Transcript ES10 Halogenoalkanes

Which is the
odd one out?
Ions in
solution
Ionic
Formulae
Manufacturing
Halogenoalkanes
Redox
Bonding
Atoms
and
Ions
Halogens
Dipoles
Elements of the sea
Content
• Nomenclature of halogenoalkanes
• Physical and chemical reactions of
halogenoalkanes including hetrolytic
fission
Process
• Carry out an experiment
Benefit
• Explain reaction mechanisms
Nomenclature
Homologous series (actually one for each
halogen!)
1. Location of halogen (smallest possible)
2. Prefix of halogeno – with an o (i.e
chloro/flouro/bromo – if more than 1 –
alphabetically)
3. Root is parent C chain
Name these/draw these
2,3-dichloropentane
CHCl3
3-bromobut-1-ene
2,3-dibromo-1-chloro-2-methylbutane
Physical properties
Halogen makes gp polar – but not
sufficient to make it miscible with H2O
Complete this worksheet
1. Explain the physical properties if
astatine was attached.
Chemical Reactions
• Try to break Hal-C bond (hal short for
halogen)
• Bond breaking (fission) can be either
hetrolytic or homolytic.
H3C-Cl
• Guess what do you think they mean?
Homolytic fission
• Can occur by visible/UV radiation (hv)
hv + H3C Cl
H3C + Cl
• Each of the bonding e- goes to each of the
atom.
• Creating a highly reactive atom/gp of
atoms with an unpaired e- are called a
radicals.
HOT question
Should there be a charge
here?
• This causes ozone issues in stratosphere
Heterolytic fission
• Reactions depend on conditions (nonpolar solvent/gas phase with high temp
HOT question
homolytic fission)
Give an example of a polar solvent
• Common in lab conditions (polar solvent)
H3C Cl
H3C + Cl
• Both of the bonding e- goes to one of the
atom/groups of atoms.
• Forms a –ive halide ion and a +ive
carbocation (carbon + ca+ion).
ES 6.2
• Do these Hal-C bonds break at the same
time?
• Remember to answer the questions.
ES 4.5
If a precipitate appears, this means that hydrolysis has taken place – the carbon–halogen bond has
broken and halide ions have been released from the halogenoalkane.
1. Which halogenoalkane underwent the fastest hydrolysis?
• Which was slowest?
2. Student X suggests that the rate of hydrolysis depends on the polarity of the C–Hal bond, and that
the halogenoalkane with the most polar bond will hydrolyse most quickly.
• Student Y suggests that the rate of hydrolysis depends on the strength of the C–Hal bond, and that
Which
the halogenoalkane with the weakest bond will hydrolyse most quickly.
• Use your Data Sheets to find data that you think will help
• you and write it down. Use the data to decide whether
• bond polarity or bond enthalpy is more important in
• determining the relative reactivity of halogenoalkanes.
3. What result would you predict for 1-fluorobutane? Explain your answer.
4. Why was this experiment done using halogenobutanes rather than halogenomethanes?
Which is more
important in
reactivity of
halogenoalkanes
bond enthalpy or
bond polarity?
Extension – predict how would fluorobutane react?
ES 4.5
Enthalpy more influential – so fluoroalkane
would happen slower/less reactive than
chloroalkane as higher bond enthalpy
for fluroalkane.
• Remember to answer the questions.
CFCs
CFC’s release – hang around in the
troposphere and then .......
CFCs
1. Complete ES6.2
2. Read 13.1 and make notes – we will cover
nucleophilic substitution but reading
ahead will help you understand it better.