two step mechanism
What two step mechanism means in Chemistry A-Level, as defined for AQA.
Definitions of two step mechanism
Exam boards and our study guides word this term in slightly different ways. Learn the version your board uses.
Check what you remember
Read the wording for your board, then hide it and explain two step mechanism in your own words. Rough notes are fine. This is a self-check, with no mark or grade.
Reference: AQA
The attack in which a pair of electrons leaves the delocalised system to form a bond, then the C-H bond breaks heterolytically and the pair returns to the ring.
The catalyst is consumed in the first step and regenerated in the second, and the species it forms in between is the intermediate.
Topics that use two step mechanism
- Catalysts (A-level only) (AQA A-Level)
- Electrophilic substitution (A-level only) (AQA A-Level)
Related terms
- active sites
- acylium ion
- autocatalysis
- catalyst
- catalytic converters
- curly arrow mechanism
- economic consequences
- electrophile
Using two step mechanism in the exam
Check the command word and mark scheme for your exact question. After comparing your explanation with the reference, use the term in an answer on the linked topic. This practice does not predict an exam mark.
Practise Chemistry questions
Create a free account to answer exam-style questions on this topic and get feedback on your answers.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge