Heterolytic and Homolytic Cleavage

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In summary, heterolytic cleavage can occur in both aqueous and non-aqueous solutions, but is often disfavored due to energetic considerations. Homolytic cleavage can generate unstable radicals, but the bond dissociation energy must be overcome to initiate the cleavage.
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andyrk
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When heterolytic cleavage occurs, an anion and a cation are formed. Why don't they get attracted towards each other to form an ionic bond? And does this cleavage occur in an aqueous solution or just by itself?

Similarly, when homolytic cleavage occurs, none of the atoms produced have a complete octet as before. So why did the cleavage occur?
 
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andyrk said:
When heterolytic cleavage occurs, an anion and a cation are formed. Why don't they get attracted towards each other to form an ionic bond? And does this cleavage occur in an aqueous solution or just by itself?
They do attract. Generally, though, something keeps them from recombining. In solution, solvent molecules can form a complex around the newly formed ions called a solvent shell. Even without solution, heterolytic cleavage can still happen, but it's often disfavored energetically because, as you have pointed out, you have to get the fragments far enough away from each other that they don't react immediately.
andyrk said:
Similarly, when homolytic cleavage occurs, none of the atoms produced have a complete octet as before.
Homolytic cleavage of a bond in a closed-shell species (a "normal" chemical compound that obeys the octet rule or otherwise has a complete valence shell without unpaired electrons) generates radicals, which are species with unpaired electrons, or (sticking with the octet rule) unfilled octets. Just because a compound no longer obeys the octet rule doesn't mean it doesn't exist. But the octet rule does allow you to predict that radicals are generally unstable and reactive--although there are exceptions here as well.
andyrk said:
So why did the cleavage occur?
A bond doesn't usually cleave spontaneously. A chemical bond in equilibrium represents a minimum in potential energy, so that to break the bond requires adding energy to the system. So to break a bond, you pump energy into it to push the two fragments apart. For each extra unit of length you stretch the bond, the amount of extra energy required gets a little less until you asymptotically approach what's known as the bond dissociation energy. This is the amount of energy required to separate the fragments by an infinite distance (which is a pretty good definition for a broken bond).
 

1. What is the difference between heterolytic and homolytic cleavage?

Heterolytic cleavage is a type of bond dissociation in which the electrons involved in the bond are not equally shared between the two atoms, resulting in the formation of ions. Homolytic cleavage, on the other hand, is a type of bond dissociation in which the electrons involved in the bond are equally shared between the two atoms, resulting in the formation of free radicals.

2. How does heterolytic cleavage occur?

Heterolytic cleavage can occur through the action of a polar solvent or a strong electron-withdrawing group, which can pull the shared electrons towards one atom, causing the bond to break and resulting in the formation of ions.

3. What is the significance of heterolytic and homolytic cleavage in organic chemistry?

Heterolytic and homolytic cleavage play a crucial role in organic chemistry as they are involved in various chemical reactions such as substitution, addition, and elimination reactions. These reactions are essential in the synthesis of new compounds and the study of reaction mechanisms.

4. Can heterolytic and homolytic cleavage occur in the same molecule?

Yes, it is possible for both heterolytic and homolytic cleavage to occur in the same molecule. This can happen when there are different types of bonds present in the molecule, and each bond is subjected to different conditions that favor either heterolytic or homolytic cleavage.

5. How do chemists control whether heterolytic or homolytic cleavage occurs in a reaction?

Chemists can control whether heterolytic or homolytic cleavage occurs in a reaction by manipulating the reaction conditions such as temperature, solvent, and the presence of certain catalysts. They can also design molecules with specific functional groups that favor one type of cleavage over the other.

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