Halogenoalkanes Flashcards
What happens when alkanes react with uv-light?
they form halogenoalkanes and hydrogen halides
What is the equation for the reaction with alkanes in uv-light
halogen + alkane > halogenoalkane + hydrogen halide
what is a free radical?
reactive species due to the presence of an unpaired electron
what happened in the initiation step?
uv light causes a covalent bond between halogens atoms to break and this creates 2 halogen radicals
X2 > 2X•
What happens in the first propagation step?
The halogen radical reacts with an alkane
radical removes a hydrogen from the alkane creating a hydrogen halide molecule
CH4 + X• > •CH3 + XH
alkane is left as a alkyl radical
What happens in the second propagation step?
alkyl radical reacts with a halogen molecule and created a halogenoalkane
remaining halogen is left as a halogen radical
•CH3 + X2 > •X + CH3X
What happens in the termination step?
2 radicals will react to form a molecule
either:
two halogen radicals
halogen radical + alkyl radical
two alkyl radicals
what are short chain chlorofluorocarbons used for?
they are gases and were used for refrigerators
what are long chain chlorofluorocarbons used for?
dry cleaning and de-greasing solvents
what happened when chlorofluorocarbons are decomposed?
they form chlorine free radicals when in the atmosphere
why is the ozone layer important?
absorbs harmful uv radiation
how is a chlorine radical formed?
C-Cl breaks in the presence of uv radiation to form Cl•
R-Cl > R• + Cl•
What is the equation for the decomposition of ozone?
Cl• + O3 > ClO• + O2
What is the equation for ClO• attacking more radicals?
ClO• + O3 > 2O2 + Cl•
What is the overall equation to show ozone breakdown?
2O3 > 3O2
What is a primary halogenoalkane?
halogen is bonded to a C that is bonded to 1 other C
What is a secondary halogenoalkane?
halogen is bonded to a C that is bonded to 2 other Cs
What is a Teritary halogenoalkane?
halogen is bonded to a C that is bonded to 3 other Cs
What is a mechanism?
pictorial representation of the movement of a pair of electrons during a chemical reaction
What is a nucleophile?
donate electron pairs to electrophiles
What happens in nucleophilic substitution?
- nucleophile donates lone pair to carbon and forma a covalent bond
- carbon gives electrons back to halogen and bond breaks
What are the conditions for nucleophilic substitution?
warm aqueous solution
What are the conditions for nucleophilic substitution to form amines?
warmed in excess of ammonia
What is the overall equation for nucleophilic substitution to form amines?
CH3CH2X + 2NH3 > CH3CH2NH2 + NH4X
what is formed when a primary amine recast with another halogenoalkane
secondary amine
what forms when a secondary amine reacts with another halogenoalkane?
tertiary amine
what is formed when a tertiary amine reacts with another halogenoalkane?
quaternary ammonium salt
What are the conditions for elimination?
hot ethanol
What is formed after elemination
an alkene and water
What are the steps of elimination?
- hydroxide removes a hydrogen from an adjacent carbon to the halogen
- electrons in C-H move to the C-C bond to create a double bond
- electrons in C-Halogen move into halogen breaking the bond and forming a halide ion
