Functional group chemistry for designer molecules
Haloalkanes
Introduction
Haloalkanes are molecules that contain a hydrogen atom bonded to an alkane. Haloalkanes that
have one halogen have the general formula C n H 2 n+ 1X with X representing the halogen. For
haloalkanes like 2-bromopropane, the numbers are used to show the position of the halogen in the
molecule. For haloalkanes such as 1,2 dichloroethane, you can see that the molecule has two
halogen atoms hence, the word ‘di’ in the name. for 2-bromo-1- chloropropane, because they have
different halogens, they are listed alphabetically and not by position number.
The bond between a carbon and halogen atom is polar, this polarity affects the reactivity and
physical properties of the haloalkanes. The halogen is always electronegative which means that
there is a pair of electrons in the covalent bond between the carbon and halogen atom with the
electrons being closer to the halogen atom, causing the halogen atom to become slightly negative
and the carbon to become slightly positive.
Haloalkanes have a higher boiling point compared to their equivalent alkanes because alkanes have
Van der Waals forces between then and haloalkanes although they also have van der Waals forces
between them the polarity of the carbon to halogen bond contain permanent dipole-dipole forces
which are stronger then van der Waals forces requiring more energy to break. This makes them
useful to make things like alcohols, nitrates and alkanes. Finally, haloalkanes are insoluble in water
because haloalkanes cannot form hydrogen bonds. However, haloalkanes are soluble in non-polar
solvents such as cyclohexane.
Commercial importance
Halagoalkanes are used as:
Flame retardants
, Fire extinguishers
Solvents
Pharmaceuticals
Halogenoalkanes can react with a hydroxide ion to produce an alcohol, as shown below.
Equation
RCH 2 CH 2 CL + NaOH −¿ ¿ RCH 2 CH 2 OH +NaCL−¿¿
Chloroalkane+ sodium hydroxide ethanol+ sodium chloride
Reaction conditions for halogenoalkanes reacting with hydroxide ions
Warm sodium hydroxide
Under reflux
Mechanism: nucleophilic substitution
Halogenoalkanes can also react with cyanide ion to produce nitriles, as shown below
Equation
CH 3 CH 2CL+ KCN CH 3 CH 2 CH 2 CN +¿ Cl−¿¿
Chloroethane + potassium cyanide propionitrile + chloride ion
Reaction conditions for halogenoalkanes reacting with cyanide ions
Warm ethanoic potassium cyanide
Under reflux
Mechanism: nucleophilic substitution
Halogenoalkanes can also react with ammonia as shown below
Equation
CH 3 CH 2CL + NH 3 CH 3 CH 2CN + Cl−¿¿
Chloroethane+ ammonia ethyl ammonium + chloride ion
Reaction conditions for halogenoalkanes reacting with ammonia
Hot ethanoic ammonia
Mechanism: nucleophilic substitution
Alcohols
All alcohols have an alcohol functional group which is known as a hydroxyl group. To name a alcohol
you start with the name of the alkane for example ethanol is based off of the alkane ethane, you
remove the final ‘e’ and add the suffix ‘ol’ to make ethanol. Numbers can be used to show which
carbon atom is bonded to the hydroxyl group for example propan-2-ol. Alcohols are polar which
allow them to dissolve organic compounds which do not mix well with water.
, Commercial importance
Alcohols are used in perfumes and cosmetics but in industry they are used to make carboxylic acids
and aldehydes. Ethanol is also used for dyes, paints and varnishes and is used to make organic
compounds like chloroform. Methanol is used to make plastics, paints and explosives
Primary alcohols can be oxidised to produce an aldehyde and are then oxidized further to produce
carboxylic acids
Equation for aldehyde
concentated H 2 SO 4
CH 3 CH 2OH + [O] --->CH 3 CH O + H 2O
[O] = K 2 Cr2 O7 / potassium dichromate
concentated H 2 SO 4
Ethanol + acidified potassium dichromate --- > ethanal + water
An aldehyde is made by removing 2 hydrogens from ethanol for it to bond with oxygen from the
oxidising agent to form a water molecule and ethanal.
Equation for carboxylic acid
CH 3 CH O + [O] CH 3 COOH
[O] = K 2 Cr2 O7 / potassium dichromate
Ethanal + oxidising agent (potassium dichromate) ethanoic acid
A carboxylic acid is formed when ethanal is oxidised to form a carboxylic acid
Conditions of oxidizing primary alcohols
Reflux
Distillation
Haloalkanes
Introduction
Haloalkanes are molecules that contain a hydrogen atom bonded to an alkane. Haloalkanes that
have one halogen have the general formula C n H 2 n+ 1X with X representing the halogen. For
haloalkanes like 2-bromopropane, the numbers are used to show the position of the halogen in the
molecule. For haloalkanes such as 1,2 dichloroethane, you can see that the molecule has two
halogen atoms hence, the word ‘di’ in the name. for 2-bromo-1- chloropropane, because they have
different halogens, they are listed alphabetically and not by position number.
The bond between a carbon and halogen atom is polar, this polarity affects the reactivity and
physical properties of the haloalkanes. The halogen is always electronegative which means that
there is a pair of electrons in the covalent bond between the carbon and halogen atom with the
electrons being closer to the halogen atom, causing the halogen atom to become slightly negative
and the carbon to become slightly positive.
Haloalkanes have a higher boiling point compared to their equivalent alkanes because alkanes have
Van der Waals forces between then and haloalkanes although they also have van der Waals forces
between them the polarity of the carbon to halogen bond contain permanent dipole-dipole forces
which are stronger then van der Waals forces requiring more energy to break. This makes them
useful to make things like alcohols, nitrates and alkanes. Finally, haloalkanes are insoluble in water
because haloalkanes cannot form hydrogen bonds. However, haloalkanes are soluble in non-polar
solvents such as cyclohexane.
Commercial importance
Halagoalkanes are used as:
Flame retardants
, Fire extinguishers
Solvents
Pharmaceuticals
Halogenoalkanes can react with a hydroxide ion to produce an alcohol, as shown below.
Equation
RCH 2 CH 2 CL + NaOH −¿ ¿ RCH 2 CH 2 OH +NaCL−¿¿
Chloroalkane+ sodium hydroxide ethanol+ sodium chloride
Reaction conditions for halogenoalkanes reacting with hydroxide ions
Warm sodium hydroxide
Under reflux
Mechanism: nucleophilic substitution
Halogenoalkanes can also react with cyanide ion to produce nitriles, as shown below
Equation
CH 3 CH 2CL+ KCN CH 3 CH 2 CH 2 CN +¿ Cl−¿¿
Chloroethane + potassium cyanide propionitrile + chloride ion
Reaction conditions for halogenoalkanes reacting with cyanide ions
Warm ethanoic potassium cyanide
Under reflux
Mechanism: nucleophilic substitution
Halogenoalkanes can also react with ammonia as shown below
Equation
CH 3 CH 2CL + NH 3 CH 3 CH 2CN + Cl−¿¿
Chloroethane+ ammonia ethyl ammonium + chloride ion
Reaction conditions for halogenoalkanes reacting with ammonia
Hot ethanoic ammonia
Mechanism: nucleophilic substitution
Alcohols
All alcohols have an alcohol functional group which is known as a hydroxyl group. To name a alcohol
you start with the name of the alkane for example ethanol is based off of the alkane ethane, you
remove the final ‘e’ and add the suffix ‘ol’ to make ethanol. Numbers can be used to show which
carbon atom is bonded to the hydroxyl group for example propan-2-ol. Alcohols are polar which
allow them to dissolve organic compounds which do not mix well with water.
, Commercial importance
Alcohols are used in perfumes and cosmetics but in industry they are used to make carboxylic acids
and aldehydes. Ethanol is also used for dyes, paints and varnishes and is used to make organic
compounds like chloroform. Methanol is used to make plastics, paints and explosives
Primary alcohols can be oxidised to produce an aldehyde and are then oxidized further to produce
carboxylic acids
Equation for aldehyde
concentated H 2 SO 4
CH 3 CH 2OH + [O] --->CH 3 CH O + H 2O
[O] = K 2 Cr2 O7 / potassium dichromate
concentated H 2 SO 4
Ethanol + acidified potassium dichromate --- > ethanal + water
An aldehyde is made by removing 2 hydrogens from ethanol for it to bond with oxygen from the
oxidising agent to form a water molecule and ethanal.
Equation for carboxylic acid
CH 3 CH O + [O] CH 3 COOH
[O] = K 2 Cr2 O7 / potassium dichromate
Ethanal + oxidising agent (potassium dichromate) ethanoic acid
A carboxylic acid is formed when ethanal is oxidised to form a carboxylic acid
Conditions of oxidizing primary alcohols
Reflux
Distillation
