Why is Br more selective than CL?
Bromination of alkanes occurs by a similar mechanism, but is slower and more selective because a bromine atom is a less reactive hydrogen abstraction agent than a chlorine atom, as reflected by the higher bond energy of H-Cl than H-Br.
Why is chlorine reactive not selective?
1 Answer. Ernest Z. Chlorination is less selective than bromination because chlorination has smaller differences in activation energy for attack at 1°, 2°, and 3° positions. Consider the halogenation of propane at the 1° and 2° positions.
What is the selectivity ratio of chlorine?
This gives us a ratio of 55:15 , or 3.66. So for this reaction, the free radical chlorination of propane at 25°C, chlorine is 3.66 times more selective for secondary hydrogens than for primary hydrogens.
Which halogenation is most selective?
Bromination is 1640 times more likely to occur at a 3o position than 1. Chlorination is 5.2 times more likely to occur at a 3o position than 1. Bromination is more selective than chlorination.
Is chlorination more or less selective than bromination?
The Transition State For Chlorination Resembles The Reactants (An “Early” Transition State) Which Are Close Together In Energy. So Selectivity Is Low. The Transition State For Bromination Resembles The Products (A “Late” Transition State) Which Are Farther Apart In Energy. So Selectivity Is High.
Is chlorine or bromine more electrophilic?
Group 7 elements need to gain electrons to react. Chlorine has less electron shells than bromine and this lack of shielding makes it easier for chlorine to gain electrons. Therefore, chlorine is more reactive.
Is chlorination or bromination more selective?
Is bromine more reactive than chlorine?
Because chlorine is more reactive than bromine, it displaces bromine from sodium bromide. The solution turns brown.
Where is bromination most likely to occur?
Bromination is 1640 times more likely to occur at a 3o position than 1. Chlorination is 5.2 times more likely to occur at a 3o position than 1….
| Br | Cl | |
|---|---|---|
| 1o | 1 | 1 |
| 2o | 82 | 3.9 |
| 3o | 1640 | 5.2 |
How is chlorination different from bromination?
We’ll do the math in a second, but the key difference is that in chlorination, the key propagation step is exothermic and in bromination, the key propagation step is endothermic. This is because chlorination forms a strong H-Cl bond (103 kcal/mol) and bromination forms a much weaker H-Br bond (87 kcal/mol).
What is the principle of selectivity?
A qualitative statement of reactivity–selectivity principle is that highly reactive species are unselective in their choice of reactants compared to stable and, therefore, unreactive species.
Which catalyst is used in chlorination?
C1-symmetric amino sulfoximine–copper complex 23 has been used as chiral catalyst in chlorination reactions of β-keto esters in the presence of NCS as a source of electrophilic chlorine (entry 6, Table 1).