{"id":4821,"date":"2026-06-03T06:24:28","date_gmt":"2026-06-03T05:24:28","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/isomerism\/"},"modified":"2026-10-14T09:06:49","modified_gmt":"2026-10-14T08:06:49","slug":"isomerism","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/isomerism\/","title":{"rendered":"Isomerism"},"content":{"rendered":"\n<section class=\"ols-revision-page ols-isomerism-page\">\n  <style>\n    .ols-revision-page {\n      --navy: #1C244B;\n      --blue: #2563eb;\n      --soft-blue: #eef4ff;\n      --soft-red: #fff7f7;\n      --soft-purple: #f7f0ff;\n      --soft-green: #f0f7f1;\n      --soft-yellow: #fff8e6;\n      --red: #c81e1e;\n      --gold: #c9973a;\n      --green: #3f8f46;\n      --grey-text: 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.ols-linkedin-pill:hover, .ols-linkedin-pill:focus { color:#ffffff !important; }\n\n\n.ols-faq-card,\n    .ols-quicksnap-card {\n      background: #ffffff;\n      border: 1px solid var(--border);\n      border-radius: 28px;\n      box-shadow: var(--shadow);\n      padding: 34px;\n      margin-bottom: 24px;\n      overflow: hidden;\n    }\n.ols-faq-card h2,\n    .ols-quicksnap-card h2,\n    .ols-infographic-title {\n      margin: 0;\n      font-size: clamp(28px, 3.5vw, 42px);\n      line-height: 1.15;\n      font-weight: 800;\n      color: #111827;\n      letter-spacing: -0.03em;\n    }\n.ols-faq-card h2,\n    .ols-quicksnap-card h2 {\n      margin-bottom: 14px;\n    }\n.ols-faq-card p,\n    .ols-quicksnap-card p {\n      font-size: clamp(15px, 1.25vw, 17px);\n      line-height: 1.65;\n      font-weight: 300;\n      color: var(--body-text);\n    }\n.ols-faq-card strong,\n    .ols-quicksnap-card strong {\n      font-weight: 700;\n      color: var(--navy);\n    }\n.ols-faq-list {\n      display: grid;\n      gap: 14px;\n      margin-top: 18px;\n    }\n.ols-faq-item {\n      background: #ffffff;\n      border: 1px solid var(--border);\n      border-radius: 18px;\n      padding: 18px 20px;\n      box-shadow: var(--inner-shadow);\n    }\n.ols-faq-item h3 {\n      margin: 0 0 8px;\n      font-size: 20px;\n      line-height: 1.3;\n      color: var(--navy);\n    }\n.ols-faq-item p {\n      margin: 0;\n      font-size: 16px;\n      line-height: 1.65;\n      color: var(--body-text);\n    }\n.ols-faq-card,\n      .ols-quicksnap-card,\n      .ols-attribution-card {\n        padding: 24px 18px;\n        border-radius: 22px;\n      }\n<\/style>\n\n  <aside class=\"ols-sidebar\">\r\n  <div class=\"ols-sidebar-header\">\r\n    <h3>Revision Notes<\/h3>\r\n    <p>A Level Chemistry<\/p>\r\n  <\/div>\r\n\r\n  <div class=\"ols-topic-group\">\r\n    <h4>Topic 6 Organic Chemistry I<\/h4>\r\n\r\n    <ul class=\"ols-topic-list\">\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/\">Introduction to Organic Chemistry<\/a>\r\n\r\n        <ul class=\"ols-subtopic-list\">\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/iupac-rules\/\">IUPAC Rules<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/alkene\/\">Alkene<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/alcohol\/\">Alcohol<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/halogenoalkanes\/\">Halogenoalkanes<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/aldehyde\/\">Aldehyde<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/ketone\/\">Ketone<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/carboxylic-acid\/\">Carboxylic Acid<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/ester\/\">Ester<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/isomerism\/\">Isomerism<\/a>\r\n          <\/li>\r\n        <\/ul>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/\">Alkanes<\/a>\r\n\r\n        <ul class=\"ols-subtopic-list\">\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/crude-oil\/\">Alkanes from Crude Oil<\/a>\r\n\r\n            <ul class=\"ols-subtopic-list\">\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/crude-oil\/fractional-distillation\/\">Fractional Distillation<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/crude-oil\/cracking\/\">Cracking<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/crude-oil\/reforming\/\">Reforming<\/a>\r\n              <\/li>\r\n            <\/ul>\r\n          <\/li>\r\n\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/fuel\/\">Alkanes as Fuel<\/a>\r\n\r\n            <ul class=\"ols-subtopic-list\">\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/fuel\/combustion\/\">Combustion<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/fuel\/oxides-of-sulfur\/\">Oxides of Sulfur<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/fuel\/oxides-of-nitrogen\/\">Oxides of Nitrogen<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/fuel\/catalytic-converter\/\">Catalytic Converter<\/a>\r\n              <\/li>\r\n            <\/ul>\r\n          <\/li>\r\n\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/alternative-fuel\/\">Alternative Fuel<\/a>\r\n          <\/li>\r\n\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/\">Reactions of Alkanes<\/a>\r\n\r\n            <ul class=\"ols-subtopic-list\">\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/free-radical-substitution\/\">Free Radical Substitution<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/initiation\/\">Initiation<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/propagation\/\">Propagation<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/termination\/\">Termination<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/further-substitution\/\">Further Substitution<\/a>\r\n              <\/li>\r\n            <\/ul>\r\n          <\/li>\r\n        <\/ul>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/\">Alkenes<\/a>\r\n\r\n        <ul class=\"ols-subtopic-list\">\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/alkene-bonding\/\">Alkene Bonding<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/geometric-isomerism\/\">Geometric Isomerism<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/electrophilic-addition-mechanism\/\">Electrophilic Addition Mechanism<\/a>\r\n          <\/li>\r\n\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/reactions-of-alkenes\/\">Reactions of Alkenes<\/a>\r\n\r\n            <ul class=\"ols-subtopic-list\">\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/reactions-of-alkenes\/halogens\/\">Halogens<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/reactions-of-alkenes\/hydrogen-halide\/\">Hydrogen Halide<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/reactions-of-alkenes\/bromine-water\/\">Bromine Water<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/reactions-of-alkenes\/hydrogen\/\">Hydrogen<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/reactions-of-alkenes\/steam\/\">Steam<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/reactions-of-alkenes\/kmno4\/\">KMnO4<\/a>\r\n              <\/li>\r\n            <\/ul>\r\n          <\/li>\r\n\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/polymerisation-reactions\/\">Polymerisation Reactions<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/polymer-waste\/\">Polymer Waste<\/a>\r\n          <\/li>\r\n        <\/ul>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/halogenoalkanes\/\">Halogenoalkanes<\/a>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alcohols\/\">Alcohols<\/a>\r\n      <\/li>\r\n\r\n    <\/ul>\r\n  <\/div>\r\n\r\n  <div class=\"ols-topic-group\">\r\n    <h4>Next Topics<\/h4>\r\n\r\n    <ul class=\"ols-topic-list\">\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-7-modern-analytical-techniques-i\/\">Topic 7 Modern Analytical Techniques I<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-5-formulae-equations-and-amounts-of-substance\/\">Topic 5 Formulae, Equations &amp; Amounts<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/\">Topic 4 Inorganic Chemistry &amp; The Periodic Table<\/a>\r\n      <\/li>\r\n    <\/ul>\r\n  <\/div>\r\n<\/aside>\r\n\r\n<script>\r\n(function() {\r\n  function normalisePath(path) {\r\n    return String(path || '')\r\n      .split('?')[0]\r\n      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href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/\">Revision Notes<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/\">A Level Chemistry<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/\">Edexcel<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/\">Topic 6 Organic Chemistry I<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/\">Introduction to Organic Chemistry<\/a> \/\n        <span>Isomerism<\/span>\n      <\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Isomerism<\/h1>\n        <p class=\"ols-page-intro\">A concise revision guide to structural isomerism in organic chemistry, including chain isomerism, position isomerism and functional group isomerism.<\/p>\n\n        <div class=\"ols-badges\">\n          <div class=\"ols-badge\">Paper 2<\/div>\n          <div class=\"ols-badge\">Topic 6: Organic Chemistry I<\/div>\n          <div class=\"ols-badge\">9CH0\/02<\/div>\n        <\/div>\n      <\/header>\n\n      <section class=\"ols-h5p-card ols-h5p-inline ols-h5p-recap\">\n<span class=\"ols-h5p-kicker\">Before you start<\/span>\n<h2>GCSE Recap: Molecular and Structural Formulae<\/h2>\n<p>Check that you can count atoms in a structural formula and know what a molecular formula leaves out.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"701\"><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card soft\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">1<\/div>\n          <h2>What Are Structural Isomers?<\/h2>\n        <\/div>\n\n        <p><strong>Structural isomers<\/strong> are compounds that have the <strong>same molecular formula<\/strong> but <strong>different structural formulae<\/strong>.<\/p>\n        <p>This means the compounds contain the same number of each type of atom, but the atoms are connected in a different order. In organic chemistry, this usually changes the carbon skeleton, the position of a functional group or the functional group itself.<\/p>\n\n        <div class=\"ols-definition-box\">\n          <div class=\"ols-definition-circle\">Isomers<\/div>\n          <p><strong>Definition:<\/strong> Structural isomers have the same molecular formula but different structural formulae. The difference is in how the atoms are arranged and bonded together.<\/p>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Exam focus:<\/strong> To decide whether two compounds are structural isomers, compare the molecular formula first, then compare how the atoms are connected.<\/p>\n        <\/div>\n      <div class=\"ols-figure-card ols-zoom-pop\">\n<div class=\"ols-figure-image\">\n<a class=\"ols-image-fullscreen-link\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-img-16-isomertree.jpg\" target=\"_blank\" rel=\"noopener\" aria-label=\"Open image fullscreen\">\n<img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-img-16-isomertree.jpg\" alt=\"Decision tree that sorts two compounds into not isomers, functional group, chain or position isomers, with named examples\" data-fullscreen-src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-img-16-isomertree.jpg\">\n<\/a>\n<\/div>\n<div class=\"ols-figure-caption\"><p>Chain, position and functional group isomers all share a molecular formula but differ in structural formula.<\/p><\/div>\n<\/div>\n<\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Same Molecular Formula?<\/h2>\n<p>Work out each molecular formula to find the one true isomer of hexane.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-97\" class=\"h5p-iframe\" data-content-id=\"97\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Isomerism MCQ: Finding a Structural Isomer of Hexane\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">2<\/div>\n          <h2>Chain Isomerism<\/h2>\n        <\/div>\n\n        <p><strong>Chain isomerism<\/strong> occurs when compounds have the <strong>same molecular formula<\/strong> but different structures of the <strong>carbon skeleton<\/strong>.<\/p>\n        <p>The carbon chain may be straight or branched. For example, pentane, 2-methylbutane and 2,2-dimethylpropane all have the molecular formula <strong>C<sub>5<\/sub>H<sub>12<\/sub><\/strong>, but their carbon skeletons are different.<\/p>\n\n        <div class=\"ols-molecule-grid\">\n          <div class=\"ols-molecule-card\">\n            <div class=\"ols-structure\"><img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-mv-04-displayed.svg\" alt=\"Displayed formulae of pentane, 2-methylbutane\"><\/div>\n            <h3>Pentane<\/h3>\n            <p>A straight-chain alkane with five carbon atoms.<\/p>\n          <\/div>\n          <div class=\"ols-molecule-card\">\n            <div class=\"ols-structure\"><img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/skel-P075-2-methylbutane-displayed.svg\" alt=\"Displayed formula of 2-methylbutane with every carbon and hydrogen atom shown\"><\/div>\n            <h3>2-methylbutane<\/h3>\n            <p>A branched isomer with the same molecular formula as pentane.<\/p>\n          <\/div>\n          <div class=\"ols-molecule-card\">\n            <div class=\"ols-structure\"><img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/mol-2-2-dimethylpropane.svg\" alt=\"Skeletal formula of 2,2-dimethylpropane\"><\/div>\n            <h3>2,2-dimethylpropane<\/h3>\n            <p>A more highly branched isomer of C<sub>5<\/sub>H<sub>12<\/sub>.<\/p>\n          <\/div>\n        <\/div>\n      <\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Isomers or the Same Compound?<\/h2>\n<p>Decide whether each pair shows chain isomers, one compound drawn twice, or two compounds that are not isomers.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-98\" class=\"h5p-iframe\" data-content-id=\"98\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Isomerism Single Choice: Chain Isomers, the Same Compound or Not Isomers\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card purple\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">3<\/div>\n          <h2>Position Isomerism<\/h2>\n        <\/div>\n\n        <p><strong>Position isomerism<\/strong> occurs when compounds have the <strong>same molecular formula<\/strong> but different structures because the same functional group is in a <strong>different position<\/strong> on the same carbon skeleton.<\/p>\n        <p>For example, 1-bromopropane and 2-bromopropane both have the formula <strong>C<sub>3<\/sub>H<sub>7<\/sub>Br<\/strong>, but the bromine atom is attached to a different carbon atom.<\/p>\n\n        <div class=\"ols-molecule-grid two\">\n          <div class=\"ols-molecule-card\">\n            <div class=\"ols-structure\"><img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/mol-1-bromopropane.svg\" alt=\"Skeletal formula of 1-bromopropane\"><\/div>\n            <h3>1-bromopropane<\/h3>\n            <p>The bromine atom is attached to carbon 1 of the propane chain.<\/p>\n          <\/div>\n          <div class=\"ols-molecule-card\">\n            <div class=\"ols-structure\"><img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/mol-2-bromopropane.svg\" alt=\"Skeletal formula of 2-bromopropane\"><\/div>\n            <h3>2-bromopropane<\/h3>\n            <p>The bromine atom is attached to carbon 2 of the propane chain.<\/p>\n          <\/div>\n        <\/div>\n\n        <div class=\"ols-figure-card\">\n          <div class=\"ols-figure-image\">\n            <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/mol-2-bromobutane.svg\" alt=\"Skeletal formula of 2-bromobutane\" width=\"394\" height=\"290\">\n          <\/div>\n          <div class=\"ols-figure-caption\">\n            <p>Halogenoalkanes are useful examples for practising position isomerism because the halogen can occupy different positions on the carbon chain.<\/p>\n          <\/div>\n        <\/div>\n      <\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Spot the Position Isomer<\/h2>\n<p>Only one of these four structures is a position isomer of pentan-1-ol.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-99\" class=\"h5p-iframe\" data-content-id=\"99\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Isomerism MCQ: The Position Isomer of Pentan-1-ol\"><\/iframe><\/div><\/div>\n<\/section>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Counting Isomers<\/h2>\n<p>Draw the isomers on paper and count them before you flip each card.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-702\" class=\"h5p-iframe\" data-content-id=\"702\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Isomerism Flip Cards: How Many Structural Isomers?\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card green\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">4<\/div>\n          <h2>Functional Group Isomerism<\/h2>\n        <\/div>\n\n        <p><strong>Functional group isomerism<\/strong> occurs when compounds have the <strong>same molecular formula<\/strong> but the atoms are arranged to give <strong>different functional groups<\/strong>.<\/p>\n        <p>This is more than a change in the position of the same group. The compounds belong to different homologous series, so they may have different chemical reactions and physical properties.<\/p>\n\n        <div class=\"ols-molecule-grid two\">\n          <div class=\"ols-molecule-card\">\n            <div class=\"ols-structure\"><img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-mv-05-isomer-pairs.svg\" alt=\"Skeletal formulae of cyclohexane, hex-1-ene, propanal, propanone\"><\/div>\n            <h3>Butan-1-ol<\/h3>\n            <p>An alcohol, C<sub>4<\/sub>H<sub>10<\/sub>O, identified by the hydroxyl group, <strong>-OH<\/strong>. Ethoxyethane, an ether, has the same molecular formula.<\/p>\n          <\/div>\n          <div class=\"ols-molecule-card\">\n            <div class=\"ols-structure\"><img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/mol-cyclohexane.svg\" alt=\"Skeletal formula of cyclohexane\"><\/div>\n            <h3>Cyclohexane<\/h3>\n            <p>A cycloalkane, C<sub>6<\/sub>H<sub>12<\/sub>. It is a functional group isomer of hex-1-ene: a ring in place of a C=C bond. It is not an isomer of butan-1-ol.<\/p>\n          <\/div>\n        <\/div>\n\n        <div class=\"ols-warning-box\">\n          <p><strong>Important:<\/strong> Two structures are only isomers if they have the same molecular formula. Do not classify compounds as isomers simply because their structures look similar or contain related atoms.<\/p>\n        <\/div>\n      <\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Every Isomer of Pent-1-ene<\/h2>\n<p>Click all the compounds that share the molecular formula of pent-1-ene.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-703\" class=\"h5p-iframe\" data-content-id=\"703\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Isomerism Mark the Words: Isomers of Pent-1-ene\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card yellow\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">5<\/div>\n          <h2>Comparing the Types of Structural Isomerism<\/h2>\n        <\/div>\n\n        <p>The table below summarises the difference between the three common types of structural isomerism used in this topic.<\/p>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Type of isomerism<\/th>\n                <th>What changes?<\/th>\n                <th>Typical example<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Type of isomerism\"><strong>Chain isomerism<\/strong><\/td>\n                <td data-label=\"What changes?\">The arrangement of the carbon skeleton changes.<\/td>\n                <td data-label=\"Typical example\">Pentane, 2-methylbutane and 2,2-dimethylpropane.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Type of isomerism\"><strong>Position isomerism<\/strong><\/td>\n                <td data-label=\"What changes?\">The same functional group is attached at a different position on the same carbon skeleton.<\/td>\n                <td data-label=\"Typical example\">1-bromopropane and 2-bromopropane.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Type of isomerism\"><strong>Functional group isomerism<\/strong><\/td>\n                <td data-label=\"What changes?\">The atoms are arranged to give different functional groups.<\/td>\n                <td data-label=\"Typical example\">Propanal and propanone, C<sub>3<\/sub>H<sub>6<\/sub>O; hex-1-ene and cyclohexane, C<sub>6<\/sub>H<sub>12<\/sub>.<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Exam focus:<\/strong> Always check the molecular formula before naming the type of isomerism. Same formula first, then decide what structural feature has changed.<\/p>\n        <\/div>\n      <div class=\"ols-figure-card ols-zoom-pop\">\n<div class=\"ols-figure-image\">\n<a class=\"ols-image-fullscreen-link\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-img-17-countisomers.jpg\" target=\"_blank\" rel=\"noopener\" aria-label=\"Open image fullscreen\">\n<img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-img-17-countisomers.jpg\" alt=\"Method for finding every isomer using bead-string chains, with tallies of 2 for C4H10, 3 for C5H12 and 4 for C4H9Br\" data-fullscreen-src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-img-17-countisomers.jpg\">\n<\/a>\n<\/div>\n<div class=\"ols-figure-caption\"><p>Shorten the chain one carbon at a time and name each candidate: C\u2086H\u2081\u2084 has five structural isomers.<\/p><\/div>\n<\/div>\n<\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Which Type of Isomerism?<\/h2>\n<p>Pick the accurate statement about each new pair of compounds.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-96\" class=\"h5p-iframe\" data-content-id=\"96\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Isomerism Summary: Classifying Five New Pairs\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card soft\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">6<\/div>\n          <h2>Common Exam Mistakes<\/h2>\n        <\/div>\n\n        <ul>\n          <li>Do not say structural isomers have the same structural formula. They have the same molecular formula but different structural formulae.<\/li>\n          <li>Do not confuse <strong>chain isomerism<\/strong> with <strong>position isomerism<\/strong>. Chain isomerism changes the carbon skeleton.<\/li>\n          <li>Do not describe position isomerism as a different functional group. It is the same functional group in a different position.<\/li>\n          <li>Do not ignore the molecular formula. If the molecular formula is different, the compounds are not isomers.<\/li>\n        <\/ul>\n      <\/article>\n\n      \n\n      <section class=\"ols-infographic-full\" aria-label=\"Isomerism summary\">\n        <h2 class=\"ols-infographic-title\">Isomerism Summary<\/h2>\n        <div class=\"ols-infographic-grid\">\n          <div class=\"ols-info-panel\">\n            <h3>Structural isomers<\/h3>\n            <p>Same molecular formula, different structural formulae.<\/p>\n            <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/skel-P074-pentane-displayed.svg\" alt=\"Displayed formula of pentane with all five carbon atoms and twelve hydrogen atoms shown\">\n          <\/div>\n          <div class=\"ols-info-panel\">\n            <h3>Chain isomerism<\/h3>\n            <p>The carbon skeleton changes from straight-chain to branched.<\/p>\n            <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/skel-P075-2-methylbutane-displayed.svg\" alt=\"Displayed formula of 2-methylbutane with every carbon and hydrogen atom shown\">\n          <\/div>\n          <div class=\"ols-info-panel\">\n            <h3>Position isomerism<\/h3>\n            <p>The same functional group is in a different position on the carbon skeleton.<\/p>\n            <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/mol-2-bromopropane.svg\" alt=\"Skeletal formula of 2-bromopropane\">\n          <\/div>\n          <div class=\"ols-info-panel\">\n            <h3>Functional group isomerism<\/h3>\n            <p>The same atoms are arranged to give different functional groups.<\/p>\n            <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/mol-butan-1-ol.svg\" alt=\"Skeletal formula of butan-1-ol\">\n          <\/div>\n        <\/div>\n      <\/section>\n\n      \n\n      <section class=\"ols-faq-card\">\n        <h2>FAQs<\/h2>\n        <p>These questions cover the isomer decisions students most often get wrong.<\/p>\n        <div class=\"ols-faq-list\">\n          <div class=\"ols-faq-item\">\n            <h3>Are butan-1-ol and cyclohexane isomers?<\/h3>\n            <p>No. Butan-1-ol is C\u2084H\u2081\u2080O and cyclohexane is C\u2086H\u2081\u2082. Compounds can only be isomers if the molecular formulae match.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>Are but-1-ene and cyclobutane structural isomers?<\/h3>\n            <p>Yes. Both are C\u2084H\u2088. One has a C=C bond and the other a ring, so they are functional group isomers.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>Is CH\u2083CH(CH\u2083)CH\u2082CH\u2083 a different compound from CH\u2083CH\u2082CH(CH\u2083)CH\u2083?<\/h3>\n            <p>No. Both are 2-methylbutane written from opposite ends. Name each structure before deciding it is a new isomer.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>Is propan-2-ol a chain or a position isomer of propan-1-ol?<\/h3>\n            <p>A position isomer. The carbon chain is unchanged; only the position of the -OH group moves.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>How many structural isomers does C\u2084H\u2081\u2080 have?<\/h3>\n            <p>Two: butane and 2-methylpropane. A methyl group on carbon 1 just lengthens the chain back to butane.<\/p>\n          <\/div>\n        <\/div>\n      <\/section>\n\n      <!-- author card (moved to the end, 10 Oct 2026) -->\n      <div class=\"ols-author\">\n        \n            <img decoding=\"async\"\n              class=\"ols-author-avatar-img\"\n              src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/Author-Profile.jpeg\"\n              alt=\"Dr. Mohammed Al-Fatah\"\n            >\n        \n            <div class=\"ols-author-content\">\n        \n              <h2 class=\"ols-author-title\">\n                Written by: Dr. Mohammed Al-Fatah\n              <\/h2>\n        \n              <p class=\"ols-author-description\">\n                Chemistry specialist revision notes for A Level Chemistry.\n              <\/p>\n        \n              <a\n                class=\"ols-linkedin-pill\"\n                href=\"https:\/\/www.linkedin.com\/in\/doctormohammedfatah\/\"\n                target=\"_blank\"\n                rel=\"noopener noreferrer\"\n              >\n        \n                <svg class=\"ols-linkedin-icon\" viewBox=\"0 0 24 24\" fill=\"currentColor\" aria-hidden=\"true\">\n                  <path d=\"M4.98 3.5C4.98 4.88 3.86 6 2.48 6S0 4.88 0 3.5 1.12 1 2.48 1s2.5 1.12 2.5 2.5zM.5 8h4V24h-4V8zm7 0h3.8v2.2h.1c.5-.9 1.8-2.2 3.9-2.2 4.2 0 5 2.8 5 6.4V24h-4v-7.6c0-1.8 0-4.2-2.6-4.2s-3 2-3 4v7.8h-4V8z\"\/>\n                <\/svg>\n        \n                View LinkedIn Profile\n        \n              <\/a>\n        \n            <\/div>\n        \n          <\/div>\n\n\n<section class=\"ols-related-card\">\n        <h2>Related Topics<\/h2>\n        <p>Continue revising Topic 6 Organic Chemistry I with these linked pages.<\/p>\n        <div class=\"ols-related-grid\">\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/\">Introduction to Organic Chemistry<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/crude-oil\/fractional-distillation\/\">Alkanes from Crude Oil<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/free-radical-substitution\/\">Reactions of Alkanes<\/a>\n        <\/div>\n      <\/section>\n\n      <!-- OLS Author Copyright Footprint \/ Attribution Card -->\n<section class=\"ols-attribution-card ols-attr-std\" aria-label=\"Copyright notice\">\n<style id=\"ols-attribution-card-css\">.ols-attribution-card.ols-attr-std{background:linear-gradient(135deg,#ffffff,#f8fbff);border:1px solid rgba(28,36,75,0.14);border-radius:28px;box-shadow:0 18px 45px rgba(28,36,75,0.10);padding:34px;margin:24px 0;overflow:hidden;font-family:Poppins,Arial,sans-serif;box-sizing:border-box}.ols-attribution-card.ols-attr-std *{box-sizing:border-box}.ols-attribution-card.ols-attr-std p{margin:0;font-size:14px;line-height:1.65;font-weight:300;color:#667085}.ols-attribution-card.ols-attr-std strong{font-weight:700;color:#1C244B}@media (max-width:760px){.ols-attribution-card.ols-attr-std{padding:24px 18px;border-radius:22px}}<\/style>\n<p><strong>Copyright notice:<\/strong> This OLS revision content, including the explanations, layout, diagrams, tables and embedded learning structure, is authored for Online Learning System by Dr. Mohammed Al-Fatah. It may not be copied, reproduced, redistributed or adapted without written permission.<\/p>\n<\/section>\n\n<\/main>\n\n  <script type=\"application\/ld+json\">\n{\n    \"@context\": \"https:\/\/schema.org\",\n    \"@graph\": [\n        {\n            \"@type\": \"WebPage\",\n            \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/isomerism\/#webpage\",\n            \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/isomerism\/\",\n            \"name\": \"Isomerism | Edexcel A Level Chemistry Revision Notes\",\n            \"description\": \"A concise A Level Chemistry revision page explaining structural isomerism, chain isomerism, position isomerism and functional group isomerism using organic molecule examples.\",\n            \"inLanguage\": \"en-GB\",\n 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Compounds can only be isomers if the molecular formulae match.\"\n                    }\n                },\n                {\n                    \"@type\": \"Question\",\n                    \"name\": \"Are but-1-ene and cyclobutane structural isomers?\",\n                    \"acceptedAnswer\": {\n                        \"@type\": \"Answer\",\n                        \"text\": \"Yes. Both are C\u2084H\u2088. One has a C=C bond and the other a ring, so they are functional group isomers.\"\n                    }\n                },\n                {\n                    \"@type\": \"Question\",\n                    \"name\": \"Is CH\u2083CH(CH\u2083)CH\u2082CH\u2083 a different compound from CH\u2083CH\u2082CH(CH\u2083)CH\u2083?\",\n                    \"acceptedAnswer\": {\n                        \"@type\": \"Answer\",\n                        \"text\": \"No. Both are 2-methylbutane written from opposite ends. 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