Chemistry: Halogenoalkanes
This flashcard set introduces halogenoalkanes, detailing their general formula and functional group. It explains their increased reactivity due to polar bonds and outlines common applications such as refrigerants, solvents, and pharmaceuticals. Naming conventions are based on the parent alkane with halogen prefixes.
general formula halogenoalkanes
CnH2n+1Hal
Key Terms
general formula halogenoalkanes
CnH2n+1Hal
functional group
C-Hal
what does the presence of the polar bond in halogenoalkanes mean
they’re more reactive than alkanes
3 uses of halogenoalkanes
refrigerants
solvents
pharmaceuticals
how are halogenoalkanes named
after the parent alkane with the prefix chloro, bromo, iodo etc.
what must be indicated if there are more than 3 carbon atoms in the molecule
the position of the halogen
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| Term | Definition |
|---|---|
general formula halogenoalkanes | CnH2n+1Hal |
functional group | C-Hal |
what does the presence of the polar bond in halogenoalkanes mean | they’re more reactive than alkanes |
3 uses of halogenoalkanes |
|
how are halogenoalkanes named | after the parent alkane with the prefix chloro, bromo, iodo etc. |
what must be indicated if there are more than 3 carbon atoms in the molecule | the position of the halogen |
what must be indicated if 2 or more halogens are present | their positions in the chain |
how are the halogens named if there are 2 of them in the chain and they are different | in alphabetical order |
what 2 reactions do halogenoalkanes take part in | nucleophilic substitution and elimination |
what is the halogen atom replaced with in a nucleophilic substitution reaction | by a new group of atoms |
nucleophile | electron pair donor |
why do halogenoalkanes take part in nucleophilic substitution | the carbon is bonded to a halogen and so it is rendered electron deficient |
where does the nucleophile donate its pair of electrons to in nucleophilic substitution | the delta plus c atom to form a new bond |
how does the C-Hal bond break in nucleophilic substitution and what does it form | Heterolytic fission halide ion formed |
examples of common nucleophiles | hydroxide |
what do halogenoalkanes react with aqueous hydroxides to form | alcohols |
what is the reaction between halogenoalkanes and aqueous hydroxides often referred to as | hydrolysis |
hydrolysis | the breaking of a bond using water |
what is the reagent in nucleophilic substitution with aqueous hydroxides | the hydroxide |
what conditions are needed for nucleophilic substitution using hydroxide | warm and aqueous |
general equation for the nucleophilic substitution between halogenoalkane and hydroxide | R-Hal + NaOH > R-OH + NaHal |
reagent for nucleophilic substitution between halogenoalkane and cyanide | cyanide ion |
conditions for nucleophilic substitution between halogenoalkane and cyanide | warm and ethanolic |
general equation for for nucleophilic substitution between halogenoalkane (bromo) and (potassium) cyanide | RBr + KCN > RCN + KBr |
what does reacting a halogenoalkane with cyanide increase | the length of the carbon chain |
what do halogenoalkanes react with excess ammonia to form | amines |
reagent for nucleophilic substitution between halogenoalkane and ammonia | NH3 |
conditions for nucleophilic substitution between halogenoalkane and ammonia | ethanolic and warm |
general equation for nucleophilic substitution between halogenoalkane and ammonia | R-Hal + 2NH3 > RNH2 + NH4 + Hal- |
what does the rate of substitution reactions of halogenoalkanes depend on | the c-hal bond enthalpy |
what does a halogenoalkane react to form in an elimination reaction | an alkene |
elimination | a reaction in which an atom/group of atoms is removed from a reactant |
reagent for elimination reaction with halogenoalkanes | hydroxide |
conditions for elimination reaction with halogenoalkanes | HOT and ethanolic |
sequence of events in elimination reactions with halogenoalkanes |
|
what is the role of the hydroxide in elimination with halogenoalkanes | base |
substitution vs elimination using hydroxide: conditions | s: warm and aqueous |
substitution vs elimination using hydroxide: major product | s: alcohol |
substitution vs elimination using hydroxide: role of OH- | s: nucleophile |
what properties of chloroflourocarbons make them suitable for use as solvents and refrigerants | non-toxic and low reactivity |
what did the properties of chloroflourocarbons lead to | the depletion of the ozone layer |
where does ozone form | in the upper atmosphere |
how does ozone form | from the reaction of oxygen atoms with oxygen molecules |
equation for formation of ozone: | O + O2 > O3 |
why is the ozone layer beneficial | it absorbs UV radiation that can cause skin cancer |
what did scientists discover that waste CFCs didnt do | break down easily and so would rise up to the upper atmosphere and break down to form chlorine radicals |
what do chlorine radicals do and what has this led to | catalyse the breakdown of ozone led to a hole in the ozone layer |
equation for chlorine radicals reacting with ozone | O3 + Cl. > O2 + ClO. ClO+ O3> 2O2 + Cl. |
what alternatives to CFCs are now used | organohalogens that don't contain chlorine |