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Britain & the wider world: 1745 -1901
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Chemistry
15 Dec 2025
99
3 pages
Hannah Egan @hannahegan_xyym
Isomerism is a key concept in organic chemistry where molecules share the same molecular formula but have different... Show more
Structural isomers are molecules with identical molecular formulas but completely different structural arrangements. Think of them as having the same building blocks but assembled in different ways.
Chain isomers involve different carbon skeleton arrangements. Butane can exist as a straight chain or as methylpropane with a branched structure - same atoms, totally different shapes.
Positional isomers keep the same carbon chain but move functional groups to different positions. For example, 1-chlorobutane has chlorine on the first carbon, while 2-chlorobutane has it on the second carbon.
Functional group isomers rearrange the same atoms into completely different functional groups. Hex-1-ene (an alkene) and cyclohexane (a cycloalkane) contain identical atoms but form entirely different molecular structures.
Quick Tip Remember that structural isomers have different displayed formulas - you can literally see the different connections when you draw them out!
Stereoisomers have identical structural formulas but arrange differently in three-dimensional space. This happens because double bonds can't rotate - the carbon atoms lock into the same plane.
E/Z isomerism occurs in alkenes when different groups attach to the carbon atoms of a double bond. Since the bond can't rotate, these groups get "stuck" in specific positions, creating distinct isomers.
Z-but-2-ene and E-but-2-ene demonstrate this perfectly - they're the same molecule but with methyl groups positioned differently around the double bond. The restricted rotation means they can't convert into each other.
To identify E and Z isomers, you'll need the Cahn-Ingold-Prelog priority rules. These help determine which groups take priority when naming these stereoisomers.
Remember Single bonds CAN rotate freely, so they never form stereoisomers - don't let tricky exam questions fool you!
The Cahn-Ingold-Prelog priority rules help you assign E or Z labels to stereoisomers. Start by giving priority to the two atoms directly attached to each carbon of the double bond - higher atomic number equals higher priority.
For simple cases, fluorine beats chlorine, and chlorine beats hydrogen. When the highest priority groups sit across from each other, you've got an E isomer.
When the atoms directly bonded are identical, look at the next group along the chain. A methyl group attached to hydrogen has lower priority than an ethyl group attached to carbon - it's all about what comes next in the chain.
Master these priority rules and you'll confidently tackle any E/Z isomerism question. The key is working systematically through the atomic numbers and chain structures.
Exam Success Always check for single vs double bonds first - this immediately tells you whether stereoisomerism is even possible!
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
You can download the app from Google Play Store and Apple App Store.
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
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Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore the chemistry of amino acids, amides, and chirality in this detailed summary. Understand the formation of esters, the concept of optical isomers, and the role of amino acids in acid-base reactions. This resource covers key concepts such as isomerism, making salts, and the unique properties of chiral molecules, making it essential for organic chemistry studies.
ChemistryExplore the fundamentals of hydrocarbons, including their classification into aliphatic, alicyclic, and aromatic types. This summary covers key concepts such as homologous series, functional groups, and the general formulas for alkanes, alkenes, and alkynes. Ideal for OCR A A-Level Chemistry students seeking a concise understanding of organic chemistry.
ChemistryExplore the fundamentals of isomerism in organic chemistry, including structural isomers, position isomers, and functional group isomers. Understand the impact of molecular structure on physical properties, and learn the rules for naming carbon chains using IUPAC nomenclature. This summary covers key concepts such as stereochemistry, intermolecular forces, and the characteristics of alkanes, alkenes, and carboxylic acids.
ChemistryExplore key concepts in organic chemistry, including nomenclature, reaction mechanisms, and isomerism. This summary covers IUPAC naming rules, functional groups, and stereochemistry, providing a comprehensive overview for AQA AS Organic Chemistry students.
ChemistryExplore the structural characteristics and bonding of benzene, including the comparison between the Kekulé and delocalized models. This summary covers key concepts such as resonance, sigma bonds, and the implications of enthalpy changes in hydrogenation. Ideal for OCR A-Level Chemistry students seeking to understand the stability and reactivity of benzene and its derivatives.
ChemistryHope this helps!
ChemistryApp Store
Google Play
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
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
Hannah Egan
@hannahegan_xyym
Isomerism is a key concept in organic chemistry where molecules share the same molecular formula but have different arrangements of atoms. Understanding the different types of isomers will help you predict molecular behaviour and tackle exam questions with confidence.
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Structural isomers are molecules with identical molecular formulas but completely different structural arrangements. Think of them as having the same building blocks but assembled in different ways.
Chain isomers involve different carbon skeleton arrangements. Butane can exist as a straight chain or as methylpropane with a branched structure - same atoms, totally different shapes.
Positional isomers keep the same carbon chain but move functional groups to different positions. For example, 1-chlorobutane has chlorine on the first carbon, while 2-chlorobutane has it on the second carbon.
Functional group isomers rearrange the same atoms into completely different functional groups. Hex-1-ene (an alkene) and cyclohexane (a cycloalkane) contain identical atoms but form entirely different molecular structures.
Quick Tip: Remember that structural isomers have different displayed formulas - you can literally see the different connections when you draw them out!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Stereoisomers have identical structural formulas but arrange differently in three-dimensional space. This happens because double bonds can't rotate - the carbon atoms lock into the same plane.
E/Z isomerism occurs in alkenes when different groups attach to the carbon atoms of a double bond. Since the bond can't rotate, these groups get "stuck" in specific positions, creating distinct isomers.
Z-but-2-ene and E-but-2-ene demonstrate this perfectly - they're the same molecule but with methyl groups positioned differently around the double bond. The restricted rotation means they can't convert into each other.
To identify E and Z isomers, you'll need the Cahn-Ingold-Prelog priority rules. These help determine which groups take priority when naming these stereoisomers.
Remember: Single bonds CAN rotate freely, so they never form stereoisomers - don't let tricky exam questions fool you!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
The Cahn-Ingold-Prelog priority rules help you assign E or Z labels to stereoisomers. Start by giving priority to the two atoms directly attached to each carbon of the double bond - higher atomic number equals higher priority.
For simple cases, fluorine beats chlorine, and chlorine beats hydrogen. When the highest priority groups sit across from each other, you've got an E isomer.
When the atoms directly bonded are identical, look at the next group along the chain. A methyl group attached to hydrogen has lower priority than an ethyl group attached to carbon - it's all about what comes next in the chain.
Master these priority rules and you'll confidently tackle any E/Z isomerism question. The key is working systematically through the atomic numbers and chain structures.
Exam Success: Always check for single vs double bonds first - this immediately tells you whether stereoisomerism is even possible!
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
You can download the app from Google Play Store and Apple App Store.
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
1
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore the chemistry of amino acids, amides, and chirality in this detailed summary. Understand the formation of esters, the concept of optical isomers, and the role of amino acids in acid-base reactions. This resource covers key concepts such as isomerism, making salts, and the unique properties of chiral molecules, making it essential for organic chemistry studies.
ChemistryExplore the fundamentals of hydrocarbons, including their classification into aliphatic, alicyclic, and aromatic types. This summary covers key concepts such as homologous series, functional groups, and the general formulas for alkanes, alkenes, and alkynes. Ideal for OCR A A-Level Chemistry students seeking a concise understanding of organic chemistry.
ChemistryExplore the fundamentals of isomerism in organic chemistry, including structural isomers, position isomers, and functional group isomers. Understand the impact of molecular structure on physical properties, and learn the rules for naming carbon chains using IUPAC nomenclature. This summary covers key concepts such as stereochemistry, intermolecular forces, and the characteristics of alkanes, alkenes, and carboxylic acids.
ChemistryExplore key concepts in organic chemistry, including nomenclature, reaction mechanisms, and isomerism. This summary covers IUPAC naming rules, functional groups, and stereochemistry, providing a comprehensive overview for AQA AS Organic Chemistry students.
ChemistryExplore the structural characteristics and bonding of benzene, including the comparison between the Kekulé and delocalized models. This summary covers key concepts such as resonance, sigma bonds, and the implications of enthalpy changes in hydrogenation. Ideal for OCR A-Level Chemistry students seeking to understand the stability and reactivity of benzene and its derivatives.
ChemistryHope this helps!
ChemistryApp Store
Google Play
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
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
Sociology