The Chemistry of Haloalkanes (15.1) Flashcards
(17 cards)
What are haloalkanes?
Alkanes with at least one halogen in their molecular formula
How are haloalkanes named?
-The halogens prefix goes before the longest chain and alkyl groups
-When there is more than 1 halogen, they are in alphabetical order
-When there are 3 or more carbons in a chain the number of the carbon the halogen is attached to is used
-When there is more than 1 halogen on a 2 carbon chain, numbering is used
What are the prefixes for halogens in haloalkanes?
-Fluoro for Fl
-Chloro for Cl
-Bromo for Br
-Iodo for I
How do you know if a haloalkane is primary, secondary or tertiary?
-Primary = If the carbon the halogen is attached to 1 more carbon
-Secondary = If the carbon the halogen is attached to 2 more carbons
-Tertiary = If the carbon the halogen is attached to 3 more carbons
Which part of the C-Halo is more electronegative?
The halogen atom
Are haloalkanes polar covalent?
Yes because their electronegativity difference is the same as/over 0.5
Why are species with lone pairs of electrons attracted to the carbon atom in a haloalkane?
Because the carbon has a partially positive charge
What is the name of the reaction that takes place with nucleophiles and halogenoalkanes?
Nucleophilic substitution
What are nucleophiles?
An atom or group of atoms attracted to an electron deficient carbon atom
What are some examples of nucleophiles?
-Hydroxide ions
-Water
-Ammonia molecules
What is hydrolysis?
When a molecule’s bonds break after reacting with water/aqueous solutions
Why do different haloalkanes undergo hydrolysis at different rates?
C-Halo bonds with higher bond enthalpies require more energy to break, causing them to react more slowly
Which of C-Br, C-Cl and C-F will react the fastest?
C-Br
What can be prepared from haloalkanes by hydrolysis with NaOH?
Alcohols
What is the halogen replaced by after a haloalkane undergoes hydrolysis?
an -OH group
How does hydrolysis of haloalkanes occur?
1.) The nucleophilic OH- ion approaches the carbon attached to the halogen on the opposite side (of the halogen)
2.) The OH- ion reduces repulsion between the nucleophile and the partially negative halogen alkane
3.) The lone pair of electrons on the OH- ion is donated to the partially positive carbon
4.) The carbon-halogen bond is broken by heterolytic fission
5.) An alcohol and halide is formed
What is heterolytic fission?
Where one atom involved in a covalent bond receives both the electrons when broken
