halogenoalkanes Flashcards
bpt trend of haloalkanes
increase as you go down group
the strength of intermolecular forces govern bpt
more electrons means stringer van der waals between molecules and so more energy needed to overcome forces
halogenoalkanes have a … bond and are attacked by …
polar
nucleophiles
why are halogenoalkanes polar
halogen’s are more electronegative than carbon so they pull electrons towards themselves in a covalent bond
what is a nucleophile
a substance that is an electron pair donor
examples of nucleophiles
ammonia
hydroxide ions
cyanide ions -CN
halogenoalkanes react with hydroxide ions via …
nucleophilic substitution
reaction with OH- conditions
warm aqueous sodium hydroxide
carried out under reflux
process of reaction with OH-
a nucleophile will attack delta positive carbon and will replace the halogen on the haloalkane.
the C-X breaks, both electrons move from the bond to the halogen. a new bond is formed between OH- and carbon
an alcohol is formed
halogenoalkanes react with cyanide ions to make …
nitriles
reaction with CN- conditions
warm ethanol potassium cyanide
carried out under reflux
process of reaction with CN-
a nucleophile will attack the delta positive carbon and replace the halogen.
the CX breaks, both electrons move from the bond to the halogen. a new bond is formed between CN- and carbon
a nitrile is formed
halogenoalkanes react with ammonia via …
nucleophilic substitution
reaction with ammonia conditions
heat with ethanol ammonia
must have excess ammonia
ammonia will attack delta positive carbon and will replace the halogen forming an intermediate
nitrogen is left with positive charge as it can only form three bonds and so it is unstable
another molecule of ammonia acts as a base by reacting with hydrogen (why we need excess
amine and ammonium ion is produced
how to identify amine
fishy smell
reactivity trend of halogenoalkane
more reactive as you go down the group
the bond enthalpy is lower as you go down making it easier to break and therefore react
halogenoalkanes react wit hydroxide Iona via … using ethanol solvent
elimination
condition of OH- elimination
warm ethanol sodium hydroxide
carried under reflux
process of OH- elimination
the OH- will attack the hydrogen on a carbon adjacent to carbon with halogen on. OH- acts as a base forming water
electrons in the bond move to form a double bond in between two carbons
the C-X breaks, both electrons move from the bond to the halogen
an alkene, water and chloride ion is formed
the … plays an important role whether its an elimination or substitution
solvent
what are CFCs
chlorofluorocarbons are molecules that have had all hydrogens replaced by chlorine and fluorine
what is the issue with CFC
they are stable but are broken down by UV ad can break down ozone in the atmosphere. radicals are formed and they catalyse the breakdown of ozone
which halogenoalkane is easiest to break
C-Cl because it has the lowest bond enthalpy
describe the process of CFC destroying zone
initiation
sunlight breaks the C-Cl bond and produces 2 radicals which will react with ozone molecules
propagation
the Cl* reacts with O3 to form ClO* intermediate and O2-
the ClO* reacts with more O3 to make O2 and Cl. As Cl is reformed it acts as a catalyst
termination
2 radicals react with each other
overall: 2O3 => 302
