Organic ReactionsSubstitutionElimination

AdditionEsterification

Organic Reactions So far in this unit we have discussed

hydrocarbons and their isomers

We have also learned about organic compounds with different functional groups

Throughout this we have learned naming rules for each

Now we are going to focus on several types of organic reactions

Types of Organic Reactions

There are many types of organic reactions

We are only going to focus on a few.› Substitution› Elimination› Addition› Esterification

Substitution Any reaction in which one atom is

replaced by another

Used to place a halogen onto an alkane

The products are always a halocarbon and the acid of the halogen

Reaction requires ultraviolet light to initiate the reaction› This provides the energy needed to form

the excited state

Substitution - Example

ethane + chlorine chloroethane + hydrochloric acid

The Cl atom will replace a H atom resulting in an alkyl halide and the acid of the halogen (hydrochloric acid)

Substitution

You can also have an alcohol react with a halogen resulting in an alkyl halide and water

Ethanol + hydrochloric acid chloroethane + water

Elimination

Any reaction in which atoms are eliminated from another molecule

Done in three ways:› Elimination of H2

› Elimination of HX› Elimination of H2O

Loss of H2

Called dehydrogenation

Occurs in the presence of a base (eg. NaOH) and heat

ethane ethene + hydrogen

Loss of HX Alkyl halides undergo elimination reaction

This is known as dehydrohalogenation

Occurs in the presence of a base

Base extracts H+ and X- will leave; resulting in double bond formation

Loss of H2O

Alcohol can undergo elimination via the loss of water

Known as dehydration

a) Acid protonates the OH group, water leaves and C+ remains behind

b) An adjacent H+ leaves next leaving electron pair to form double bond

Addition Takes place with unsaturated compounds which

are usually more reactive than saturated compounds

Takes place with double and triple bonds

Two atoms are added across the electron rich bond

Four types of addition:› Addition of X2 (halogen)

› Addition of H2

› Addition of H2O

› Addition of HX (hydrogen halide)

Addition of Halogen Normally occurs in dissolved solvents

such as CCl4

Alkenes form dihaloalkanes

Alkynes produce dihaloalkenes or tetrahaloalkanes

ethene + chlorine 1,2-dichloroethane

Addition of Hydrogen Catalysts used such as Pt, Pd or Ni Known as hydrogenation Alkene becomes alkane Alkyne becomes alkene or alkane

ethene + hydrogen ethane

ethyne + hydrogen ethene

ethyne + (2 mol) hydrogen ethane

Addition of Water Occurs in the presence of an acid Know as hydration Alkene becomes alcohol Alkyne produces ketone or aldehyde

ethene + water ethanol

Addition of Hydrogen Halide HX = HCl or HBr or HI (NOT HF)

Alkene becomes alkyl halide

Alkynes form monohalo alkenes or dihalo alkanes (with halogen on the same C)

Rule for adding H and X› The halogen (X) will always add to the

more substituted carbon atom – the carbon that is bonded to the most carbon atoms

1-propene + hydrobromic acid 2-bromopropane

Step1: 1-propyne + hydrobromic acid 2-bromo-1-propene

Step 2: 2-bromo-1-propene+ hydrobromic acid 2,2-dibromopropane

Esterification Alcohol + organic acid water + ester

Used to make perfumes, scents and flavours

Combination reaction which involves dehydration

Alcohol becomes the alkyl group and the acid becomes -oate

propanol + ethanoic acid

propyl ethanoate + water