A halogenoalkane is a alkane with at least one halogen atom in place of a hydrogen atom.
Halogens are much more electronegative than carbon, so carbon-halogen bonds are polar.
The slight positive charge on the carbon makes it prone to attacks from nucleophiles.
A nucleophile is an electron pair donor.
OH-, CN- and NH3 are all nucleophiles that can react with halogenoalkanes.
Halogeneoalkanes react with hydroxides to form alcohols.
Nitriles are formed by reacting halogenoalkanes with cyanide.
Reacting halogenoalkanes with ammonia forms amines.
If you warm a halogenoalkane with hydroxideions dissolved in ethanol instead of water, an eliminationreaction happens, and you end up with an alkene.
When reacting a halogenoalkane with hydroxide, you need to look at the conditions to see what reaction is occuring.
Alkanes are saturated hydrocarbons.
Alkanes have the general formula CnH2n+2.
Alkanes contain only single bonds due to being saturated.
Cycloalkanes have a ring of carbon atoms with two hydrogens attached to each carbon.
Cycloalkanes have the general formula CnH2n, but are still saturated.
Crude oil goes through a fractionating column to form separate alkanes (fractions).
Cracking is breaking long chain hydrocarbons down into smaller, more useful hydrocarbons.
Thermal Cracking:
Takes place at high temperatures (up to 1000 degrees) and high pressure (up to 70 atm).
Produces a large amount of alkenes.
These alkenes are used to produce valuable products like polymers.
Catalytic Cracking:
Uses a zeolite catalyst, at slight pressure and high temperature (about 450 degrees).
It mostly produces aromatic hydrocarbons and motor fuels.
Cuts cost, because reaction can be done at a low pressure and a lower temperature.
Catalyst speeds up the reaction which saves time.
If you burn alkanes with plenty of oxygen, you get carbon dioxide and water. This is complete combustion.
When incomplete combustion occurs, you can get carbon monoxide gas instead of, or as wellas, carbon dioxide.
Carbon Monoxide:
Is a silent killer.
Isn't visible.
Binds to haemoglobin molecules in red blood cells so oxygen can't be carried around the body.
Can be removed from exhaust gases by catalytic converters on cars.
Carbon molecules can also be formed by incomplete combustion.
Burning fossil fuels produces carbon dioxide which is a greenhouse gas.
Engines don't burn all of the fuel molecules. Some come out as unburnt hydrocarbons.
Hydrocarbons and nitrogen oxides react in the presence of sunlight to form ground-level ozone which is a major component of smog.
Ground-level Ozone:
Irritates peoples eyes.
Aggravates repiratory problems.
Causes lung damage.
Catalytic converters on cars remove unburnt hydrocarbons and oxides of nitrogen from the exhaust.
Some fossil fuels contain sulfur. When they are burnt, the sulfur reacts to form sulfur dioxide gas.
If sulfur dioxide gets into the atmosphere, it dissolves in the moisture and is converted into sulfuric acid causing acid rain.
Acid rain destroys trees and vegetation, as well as corroding buildings and statues and killing fish in lakes.
Sulfur dioxide can be removed from power station flue gases before it gets into the atmosphere.
A free radical is a particle with an unpaired electron.
Free radicals form when a covalent bond splits equally, giving one electron to each atom.
The unpaired electron makes them very reactive.
You can show a free radical in a mechanism by putting a dot next to it like this (Cl·)
Halogens react with alkanes in photochemical reactions - reactions that are started by ultraviolet light.
Example: Reacting Chlorine with Methane
Stage 1: Initiation reaction - free radicals are produced.
Sunlight provides enough energy to break the Cl-Cl bond.
The bond splits equally and each atom gets to keep one electron. The atom becomes a highly reactive free radical, Cl·, because of its unpaired electron.
Example: Reacting Chlorine with Methane
Stage 2: Propagation reactions - free radicals are used up and created in a chain reaction.
Cl· attacks a methane molecule.
The new methyl free radical, CH³·, can attack another Cl² molecule.
The new Cl· can attack another CH⁴ molecule, and so on, until all the Cl² or CH⁴ molecues are used up.
Example: Reacting Chlorine with Methane
Stage 3: Termination reactions - free radicals are mopped up.
If two free radicals join together, they make a stable molecule. The two unpaired eletrons form a covalent bond.