4.5 Haloalkanes Flashcards
What are haloalkanes ?
Haloalkanes are compounds containing carbon, hydrogen and at least 1 halogen.
What are aliphatic haloalkanes ?
Halogen joined to a straight chain or branched carbon chain.
What is a primary haloalkane ?
0/1 alkyl groups attached to carbon with halogen.
What is a secondary haloalkane ?
2 alkyl groups attached to the carbon atom with halogen attached.
What is a tertiary haloalkane ?
3 alkyl groups attached to carbon atom with halogen attached.
What type of bond is the halogen-carbon bond in a haloalkane ?
Polar bond are halogens are more electronegative than carbon so pair of electrons in the bond are closer to the halogen than the carbon.
Why can carbon atom attract a nucleophile in haloalkane ?
Carbon has slight positive charge so attracts nucleophile, that acts as an electron pair donor.
Eg., OH-, H20, NH3
What is a nucleophile ?
A chemical species that can donate a pair of electrons to a different chemical species (generally to an electrophile) to form a chemical bond in a reaction.
What is nucleophilic substitution of haloalkanes ?
When primary haloalkanes react with a nucleophile in a substitution reaction, where the halogen is substituted for the nucleophile.
What is hydrolysis of haloalkanes ?
Chemical reaction involving water or an aqueous solution that causes the braking of a bond in a molecule.
What is the first step in nucleophilic substitution ?
Nucleophile approaches carbon atom attached to the halogen from the opposite side of the molecule.
What is minimised by the direction of attack in nucleophilic substitution ?
Minimises repulsion between nucleophile and delta negative halogen.
What is attracted to carbon atom in nucleophilic substitution ?
Lone pair of electrons is attracted and donated to the delta positive carbon atom attached to the halogen.
What occurs when attraction is formed between lone pair of electrons and carbon atom of haloalkane ?
-Carbon-halogen bond is broken by heterolytic fission.
-New bond is formed between oxygen, from nucleophile, and carbon atom on haloalkane.
This forms new organic product, an alcohol, and a halide ion.
What is the rate of hydrolysis determined by in a haloalkane ?
Depends on strength of carbon-halogen bond in haloalkane.
C-F bond is strongest
C-I bond is weakest