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The alkenes are a homologous series of unsaturated hydrocarbons - Leaving Cert Chemistry - Question 9 - 2008
Question 9
The alkenes are a homologous series of unsaturated hydrocarbons. Ethene (C2H4) is the first member of the series. Alkenes undergo addition reactions and polymerisati... show full transcript
Worked Solution & Example Answer:The alkenes are a homologous series of unsaturated hydrocarbons - Leaving Cert Chemistry - Question 9 - 2008
Step 1
Draw a labelled diagram of an apparatus used to prepare ethene gas in the school laboratory.
Answer
To prepare ethene gas, the apparatus typically consists of a flask containing ethanol (C2H5OH) and a strong dehydrating agent such as aluminium oxide (Al2O3). The flask is connected to a delivery tube that leads to a collection container. A heat source is applied to the flask to initiate the dehydration process, producing ethene gas.
Step 2
Draw the structure of any one of the isomers of the third member of the alkene series.
Answer
The third member of the alkene series is propene (C3H6). One possible structure is:
H H
| |
H - C = C - C - H
| |
H H
In this structure, the central carbon atoms (C=C) have planar bonding, while the terminal carbon atoms are bonded tetrahedrally.
Step 3
Explain the term unsaturated.
Answer
An unsaturated compound is defined as a molecule that contains one or more double or triple bonds between carbon atoms. These bonds indicate that the compound can potentially react with additional atoms or groups of atoms by breaking these multiple bonds and forming new ones. Unsaturated hydrocarbons, such as alkenes, typically have fewer hydrogen atoms than their saturated counterparts due to these multiple bonds.
Step 4
Draw the structure of the ionic intermediate species formed in the reaction of ethene with bromine water.
Answer
The intermediate species in the ionic addition reaction of ethene with bromine water can be represented as:
Br
|\n H - C - C - H
| |
Br H
Here, the bromine atom is added to the double bond, creating a cyclic bromonium ion as a reactive intermediate.
Step 5
Give the names or structural formulas of the three products formed with bromine water that contains sodium chloride.
Answer
The three products that would be formed are:
-
1,2-dibromopropane:
Br |
H - C - C - H | | Br H
2. **2-bromopropan-1-ol**:
Br
|
H - C - C - OH | | H H
3. **1-bromo-2-propanol**:
Br H
| |
H - C - C - OH | | H H
Step 6
How does the formation of these three products support the mechanism of ionic addition?
Answer
The formation of multiple products illustrates the mechanism of ionic addition, as it demonstrates the stages of reaction involving the formation of an intermediate. The initial addition of bromine forms the bromonium ion, which allows for nucleophilic attack by either bromide ions or hydroxide ions derived from the solvent, leading to different products. This behavior indicates the presence of multiple pathways and products as a result of the initial ionic addition.
Step 7