page 11 Flashcards
Boiling Points and Melting Points (BPs and MPs):
General Trend:
Alkyl halides have higher boiling and melting points than alkanes with the same number of carbons.
This is due to the polar nature of the C-X bond, which introduces dipole-dipole interactions.
Dependence on R Group (Size of the Alkyl Group):
As the size of the alkyl group (
R
R) increases, BPs and MPs also increase.
Example:
CH3CH2Cl: MP = -136°C, BP = 12°C.
CH3CH2CH2Cl: MP = -123°C, BP = 47°C.
Reason: A larger surface area leads to stronger van der Waals forces.
Dependence on X (Size of the Halogen):
As the size of the halogen increases, BPs and MPs increase.
Example:
CH3CH2Cl: MP = -136°C, BP = 12°C.
CH3CH2Br: MP = -119°C, BP = 39°C.
Reason: Larger, more polarizable halogens increase intermolecular interactions.
Solubility:
Alkyl halides (
RX):
Soluble in organic solvents due to their moderate polarity and compatibility with nonpolar solvents.
Insoluble in water because they cannot form hydrogen bonds with water molecules.
Why do alkyl halides have higher boiling points than alkanes?
Answer: Due to the polar C-X bond, which creates dipole-dipole interactions not present in alkanes.
What happens to the boiling point as the size of the alkyl group increases?
Answer: The boiling point increases because the larger surface area leads to stronger van der Waals forces.
Which has a higher boiling point:
CH3CH2Cl or CH3CH2CH2Cl?
Answer:
CH3CH2CH2Cl, because it has a larger alkyl group.
What happens to the boiling point as the size of the halogen increases?
Answer: The boiling point increases due to the more polarizable nature of larger halogens.
Which has a higher boiling point:
CH3CH2Cl or
CH3CH2Br?
Answer:
CH3CH2Br, because bromine is larger and more polarizable than chlorine.
Are alkyl halides soluble in water? Why or why not?
Are alkyl halides soluble in water? Why or why not?
Answer: No, alkyl halides are insoluble in water because they cannot form hydrogen bonds with water.
