{"id":4817,"date":"2026-06-03T06:24:25","date_gmt":"2026-06-03T05:24:25","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/aldehyde\/"},"modified":"2026-10-14T09:06:44","modified_gmt":"2026-10-14T08:06:44","slug":"aldehyde","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\/aldehyde\/","title":{"rendered":"Aldehyde"},"content":{"rendered":"\n<section class=\"ols-revision-page ols-aldehyde-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-orange: #fff7ed;\n      --grey-text: #667085;\n      --body-text: #1f2937;\n      --border: rgba(28, 36, 75, 0.14);\n 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line-height: 1.5; transition: transform 0.2s ease, box-shadow 0.2s ease; }\n    .ols-related-item:hover { transform: translateY(-2px); box-shadow: 0 10px 22px rgba(28, 36, 75, 0.08); }\n\n    @media (max-width: 1050px) {\n      .ols-main { max-width: none; }\n      .ols-related-grid, .ols-image-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }\n    }\n\n    @media (max-width: 760px) {\n      .ols-title-card, .ols-note-card, .ols-h5p-card, .ols-related-card { padding: 24px 18px; border-radius: 22px; }\n      .ols-note-title { align-items: flex-start; }\n      .ols-figure-card, .ols-mini-figure { border-radius: 22px; }\n      .ols-figure-image { min-height: 220px; padding: 16px; }\n      .ols-mini-figure-image { min-height: 200px; padding: 16px; }\n      .ols-figure-caption, .ols-mini-figure-caption { padding: 16px; }\n      .ols-table-wrap { border: none; background: transparent; }\n      .ols-table, .ols-table thead, .ols-table tbody, .ols-table th, .ols-table td, .ols-table tr { display: block; width: 100%; }\n      .ols-table { border-collapse: separate; border-spacing: 0; }\n      .ols-table thead { display: none; }\n      .ols-table tr { margin-bottom: 14px; border: 1px solid var(--border); border-radius: 18px; overflow: hidden; background: #ffffff; box-shadow: var(--inner-shadow); }\n      .ols-table td { border-bottom: 1px solid var(--border); padding: 14px 16px; overflow-wrap: anywhere; }\n      .ols-table td:last-child { border-bottom: none; }\n      .ols-table td::before { content: attr(data-label); display: block; margin-bottom: 6px; font-size: 13px; font-weight: 700; color: var(--blue); }\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>Aldehyde<\/span>\n      <\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Aldehyde<\/h1>\n        <p class=\"ols-page-intro\">A concise revision guide to aldehyde functional groups, the -al suffix, formyl- prefix, terminal carbonyl groups, dialdehyde naming and priority over alcohols in IUPAC names.<\/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      \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: Counting Carbons with Name Stems<\/h2>\n<p>Remind yourself how a name stem tells you the number of carbon atoms.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"706\"><\/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 Is an Aldehyde?<\/h2>\n        <\/div>\n\n        <p>An <strong>aldehyde<\/strong> is an organic compound containing the <strong>-CHO<\/strong> functional group. This group contains a <strong>carbonyl group<\/strong>, written as <strong>C=O<\/strong>, with the carbonyl carbon also bonded to a hydrogen atom.<\/p>\n        <p>The aldehyde functional group must occur at the <strong>end of a carbon chain<\/strong>. This is because the carbonyl carbon in an aldehyde is bonded to one hydrogen atom and only one carbon atom from the rest of the molecule.<\/p>\n        <p>The carbonyl carbon is automatically treated as <strong>carbon 1<\/strong>, so a position number is normally not needed for a simple aldehyde suffix.<\/p>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Key idea:<\/strong> An aldehyde contains a terminal -CHO group. The carbonyl carbon is automatically numbered as carbon 1.<\/p>\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\/skel-P057-aldehyde-group.svg\" alt=\"The aldehyde functional group, \u2013CHO: a C=O double bond with a hydrogen atom on the carbon\" width=\"375\" height=\"402\">\n          <\/div>\n          <div class=\"ols-figure-caption\">\n            <p>The aldehyde functional group is terminal because the carbonyl carbon is bonded to a hydrogen atom and the rest of 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 Aldehyde<\/h2>\n<p>Pick out the aldehyde from four isomers with the same molecular formula.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-81\" class=\"h5p-iframe\" data-content-id=\"81\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Aldehyde MCQ: Picking the Aldehyde from Four C\u2084H\u2088O Isomers\"><\/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>Naming Aldehydes Using the -al Suffix<\/h2>\n        <\/div>\n\n        <p>The name of an aldehyde usually ends in the suffix <strong>-al<\/strong>. The final <strong>-e<\/strong> of the parent alkane is removed before adding <strong>-al<\/strong>.<\/p>\n        <p>For example, <strong>ethane<\/strong> becomes <strong>ethanal<\/strong>. The aldehyde carbon is automatically carbon 1, so the name does not need to be written as ethan-1-al.<\/p>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Homologous series<\/th>\n                <th>Functional group<\/th>\n                <th>Prefix<\/th>\n                <th>Suffix<\/th>\n                <th>Example<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Homologous series\">Aldehydes<\/td>\n                <td data-label=\"Functional group\">-CHO<\/td>\n                <td data-label=\"Prefix\">formyl-<\/td>\n                <td data-label=\"Suffix\">-al<\/td>\n                <td data-label=\"Example\">ethanal<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n\n        <div class=\"ols-image-grid\">\n          <div class=\"ols-mini-figure\">\n            <div class=\"ols-mini-figure-image\">\n              <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-mv-03-displayed.svg\" alt=\"Displayed formulae of ethanal\" width=\"393\" height=\"390\">\n            <\/div>\n            <div class=\"ols-mini-figure-caption\">\n              <p>Ethanal has two carbon atoms and a terminal -CHO group, so its name uses eth- and the aldehyde suffix -al.<\/p>\n            <\/div>\n          <\/div>\n\n          <div class=\"ols-mini-figure\">\n            <div class=\"ols-mini-figure-image\">\n              <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/mol-ethanal.svg\" alt=\"Skeletal formula of ethanal\" width=\"312\" height=\"200\">\n            <\/div>\n            <div class=\"ols-mini-figure-caption\">\n              <p>In skeletal formulae, the carbonyl group is shown at the end of the chain to show that the compound is an aldehyde.<\/p>\n            <\/div>\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: Name That Aldehyde<\/h2>\n<p>Choose the correct name for each unbranched aldehyde.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-82\" class=\"h5p-iframe\" data-content-id=\"82\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Aldehyde Single Choice: Name Four Unbranched Aldehydes\"><\/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>Why Aldehydes Do Not Usually Need Position Numbers<\/h2>\n        <\/div>\n\n        <p>For most aldehydes, the <strong>C=O group is on the first carbon<\/strong> of the carbon chain. This means the position of the aldehyde group is fixed by the functional group itself.<\/p>\n        <p>Because the carbonyl carbon is automatically numbered as carbon 1, a simple aldehyde name uses <strong>-al<\/strong> without a location number for the suffix.<\/p>\n\n        <div class=\"ols-rule-list\">\n          <div class=\"ols-rule-item\">\n            <h3>Identify the longest chain containing -CHO<\/h3>\n            <p>Include the carbonyl carbon of the aldehyde group as part of the parent chain.<\/p>\n          <\/div>\n          <div class=\"ols-rule-item\">\n            <h3>Number from the aldehyde carbon<\/h3>\n            <p>The aldehyde carbonyl carbon is carbon 1, so substituents are numbered from this end.<\/p>\n          <\/div>\n          <div class=\"ols-rule-item\">\n            <h3>Add the -al suffix<\/h3>\n            <p>Replace the final -e of the parent alkane name with <strong>-al<\/strong>, such as ethane to ethanal.<\/p>\n          <\/div>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Exam focus:<\/strong> Do not place the aldehyde group in the middle of the chain. A terminal C=O group with an attached hydrogen is what makes the compound an aldehyde.<\/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-09-aldehydeketone.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-09-aldehydeketone.jpg\" alt=\"Side-by-side comparison of aldehydes (RCHO, -al) and ketones (RCOR\u2032, -one): position of C=O, suffix, numbering and isomerism\" data-fullscreen-src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-img-09-aldehydeketone.jpg\">\n<\/a>\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: Numbering from the CHO Carbon<\/h2>\n<p>Choose the accurate statement about how each compound is numbered and named.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-80\" class=\"h5p-iframe\" data-content-id=\"80\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Aldehyde Summary: Numbering Substituents from the CHO Carbon\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card orange\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">4<\/div>\n          <h2>Molecules with Two Aldehyde Groups<\/h2>\n        <\/div>\n\n        <p>If a molecule contains <strong>two aldehyde groups<\/strong>, the suffix includes <strong>di<\/strong> before <strong>-al<\/strong>. The parent alkane name keeps the final <strong>e<\/strong> before the dial suffix.<\/p>\n        <p>For example, a four-carbon chain with aldehyde groups at both ends is named <strong>butanedial<\/strong>. The e of butane is kept because the suffix -dial starts with a consonant, so &#8220;butandial&#8221; is wrong.<\/p>\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-butanedial.svg\" alt=\"Skeletal formula of butanedial\" width=\"557\" height=\"212\">\n          <\/div>\n          <div class=\"ols-figure-caption\">\n            <p>Two terminal aldehyde groups are indicated by the dial ending, with one -CHO group at each end of the carbon chain.<\/p>\n          <\/div>\n        <\/div>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Number of aldehyde groups<\/th>\n                <th>Name ending<\/th>\n                <th>Meaning<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Number of aldehyde groups\">One<\/td>\n                <td data-label=\"Name ending\">-al<\/td>\n                <td data-label=\"Meaning\">One terminal -CHO group is present.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Number of aldehyde groups\">Two<\/td>\n                <td data-label=\"Name ending\">-dial<\/td>\n                <td data-label=\"Meaning\">Two terminal -CHO groups are present.<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\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: Two Aldehyde Groups<\/h2>\n<p>Name a molecule that has an aldehyde group at each end of the chain.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-83\" class=\"h5p-iframe\" data-content-id=\"83\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Aldehyde MCQ: Naming a Five-Carbon Dialdehyde\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">5<\/div>\n          <h2>Aldehydes Have Higher Priority Than Alcohols<\/h2>\n        <\/div>\n\n        <p>Aldehydes have a <strong>higher priority than alcohols<\/strong> in IUPAC naming. If a molecule contains both an aldehyde group and an -OH group, the aldehyde normally provides the main suffix <strong>-al<\/strong>.<\/p>\n        <p>The alcohol group is then named as a substituent using the prefix <strong>hydroxy-<\/strong>, rather than using the alcohol suffix <strong>-ol<\/strong>.<\/p>\n        <p>For example, <strong>4-hydroxybutanal<\/strong> contains an aldehyde group at carbon 1 and an -OH group on carbon 4.<\/p>\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-4-hydroxybutanal.svg\" alt=\"Skeletal formula of 4-hydroxybutanal\" width=\"581\" height=\"212\">\n          <\/div>\n          <div class=\"ols-figure-caption\">\n            <p>The aldehyde group controls the suffix, while the -OH group is named using the hydroxy- prefix because it has lower naming priority here.<\/p>\n          <\/div>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Remember:<\/strong> If -CHO and -OH are both present, use <strong>-al<\/strong> for the aldehyde and <strong>hydroxy-<\/strong> for the alcohol group.<\/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-02-priorityladder.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-02-priorityladder.jpg\" alt=\"Ladder of naming priority from carboxylic acid down to halogen, with the suffix and prefix used for each group\" data-fullscreen-src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-img-02-priorityladder.jpg\">\n<\/a>\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: Aldehyde and Alcohol Together<\/h2>\n<p>Build the name of a molecule that contains both an aldehyde group and an -OH group.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-707\" class=\"h5p-iframe\" data-content-id=\"707\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Aldehyde Drag the Words: Naming CH\u2083CH(OH)CH\u2082CHO\"><\/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: Aldehyde Naming Round-Up<\/h2>\n<p>Finish by applying all of the aldehyde naming rules to four new molecules.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"1280\"><\/div><\/div>\n<\/section>\n\n      \n\n            <section class=\"ols-faq-card\">\n        <h2>FAQs<\/h2>\n        <p>These questions cover the aldehyde naming points that cost marks.<\/p>\n        <div class=\"ols-faq-list\">\n          <div class=\"ols-faq-item\">\n            <h3>Why is it ethanal and not ethan-1-al?<\/h3>\n            <p>The aldehyde carbon is always carbon 1, so the number adds nothing and is left out.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>Is the CHO carbon counted in the chain length?<\/h3>\n            <p>Yes. Propanal, CH\u2083CH\u2082CHO, has three carbons including the carbonyl carbon.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>How do I tell an aldehyde from a ketone?<\/h3>\n            <p>Look at the carbonyl carbon. In an aldehyde it carries a hydrogen atom and sits at the end of the chain. In a ketone it is bonded to two carbon atoms.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>Why is it butanedial and not butandial?<\/h3>\n            <p>The suffix -dial starts with a consonant, so the e of butane is kept.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>What is HOCH\u2082CH\u2082CHO called?<\/h3>\n            <p>3-hydroxypropanal. The aldehyde takes the suffix and carbon 1, so the -OH group becomes the prefix hydroxy- on carbon 3.<\/p>\n          <\/div>\n        <\/div>\n      <\/section>\n\n      <!-- author card (moved to the end, 10 Oct 2026) -->\n      <div class=\"ols-author\">\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            <h2 class=\"ols-author-title\">Written by: Dr. Mohammed Al-Fatah<\/h2>\n            <p class=\"ols-author-description\">Chemistry specialist revision notes for A Level Chemistry.<\/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              <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              View LinkedIn Profile\n            <\/a>\n          <\/div>\n        <\/div>\n\n\n<section class=\"ols-related-card\">\n        <h2>Related Organic Chemistry Revision Notes<\/h2>\n        <p>Continue through Topic 6 by linking aldehyde naming to IUPAC rules, alcohols and ketones.<\/p>\n\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\/iupac-rules\/\">IUPAC Rules<\/a>\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\/alcohol\/\">Alcohol<\/a>\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\/ketone\/\">Ketone<\/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    <\/main>\n<\/section>\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\/aldehyde\/#webpage\",\n            \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/aldehyde\/\",\n            \"name\": \"Aldehyde - Edexcel A Level Chemistry\",\n            \"description\": \"Revision notes for Edexcel A Level Chemistry Topic 6 Organic Chemistry I covering aldehyde functional groups, the -al suffix, terminal carbonyl groups, dialdehydes and aldehyde priority over alcohols.\",\n            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The aldehyde takes the suffix and carbon 1, so the -OH group becomes the prefix hydroxy- on carbon 3.\"\n                    }\n                }\n            ]\n        }\n    ]\n}\n<\/script>\n","protected":false},"excerpt":{"rendered":"<p>Revision Notes \/ A Level Chemistry \/ Edexcel \/ Topic 6 Organic Chemistry I \/ Introduction to Organic Chemistry \/ Aldehyde Aldehyde A concise revision guide to aldehyde functional groups, the -al suffix, formyl- prefix, terminal carbonyl groups, dialdehyde naming and priority over alcohols in IUPAC names. Paper 2 Topic 6: Organic Chemistry I 9CH0\/02 [&hellip;]<\/p>\n","protected":false},"author":12,"featured_media":0,"parent":4692,"menu_order":4,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-4817","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/4817","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/users\/12"}],"replies":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/comments?post=4817"}],"version-history":[{"count":0,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/4817\/revisions"}],"up":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/4692"}],"wp:attachment":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/media?parent=4817"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}