A free radical is an atom or group with an unpairedelectron
The halogenoalkanes are a homologous series of saturated carbon compounds containing one or more halogen atoms
Halogenoalkanes are used as refrigerants, propellants, solvents, flame retardants, anaesthetics and pharmaceuticals
The C–X bond (X being the halogen) in halogenoalkanes is polar because the halogen atom is more electronegative than the C atom
The halogenoalkanes are insoluble or only very slightly soluble in water
Halogenoalkanes are soluble in organic solvents and due to their ability to mix with other hydrocarbons are used extensively as dry cleaning fluids and degreasing agents
Steps in free radical substitution:
Initiation
Propagation
Termination
Step 1. Initiation
The molecules of chlorine absorb energy from UV light and the Cl-Cl covalent bond breaks symmetrically. Each atom from the bond leaves with one electron from the shared pair of electrons. Twochlorine atoms are formed. Each atom has an unpaired electron in the outer shell.
They are called freeradicals and are extremely reactive
Step 2. Propagation
The highly reactive chlorine free radicals, Cl●, react with the methane molecules forming hydrogen chloride gas and leaving a methyl free radical, ●CH3. In turn the methyl free radical reacts with a second chlorine molecule forming chloromethane, CH3Cl, and another chlorine free radical. This continuing process of producing free radicals is known as a chainreaction.
The continuing process of producing free radicals is known as a chainreaction
In order for the reaction to stop twofreeradicals must collide and react to form a molecule
Halogenoalkanes are the organic product of the photochemical reaction of the halogens with alkanes in UV light.
They are produced via a freeradicalsubstitution mechanism in a chain reaction
A nucleophile is an electron pair donor
The carbon–halogen bond is polar due to the difference in electronegativity between the carbon atom and the halogen atom
The nucleophiles we learn about are:
hydroxide ions
cyanide ions
ammonia
Conditions for the reaction of halogenoalkanes with an aqueous solution of hydroxide ions
Dissolve in a smallvolume of ethanol
Add an aqueous solution of sodium hydroxide
Refluxgently
The rate of the nucleophilic substitution of the halogenoalkanes depends on the ease of breaking the carbon–halogen bond
Conditions for the reaction of halogenoalkane with an aqueous solution of cyanide ions:
Dissolve in a small volume of ethanol
Add an aqueous solution of potassiumcyanide
Refluxgently
Conditions for the reaction of halogenoalkane with a concentrated solution of ammonia:
Dissolve in a small volume of ethanol
Add a concentrated solution of ammonia in excess
In a sealed container under pressure
amine names!!!
A) primary amine
B) secondary amine
C) tertiary amine
An elimination reaction is one in which a small molecule is removed from the organiccompound
A halogenoalkane is a halogenated alkane. This means that one (or more) of the hydrogen atoms in an alkane has been replaced by a halogen atom.
Properties of halogenoalkanes
Halogenoalkanes are polar molecules and contain polar bonds. The polar bonds are important in their reactions.
Because halogens are more electronegative than carbon, the carbon atoms carry a partial positive charge and the halogen atoms carry a partial negative charge.
Halogenoalkanes undergo substitution reactions with ammonia, hydroxide ions, and cyanide ions.
A nucleophile is an electronpairdonor that is attracted to a nucleus.
Nuclei have positive charges, so nucleophiles tend to be negatively charged.
Molecules with lone pairs are also nucleophilic.
An electrophile is a molecule that is attracted to a pair of electrons.
Electrons have negative charges, so electrophiles tend to be positively charged.
The mechanism for nucleophilic substitution with hydroxide ions makes an alcohol
Nucleophilic substitution can be used to make amines with ammonia
With cyanide ions, nucleophilic substitution can be used to make nitriles
Elimination reactions form alkenes
Hydroxide reacting with a halogenoalkane can either eliminate to produce an alkene or substitute to produce an alcohol.
To promote the elimination reaction, we can:
Use ethanol as the solvent rather than water
Heat the reaction under reflux conditions
Reflux involves using a reflux condenser to condense gases back into the reaction flask.
In the elimination mechanism, the hydroxide is behaving more like a base than a nucleophile
A CFC is a chloroflurocarbon molecule.
CFCs only contain carbon, chlorine and fluorine atoms
Ozone has the formula O3.
O3 is much less stable than O2.
O3 is formed from O2 and UVlight.
O3 is present in low concentrations.
Reducing ozone:
Chlorofluorocarbons undergo photolysis in the atmosphere.
This process creates chlorine radicals.
Chlorine radicals react with ozone (O3).
A reduction in the ozonelayer means that more of the Sun’s harmful UV rays reach the earth’s surface, which can cause a variety of environmental and health problems.