C13 Flashcards
how to name haloalkane
- prefix fluoro, chloro, bromo, iodo
- numbers for C atom
- prefixes di, tri, tetra
- when different halogens, ALPHABETICAL order
physical properties of haloalkanes
- solubility
- bp
solubility
- the polar C-X bonds are not polar enough to make haloalkanes soluble in water
- main IM forces are dipole-dipole and VdW
- mix with hydrocarbons so can be used as dry cleaning fluids and to remove oily stains (oil is a mixture of hydrocarbons)
- do not dissolve in water but dissolve in ethanol
boiling point
- bp depends on the number of C and X atoms
- bp increases with increasing chain length
- bp increases going down halogen group
both caused by increased VdW forces because the larger the molecules, the greater the number of electrons and so larger VdW forces
- as in other homologous series, increased branching of the carbon chain will tend to lower the melting point
- haloalkanes have higher bp than alkanes with similar chain lengths, because they have higher relative Mr and are more polar
how haloalkanes react- the reactivity of the C-X bond
bond enthalpy/ polarity
when haloalkanes react, it is almost always the C-X bond that breaks
- there are two factors that determine how readily the C-X bond reacts :
—–> C-X bond enthalpy
—–> C-X bond polarity
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bond polarity
- C-X bond is polar
- halogens are more electronegative than carbon
- C has partial positive charge
–> attacked by nucleophiles (electron pair donor)
the polarity of the C-X bond would predict that C-F bond would be more reactive
–> it is the most polar, so the C has the most positive charge and is therefore most easily attacked by a nucleophile
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bond enthalpies
- C-X bond gets weaker down the group
- fluorine is the smallest atom of the halogens and the shared electrons of the C-F bond are strongly attracted to the fluorine nucleus: strong bond
- going down the group, the shared e- get further away from the halogen nucleus, so the bond becomes weaker
- bond enthalpies predict that iodo-compounds are most reactive
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experiments confirm that reactivity increases going down the group
so bond enthalpy is more important than bond enthalpy
nucleophillic substitution
see sheets
elimination reactions
large molecule loses atoms or groups of atoms
OH- ion acts as a base, removing H+ ion from haloalkane
NaOH/ KOH = dissolved in ethanol and mixed with haloalkane
NO WATER present
mixture is heated
substitution or elimination
products depend on…
conc of OH- ions
–> acts as base if conc enough
solvent
- water = sub
- ethanol = elimination
temperature
- room = sub
- high = elimination
type of haloalkane:
primary = substitution
tertiary = elimination
secondary = both
chlorofluorocarbons uses
short chain: aerosol propellants, refrigerants, blowing agents for foams e.g. expanded polystyrene
longer chain: dry cleaning and de-greasing solvents
