Chapter 15 - Haloalkanes Flashcards
What is the general formula of a haloalkane?
CnH2n+1X
X = halogen atom
Are haloalkanes polar? Why?
Haloalkanes are polar as they contain a polar C-X bond The C-X bond is polar because halogen atoms are significantly more electronegative than carbon.
State and explain the trend in the bond polarity of the C-X bond down the halogen group.
The C-X bond polarity decreases down the group as the electronegativity of halogens decrease from F → I.
What is hydrolysis?
A reaction where a substance is split up using water molecules or hydroxide ions.
Haloalkanes can undergo hydrolysis with aqueous hydroxide ions (e.g. NaOH) to produce…
…an alcohol and halide ion.
Halide ion (.e.g Cl-) reacts with positive ion (e.g. Na+) to form a compound (e.g. NaCl).
Describe the hydrolosis of haloalkanes with water.
Haloalkanes can be hydrolysed by water in the presence of aqueous silver nitrate in an ethanol solvent to form alcohols.
The halide ions react with silver ions to form a halide precipitate.
Outline how you could compare the rates of hydrolosis of different haloalkanes.
The haloalkanes are warmed with AgNO3 (aq) in ethanol. Compare the times for a precipitate of the silver halide to appear.
How are Cl radicals formed in the upper atmosphere?
•Cl radicals form when C-Cl bonds in the CFC molecules are broken by homolytic fission in the presence of UV.
What is a nucleophile?
A species that donates a pair of electrons to form a new covalent bond (e.g. negative ions).
Show the breakdown of ozone by chlorine radicals with equations.
Halogen radicals formed by breakdown of CFCs by homolytic fission in the presence of UV radiation.
e.g. CF2Cl2 → CF2Cl • + •Cl
Halogen radicals break down ozone.
e.g.
•Cl + O3 → •ClO + O2
•ClO + O → •Cl + O2
Overall: O3 + O → 2 O2
Same overall equation with any radicals (halogen radicals, •NO radicals etc.)
Show the breakdown of ozone by nitrogen oxide radicals as equations.
- NO + O3 → •NO2 + O2
- NO2 + O → •NO + O2
Overall: O3 + O → 2 O2
Are haloalkanes more reactive than alkanes? Explain why.
Haloalkanes are more reactive than alkanes as the polar C-X bond attracts nucleophiles to the partially positively charged carbon atom.
Furthermore, C-X bond enthalpies (apart from C-F) are weaker than that of the C-H bond.
What is the trend in the strength of the C-X bond down the halogen group?
The strength of the C-X bond decreases down the group as the bond enthalpy of the C-X bond decreases down the group.
What is the trend in the rate of hydrolosis of haloalkanes.
As bond enthalpy of C-X bond decreases down the halogen group, rate of hydrolosis increases.
