Haloalkanes are alkane molecules that contain at least one group 7 atom - Scottish Highers Chemistry - Question 9 - 2023
Question 9
Haloalkanes are alkane molecules that contain at least one group 7 atom.
(a) The table shows information on the boiling points of some haloalkanes.
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Worked Solution & Example Answer:Haloalkanes are alkane molecules that contain at least one group 7 atom - Scottish Highers Chemistry - Question 9 - 2023
Step 1
Using the information in the table, describe two different trends in the boiling points.
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Answer
The boiling point increases with longer carbon chains; for example, moving from CH₃Br to CH₃CH₂Br raises the boiling point due to increased van der Waals forces from a larger surface area.
The boiling point also increases with the atomic weight of the halogen. For instance, CH₃Cl has a lower boiling point than CH₃I, due to iodine being heavier and providing stronger van der Waals interactions.
Step 2
Name the strongest type of intermolecular forces broken when bromoethane, CH₃CH₂Br, boils.
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The strongest type of intermolecular forces broken when bromoethane boils is permanent dipole–dipole interactions due to the presence of the polar C–Br bond.
Step 3
State why 2-bromobutane can be classified as a secondary haloalkane.
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2-bromobutane can be classified as a secondary haloalkane because the carbon atom bonded to the bromine atom is attached to two other carbon atoms.
Step 4
Draw a structural formula for an isomer of 2-bromobutane that is a tertiary haloalkane.
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A possible structural formula for a tertiary haloalkane is:
Br
|
CH₃-C-CH₃
|
CH₃
In this structure, the bromine is attached to a carbon that is bonded to three other carbon atoms.
Step 5
State what is required for initiation to take place.
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Initiation requires ultraviolet (UV) radiation to provide the energy necessary to break the Br-Br bond, forming two bromine radicals.
Step 6
Complete the table to show a possible termination step.
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A possible termination step is:
Br• + Br• → Br₂
Step 7
Draw a structural formula for compound P.
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Compound P can be represented by the structural formula:
H H
| |
H-C-C-Br
| |
H H
Step 8
Using these rules, name this molecule.
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Answer
The molecule is named 1-bromo-2-chloro-1,1,1-trifluoropropane. This is based on the longest carbon chain and the alphabetical order of the substituents.
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