Topic 10- Halogenoalkanes Part 2 Flashcards
What is shown by a black curly arrow in a nucleophilic substitution reaction?
What are mechanisms?
What do curly arrows always show in mechanisms?
What does the lone pair of electrons create?
What can carbon only be bonded to?
What does the addition of the nucleophile break and what is this shown by?
What happens to the pair of electrons from the carbon-halogen bond and what does this form?
The lone pair of electrons on the nucleophile attacks the slightly positive charge on the carbon
Diagrams that show how a reaction works
Curly arrows always show the movement of an electron pair
A new bond between the nucleophile and the carbon
The carbon can only be bonded to four other atoms
Breaks the bond between the carbon and the halogen- this is shown by another curly arrow
The pair of electrons from the carbon-halogen bond are taken by the halogen and become a lone pair.
What does the reaction of halogenoalkanes with hydroxides produce?
What one of two substances does this reaction require to work?
What are nitriles?
What are the carbon atom and nitrogen atom held together with?
How do you get a nitrile concerning halogenoalkanes?
What do you have to use as a solvent instead of water in the making of nitriles from halogenoalkanes?
Why can’t water be used as the solvent?
Halogenoalkanes will react with hydroxides to produce alcohols
You have to use warm aqueous sodium or potassium hydroxide or it won’t work
Nitriles have CN groups
A triple bond
If you warm a halogenoalkane with ethanolic potassium cyanide (potassium cyanide dissolved in ehtanol)
You have to use ethanol as a solvent here instead of water
If you used water, it could act as a competing nucleophile and you’d get some alcohol product.
What is the definition of heating under reflux?
Means you can increase the temperature of an organic reaction to boiling point without losing volatile solvents, reactants or products.
What is the structure of an amine?
What two things can the R groups be?
What does the nitrogen always have in amines?
How do you form amines?
Explain how this is done?
What is this another example of?
What does the amine group in the product still have?
What does this mean?
R3N
Hydrogen’s or another group
The nitrogen always has a lone pair
By reacting halogenoalkanes with ammonia
If you warm a halogenoalkane with excess ethanolic ammonia, the ammonia swaps places with the halogen
A nucleophilic substitution reaction
A lone pair of electrons
It can also act as a nucleophile- so it may react with halogenoalkane molecules itself, giving a mixture of products.
What decides reactivity in halogenoalkanes?
What bond is the strongest bond in halogenoalkanes and why?
What does this result in?
What does this mean that fluoralkanes do?
What bond is the weakest in halogenoalkanes and why?
What does this result in?
What does this mean that iodoalkanes do?
What is the strength of a halogenoalkane related to?
The carbon-halogen bond strength (or enthalpy)
The C-F bond is the strongest- it has the highest bond enthalpy
Hardest bond to break
Fluoroalkanes undergo nucleophilic substitution reactions more slowly than other halogenoalkanes
The C-I bond is the weakest- it has the lowest bond enthalpy
Easiest to break
Iodoalkanes are substituted more quickly
The size of the halogen.
Describe the summary of a nucleophilic substitution reaction?
List the order of polarity (from weakest to strongest) in halogenoalkanes?
One new bond is formed (between the nucleophile and the f+ carbon atom) and one bond is broken (the carbon-halogen bond)
C-I ; C-Br ; C-Cl ; C-F.
What is the definition of a free radical?
How do free radicals form?
What makes them very reactive?
A particle with an unpaired electron
When a covalent bond splits equally, giving one electron to each atom
The unpaired electron.
How do halogens react with alkanes and describe?
What happens to a hydrogen atom?
What is this called?
In photochemical reactions- reactions that are started by ultraviolet light
A hydrogen atom is substituted (replaced) by chlorine or bromine
A free-radical substitution reaction.
Describe initiation reactions?
Describe propagation reactions?
Describe termination reactions?
Free radicals are produced
Free radicals are used up and created in a chain reaction
Free radicals are mopped up.
What are chlorofluorocarbons (CFCs)?
Halogenoalkane molecules where all the hydrogen atoms have been replaced by chlorine and fluorine atoms.
What happens if you warm a halogenoalkane with hydroxide ions dissolved in ethanol?
What do you end up with?
What do you have to do to the mixture and why?
What are the conditions?
What does the OH- ion act as and what does this make?
What does the left carbon now have?
How does the double bond form?
A elimination reaction happens
An alkene
You have to heat the mixture under reflux or you’ll lose volatile stuff
Anhydrous (without water)
The OH- acts as a base and takes a proton H+ from the carbon on the left, making water
A spare electron, so it forms a double bond with the middle carbon
The middle carbon has to let go of the halogen atom, which drops off as a halide ion.
What happens in an elimination reaction?
What doesn’t happen to this group?
What would instead happen in a substitution reaction?
A small group of atoms breaks away from a molecule
This group is not replaced by anything else
This group would be replaced by something else in a substitution reaction.
