15.1 The chemistry of haloalkanes Flashcards
How do you classify haloalkanes?
Primary, Secondary, Tertiary
What elements do haloalkanes contain?
C, H, at least one halogen
How does naming work if there is more than 1 halogen in a carbon chain?
List the halogens alphabetically
Definition of nucleophile
An electron pair donor
What is a nucleophile?
An atom or group of atoms that are attracted to an electron deficient carbon atom, where it donates a pair of electrons to form a new (dative) covalent bond
Examples of nucleophiles
Explain the reactivity of halogens
-Have a C-X (carbon-halogen) bond in their structure
-Halogens are more electronegative (δ−) than carbon atoms
-The electron pair in the C-X bond is closer to the halogen atom, causing a polar bond
What is the prefix for the halogens (F, Cl, Br, I)?
F - fluoro-
Cl - chloro-
Br - bromo-
I - iodo-
What happens when a halogen reacts with a nucleophile?
Nucleophile replaces the halogen in a substitution reaction
What is the name of the mechanisms for hydrolysis of primary haloalkanes?
Nucleophillic substitution
What is a hydrolysis reaction
A chemical reaction involving water or an aqueous solution of hydroxide ions (:OH-) that causes the breaking of a bond in a molecule, resulting in two products
What happens in the hydrolysis of haloalkanes?
Halogen is replaced by the -OH group
What is the mechanism for the hydrolysis of chloroethane?
- :OH- nucleophile approaches the C atom attached to the X on the opposite side
- The direction of the attack by the :OH ions minimises the repulsion between the nucleophile and the δ− halogen
- Lone pair of e- on the :OH- ion is attracted and donated to the δ+ carbon atoms
- New bond is formed between the O of the hydroxide ion and the δ+ carbon
- C-X bond breaks by heterolytic fission, both electrons go to the halogen
- Alcohol and halide ion are formed
What are the products of hydrolysis of an haloalkanes under nucleophillic substitution
Alcohol and a halide ion (X-)
How is the C-X bond broken in nucleophilic substitution?
Heterolytic fission
What is the equation for the reaction of 1-bromobutane with NaOH?
What are the reagents and conditions for the hydrolysis reaction of haloalkanes to alcohols?
aqueous sodium hydroxide (NaOH), heated under reflux
What are the products of the hydrolysis of haloalkanes to form alcohols?
Alcohol, sodium halide (NaBr, NaCl)
Why is the hydrolysis of haloalkanes to alcohols heated under reflux?
-Reaction is very slow at room temperature
-Produces a good yield of product (alcohol)
What are nucleophiles attracted to?
low electron density
Is hydroxide acid or alkaline?
Alkaline
What type of reaction is the hydrolysis of haloalkanes?
Substitution
What does the rate of hydrolysis depend on?
The strength of the carbon-halogen bond in the haloalkane
Which C-X bond has the highest bond enthalphy to the lowest?
Fluorine - highest bond enthalphy
Iodine - lowest bond enthalphy
