum, ammonia, benzene, bromine pentafluoride, diborane, and many others combines with moisture to form reactive hydrogen chloride gas use water spray or fog for firefighting purposes. 

In contrast to closo-carboranes (e.g. CBuHn, l,2-C2BioHi2, ) where electrophilic substitution occurs predominantly at the most electronegative boron atoms which are opposite to the carbon vertices, the SBnHn molecule is sensitive to reaction conditions and affords either B(7) or B(12) derivatives or their mixture. Halogenation affords at lower temperatures first the 7-X-derivatives whereas at reflux in low boiling medium (benzene, bromine, tetrachloromethane) the 12-X-compounds 2, 3 and 4 are the main products (see scheme). The absence of a direct electrophilic halogenation in the B(12) position under mild conditions seems to deny a high electron density at this end of the SBnHn molecule. 

The intermediate in both reactions is a cation but the first (from cyclohexene) adds an anion while the second (from benzene) loses a proton so that the aromatic system can be restored. Notice also that neutral bromine reacts with the alkene but the cationic AICI3 complex is needed to get reaction with benzene. Bromine itself is a very reactive electrophile. It is indeed a dangerous compound and should be handled only with special precautions. Even so it does not react with benzene. It is difficult to get benzene to react with anything. 

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