halogenoalkanes Flashcards
what is meant by primary, secondary and tertiary structure of halogenoalkanes?
a primary halogen alkane has two hydrogen atoms and just one allyl group
a secondary halogenoalkne has just one hydrogen atom and two alkyl groups
a tertiary has no hydrogens and 3 alkyl groups.
in what type of reaction can halogenoalkanes be hydrolysed to form alcohols?
a nucleophilic substitution reaction - using water
how can you compare the reactivity of halogenoalkanes?
when you mix a halogenoalkane with water, it forms an alcohol
if you also put silver nitrate solution in the mixture two then, the silver ions will react with the halide ions as soon as they form, this gives a silver halide precipitate.
to compare the reactivities of different halogenoalkanes, set up three test tubes each containing a different halogenoalkane, ethanol as a solvent and silver nitrate solution. and then time
what are the different reactivities of the hologenoalkanes?
primary are the slowest and tertiary are the fastest. todo alkanes are hydrolysed the fastest- in order to hydrolyse the carbon-halogen bond. all depends on the bond enthalpy - weaker bonds break more easily.
what does cyanide react with halogenoalkanes to form?
Nitriles. if you reflex a halogenoalkane with potassium cyanide in ethanol, then the cyanide ions will react with the halogenoalkanes by nucleophilic substitution to form a nitrile
what do halogenoalkanes react with ammonia to form?
they form amines. amines are organic compounds based on ammonia but one or more of the hydrogen atoms are replaced with alkyl groups. if you warm halogenoalkanes with excess ethanolic ammonia, the ammonia swaps places with the halogen to form a primary amine - nucleophilic substitution.
what happens when halogenoalkanes undergo elimination reactions?
if you react a halogenoalkane wth a warm alkali dissolved in ethanol, you get an alkene. the mixture must be heated under reflux or volatile stuff will be lost
in this reaction the hydroxide ions act as a base in order to remove one H+ ion from the halogenoalkane
what is a nucleophilic substitution reaction?
halogens are generally more electronegative than carbon, the carbon-halogen bond is the therefore polar. the + carbon doesn’t have enough electrons meaning that it can be attacked by a nucleophile. a nucleophile can bond with the carbon and be substituted for the halogen.
what are the three examples of a nucleophilic substitution?
halogenoalkanes reacting with aqueous KOH to form Alcohols
cyanide ions react with halogenoalkanes to form nitriles
halogens react with ammonia to form amines.
