3.3 Halogenoalkanes Flashcards
(39 cards)
What is a primary Haloalkane?
The carbon with halogen is attached to one alkyl group
I
C-C-I
I
Only one link from the CH2 to the alkyl
What is a secondary haloalkane?
Carbon with halogen is attached to two other groups
-C-C-C
I
Br
What is a tertiary haloalkane?
Carbon holding the halogen is attached to three other alkyl group
C
I
C-C-C
I
Br
What is the trend in haloalkane bond enthalpies?
Get weaker going down the group due to greater distance and shielding
What is hydrolysis?
Using water to break up a compound
What is the formula for the addition of silver nitrate?
Ag+ + X —> AgX
Why is iodine the fastest to form a precipitate?
It’s the biggest atom so weakest attraction (more distance and shielding) so precipitation is formed quicker
What colour precipitates does Iodine,Bromine and Chlorine form with silver nitrate?
Iodine- Yellow
Bromine- Cream
Chlorine- White
What is the definition of a nucleophile?
A negatively charge ion or an atom with a delta negative charge
Has a lone pair
Electron donator
What are the common nucleophiles?
Hydroxide ions- :OH-
Ammonia- :NH3
Cyanide- : CN
In a haloalkane nucleophillic substitution reaction what is the leaving group ?
Halide ion
What is the order of reactivity with Haloalkanes?
C - Hal bond determines reactivity
C-F stronger (fewer shells)
What do nucleophilic substitution of OH ions form?
- Alcohols
What happens in nucleophilic substitution of OH?
- Lone pair on the O
- Attacks positive C atom
- Halogen is replaced by OH
- HYDROLYSIS
What happens if OH ions undergo nucleophilic substitution in water?
- Reaction works same as normal
- Slower than other reactions
What do CN- ions form with Haloalkanes?
- Forms nitriles
What happens in a nucleophilic substitution reaction with CN- ions?
- Weakly nucleophilic
- Partially positive carbon atom attacked by lone pair on CN-
What happens to the length of the carbon chain in Nucleophilic Substitution with CN ions?
It increases as the CN adds another carbon to the halogen
What conditions must CN- nucleophilic substitution reactions take place under?
- Reflux conditions
- Ethanol
Why must CN- nucleophilic substitution not occur in aqueous conditions?
- The water would act as a nucleophilic and take over
What happens in the nucleophilic substitution of NH3
- Lone pair on NH3 attacks partially charged Carbon
- C-N bond replace C-Hal and has a positive charge
- Annother Ammonia molecule then picks up a H+ from the NH3 leaving an amine group
What conditions are required for NH3 to undergo nucleophilic substitution?
- Ethanol
- Excess Ammonia
Why must there be excess Ammonia for NH3 nucleophilic substitution?
- Because the amine group created is also nucleophilic
- Would react again with haloalkane
- To prevent further substitution
What are formed as a by product of nucleophilic substitution with NH3?
- Quartenery ionic salts
- Extra H+ is picked up by NH3
- Forms NH4 +
