Bromine molecule explained

In the above section we describe the convenient preparation of 2-allyl-6-bromophenol without any bromine adduct. It seems that these results are not able to be explained by the mechanisms via bromine molecule, which are described later. 

These observations are explainable by a pathway in which one end of a bromine molecule becomes positively polarised through electron repulsion by the n electrons of the alkene, thereby forming a n complex with it (8 cf. Br2 + benzene, p. 131). This then breaks down to form a cyclic bromonium ion (9)—an alternative canonical form of the carbocation (10). Addition is completed through nucleophilic attack by the residual Br (or added Ye) on either of the original double bond carbon atoms, from the side opposite to the large bromonium ion Br , to yield the meso dibromide (6) ... 

Is used to explain why bromine molecules are held together in the liquid state at room temperature... 

The increased strength of London forces with increased size of molecules explains a trend in the properties of halogens. Fluorine, F2, and chlorine, CI2, which consist of relatively small molecules, are gases at room temperature and pressure. Bromine, Br2, with larger molecules and therefore stronger London forces between them, is a liquid. Iodine, I2, with still larger molecules, is a solid. 

Which is more likely to weaken or break the bond between the nitrogen atom and the bromine atom in ONBr—a violent collision between two ONBr molecules or a gentle collision between two ONBr molecules Explain. 

A mechanism that explains anti addition is one in which a bromine molecule transfers a bromine atom to the alkene to form a cyclic bromonium ion and a bromide ion, as shown in step 1 of A Mechanism for the Reaction that follows. The cyclic bromonium ion causes net anti addition, as follows. 

Even in its more complex form, collision theory does not accurately predict the reaction between metal atoms such as sodium or potassium and halogen molecules such as bromine, for example K(g) + Brjfg) KBr(g) + Br(g). As the alkali metal atom approaches the bromine molecule its valence electron moves to the bromine molecule (thus providing a harpoon ). There are then two ions with an electrostatic attraction between them. As a result the ions move together and the reaction takes place. This mechanism, which has been worked out quantitatively, explains why the reaction occurs far more readily than might be expected taking into account only mechanical collisions between the alkali metal atoms and halogen molecules. 

The formation of alkyl shifted products H and 14 can be explained in terms of the formation of endo-intermediate 21 formed by endo attack of bromine to 2 (Scheme 4). The determined endo-configuration of the bromine atom at the bridge carbon is also in agreement with endo-attack. Endo-Intermediate 21 is probably also responsible for the formation of cyclopropane products 12 and 15. The existence of cyclopropane ring in 12 and 15 has been determined by and 13c NMR chemical shifts and especially by analysis of cyclopropane J cH coupling constants (168 and 181 Hz). On the basis of the symmetry in the molecule 12 we have distinguished easily between isomers 12 and 15. Aryl and alkyl shift products IQ, H, and 14 contain benzylic and allylic bromine atoms which can be hydrolized easily on column material. 

C02-0036. If a drop of liquid bromine is placed inside a sealed flask, the entire volume above the liquid soon takes on a deep red-brown color. Explain how this demonstrates that molecules are always moving. 

Reaction of alkenes with BrCl proceeds via the intermediate [alkene-Br]+ rather than the intermediate [alkene-Cl]+. Explain using a two-orbital interaction diagram. (The structure of the complex between ethylene and BrCl in the gas phase has been determined by microwave spectroscopy. It is T-shaped, with the BrCl molecule lying perpendicular to the ethylene plane and pointing bromine-end first toward the midpoint of the C=C bond Legon, A. C. Bloemink, H. I. Hinds, K. Thorn, J. C., Chem. Eng. News, 1994 Nov. 7, 26-29.)... 

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