3.3.2.3 Chlorination of Alkanes Flashcards
Why is a C-X bond polar?
The C-X bond in halogenoalkane is polar because the halogen atom is more electronegative than the C atom.
Describe the solubility of halogenoalkanes
The carbon bond is quite polar so shorter halogenoalkanes tend to dissolve in polar solvents. As the carbon chain gets longer, there is a larger effect from the non-polar hydrocarbons, so it is less soluble in polar solvents and more soluble in non-polar solvents.
What are the two types of intermolecular force between halogenoalkanes?
Van der Waal’s
Permanent dipole-dipole
Describe the boiling points of halogenoalkanes
As carbon chain length increases, boiling point increases. The VdW forces increase as the relative molecular mass increases, so b.p. increases as chain length of carbon increases
When can chlorine react with halogenoalkanes?
In the presence of UV light
What is a mechanism?
A detailed step-by-step sequence, illustrating how an overall chemical reaction occurs
What is a substitution?
When an atom/small molecule has been removed and replaced by another atom/small molecule
What are the three steps in a free-radical substitution?
Initiation
Propagation
Termination
Describe the initiation step of a free-radical mechanism
To produce free-radicals, UV light must be present. The Cl-Cl bond then breaks through homolytic fission.
e.g.
Cl2 -> *Cl + *Cl
Describe the propagation step of a free-radical mechanism
Always has 2 steps..
Highly reactive halogen radicals react with a molecule e.g. methane, forming a methyl free radical
The free-radical formed then reacts with a second chlorine molecule to form chloromethane and another chlorine radical.
What is a free-radical?
An atom/ion with at least one unpaired electron
