Halogenoalkanes (Chapter 13) Flashcards
(26 cards)
Define Haloalkanes
Alkanes which have one or more hydrogen atoms that have been replaced by halogen atoms.
What is the generic formula for haloalkanes
R-X
R = Carbon chain X = Halogen
Why are covalent bonds polar?
The electrons are not equally shared because one atom spends more time with the electrons than the other atom.
Where do the reactions take place on a haloalkane?
On the polar bond
What is the difference between symmetrical and asymmetrical CX4 molecules?
Asymmetrical ARE polar
Symmetrical ARE NOT polar
How do haloalkanes form?
Free radical substitution
What are the steps of free radical substitution?
Initiation, Propagation and Termination
What happens in initiation?
UV light is required which forms two free radicals
What happens in propagation?
2 reactions which form chain reaction
What happens in termination?
Two free radicals join to form one molecule
How are unpaired electrons shown?
Using a dot •
What is the link between bond enthalpy and polarity?
As bond enthalpy decreases, polarity also decreases
What does a double-headed arrow show?
The movement of two electrons
What does a single-headed arrow show?
The movement of one electron
What are the products of propagation?
Multiple substitutions (di-, tri-, tetra etc haloalkanes)
What are the products of termination?
Longer chains which also react during a subsequent initiation step .
This is because X• can replace any hydrogen atoms so more isomers form.
How are the products of FRS separated?
Fractional distillation
What reactions do haloalkanes undergo?
Nucleophilic and elimination reactions
What is a nucleophile?
An atom/molecule with a lone pair of electrons (so has a negative charge) so is attracted to a positive charge.
Describe a nucleophilic substitution reaction
A nucelophile substitutes the halogen atom on the haloalkane molecule.
Different nucleophiles form diferent organic products (which undergo additional reaction).
What are the conditions for nucleophilic substitution?
50:50 mix of ethanol and water
Warm gently
How is a nitrile (RCN) formed?
Reacting a cyanide (:CN) with a haloalkane (RX)
How is an amine (RNH2) formed?
Reacting ammonia (:NH3) and a haloalkane (RX) in a 2:1 ratio.
The Ammonia replacesa H atom on the RX
How is an alchol (ROH) formed?
Reacting a hydroxide (:OH) with a haloalkane (ROH)
