4.6 Addition, elimination and substitution reactions 4.6 Addition, elimination and substitution reaction

4.6 Addition, elimination and substitution reactions (ESCKY)

Mechanisms and also arrow-pushing space not required by CAPS. The learners need to know the types of reactants, the species of reactions and the reaction conditions.

You are watching: Classify the mechanism as a substitution, elimination, or addition reaction.

We will examine three main species of reaction - addition, elimination and also substitution.

An addition reaction occurs as soon as two or much more reactants combine to form a solitary product. This product will contain all the atoms that were present in the reactants. Addition reactions take place with unsaturated compounds.

The basic equation because that an addition reaction: ( extA+ extB) ( o) ( extC)

Notice the C is the final product v no A or B staying as a residue.

An elimination reaction occurs when a reactant is broken up into two products. Elimination reactions occur with saturated compounds.

The basic equation because that an elimination reaction: ( extA) ( o) ( extB+ extC)

A substitution reaction occurs as soon as an exchange of aspects in the reactants takes place. The initial reactants are revolutionized or swopped around to give a last product.

The basic equation because that a substitution reaction: ( extAB + extCD) ( o) ( extAD + extBC)

Some specific examples of these reactions are provided in the complying with pages.

Addition reaction (ESCKZ)

Remember from the section on saturated and unsaturated frameworks that you deserve to perform test to identify if a compound is saturation or not. If bromine water or potassium permanganate room decolourised through a compound the compound is unsaturated, if they space not decolourised the compound is saturated.


Hydrohalogenation requires the enhancement of a hydrogen atom and also a halogen atom to an unsaturated compound (containing a carbon-carbon twin bond). An instance is offered in number 4.76. X have the right to be fluorine (F), chlorine (Cl), bromine (Br) or iodine (I).


Figure 4.76: The hydrohalogenation that ethene to a haloethane.

If an ext than one product is possible the major product will certainly be the compound where:

Remember that a (colorred extbftertiary carbon atom) is external inspection to three various other carbon atoms, a (colororange extbfsecondary carbon atom) is external inspection to two other carbon atoms, and also a (colorblue extbfprimary carbon atom) is bonded to one various other carbon atom. Therefore tertiary is the most substituted, second is much less substituted 보다 tertiary and more substituted than primary, and primary is the least substituted.

the (colordarkgreen extbfhydrogen atom) is added to (colorblue extbfleast substituted carbon atom)

i.e. The carbon atom through the least variety of carbon atoms bonded to it

the (colorpurple extbfhalogen atom) is included to the (colorred extbfmore substituted carbon atom)

i.e. The carbon atom with the most variety of carbon atom bonded to it

This is presented in figure 4.77.

major and minor commodities

The major product the a reaction is the product that is most likely to form. Minor assets are those the are much less likely to form.


Figure 4.77: The hydrohalogenation the 2-methylpropene to kind 2-fluoro-2-methylpropane (major product) and 1-fluoro-2-methylpropane (minor product).

Reaction conditions:

no water present in the reaction


Halogenation is very comparable to hydrohalogenation yet a diatomic halogen molecule is added throughout the double bond. An instance is provided in figure 4.78.


Figure 4.78: The reaction between ethene and also bromine to form 1,2-dibromoethane.


A hydration reaction involves the enhancement of water (( extH_2 extO)) to an unsaturated compound. This is one way of preparing an alcohol indigenous the matching alkene (Figure 4.79).


Figure 4.79: The hydration the ethene come ethanol.

If an ext than one product is feasible the major product will certainly be the link where:

the (colordarkgreen extbfhydrogen atom) is included to the (colorblue extbfleast substituted carbon atom)

the (colorpurple extbfhydroxyl anion) (( extOH^-)) is added to the (colorred extbfmore substituted carbon atom)


Figure 4.80: The hydration of 2-methylpropene to kind 2-methylpropan-2-one (major product) and also 2-methyl-propan-1-one (minor product).

Reaction conditions:

water need to be current in excess

an acid catalyst is required for this reaction to take place

the catalyst that is most commonly used is phosphoric acid (( extH_3 extPO_4))

Fermentation deserve to refer to the counter of sugar to alcohol using yeast (a fungus). The procedure of fermentation produces item such as wine, beer and also yogurt. To do wine, grape juice is fermented to develop alcohol. This reaction is shown below:

( extC_6 extH_12 extO_6) ( o) (2 extCO_2 + 2 extC_2 extH_5 extOH+) energy

The learners should emphasis their study on the chemistry behind this fermentation processes. They have the right to either present their findings together a conversation to the class, or in a quick (1-page) report format. The research should be ~ above local-level fermentation processes, not commercial scale breweries.

Formation that alcohol through fermentation

Ethanol can also be created through the process of fermentation. In practically every country there is a neighborhood product that civilization make through fermenting local fruits. For example in Malawi people ferment potatoes, sugar cane or maize to form katchasu. Right here in southern Africa human being ferment marula fruit to make mampoer, grapes to make witblits and sorghum to do beer.

Research the chemistry behind the fermentation process.

What various other plants do human being ferment?

Fermentation leads to acid formation, study why this occurs.

Sorghum is likewise used to do sour porridge. Just how is the made?


Hydrogenation involves adding hydrogen (( extH_2)) to an alkene. During hydrogenation the dual bond is broken (as through hydrohalogenation and halogenation) and more hydrogen atom are included to the molecule. A details example is presented in number 4.81.


Figure 4.81: The hydrogenation the ethene to ethane.

Reaction conditions:

a catalyst such as platinum (( extPt)), palladium (( extPd)) or nickel (( extNi)) is needed for this reactions

heating is required

the reaction should be excellent under one inert atmosphere, not air (e.g. ( extN_2( extg)) atmosphere)

The hydrogenation of vegetable oils to type margarine is an additional example of this addition reaction (see number 4.82).

See more: Clue: Basic Ideas Crossword Clue, Basic Idea Crossword Clue


Figure 4.82: The hydrogenation of sunflower oil to do margarine.

Polymerisation reaction

A polymer is consisted of of lots of smaller units called monomers. When these monomers are added together, they type a polymer. One means for polymerisation to take place is with an addition reaction. More details are offered later in this chapter in Plastics and polymers (Section 4.7).


Figure 4.83: The polymerisation that vinyl chloride monomers to kind a polyvinyl chloride polymer.

Polyvinyl chloride (Figure 4.83) is used in construction and also in clothing, and also having countless other uses.