ORGANIC CHEMISTRY
HYDROCARBONS
Examples of Alkenes
H
ETHENE, C2H4
H
C
H
H
C
PROPENE
C
H
H
OR CH2 CH2
C
H
CH2
CH
CH3
CH3
TASK: Use ball & stick models or sketches to construct and name 3
different structures for C4H8 each one with one double bond.
CH3CH2CH
CH3CH
CH2 BUT-1-ENE
CHCH3
BUT-2-ENE
CH3C
CH2 2METHYL
PROP 1 ENE
CH3
More Alkenes
Illustrate structures of the following alkenes:
Pent-1-ene
CH2 CHCH2CH2CH3
Hex-3-ene
CH3CH2CH CHCH2CH3
2-methylbut-1-ene
CH2 C(CH3)CH2CH3
Cyclohexene
Name the following alkenes
CH3CH
CH2
CHCH2CH3
CHCH(CH3)CH2CH3
CH3CH(CH3)CH
(CH3)3CCH
Pent-2-ene
3-methylpent-1-ene
CHCH2CH3
C(CH3)2
2-methylhex-3-ene
2,4,4-trimethylpent-2-ene
Alkynes
H-C≡C-H
Ethyne
H-C≡C-CH3
propyne
H-C≡C-CH2-CH3
But–1-yne
CH3-C≡C-CH3
But–2-yne
Very reactive
Triple bond unstable!
Attracts electrophiles.
Naming Aromatics
1. Same rules
2. If benzene is the parent chain “benzene” suffix
3. If benzene is a branch group “phenyl”
Structural Isomers
• Structural isomers are compounds with the
same molecular formula but different structural
arrangements
• They will have different physical and chemical
properties
• Example:
– pentane
– 2-methylbutane
– 2,2-dimathylpropane
Cis-Trans Isomers
• Cis-trans isomers occur when different groups of
atoms are arranged around a double bond
• Unlike a single C-C bond that can rotate, the double
C=C bond is fixed
Same side
Opposite
side
cis-1,2-dichloroethene
trans-1,2-dichloroethene
GEOMETRIC ISOMERS
 There is no rotation about the double bond.
GEOMETRIC ISOMERISM each C atom in the double bond has two
different atoms/groups attached.
BUT–2-ENE CH3 CH CH CH3
CH3
C
H
CH3
C
H
cis but-2-ene
CH3
C
H
C
H
CH3
trans but-2-ene
Geometric isomerism is a form of STEREOISOMERISM –
Same molecular and structural formula but atoms are arranged
differently in space
All Hydrocarbons will Undergo
Combustion:
Complete:
CH4 + 2O2 CO2 + 2H2O
Incomplete:
CH4 + O2 CO2 + CO + C + H2O
Alkanes & Aromatics Undergo
Substitution Reactions
• One or more of the hydrogen atoms can be
replaced by a halogen
• You can then add other functional groups by
replacing the halogen
• Requires heat, UV light or a catalyst (not easily
done with alkanes! But is easier with
aromatics)
• Alkane + halogen → hydrogen halide + alkyl
halide
Alkenes & Alkynes Undergo Addition
Reactions:
· Much greater chemical reactivity
than alkanes
· Easily undergo addition reactions at
room temperature (called
addition reaction b/c there is no loss
of hydrogen atom(s))
Addition Reactions
• Reactants
• \
/
• C = C + HX
• /
\
•
→
Product
| |
-C–C| |
X
Descriptive Name
Hydrohalogenation
(X = Br, F, I, Cl…)
Markovnikov’s Rule:
When a hydrogen halide (e.g. HBr) or water
(HOH) is added to an alkene the hydrogen atom
will bond to the carbon atom within the multiple
bond that already had more hydrogen atoms.
CH3-CH2-CH=CH2 + HCl -------------------------> CH3-CH2-CH(Cl)-CH3
This rule doesn't apply for the addition of
symmetrical reagents like Br2 or Cl2