Reactions of the Alkanes
1. Halogenation with light:
This is a substitution reaction:
R-H + halogen -----------> R-F +
HF
(R can be any alkane)
2. Dehydrohalogenation:
This reaction is used to remove a hydrogen and a halogen from an alkane chain. The
result is the formation of a double bond.
2-bromo-butane
but-1-ene
but-2-ene
The Br- gets pulled off and the H+ gets pulled off randomly from either side of the Br's
position so there are two possible products.
3. Dehydration
This reaction removes water from a molecule. It works great on alcohols.
Works best for 3o alcohols > 2o alcohols > 1o alcohols
eg. iso-propyl alcohol being dehydrated into propene and water
eg. pentan-3-ol gives cis-pent-2-ene
trans-pent-2-ene
Reactions of the Alkenes and Alkynes
Markinikov's Rule:
When a substitution is made across a C=C or triple bond the H will be added to the
carbon that already has the most H's on it. When a dehydration occurs across a C=C or
triple bond then the H removed will be from the C that has the most H's on it.
4. Addition of Hydrogen
This is an addition or saturation reaction.
unsaturated
hydrocarbon
saturated
hydrocarbon
eg. pent-2-ene being changed into pentane
eg, 2 ethyne (acetylene) being converted into ethane
5. Hydrohalogenation
The addition of a H and a halogen. It is beneficial to add both the H and the halogen in
one reagent so one of the binary halogen acids is usually used like HI, HBr, HCl, or HF.
eg. propene is hydrohalogenated with hydrobromic acid to create 2-bromo-propane
6. Hydration
This reaction involves the addition of water in the presence of a weak acid. Strong acids
tend to draw water away from molecules. Weak acids only stimulate double bonds (Pi
bonds) into breaking. Water is ionized slightly in weak acids and can then move into take
their proper place in the broken alkene bonds.
eg. 2-methylpropene is hydrated to 2-methyl-2-propanol
7. Oxidation of Alcohols
Primary alcohols can be oxidized into aldehydes first and then further oxidized into
carboxylic acids
This same reaction occurs in apples. The alcohol groups on the sugars oxidize into
aldehydes. This turns the white pulp into brown. The smell also becomes "musty" which is
a characteristic smell of rotting apples. Further oxidation converts the aldehydes into
carboxylic acids which makes the pulp go mushy.
eg. propan-1-ol is first oxidized into propanal and then further oxidized into propanoic
acid
Secondary alcohols can be oxidized into ketones