Introduction to organic reactions

Introduction to organic reactions Objective: To know the different types of organic reactions and the reactants used Outcomes: To define the different organic reagents we use (e.g. nucleophiles) To describe different organic reactions (e.g. addition, polymerisation) To describe different types of reaction mechanisms To explain what a reaction mechanism is To be able to give examples of all of the above and recognise examples of all of the above

Reaction types Addition reactions: joining two or more molecules together to form a larger molecule Polymerisation: joining together lots of simple molecules to form a giant molecule

Reaction types Elimination: when a small group of atoms breaks away from a larger molecule Substitution: when one species is replaced by another

Reaction types Hydrolysis: splitting a molecule into two new molecules by adding H+ and OH- derived from water Oxidation: any reaction in which a species loses electrons Reduction: any reaction in which a species gains electrons

A mechanism breaks down a reaction into individual stages Reaction mechanisms A mechanism breaks down a reaction into individual stages They use curly arrows to show how electron pairs move around when bonds are made or broken The arrow starts at the bond or lone pair where the electrons are at the beginning of the reaction The arrow points to where the new bond is formed at the end of the reaction, or to the atom where the electrons go Pg 72 cgp edexcel

Different reagents Nucleophiles Are electron pair donors. They’re often negatively charged ions (e.g. halide ions) or species that contain a lone pair of electrons (e.g. the oxygen atoms in water). They’re electron rich, so they’re attracted to places that are electron poor. E.g. positive ions, δ+ areas on polar bonds E.g. Nucleophiles are attracted to the C δ+ in a polar carbon hydrogen bond

Different reagents Electrophiles Are electron pair acceptors They’re often positively charged ions (e.g. H+) or δ+ areas in polar bonds They are electron poor so are attracted to places that are electron rich. They like to react with negative ions, atoms with lone pairs and the electron rich area around a C = C bond E.g. alkene molecules reacting with HBr, H δ+ acts as an electrophile

Different reagents Radicals Have an unpaired electron e.g. when a chlorine molecule splits The unpaired electron makes them highly reactive They react with anything E.g. they react with non polar bonds like those found in alkanes

Different types of mechanisms Substitution reactions In a substitution reaction one atom or group is replaced by another atom or group e.g. When methane reacts with chlorine is an example of radical substitution You can get other types of substitution reactions such as nucleophic substitution e.g. halogenalkanes reacting with aqueous KOH Pg 50 edexcel revision guide Pg 92 cgp

Different types of mechanisms Addition reactions Two reactants produce one product E.g. ethene + hydrogen bromide  bromoethane is an example of electrophilic addition Pg 51 edexcel revision guide

The non – polar alkane, methane, CH4 Hydroxide ions, OH- Questions Which of the following species would you expect to act as a nucleophile? Bromine radicals, Br. The non – polar alkane, methane, CH4 Hydroxide ions, OH- The C δ+ atom in the polar C – OH bond in ethanol, CH3CH2OH Page 73 cgp

Classify each of the following reactions according to its type: Questions Classify each of the following reactions according to its type: A reaction in which lots of ethene molecules join together to from one long molecule, polyethene The reaction between chloroethane and water, in which a water molecule breaks chloroethane into ethanol and hydrogen chloride The reaction between chlorine radicals and ethane, in which a hydrogen atom in ethane replaced by chlorine to form chloroethane Polymerisation Hydrolysis Page 73 cgp Substitution

Introduction to organic reactions Objective: To know the different types of organic reactions and the reactants used Outcomes: To define the different organic reagents we use (e.g. nucleophiles) To describe different organic reactions (e.g. addition, polymerisation) To describe different types of reaction mechanisms To explain what a reaction mechanism is To be able to give examples of all of the above and recognise examples of all of the above