Organic (Y1) Halogenoalkanes Flashcards
Learn all about the halogenoalkane content from year one
How are halogenoalkanes named?
Based on original alkane with prefix indicated halogen atom e,g, F; Fluoro
Cl; Chloro etc.
- substituents are listed alphabetically
What type of reactions do halogenoalkanes undergo?
They undergo either substitution or elimination reactions
What’s nucleophilic substitution?
Substitution: swapping a halogen atom for another atom or groups of atoms.
Nucleophile: Electron pair donator e.g. :OH- or :NH3 or CN-
What’s the general mechanism for nucleophilic substitution
- Arrow from lone pair of electrons on the nucleophile to the delta positive carbon
- Arrow from C-X bond to the X
- X- is formed
:Nu acts as nucleophile - always a lone pair.
what is the rate of the substitution reactions dependant on?
The rete of these substitution reactions depends on the strength of the C-X bond. Weaker the bond is, the easier it is to break and the faster the reaction. Iodoalkanes are fastest to substitute and the fluoroalkanes are the slowest.
Define hydrolysis
Hydrolysis is defined as the splitting of a molecule (in this case a halogenoalkane) by the reaction with water.
What is formed when silver nitrate is added to a halogenoalkane?
Aqueous silver nitrate is added to halogenoalkane. The halide leaving group combines with a silver ion to form a silver halide precipitate.
What colour precipitate is AgI, AgBr and AgCl respectively?
yellow, cream, white.
Suggest reagent, conditions, mechanism and type of mechanism for nucleophilic substitution with hydroxide ions
Reagent: KOH/ NaOH
Conditions: - In aqueous solution, heated under reflux
Mechanism: Nucleophilic substitution
Type of reagent: Nucleophile.
What is different for nucleophilic substitution for tertiary halogenoalkanes?
The halogen breaks off first leaving a positive carbon ( make sure to draw +) which is attacked by nucleophile.
Suggest functional group, reagent, conditions, mechanism and type of reagent for nucleophilic substitution reaction with cyanide ions
Halogenoalkane --> Nitrile Reagent: KCN dissolved in ETHANOL/Water mixt. Conditions: Heated by reflux Mechanism: Nucleophilic substitution Type of reagent: Nucleophile :CN-
Suggest reagent, conditions, mechanism, type of reagent for reaction who’s functional group changes from halogenoalkane to amine
Reagent: NH3 dissolved in ethanol
Conditions: Heating under pressure.
Mechanism: Nucleophilic substitution
Type of reagent: Nucleophile, :NH3
What difference does it make if aqueous/alcoholic solvent is used to dissolve hydroxide ions
Aqueous: Substitution
Alcoholic: Elimination
What’s the type of mechanism that can make the functional group change from halogenoalkane to alkene?
Elimination with alcoholic hydroxide ions.
Suggest reagent, conditions, mechanism and type of reagent for elimination with alcoholic hydroxide ions.
Reagents: KOH/NaOH
Mechanism: Elimination
Type of Reagent: Base, OH-
Suggest a mechanism for elimination reaction of 2-bromopropane with KOH (Alc)
:OH- attacks adjacent H.
The same C-H bond arrow from the bond to C-C bond adjacent.
Arrow from C-Br bond to Br.
How can different structural isomers be formed?
Unsymmetrical secondary and tertiary HAs two different structural isomers can be formed.
When 2-methyl-2-chlorobutane is eliminated, what 2 isomers can form?
2-methylbut-1-ene
2-methylbut-2-ene
The structure of halogenoalkane has effect on which degree substitution/elimination occurs in the reaction. What does primary and tertiary tend towards.
Primary tends towards substitution. Tertiary tends towards elimination.
Name one use of HA
- Chloroalkanes and chlorofluoroalkanes can be used as solvents.
- often used as refrigerants, pesticides and aerosol propellants
Why have many uses of HA stopped?
Stopped due to toxicity and detrimental effect on the atmosphere.
This is the point I gave up making questions on Ozone chemistry
Please learn ozone chemistry. Ok cool thanks.
