Halogenoalkanes Flashcards
What is the general formula of a halogenoalkane?
CnH2n+1X
(where x = halogen)
What do the prefixes (iodo-, fluoro-, bromo- and chloro-) tell about the halogenoalkane?
Dictate which halogen are present
Why is the C-X bond in halogenoalkanes polar?
The C-X bond is polar because halogens are more electronegative than carbon
How does bond polarity change as you go down Group 7 in halogenoalkanes?
As you go down Group 7, the electronegativity of the halogens decreases, making the C-X bond less polar
Why are halogenoalkanes not soluble in water?
The C-X bond is polar, but not polar enough to form hydrogen bonds with water molecules making halogenoalkanes insoluble in water
What are the main intermolecular forces present in halogenoalkanes?
The main intermolecular forces are dipole - dipole interactions and van der Waals forces
How does the chain length affect the boiling point of halogenoalkanes?
The boiling point increases with chain length because larger molecules have more electrons, leading to stronger van der Waals forces
How does the halogen in a halogenoalkane affect its boiling point?
The boiling point increases as you down Group 7, since larger halogen atoms result in stronger van der Waals forces due to more electrons
What effect does branching have on the boiling point of halogenoalkanes?
Increased branching lowers the boiling point because it reduces the surface area for van der Waals forces to act
Why do halogenoalkanes have higher boiling points than alkanes of similar chain length?
Halogenoalkanes have higher relative molecular masses and are more polar, leading to stronger intermolecular forces compared to alkanes
When halogenoalkanes react, which bond typically breaks?
The C-X bond (carbon - halogen bond) is the one that breaks during reactions
What type of reagents attack the electron-deficient carbon in halogenoalkanes?
Nucleophiles, which are electron pair donors
What are the two factors that determine the reactivity of the C-X bond?
- C-X bond polarity
- C-X bond enthalpy
Based on bond polarity, which halogenoalkane should be the least reactive?
Based on bond polarity, which halogenoalkane should be the most reactive?
Iodoalkanes (C-I bond) should be the least reactive because the C-I bond is the least polar, making the carbon less electrons deficient
Fluoroalkanes (C-F bond) should be the most reactive because the C-F bond is the the most polar, making the carbon more electron - deficient and more susceptible to nucleophile attack
How does C-X bond strength change going down Group 7?
The C-X bond gets weaker as you go down the group.
This is because the shared electrons are further from the halogen nucleus, reducing the bond strength
Why is the C-F bond the strongest in halogenoalkanes?
Fluorine has the smallest atom, so the shared electrons in the C-F bond are strongly attracted to the fluorine nucleus, making the bond very strong
Why is the C-I bond the weakest in halogenoalkanes?
Iodine is a larger atom, so the shared electrons in the C-I bond are further from the iodine, making the bond weaker and easier to break
Based on bond enthalpies, which halogenoalkanes is the most reactive?
Iodoalkanes are the most reactive because they have the weakest bond, making them easier to break in reactions
Based on bond enthalpies, which halogenoalkane is the least reactive?
Fluoroalkane are the least reactive because they have the strongest bond, making them harder to break
Which factor is more important in determining halogenoalkane reactivity: bond polarity or bond enthalpy?
Bond enthalpy is more important than bond polarity.
This is because experiments have shown reactivity increases as you go down the group, following the trend of decreasing bond strength
