13.1- HALOGENOALKANES- INTRODUCTION Flashcards
Do many halogenoalkanes occur naturally?
no
What are halogenoalkanes the basis of?
many synthetic compounds
Examples of halogenoalkanes being used as the basis for synthetic compounds? (4)
PVC
Teflon
anaesthetics
solvents
What is PVC used to make?
drainpipes
What is Teflon used for?
non-stick coating on pans
What do halogenoalkanes have the skeleton of but with what attached?
alkane skeleton with one/ more halogen atoms in place of hydrogen atoms
What is the general formula of halogenoalkanes?
CnH2n+1X
What tells us in the names if a halogen in present?
the prefixes e.g. fluoro-, chloro-, bromo-, and iodo-
What are numbers used for when naming halogenoalkanes?
to show on which carbon the halogen is bonded
What do the prefixes di-, tri-, tetra- and so on show when naming halogenoalkanes?
how many atoms of each halogen is present
When different halogens are present how is the halogenoalkane named?
listed in alphabetical order
What sort of bond do halogenoalkanes have?
C-X bond
As halogenoalkanes have a C-X bond, what does this mean?
bond is polar
Why do halogenoalkanes have a polar bond?
halogens are more electronegative than carbon
How does polarity change going down the halogen group?
bonds get less polar
Can halogenoalkanes dissolve in water?
no
Why can’t halogenoalkanes dissolve in water?
polar bonds are not polar enough
What are the main intermolecular forces of attraction in halogenoalkanes?
dipole-dipole attractions and van der Waal forces
What do halogenoalkanes mix with?
hydrocarbons
As halogenoalkanes mix with hydrocarbons, what can they be used as?
used as dry-cleaning fluids and to remove oily stains
What is oil a mixture of?
mixture of hydrocarbons
What does the boiling point of a halogenoalkane depend on?
depends on number of carbon atoms and halogen atoms
Two factors that affect boiling point of halogenoalkanes?
boiling point increases with increased chain length
boiling point increases going down halogen group
What is both the effects of increased boiling point of halogenoalkanes caused by?
increased van der Waals forces as larger the molecule, greater the number of electrons
What will increased branching in halogenoalkanes do to the boiling point?
lower the boiling point
What is the boiling point of halogenoalkanes like compared to alkanes with similar chain lengths?
halogenoalkanes have higher boiling points
Why do halogenoalkanes have higher boiling points than alkanes with similar chain lengths? (2)
as they have higher relative molecular masses and they’re more polar
Almost always which bond in halogenoalkanes break when they react?
C-X bond
What two factors determine how readily the C-X bond reacts
bond polarity
bond enthalpy
Why is the C-X bond polar
halogens more electronegative than carbon
As the C-X bond in halogenoalkanes is polar, what does this mean for the carbon bonded to the halogen?
has a partial positive charge- electron deficient
What can happen as the carbon bonded to the halogen in halogenoalkanes is electron deficient?
can be attacked by reagents that are electron rich or have electron-rich areas
What are reagents that are electron rich or have electron-rich areas called?
nucleophiles
What is a nucleophile?
electron pair donor
What would the polarity of the C-X bond in halogenoalkanes predict?
the C-F bond would be the most reactive
Why would the C-X bond predict the C-F bond would be the most reactive?
it’s the most polar, so the C has the most positive charge so most easily attacked by a nucleophile
What would the argument about C-X bond polarity predict for C-I?
C-I bond would be least reactive as it’s the least polar
How does the C-X bond change going down the group? (strength)
bonds get weaker
What is the size of the fluorine atom like compared to the other halogens?
fluorine is the smallest atom
How attracted are the shared electrons in the C-F bond?
the shared electrons in the C-F bond are strongly attracted to the fluorine nucleus
How does the shared electrons in the C-F bond being strongly attracted to the fluorine nucleus affect the strength of the bond?
makes a strong bond
Going down the group, how does the position of the electrons in the C-X bond change?
shared electrons in the C-X bond get further and further away from the halogen nucleus
As the shared electrons in the C-X bond get further away what happens to the strength of the bond?
bond becomes weaker
What would the bond enthalpies predict would be the most reactive compounds from the halogen group?
iodo-compounds as they have the weakest bonds
What would the bond enthalpies predict would be the least reactive compounds from the halogen group?
fluoro-compounds as it has the strongest bonds
What does experiments confirm about reactivity going down the halogen group?
reactivity increases going down the group
As experiments confirm that reactivity increases going down the halogen group, what does this show?
bond enthalpy is a more important factor than bond polarity
