Halogenoalkanes Flashcards
what do halogenoalkanes have?
different rates of substitution
What are the bond energies for different halo-alkanes?
c-f is the strongest bond
c-i is the weakest bond
what will reacting halogenoalkanes with aqueous silver nitrate result in?
chlorides make white precipitate of silver chloride. bromides make a cream precipitate of silver bromide. iodides make a pale yellow precipitate of silver iodie
which precipitate formation is the fastest and the slowest?
the formation of the pale yellow silver iodide is the fastest(fastest nucleophilic substitution reaction) (most reactive) whereas the formation of the silver fluoride isthe slowest (least reactive
define a primary haloalkane
has one alkyl group attached to the carbon with the halogen atoms eg 2-bromobutane
define a secondary halo alkane
has two alkyl groups attached to the carbon with the halogen atom
define a tertiary halo alkane
has three alkyl groups attached to carbon atom with the halogen atom
why is the c-h bond in a halo-alkane said to be polar?
it has a permanent dipole
what states are halo alkanes at room temp and pressure?
liquid or gases. the bpt is dependant on the IMF that operate
what happens to halo-alkanes bpt as the chain gets longer/bigger molecule?
the boiling point increases. the molecule is bigger so greater electronegativity and so greater van der waals forces
what happens to the bpt if the atomic mass/atom size increases?
the boiling point due to increases in the van der waals forces of attraction
What is nucleophilic substitution?
Reaction in which a molecule with a partial positive charge is attacked by a nucleophile and the replacement of a leaving group for example halogen by the nucleophile
What is a nucleophile?
Electron pair donor eg a hydroxide ion cyanide ion and ammonia
What is an intermediate?
In chemistry, a reactive intermediate is a short-lived highly reactive molecule. When generated in a chemical reaction, it will be quickly converted into a more stable molecule.
What does the arrows show?
Movement of electrons
What is the nucleophile attracted to?
Area of positivity
What can the reagents for nucleophilic substitution be?
Hydroxide ions
Cyanide ions
Ammonia ions
What can the reagents for elimination be?
Hydroxide ions
What are the conditions for nucleophilic substitution with hydroxide ions?
Warm aqueous sodium hydroxide and ethanol
Reflux
What are the conditions for nucleophilic substitution with cyanide ions?
Warm ethanolic potassium or sodium cyanide
Reflux
What are the conditions for nucleophilic substitution with ammonia ions?
Heat with ethanolic ammonia
Use excess ammonia
What are the conditions for the elimation reaction with hydroxide ions?
Warm ethanolic sodium or potassium hydroxide
Reflux
What does primary secondary and tertiary halo alkanes favour? Substitution and Elimination
Primary- substitution
Secondary-both occur at the same time
Tertiary. - elimination
What do higher temperatures favour in terms of substitution or elimination?
Favour elimination
