Reactivity 3.3 Flashcards
(17 cards)
Heterolytically
Both electrons are retained by one of the bonding atoms to form ions when a covalent bond is broken
Homolytically
One electron is retained by each atom when a covalent bond is broken to form free radicals
Radical
Any chemical entity that has an unpaired electron.
Radical properties
Highly reactive, electrically neutral (due to same number of protons/electrons), have an unpaired electrons
When can hydrocarbons (alkanes) undergo reactions?
When exposed to UV light
How are halogenoalkanes formed?
Energy is supplied to a hydrocarbon by UV light, photochemical free-radical substitution reactions with halogens can be performed.
Mechanisms for free-radical substitution of alkanes
Initiation, propagation and termination
Initiation mechanism
UV light supplies energy required to break Cl-Cl bonds homolytically to form chlorine free radicals
Propagation mechanism
Chlorine free radicals react with an alkane to remove a hydrogen atom, forming HCl and propagating a free radical. Free radical is methyl radical and can continue to react and continue the propagation process
Termination mechanism
In theory the propogation process can continue forever. However it can also be terminated by the radical escaping the system, colliding with the walls of the vessel or by reacting with other radicals.
Although the relatively strong C-H bond is broken by radicals…
The H radical is never formed
Fish hook
Shows movement of an electron in propagation and termination steps
Curly arrow
Shows movement of a pair of electrons
The stronger the bond…
The higher energy (UV) is required to break
Ozone layer - how is ozone made?
Oxygen molecules absorb high energy radiation, form oxygen radicals which combine with oxygen molecules to form ozone
Steady state equilibrium between oxygen and ozone equation
3O2 –> 2 O 3
