means it is an unsaturated molecule (alkanes are...
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AlkenesAlkenes contain double bonds.
The double bond can be broken and more atoms added, this means it is an unsaturated molecule (alkanes are saturated).
Be careful! Carbon atoms can only form four bonds so if a carbon atom is involved in a double bond it can only form two other bonds.
C C C C
H
H
H H
H
H
H
Hfour bonds
four bonds
Naming alkenes
The position of the double bond in the carbon chain must be specified, using the lowest number possible.
The longest chain of carbon atoms is found and named, the position of the double bond is placed in between the suffix and prefix of the name.
The suffix for alkenes is –ene.
C C C C
H
H
H H
H
H
H
H
C C C CH
H
H
H H
H
H
H
but
21 4334 12
-1- ene but
21 4334 12
-2- eneSciPad pg 158, 159
Do now:Name these compounds:
Classify these compounds as primary, secondary or tertiary:
C C C CH
H H
H
H
H
H
H C C C CH
H CH3
H
H
H
H
H
C C C C
F
H
H
H
H H
H H
H
H2-bromo-2-methylpentane
1-bromo-2-methylpentane
but-1-ene 2-methylbut-1-ene
secondary
tertiary
primary
Isomers
Alkene can form both types of isomers:• Structural isomers• Geometric isomers
Structural isomersThe position of the double bond changes and/or the position of the branches change.
SciPad pg 160
Geometric Isomers
Requirements:• Double bond (as double bonds can not be rotated)• Each carbon atom involved in the double bond must be
attached to different atoms or groups
Make these compounds with your molymods
Geometric isomers have the same molecular formula, same structural formula but different arrangements around the double bond in space.
C C
H
ClCl
H
C C
Cl
ClH
H
C C
H
ClH
H
Geometric IsomersGeometric isomers are named either cis or trans depending on the position of the groups around the double bond. This comes at the start of the name.
CH3
C C
HH
CH3 CH3
C C
CH3H
H
Same side - cis Opposite side - trans
cis-but-2-ene trans-but-2-ene
SciPad pg 161, 162
Do now:What are the requirements for a geometric isomer to form?
Draw the geometric isomer of this compound and name it.
Extension: Draw a structural isomer of the compound above.
C C C CC
H
H
H H
H
H
C
H
H
H
H
H
H
2014 Exam Q2 b
2014 Exam Q2 b
Do now:What are the requirements for a geometric isomer to form?
Name these compounds and decide if they can form geometric isomers or not.
C C C CH
H
H
Cl H
H
H
HC C C CH
H
H H
Cl H H
H
2013 Exam Q1 a, b, cThis question pulls together all of your knowledge so far.
Hint: Draw full structural formula for compounds A - F
2013 Exam Q1 a, b, c
2013 Exam Q1 a, b, c
2013 Exam Q1 a, b, c
Reactions of alkenesAll alkenes can undergo addition reactions, where one of the covalent bonds in the double bond breaks and an atom is added to each carbon.
C C C CH
H
H
H H
H
H
H Br2 C C C CH
H
H Br
H
Br
H
H
H
H+
Different molecules can undergo addition reactions with alkenes.The first one is H2. It requires a Pt catalyst for the reaction to take place.
SciPad pg 163
Reactions of alkanes
Alkenes can also react with halogen molecules, X2, where X is a halogen (eg F2, Cl2, Br2, I2).
Reactions of alkenes
Alkanes can also react with halogen molecules, X2, where X is a halogen (eg F2, Cl2, Br2, I2). They undergo substitution reactions and require the presence of UV light.
C C C CH
H
H H
H
H
H
H
H
H Br2 C C C CH
H
H H
H
H
H
Br
H
H+ HBr+
SciPad pg 164
Do now:Draw the missing structure for these reactions
C C C CH
H
H H
H
H
H
H
H
H Br2 C C C CH
H
H H
H
H
H
Br
H
H+ HBr+
C C C CH
H
H
H H
H
H
H Br2 C C C CH
H
H Br
H
Br
H
H
H
H+
C C C CH
H
H
H H
H
H
H Cl2 C C C CH
H
Cl Cl
H
H
H
H
H
H+
C C C CH
H
H
H H
H
H
H Br2 C C C CH
H
H Br
H
Br
H
H
H
H+
C C C CH
H
H H
H
H
H
H
H
H Br2 C C C CH
H
H H
H
H
H
Br
H
H+ HBr+
C C C CH
H
H
H H
H
H
H Cl2 C C C CH
H
Cl Cl
H
H
H
H
H
H+
Today:SciPad pg 147Quick solubility test
SciPad pg 165Reactions of alkanes and alkenes with bromine water. Focus on colour changes and conditions for the reaction to occur.
Then: complete 2012 Exam question. This is a common question in exams and will help when we learn more reactions and colours after exams.
Do now:What would be the products of these reactions. Draw the structural formula and name both the reactants and the products
C C C CH
H CH3
H
H
H
H
H
C C C CH
H
H
Cl H
H
H
H
+ Br2
+ H2
Pt
2,3-dichloropropane + H2
Pt
2012 Exam Q 1 c
2012 Exam Q1 c
Reactions of alkenesAlkenes can also react with hydrogen halide molecules, HX, where X is a halogen (eg HF, HCl, HBr, HI).
If the alkene is asymmetric (ie not symmetrical) the reaction can form 2 products, major and minor.
Make 2 propene molecules and two HBr molecules with your molymods.
C C C HH
H
H
H H
C C C HH
H
H
H H
H – Br Br – H
What are the products of these reactions? Are the products the same?
Markovnikov’s RuleThe preferred product is the product where the hydrogen atom of the reagent is added to the carbon atom in the double bond that is already attached to the most hydrogen atoms.
C C C HH
H
H
H H
C C C HH
H
H
H H
H – Br Br – H
attached to 2 hydrogen atoms
attached to 1 hydrogen atom
C C C H
H
H
H
H H
H Br
C C C H
H
H
H
H H
Br H
preferred product – major product
attached to the carbon with most hydrogens
minor product
+ HBr
+ HBr
C C C CH
H
H
H H
H
H
H
BrH
C C C CH
H
H
H H
H
H
H
HBr
C C C CH
H
H
H H
H
H
H
C C C CH
H
H
Cl H
H
H
H
HBr
C C C CH
H
H
Cl H
H
H
H
BrH
C C C CH
H
H
Cl H
H
H
H
Markovnikov’s Rulejoined to more H’s
joined to same number of H’s
major
minor
symmetrical
asymmetrical
same product
For the following alkenes draw all of the products from the addition reaction with HCl.
C C CH
H
H
H
H
H
C C CC
Br H
HH
H
H
Br
H
C C C CH
H
H
CH3 H
H
H
H
Markovnikov’s Rule
SciPad pg 166, 167
2011 Exam Q2 c
Your answer should have 3 or 4 paragraphs. What would you put in each one?Paragraph 1
Paragraph 2
Paragraph 3
Paragraph 4
explaining type of reaction
explaining products from but-1-ene reaction, including chemical equations
explaining rule for assigning major and minor products
explaining product from but-2-ene reaction, including chemical equation
2011 Exam Q2 c
Paragraph 1
Paragraph 2 and 3
Paragraph 4
2011 Exam Q2 cFor A:
For M: For E:
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