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Easy Guide to AQA A Level Chemistry Reaction Mechanisms PDF

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Chemistry

Chemistry A level Reaction Mechanisms

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29 Sept 2025

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Easy Guide to AQA A Level Chemistry Reaction Mechanisms PDF

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na

@nosh

A Level Chemistry Reaction Mechanisms Summary

This comprehensive guide covers... Show more

nucleophilic substitution & elimination
Nucleophilic substitution with -OH
Reagent; source of hydroxide - NaOH or KOH
Conditions: Heat under

Nucleophilic Substitution, Elimination, and Electrophilic Addition Reactions

This page provides a comprehensive overview of key reaction mechanisms in A Level Chemistry, focusing on nucleophilic substitution, elimination, and electrophilic addition reactions. These mechanisms are crucial for understanding organic Chemistry reactions and are frequently tested in AQA A Level Chemistry exam questions.

Nucleophilic Substitution Reactions

Nucleophilic Substitution with -OH

Definition: Nucleophilic substitution with -OH involves the replacement of a halogen (X) with a hydroxyl group (OH).

  • Reagent: NaOH or KOH (source of hydroxide)
  • Conditions: Heat under reflux with warm NaOH/KOH
  • General Equation: R-X + NaOH → R-OH + NaX

Example: The mechanism shows the OH- nucleophile attacking the carbon bonded to the halogen, displacing the halogen and forming an alcohol.

Nucleophilic Substitution with NH3

  • Reagent: NH3 dissolved in ethanol
  • Conditions: Heated under pressure in a sealed container
  • General Equation: R-X + 2NH3 → R-NH2 + NH4X

Highlight: This reaction produces primary amines and requires excess ammonia to neutralize the hydrogen halide byproduct.

Nucleophilic Substitution with -CN

  • Reagent: Ethanolic KCN
  • Conditions: Heating under reflux with warm KCN
  • General Equation: R-X + KCN → R-CN + KX

Vocabulary: The cyanide ion CNCN- acts as the nucleophile, replacing the halogen to form a nitrile compound.

Elimination Reactions

  • Reagent: Ethanolic KOH/NaOH
  • Conditions: Hot ethanolic KOH/NaOH
  • General Equation: R-CH2-CHX-R' + KOH → R-CH=CH-R' + KX + H2O

Highlight: The hydrogen being eliminated must be adjacent leftorrightleft or right to the carbon with the C-X bond.

Electrophilic Addition Reactions

Electrophilic Addition with Br2

  • General Equation: C=C + Br2 → BrC-CBr

Example: The mechanism involves the formation of a bromonium ion intermediate, followed by nucleophilic attack by the bromide ion.

Electrophilic Addition with HBr

  • General Equation: C=C + HBr → HC-CBr

Highlight: This reaction follows Markovnikov's rule, with the bromine attaching to the more substituted carbon.

Electrophilic Addition with H2SO4

  • General Equation: C=C + H2SO4 → HC-C-OSO3H

Vocabulary: The sulfuric acid acts as both the electrophile and the catalyst in this reaction.

Electrophilic Addition with H2O

  • Conditions: Strong acid catalyst
  • General Equation: C=C + H2O → HC-C-OH

Definition: This reaction, also known as hydration of alkenes, produces alcohols and requires a strong acid catalyst.

These reaction mechanisms are fundamental to A Level Chemistry and are essential for understanding more complex organic Chemistry reactions. Mastering these mechanisms will greatly aid in solving AQA A Level Chemistry mechanisms exam questions and similar problems in other exam boards like OCR.



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This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.

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Chemistry

1,332

29 Sept 2025

1 page

Easy Guide to AQA A Level Chemistry Reaction Mechanisms PDF

user profile picture

na

@nosh

A Level Chemistry Reaction Mechanisms Summary

This comprehensive guide covers key organic Chemistry reactions and mechanisms for A Level Chemistry. It focuses on nucleophilic substitution, elimination, and electrophilic additionreactions, providing detailed mechanisms, reagents, and conditions for... Show more

nucleophilic substitution & elimination
Nucleophilic substitution with -OH
Reagent; source of hydroxide - NaOH or KOH
Conditions: Heat under

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Nucleophilic Substitution, Elimination, and Electrophilic Addition Reactions

This page provides a comprehensive overview of key reaction mechanisms in A Level Chemistry, focusing on nucleophilic substitution, elimination, and electrophilic addition reactions. These mechanisms are crucial for understanding organic Chemistry reactions and are frequently tested in AQA A Level Chemistry exam questions.

Nucleophilic Substitution Reactions

Nucleophilic Substitution with -OH

Definition: Nucleophilic substitution with -OH involves the replacement of a halogen (X) with a hydroxyl group (OH).

  • Reagent: NaOH or KOH (source of hydroxide)
  • Conditions: Heat under reflux with warm NaOH/KOH
  • General Equation: R-X + NaOH → R-OH + NaX

Example: The mechanism shows the OH- nucleophile attacking the carbon bonded to the halogen, displacing the halogen and forming an alcohol.

Nucleophilic Substitution with NH3

  • Reagent: NH3 dissolved in ethanol
  • Conditions: Heated under pressure in a sealed container
  • General Equation: R-X + 2NH3 → R-NH2 + NH4X

Highlight: This reaction produces primary amines and requires excess ammonia to neutralize the hydrogen halide byproduct.

Nucleophilic Substitution with -CN

  • Reagent: Ethanolic KCN
  • Conditions: Heating under reflux with warm KCN
  • General Equation: R-X + KCN → R-CN + KX

Vocabulary: The cyanide ion CNCN- acts as the nucleophile, replacing the halogen to form a nitrile compound.

Elimination Reactions

  • Reagent: Ethanolic KOH/NaOH
  • Conditions: Hot ethanolic KOH/NaOH
  • General Equation: R-CH2-CHX-R' + KOH → R-CH=CH-R' + KX + H2O

Highlight: The hydrogen being eliminated must be adjacent leftorrightleft or right to the carbon with the C-X bond.

Electrophilic Addition Reactions

Electrophilic Addition with Br2

  • General Equation: C=C + Br2 → BrC-CBr

Example: The mechanism involves the formation of a bromonium ion intermediate, followed by nucleophilic attack by the bromide ion.

Electrophilic Addition with HBr

  • General Equation: C=C + HBr → HC-CBr

Highlight: This reaction follows Markovnikov's rule, with the bromine attaching to the more substituted carbon.

Electrophilic Addition with H2SO4

  • General Equation: C=C + H2SO4 → HC-C-OSO3H

Vocabulary: The sulfuric acid acts as both the electrophile and the catalyst in this reaction.

Electrophilic Addition with H2O

  • Conditions: Strong acid catalyst
  • General Equation: C=C + H2O → HC-C-OH

Definition: This reaction, also known as hydration of alkenes, produces alcohols and requires a strong acid catalyst.

These reaction mechanisms are fundamental to A Level Chemistry and are essential for understanding more complex organic Chemistry reactions. Mastering these mechanisms will greatly aid in solving AQA A Level Chemistry mechanisms exam questions and similar problems in other exam boards like OCR.

We thought you’d never ask...

What is the Knowunity AI companion?

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This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.

Samantha Klich

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Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.

Anna

iOS user

Best app on earth! no words because it’s too good

Thomas R

iOS user

Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.

Basil

Android user

This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.

David K

iOS user

The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!

Sudenaz Ocak

Android user

In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.

Greenlight Bonnie

Android user

very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.

Rohan U

Android user

I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.

Xander S

iOS user

THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮

Elisha

iOS user

This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now

Paul T

iOS user

The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.

Stefan S

iOS user

This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.

Samantha Klich

Android user

Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.

Anna

iOS user

Best app on earth! no words because it’s too good

Thomas R

iOS user

Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.

Basil

Android user

This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.

David K

iOS user

The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!

Sudenaz Ocak

Android user

In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.

Greenlight Bonnie

Android user

very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.

Rohan U

Android user

I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.

Xander S

iOS user

THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮

Elisha

iOS user

This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now

Paul T

iOS user