{"id":4835,"date":"2026-06-03T06:24:37","date_gmt":"2026-06-03T05:24:37","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/propagation\/"},"modified":"2026-10-25T12:16:14","modified_gmt":"2026-10-25T12:16:14","slug":"propagation","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/propagation\/","title":{"rendered":"Propagation"},"content":{"rendered":"\n<section class=\"ols-revision-page ols-propagation-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: #667085;\n      --body-text: #1f2937;\n      --border: rgba(28, 36, 75, 0.14);\n      --shadow: 0 18px 45px rgba(28, 36, 75, 0.10);\n      --inner-shadow: 0 10px 26px rgba(28, 36, 75, 0.08);\n      font-family: Poppins, Arial, sans-serif;\n      color: var(--navy);\n      background: #ffffff;\n    }\n    .ols-revision-page * { box-sizing: border-box; }\n    .ols-main {\n      min-width: 0;\n      max-width: 970px;\n    }\n    .ols-breadcrumbs {\n      display: flex;\n      flex-wrap: wrap;\n      gap: 8px;\n      margin: 10px 0 22px;\n      font-size: 15px;\n      color: var(--grey-text);\n    }\n    .ols-breadcrumbs a,\n    .ols-breadcrumbs span {\n      color: var(--grey-text);\n      text-decoration: none;\n      font-weight: 600;\n    }\n    .ols-breadcrumbs a { transition: color 0.2s ease, text-decoration-color 0.2s ease; }\n    .ols-breadcrumbs a:hover {\n      color: var(--blue);\n      text-decoration: underline;\n      text-underline-offset: 3px;\n    }\n    .ols-title-card,\n    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}\n    .ols-key-box {\n      margin-top: 20px;\n      background: var(--soft-green);\n      border: 1px solid rgba(63, 143, 70, 0.25);\n      border-radius: 20px;\n      padding: 18px 20px;\n    }\n    .ols-key-box p {\n      margin: 0;\n      font-weight: 400;\n      color: var(--navy);\n    }\n    .ols-warning-box {\n      margin-top: 20px;\n      background: #fff7f7;\n      border: 1px solid rgba(200, 30, 30, 0.22);\n      border-left: 5px solid var(--red);\n      border-radius: 20px;\n      padding: 18px 20px;\n    }\n    .ols-warning-box p {\n      margin: 0;\n      font-weight: 400;\n      color: var(--navy);\n    }\n    .ols-definition-box {\n      background: linear-gradient(135deg, #ffffff, var(--soft-purple));\n      border: 2px dashed rgba(122, 62, 157, 0.35);\n      border-radius: 24px;\n      padding: 24px;\n      margin-top: 22px;\n    }\n    .ols-definition-box p {\n      margin: 0;\n      font-weight: 400;\n      color: var(--navy);\n    }\n    .ols-equation-box {\n     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.ols-figure-caption {\n      padding: 20px 24px 22px;\n      background: linear-gradient(135deg, #ffffff, #f8fbff);\n      border-top: 1px solid var(--border);\n    }\n    .ols-figure-caption p {\n      margin: 0;\n      color: #5f6b85;\n      font-size: clamp(15px, 1.25vw, 17px);\n      line-height: 1.6;\n      font-weight: 300;\n      font-style: italic;\n    }\n    .ols-table-wrap {\n      overflow: hidden;\n      border-radius: 22px;\n      border: 1px solid var(--border);\n      background: #ffffff;\n      margin-top: 18px;\n    }\n    .ols-table {\n      width: 100%;\n      border-collapse: collapse;\n      table-layout: fixed;\n    }\n    .ols-table th {\n      background: var(--navy);\n      color: #ffffff;\n      padding: 16px;\n      text-align: left;\n      font-size: clamp(14px, 1.2vw, 17px);\n      font-weight: 600;\n      overflow-wrap: anywhere;\n      word-break: normal;\n    }\n    .ols-table td {\n      padding: 16px;\n      border-bottom: 1px solid var(--border);\n   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font-size: 18px;\n      line-height: 1.35;\n      color: var(--navy);\n    }\n    .ols-faq-item p { margin: 0; }\n    .ols-related-grid {\n      display: grid;\n      grid-template-columns: repeat(3, minmax(0, 1fr));\n      gap: 16px;\n      margin-top: 18px;\n    }\n    .ols-related-item {\n      border: 1px solid var(--border);\n      border-radius: 18px;\n      padding: 18px;\n      background: #ffffff;\n      color: var(--navy);\n      text-decoration: none;\n      font-weight: 600;\n      line-height: 1.5;\n      transition: transform 0.2s ease, box-shadow 0.2s ease;\n    }\n    .ols-related-item:hover {\n      transform: translateY(-2px);\n      box-shadow: 0 10px 22px rgba(28, 36, 75, 0.08);\n    }\n\n    @media (max-width: 1050px) {\n    .ols-main { max-width: none; }\n    .ols-related-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }\n    }\n\n    @media (max-width: 760px) {\n    .ols-title-card,\n    .ols-note-card,\n    .ols-h5p-card,\n    .ols-related-card,\n    .ols-faq-card {\n        padding: 24px 18px;\n        border-radius: 22px;\n      }\n    .ols-note-title { align-items: flex-start; }\n    .ols-figure-card { border-radius: 22px; }\n    .ols-figure-image {\n        min-height: 230px;\n        padding: 14px;\n      }\n    .ols-figure-caption { padding: 18px; }\n    .ols-related-grid { grid-template-columns: 1fr; }\n    .ols-table-wrap {\n        border-radius: 20px;\n        overflow: hidden;\n      }\n    .ols-table,\n    .ols-table thead,\n    .ols-table tbody,\n    .ols-table th,\n    .ols-table td,\n    .ols-table tr {\n        display: block;\n        width: 100%;\n      }\n    .ols-table thead { display: none; }\n    .ols-table tr {\n        border-bottom: 1px solid var(--border);\n        background: #ffffff;\n      }\n    .ols-table tr:last-child { border-bottom: none; }\n    .ols-table td {\n        display: grid;\n        grid-template-columns: minmax(120px, 38%) minmax(0, 1fr);\n        gap: 12px;\n        align-items: start;\n        border-bottom: 1px solid rgba(28, 36, 75, 0.08);\n        padding: 14px;\n        overflow-wrap: anywhere;\n      }\n    .ols-table td:last-child { border-bottom: none; }\n    .ols-table td::before {\n        content: attr(data-label);\n        font-weight: 700;\n        color: var(--navy);\n        overflow-wrap: anywhere;\n      }\n    }\n\n\n    .ols-author {\n      display:flex;\n      align-items:center;\n      gap:20px;\n      padding:28px;\n      border-radius:28px;\n      background:linear-gradient(135deg,#ffffff 0%,#f8fbff 100%);\n      border:1px solid rgba(28,36,75,0.12);\n      box-shadow:0 18px 45px rgba(28,36,75,0.10);\n    }\n\n    .ols-author-avatar-img {\n      width:92px;\n      height:92px;\n      border-radius:50%;\n      object-fit:cover;\n      object-position:center;\n      flex-shrink:0;\n      border:4px solid #ffffff;\n      box-shadow:\n        0 14px 32px rgba(28,36,75,0.18),\n        0 0 0 1px rgba(28,36,75,0.10);\n      transition:\n        transform 0.25s ease,\n        box-shadow 0.25s ease;\n    }\n\n    .ols-author:hover .ols-author-avatar-img {\n      transform:scale(1.04);\n      box-shadow:\n        0 20px 42px rgba(28,36,75,0.22),\n        0 0 0 1px rgba(28,36,75,0.10);\n    }\n\n    .ols-author-content {\n      min-width:0;\n    }\n\n    .ols-author-title {\n      margin:0 0 4px;\n      font-size:clamp(24px,3vw,34px);\n      line-height:1.15;\n      font-weight:700;\n      color:#1C244B;\n      letter-spacing:-0.03em;\n    }\n\n    .ols-author-description {\n      margin:0;\n      font-size:17px;\n      line-height:1.7;\n      font-weight:300;\n      color:#667085;\n    }\n\n    .ols-linkedin-pill {\n      display:inline-flex;\n      align-items:center;\n      justify-content:center;\n      gap:10px;\n      margin-top:16px;\n      padding:11px 18px;\n      border-radius:999px;\n      background:linear-gradient(135deg,#0A66C2,#004182);\n      color:#ffffff !important;\n      text-decoration:none;\n      font-size:14px;\n      line-height:1;\n      font-weight:700;\n      letter-spacing:0.01em;\n      box-shadow:0 10px 22px rgba(10,102,194,0.24);\n      position:relative;\n      overflow:hidden;\n      transition:\n        transform 0.22s ease,\n        box-shadow 0.22s ease;\n    }\n\n    .ols-linkedin-pill::before {\n      content:\"\";\n      position:absolute;\n      top:0;\n      left:-120%;\n      width:100%;\n      height:100%;\n      background:linear-gradient(\n        120deg,\n        rgba(255,255,255,0) 0%,\n        rgba(255,255,255,0.28) 50%,\n        rgba(255,255,255,0) 100%\n      );\n      transition:left 0.7s ease;\n    }\n\n    .ols-linkedin-pill:hover {\n      transform:translateY(-3px) scale(1.03);\n      color:#ffffff !important;\n      box-shadow:\n        0 16px 34px rgba(10,102,194,0.34),\n        0 0 0 6px rgba(10,102,194,0.10);\n    }\n\n    .ols-linkedin-pill:hover::before {\n      left:120%;\n    }\n\n    .ols-linkedin-icon {\n      width:18px;\n      height:18px;\n      display:block;\n      flex-shrink:0;\n    }\n\n    .ols-figure-placeholder .ols-placeholder-box { border: 2px dashed #c9973a; background: #fffaf0; border-radius: 16px; padding: 26px 22px; font-weight: 700; color: #7a4b12; text-align: center; line-height: 1.6; }\n    .ols-figure-placeholder .ols-figure-image { background: transparent; }\n    .ols-figure-placeholder { background: #ffffff; border: 1px solid rgba(28, 36, 75, 0.12); border-radius: 22px; padding: 14px; margin: 18px 0 6px; }\n    .ols-figure-placeholder .ols-figure-caption p { margin: 10px 0 0; font-size: 14px; color: #667085; text-align: center; }\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\/alkanes\/reactions\/free-radical-substitution\/\">Reactions of Alkanes<\/a> \/\n        <span>Propagation<\/span>\n      <\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Propagation<\/h1>\n        <p class=\"ols-page-intro\">A concise revision guide to the propagation stage of free-radical substitution, including hydrogen abstraction, alkyl radical formation, halogenoalkane production and regeneration of the halogen radical.<\/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<!-- 3D card: radical-chain-methane (5 Oct 2026, Topics 1-5 upgrade) -->\n<!-- Copyright (c) 2026 Dr. Mohammed Al-Fatah, onlinelearningsystem.net. 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border:1px solid rgba(28,36,75,0.18);\n}\n.ols-radc-001 .radc-key i.k-ball{border-radius:50%;}\n\n@media (max-width:760px){\n  .ols-radc-001{padding:26px; border-radius:22px;}\n  .ols-radc-001 h2.radc-title{font-size:20.5px;}\n  .ols-radc-001 p.radc-sub{font-size:13.5px;}\n  .ols-radc-001 .radc-stage{height:400px;}\n  .ols-radc-001 .radc-rowlab{min-width:100%;}\n  .ols-radc-001 .radc-seg button{padding:9px 13px; font-size:13px;}\n  .ols-radc-001 .radc-lab{font-size:10.5px; padding:4px 8px;}\n  .ols-radc-001 .radc-lab.l-part{font-size:9.5px; padding:3px 7px;}\n  .ols-radc-001 .radc-lab.l-read{font-size:12px; padding:5px 9px;}\n  .ols-radc-001 .radc-caption{font-size:10.5px; padding:5px 9px; max-width:64%;}\n  .ols-radc-001 .radc-badge{font-size:10.5px; padding:4px 9px;}\n  .ols-radc-001 .radc-badge.b-eq{font-size:11px;}\n  .ols-radc-001 .radc-badges{max-width:calc(100% - 28px);}\n  .ols-radc-001 .radc-info{padding:18px;}\n}\n\/* on a phone the caption needs the full top row, so the drag hint goes *\/\n@media (max-width:480px){\n  .ols-radc-001 .radc-hint{display:none;}\n  .ols-radc-001 .radc-caption{max-width:calc(100% - 28px);}\n}\n@media (prefers-reduced-motion:reduce){\n  .ols-radc-001 .radc-seg button,.ols-radc-001 .radc-pill{transition:none;}\n}\n\n.ols-cc-radc-001{\n  font-family:'Poppins',system-ui,-apple-system,'Segoe UI',Roboto,Helvetica,Arial,sans-serif;\n  margin:10px auto 0; text-align:center; font-size:11px; font-style:italic; color:#aab0c0;\n}\n.ols-cc-radc-001 a{color:#aab0c0; text-decoration:none;}\n.ols-cc-radc-001 a:hover{text-decoration:underline;}\n.ols-radc-001 .radc-seg button{display:inline-flex; align-items:center;}\n.ols-radc-001 .radc-seg button .radc-n{display:inline-flex; align-items:center; justify-content:center; width:20px; height:20px; margin-right:9px; border-radius:50%; font-size:11px; font-weight:600; background:rgba(37,99,235,0.10); color:#2563eb; flex:0 0 auto;}\n.ols-radc-001 .radc-seg button[aria-pressed=\"true\"] .radc-n{background:#ffffff; color:#2563eb;}\n<\/style>\n\n<div class=\"radc-head\">\n  <h2 class=\"radc-title\">Radical Chain Reaction: Methane and Chlorine<\/h2>\n  <p class=\"radc-sub\">Choose a step to follow every electron: UV light makes the radicals, the chain repeats, and two radicals meeting end it.<\/p>\n<\/div>\n\n<div class=\"radc-stage\" id=\"radcStage\">\n  <canvas class=\"radc-canvas\" id=\"radcCanvas\"><\/canvas>\n  <div class=\"radc-overlay\" id=\"radcOverlay\"><\/div>\n  <div class=\"radc-caption\" id=\"radcCaption\"><\/div>\n  <div class=\"radc-hint\" id=\"radcHint\">Drag to rotate<\/div>\n  <div class=\"radc-badges\" id=\"radcBadges\"><\/div>\n<\/div>\n\n<div class=\"radc-controls\">\n  <div class=\"radc-row\">\n    <span class=\"radc-rowlab\">Step<\/span>\n    <div class=\"radc-seg\" role=\"group\" aria-label=\"Step\">\n      <button type=\"button\" data-step=\"1\" aria-pressed=\"true\"><span class=\"radc-n\">1<\/span>Initiation<\/button>\n      <button type=\"button\" data-step=\"2\" aria-pressed=\"false\"><span class=\"radc-n\">2<\/span>Cl\u2022 takes an H<\/button>\n      <button type=\"button\" data-step=\"3\" aria-pressed=\"false\"><span class=\"radc-n\">3<\/span>\u2022CH\u2083 takes a Cl<\/button>\n      <button type=\"button\" data-step=\"4\" aria-pressed=\"false\"><span class=\"radc-n\">4<\/span>The chain repeats<\/button>\n      <button type=\"button\" data-step=\"5\" aria-pressed=\"false\"><span class=\"radc-n\">5<\/span>Termination<\/button>\n    <\/div>\n  <\/div>\n\n  <div class=\"radc-row\">\n    <span class=\"radc-rowlab\">View<\/span>\n    <button type=\"button\" class=\"radc-pill\" id=\"radcResetV\">Reset view<\/button>\n  <\/div>\n<\/div>\n\n<div class=\"radc-info\">\n  <h3 id=\"radcInfoTitle\"><\/h3>\n  <p id=\"radcInfoText\"><\/p>\n  <div class=\"radc-facts\" id=\"radcFacts\"><\/div>\n  <div class=\"radc-key\">\n    <span><i class=\"k-ball\" style=\"background:#464a54\"><\/i>Carbon<\/span>\n    <span><i class=\"k-ball\" style=\"background:#ececf0\"><\/i>Hydrogen<\/span>\n    <span><i class=\"k-ball\" style=\"background:#34aa48\"><\/i>Chlorine<\/span>\n    <span><i class=\"k-ball\" style=\"background:#f6c426\"><\/i>Electron<\/span>\n  <\/div>\n<\/div>\n\n<script src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/JS\/radical-chain-methane.js?v=20261025p\"><\/script>\n<\/section>\n\n<p class=\"ols-cc-radc-001\">&copy; Dr. Mohammed Al-Fatah &#8211; <a href=\"https:\/\/www.onlinelearningsystem.net\" target=\"_blank\" rel=\"noopener\">onlinelearningsystem.net<\/a><\/p>\n\n\n      <article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">1<\/div>\n<h2>Before You Start<\/h2>\n<\/div>\n<p>This page builds on initiation and on what you know about covalent bonds from GCSE.<\/p>\n<ul class=\"ols-list\">\n<li>A covalent bond is a shared pair of electrons.<\/li>\n<li>Breaking a bond takes in energy; making a bond releases energy.<\/li>\n<li>Initiation uses UV light to split Cl<sub>2<\/sub> into two chlorine radicals, Cl\u2022.<\/li>\n<li>A free radical has an unpaired electron, shown by a dot.<\/li>\n<\/ul>\n<\/article>\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: Chlorine Atoms, Hydrogen Halides and Swapping Atoms<\/h2>\n<p>Check the GCSE ideas that the propagation steps build on.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"1287\"><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card soft\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">2<\/div>\n          <h2>What Happens During Propagation?<\/h2>\n        <\/div>\n\n        <p><strong>Propagation<\/strong> is the chain-carrying stage of free-radical substitution. It uses a free radical formed in initiation and produces another free radical so the reaction can continue.<\/p>\n        <p>In the substitution of an alkane by a halogen, propagation normally occurs in <strong>two repeated steps<\/strong>. First, a halogen radical removes a hydrogen atom from the alkane. Second, the alkyl radical formed reacts with a halogen molecule to make the halogenoalkane product.<\/p>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Key idea:<\/strong> In propagation, a free radical is present in both the reactants and the products. This is why the mechanism continues as a chain reaction.<\/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-36-countradicals.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-36-countradicals.jpg\" alt=\"Three rows for initiation, propagation and termination showing radicals in and out, an example equation and a spotting tip\" data-fullscreen-src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-img-36-countradicals.jpg\">\n<\/a>\n<\/div>\n<div class=\"ols-figure-caption\"><p>Propagation keeps the number of radicals the same: one in, one out.<\/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: Counting the Radicals<\/h2>\n<p>Decide whether this step changes the number of radicals in the mixture.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-142\" class=\"h5p-iframe\" data-content-id=\"142\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Propagation True or False: Counting the Radicals\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">3<\/div>\n          <h2>First Propagation Step: Hydrogen Abstraction<\/h2>\n        <\/div>\n\n        <p>In the first propagation step, a halogen free radical removes a <strong>hydrogen atom<\/strong> from the alkane. This forms a hydrogen halide and an <strong>alkyl free radical<\/strong>.<\/p>\n        <p>For chlorination of methane, the chlorine radical removes one hydrogen atom from methane. The products are hydrogen chloride and a methyl radical.<\/p>\n\n        <div class=\"ols-equation-box\">\n          <p>CH<sub>4<\/sub> + Cl\u2022 \u2192 HCl + \u2022CH<sub>3<\/sub><\/p>\n        <\/div>\n\n        <div class=\"ols-warning-box\">\n          <p><strong>Exam focus:<\/strong> The dot belongs on the radical species. The methyl radical is written as \u2022CH<sub>3<\/sub> or CH<sub>3<\/sub>\u2022, not CH<sub>3<\/sub><sup>+<\/sup> or CH<sub>3<\/sub><sup>&#8211;<\/sup>.<\/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: Find the Fault<\/h2>\n<p>Find the fault in a student&#039;s first propagation step.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-141\" class=\"h5p-iframe\" data-content-id=\"141\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Propagation MCQ: Finding the Fault in a Student Equation\"><\/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>Second Propagation Step: Halogenoalkane Formation<\/h2>\n        <\/div>\n\n        <p>In the second propagation step, the alkyl radical reacts with a <strong>halogen molecule<\/strong>. This forms the main substitution product, a halogenoalkane, and regenerates another halogen free radical.<\/p>\n        <p>For chlorination of methane, the methyl radical reacts with a chlorine molecule to form chloromethane and another chlorine radical.<\/p>\n\n        <div class=\"ols-equation-box\">\n          <p>\u2022CH<sub>3<\/sub> + Cl<sub>2<\/sub> \u2192 CH<sub>3<\/sub>Cl + Cl\u2022<\/p>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Why this matters:<\/strong> The chlorine radical is regenerated, so it can remove hydrogen from another methane molecule. This keeps the chain reaction going.<\/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: Both Steps for Cyclohexane<\/h2>\n<p>Complete both propagation steps for cyclohexane and chlorine.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-140\" class=\"h5p-iframe\" data-content-id=\"140\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Propagation Drag: The Two Steps for Cyclohexane and Chlorine\"><\/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\">5<\/div>\n          <h2>Propagation as a Chain Reaction<\/h2>\n        <\/div>\n\n        <p>A chain reaction continues because a reactive species consumed in one step is regenerated in a later step. In free-radical substitution, the regenerated species is the halogen free radical.<\/p>\n        <p>The two propagation steps can repeat many times before radicals are removed during termination.<\/p>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Propagation feature<\/th>\n                <th>What it means<\/th>\n                <th>Example<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Propagation feature\"><strong>Radical in reactants<\/strong><\/td>\n                <td data-label=\"What it means\">A halogen radical starts the propagation sequence by reacting with the alkane.<\/td>\n                <td data-label=\"Example\">Cl\u2022 reacts with CH<sub>4<\/sub>.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Propagation feature\"><strong>Radical in products<\/strong><\/td>\n                <td data-label=\"What it means\">A new radical is produced, so further reaction is possible.<\/td>\n                <td data-label=\"Example\">\u2022CH<sub>3<\/sub> forms in the first propagation step.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Propagation feature\"><strong>Radical regenerated<\/strong><\/td>\n                <td data-label=\"What it means\">The halogen radical is remade and can attack another alkane molecule.<\/td>\n                <td data-label=\"Example\">Cl\u2022 is regenerated when \u2022CH<sub>3<\/sub> reacts with Cl<sub>2<\/sub>.<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n\n        <div class=\"ols-figure-card\">\n<div class=\"ols-figure-image\"><img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-cd-08-propagation.svg\" alt=\"Two propagation steps for methane chlorination drawn with fish-hook arrows, with all chlorine lone pairs and radical dots shown\" width=\"1489\" height=\"1244\"><\/div>\n<div class=\"ols-figure-caption\"><p>Each fish-hook arrow shows one electron moving. In an exam, write the two propagation equations with the radical dots; the arrows here show why they work.<\/p><\/div>\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-35-propagationcycle.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-35-propagationcycle.jpg\" alt=\"Circular diagram of the two propagation steps for methane and chlorine, with Cl\u2022 returning to the start of the cycle\" data-fullscreen-src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-img-35-propagationcycle.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: One Turn of the Chain<\/h2>\n<p>Put the events of one turn of the chain in order.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-143\" class=\"h5p-iframe\" data-content-id=\"143\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Propagation Sort: One Turn of the Chain for Propane and Chlorine\"><\/iframe><\/div><\/div>\n<\/section>\n\n\n      <article class=\"ols-note-card yellow\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">6<\/div>\n          <h2>Example: Bromination of Propane<\/h2>\n        <\/div>\n\n        <p>With propane, a bromine free radical can remove a hydrogen atom from the middle carbon. This forms hydrogen bromide and a <strong>secondary propyl free radical<\/strong>.<\/p>\n        <p>This secondary radical is more stable than a primary radical. It can then react with Br<sub>2<\/sub> to form <strong>2-bromopropane<\/strong> and regenerate Br\u2022.<\/p>\n\n        <div class=\"ols-equation-box\">\n          <p>CH<sub>3<\/sub>CH<sub>2<\/sub>CH<sub>3<\/sub> + Br\u2022 \u2192 HBr + CH<sub>3<\/sub>CH\u2022CH<sub>3<\/sub><\/p>\n        <\/div>\n\n        <div class=\"ols-equation-box\">\n          <p>CH<sub>3<\/sub>CH\u2022CH<sub>3<\/sub> + Br<sub>2<\/sub> \u2192 CH<sub>3<\/sub>CHBrCH<sub>3<\/sub> + Br\u2022<\/p>\n        <\/div>\n\n        <div class=\"ols-warning-box\">\n          <p><strong>Common mistake:<\/strong> Do not stop after the first propagation step. The second step is needed to form the halogenoalkane and regenerate the halogen radical.<\/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: Complete the Pair of Steps<\/h2>\n<p>Type the missing formulae to complete both steps for butane and bromine.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-729\" class=\"h5p-iframe\" data-content-id=\"729\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Propagation Fill In: Completing the Pair for Butane and Bromine\"><\/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: Propagation Summary<\/h2>\n<p>Pull the whole page together by choosing the accurate statement in each round.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-1288\" class=\"h5p-iframe\" data-content-id=\"1288\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Propagation Summary: Both Steps Applied to New Alkanes\"><\/iframe><\/div><\/div>\n<\/section>\n\n      \n\n<section class=\"ols-faq-card\">\n        <h2>Propagation FAQs<\/h2>\n        <p>These questions summarise the key exam points for the propagation step in free-radical substitution.<\/p>\n\n        <div class=\"ols-faq-list\">\n          <div class=\"ols-faq-item\">\n            <h3>What is propagation in free-radical substitution?<\/h3>\n            <p>Propagation is the chain-carrying stage of the mechanism. A free radical reacts to form a product and another free radical, allowing the reaction to continue.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>What happens in the first propagation step?<\/h3>\n            <p>A halogen radical removes a hydrogen atom from the alkane. This forms a hydrogen halide and an alkyl free radical.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>What happens in the second propagation step?<\/h3>\n            <p>The alkyl radical reacts with a halogen molecule. This forms a halogenoalkane and regenerates a halogen free radical.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>Why is propagation called a chain reaction?<\/h3>\n            <p>It is called a chain reaction because the halogen radical is regenerated and can react with further alkane molecules, repeating the propagation steps many times.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>What are the propagation equations for chlorination of methane?<\/h3>\n            <p>The two propagation equations are CH<sub>4<\/sub> + Cl\u2022 \u2192 HCl + \u2022CH<sub>3<\/sub> and \u2022CH<sub>3<\/sub> + Cl<sub>2<\/sub> \u2192 CH<sub>3<\/sub>Cl + Cl\u2022.<\/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 Topics<\/h2>\n        <p>Build the full free-radical substitution sequence by revising the connected mechanism pages.<\/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\/alkanes\/reactions\/free-radical-substitution\/\">Free Radical Substitution<\/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\/initiation\/\">Initiation<\/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\/termination\/\">Termination<\/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\/further-substitution\/\">Further Substitution<\/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\/fuel\/combustion\/\">Combustion<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/\">Alkenes<\/a>\n        <\/div>\n      <\/section>\n\n      \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      <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\/alkanes\/reactions\/propagation\/#webpage\",\n            \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/propagation\/\",\n            \"name\": \"Propagation | Free Radical Substitution | Edexcel A Level Chemistry Revision Notes\",\n            \"description\": \"Edexcel A Level Chemistry revision notes on propagation in free-radical substitution, including hydrogen abstraction, alkyl radical formation, haloalkane production and radical regeneration.\",\n            \"inLanguage\": 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      \"text\": \"Propagation is the chain-carrying stage of the mechanism. A free radical reacts to form a product and another free radical, allowing the reaction to continue.\"\n                    }\n                },\n                {\n                    \"@type\": \"Question\",\n                    \"name\": \"What happens in the first propagation step?\",\n                    \"acceptedAnswer\": {\n                        \"@type\": \"Answer\",\n                        \"text\": \"A halogen radical removes a hydrogen atom from the alkane. This forms a hydrogen halide and an alkyl free radical.\"\n                    }\n                },\n                {\n                    \"@type\": \"Question\",\n                    \"name\": \"What happens in the second propagation step?\",\n                    \"acceptedAnswer\": {\n                        \"@type\": \"Answer\",\n                        \"text\": \"The alkyl radical reacts with a halogen molecule. 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