AQA A Level Chemistry復(fù)習(xí)筆記3.7.1 Fundamentals of Reaction Mechanisms

Category: A-level課程, 教材筆記, 福利干貨 Date: 2022年6月27日下午3:09

Reaction Mechanisms: Terminology

Homolytic & Heterolytic fission

Homolytic fission?is breaking a covalent bond in such a way that each atom takes an electron from the bond to form two radicals
Heterolytic fission?is breaking a covalent bond in such a way that the more electronegative atom takes both the electrons from the bond to form a negative ion and leaving behind a positive ion

3.1-An-Introduction-to-AS-Level-Organic-Chemistry-Homolytic-and-Heterolytic

The diagram shows heterolytic fission in which the most electronegative atom takes both electrons in the covalent bond and homolytic fission in which each atom takes one electron from the covalent bond

Nucleophiles & electrophiles

A?nucleophile?is an electron-rich species that can?donate?a pair of electrons
- ‘Nucleophile’ means ‘nucleus/positive charge loving’ as nucleophiles are attracted to positively charged species
- Nucleophilic?refers to reactions that involve a nucleophile
An?electrophile?is an electron-deficient species that can?accept?a pair of electrons
- ‘Electrophile’ means ‘electron/negative charge loving’ as electrophiles are attracted to negatively charged species
- Electrophilic?refers to reactions that involve an electrophile

3.1-An-Introduction-to-AS-Level-Organic-Chemistry-Nucleophile-and-Electrophile

A nucleophile ‘loves’ a positive charge and an electrophile ‘loves’ a negative charge

Types of reactions

An?addition?reaction is an organic reaction in which two (or more) molecules combine to give a?single?product?with no other products
A?substitution?reaction is a reaction that involves?replacing?an atom or group of atoms by another
An?elimination?reaction is a reaction in which a small molecule (such as H2O or HCl) is?removed?from an organic molecule
A?hydrolysis?reaction is a reaction in which a compound is?broken?down?by?water?(it can also refer to the breakdown of a substance by dilute acids or alkali)
A?condensation?reaction is a reaction in which two organic molecules join together and in the process?eliminate?small molecules (such as H2O or HCl)

Oxidation & reduction

An?oxidation?reaction is a reaction in which oxygen is added, electrons are removed or the oxidation number of a substance is increased
- In organic chemistry it often refers to the addition of oxygen or removal of hydrogen atoms to a substance
- In equations for organic redox reactions, the symbol [O] can be used to represent one atom of oxygen from an oxidising agent
A?reduction?reaction is a reaction in which oxygen is removed, electrons are added or the oxidation number of a substance is decreased
- In organic chemistry it often refers to the removal of oxygen or addition of hydrogen atoms to a substance
- In equations for organic redox reactions, the symbol [H] can be used to represent one atom of hydrogen from a reducing agent

3.1-An-Introduction-to-AS-Level-Organic-Chemistry-Organic-Chemistry-Reaction-Types-1

Different types of reactions in organic chemistry

Fundamentals of Mechanisms

In organic reaction mechanisms,?curly?arrows?represent the movement of?electron?pairs
The arrow beings at a bond or a lone pair of electrons and points to the species that accepts the lone pair of electrons