{"id":10912,"date":"2026-09-26T21:56:54","date_gmt":"2026-09-26T20:56:54","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-10-alcohols-halogenoalkanes-and-spectra\/10c-spectra\/mass-spectra-of-organic-compounds\/"},"modified":"2026-10-04T23:03:52","modified_gmt":"2026-10-04T22:03:52","slug":"mass-spectra-of-organic-compounds","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-10-alcohols-halogenoalkanes-and-spectra\/10c-spectra\/mass-spectra-of-organic-compounds\/","title":{"rendered":"Mass Spectra of Organic Compounds"},"content":{"rendered":"\n<section class=\"ols-revision-page ols-alcohols-halogenoalkanes-spectra-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      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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\">\n  <div class=\"ols-sidebar-header\">\n    <h3>Revision Notes<\/h3>\n    <p>A Level Chemistry<\/p>\n  <\/div>\n\n  <div class=\"ols-topic-group\">\n    <h4>Topic 10 Alcohols, Halogenoalkanes &amp; Spectra<\/h4>\n\n    <ul class=\"ols-topic-list\">\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-10-alcohols-halogenoalkanes-and-spectra\/\">Topic 10 Overview<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-10-alcohols-halogenoalkanes-and-spectra\/10a-alcohols\/\">Topic 10A Alcohols<\/a>\n        <ul class=\"ols-subtopic-list\">\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-10-alcohols-halogenoalkanes-and-spectra\/10a-alcohols\/alcohols-naming-classification-and-properties\/\">Alcohols: Naming, Classification and Properties<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-10-alcohols-halogenoalkanes-and-spectra\/10a-alcohols\/oxidation-of-alcohols\/\">Oxidation of Alcohols<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-10-alcohols-halogenoalkanes-and-spectra\/10a-alcohols\/reactions-of-alcohols\/\">Substitution and Elimination Reactions of Alcohols<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-10-alcohols-halogenoalkanes-and-spectra\/10a-alcohols\/preparing-and-purifying-organic-liquids\/\">Preparing and Purifying Organic Liquids<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/core-practicals\/cp-6-chlorination-of-2-methylpropan-2-ol\/\">Core Practical 6<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/core-practicals\/cp-7-oxidation-of-propan-1-ol\/\">Core Practical 7<\/a>\n          <\/li>\n        <\/ul>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-10-alcohols-halogenoalkanes-and-spectra\/10b-halogenoalkanes\/\">Topic 10B Halogenoalkanes<\/a>\n        <ul class=\"ols-subtopic-list\">\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-10-alcohols-halogenoalkanes-and-spectra\/10b-halogenoalkanes\/reaction-types-mechanisms-and-nucleophiles\/\">Reaction Types, Mechanisms and Nucleophiles<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-10-alcohols-halogenoalkanes-and-spectra\/10b-halogenoalkanes\/halogenoalkanes-naming-classification-and-bonding\/\">Halogenoalkanes: Naming, Classification and the C\u2013X Bond<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-10-alcohols-halogenoalkanes-and-spectra\/10b-halogenoalkanes\/nucleophilic-substitution-reactions\/\">Nucleophilic Substitution Reactions<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-10-alcohols-halogenoalkanes-and-spectra\/10b-halogenoalkanes\/elimination-reactions-of-halogenoalkanes\/\">Elimination Reactions of Halogenoalkanes<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-10-alcohols-halogenoalkanes-and-spectra\/10b-halogenoalkanes\/rates-of-hydrolysis-and-bond-enthalpy\/\">Rates of Hydrolysis and Bond Enthalpy<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/core-practicals\/cp-5-hydrolysis-of-halogenoalkanes\/\">Core Practical 5<\/a>\n          <\/li>\n        <\/ul>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-10-alcohols-halogenoalkanes-and-spectra\/10c-spectra\/\">Topic 10C Spectra<\/a>\n        <ul class=\"ols-subtopic-list\">\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-10-alcohols-halogenoalkanes-and-spectra\/10c-spectra\/mass-spectra-of-organic-compounds\/\">Mass Spectra of Organic Compounds<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-10-alcohols-halogenoalkanes-and-spectra\/10c-spectra\/infrared-spectroscopy\/\">Infrared Spectroscopy<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-10-alcohols-halogenoalkanes-and-spectra\/10c-spectra\/identifying-unknown-compounds\/\">Identifying Unknown Compounds<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/core-practicals\/cp-8-analysis-of-inorganic-and-organic-unknowns\/\">Core Practical 8<\/a>\n          <\/li>\n        <\/ul>\n      <\/li>\n    <\/ul>\n  <\/div>\n\n  <div class=\"ols-topic-group\">\n    <h4>Other Topics<\/h4>\n\n    <ul class=\"ols-topic-list\">\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-4-organic-chemistry-and-alkanes\/\">Topic 4 Organic Chemistry &amp; Alkanes<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-5-alkenes\/\">Topic 5 Alkenes<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-9-kinetics-and-equilibria\/\">Topic 9 Kinetics &amp; Equilibria<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/core-practicals\/\">Core Practicals<\/a>\n      <\/li>\n    <\/ul>\n  <\/div>\n<\/aside>\n\n<script>\r\n(function() {\r\n  function normalisePath(path) {\r\n    return String(path || '')\r\n      .split('?')[0]\r\n      .split('#')[0]\r\n      .replace(\/\\\/+$\/, '')\r\n      .toLowerCase();\r\n  }\r\n\r\n  function highlightActive() {\r\n    var sidebar = document.querySelector('.ols-sidebar');\r\n    if (!sidebar) return false;\r\n\r\n    var currentPath = normalisePath(window.location.pathname);\r\n    var links = sidebar.querySelectorAll('a[href]');\r\n    var matched = null;\r\n    var matchedLength = 0;\r\n\r\n    sidebar.querySelectorAll('.active, .active-main, .parent-active').forEach(function(item) {\r\n      item.classList.remove('active', 'active-main', 'parent-active');\r\n    });\r\n\r\n    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href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-10-alcohols-halogenoalkanes-and-spectra\/10c-spectra\/\">Topic 10C Spectra<\/a> \/\n<span>Mass Spectra of Organic Compounds<\/span>\n<\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Mass Spectra of Organic Compounds<\/h1>\n        <p class=\"ols-page-intro\">A concise revision guide to using mass spectra to identify organic compounds: the molecular ion and relative molecular mass, fragmentation patterns and common fragment ions, and the M and M+2 peaks of chlorine and bromine compounds.<\/p>\n        <div class=\"ols-badges\">\n<div class=\"ols-badge\">Exam board: Edexcel International<\/div>\n<div class=\"ols-badge\">Unit 2: WCH12\/01<\/div>\n<div class=\"ols-badge\">Topic 10C Spectra<\/div>\n<\/div>\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 class=\"ols-linkedin-pill\" href=\"https:\/\/www.linkedin.com\/in\/doctormohammedfatah\/\" target=\"_blank\" rel=\"noopener noreferrer\">\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\n    <\/div>\n\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: Relative Formula Mass<\/h2>\n<p>Three quick questions on relative atomic mass, working out a relative formula mass and what an ion is.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"966\"><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">1<\/div>\n<h2>The Molecular Ion<\/h2>\n<\/div>\n<p>When an organic compound is put through a mass spectrometer, its molecules are ionised by losing one electron each: M \u2192 M\u207a\u2022 + e\u207b.<\/p><p>The ion formed is the <strong>molecular ion<\/strong>, written M\u207a or M\u207a\u2022, and it is both a positive ion and a radical because it has an unpaired electron.<\/p><p>It has the same mass as the molecule, so on the spectrum the peak with the <strong>highest m\/z value<\/strong> gives the <strong>relative molecular mass<\/strong> of the compound directly, because the charge is +1.<\/p>\n<p>The molecular ion peak is often small, because most of the ions break up before they reach the detector, and it is not the tallest peak.<\/p><p>A tiny peak one unit higher, the <strong>M+1 peak<\/strong>, comes from molecules containing one \u00b9\u00b3C atom (1.1% of carbon) and must not be mistaken for the molecular ion.<\/p>\n\n<div class=\"ols-key-box\">\n<p><strong>Definition:<\/strong> The molecular ion is the molecule that has lost one electron. Its m\/z value is the relative molecular mass of the compound.<\/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>Check: Reading the Molecular Ion<\/h2>\n<p>Identify molecular ions and Mr values for compounds not used on this page.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"967\"><\/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>Fragmentation Patterns<\/h2>\n<\/div>\n<p>The energy of ionisation breaks many of the molecular ions into pieces. A covalent bond breaks so that one fragment keeps the positive charge and the other is a neutral radical: M\u207a\u2022 \u2192 X\u207a + Y\u2022.<\/p><p>Only the charged fragment is detected, so every other peak in the spectrum is a <strong>fragment ion<\/strong>.<\/p><p>The pattern of fragment peaks is characteristic of the structure and lets the molecule be pieced together.<\/p>\n<p>The most stable ions give the tallest peaks. Carbocations such as CH\u2083\u207a (m\/z 15), C\u2082H\u2085\u207a (29) and C\u2083H\u2087\u207a (43), and acylium ions such as CH\u2083CO\u207a (43) and C\u2082H\u2085CO\u207a (57), appear again and again.<\/p><p>The <strong>loss<\/strong> from the molecular ion is as useful as the fragment itself.<\/p><p>M \u2212 15 means a methyl group has been lost, M \u2212 29 an ethyl group, M \u2212 17 an OH group, M \u2212 18 a water molecule from an alcohol, M \u2212 45 a COOH group.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>m\/z of fragment<\/th><th>Likely ion<\/th><th>Suggests<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>15<\/strong><\/td><td>CH\u2083\u207a<\/td><td>a methyl group<\/td><\/tr>\n<tr><td><strong>29<\/strong><\/td><td>CH\u2083CH\u2082\u207a or CHO\u207a<\/td><td>an ethyl group or an aldehyde<\/td><\/tr>\n<tr><td><strong>31<\/strong><\/td><td>CH\u2082OH\u207a<\/td><td>a primary alcohol<\/td><\/tr>\n<tr><td><strong>43<\/strong><\/td><td>CH\u2083CH\u2082CH\u2082\u207a or CH\u2083CO\u207a<\/td><td>a propyl group or a CH\u2083C=O group<\/td><\/tr>\n<tr><td><strong>45<\/strong><\/td><td>COOH\u207a or CH\u2083CHOH\u207a<\/td><td>a carboxylic acid or a secondary alcohol<\/td><\/tr>\n<tr><td><strong>57<\/strong><\/td><td>C\u2084H\u2089\u207a or C\u2082H\u2085CO\u207a<\/td><td>a butyl group or an ethyl ketone<\/td><\/tr>\n<\/tbody>\n<\/table>\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\/09\/alcohols-halogenoalkanes-spectra-massspectrum.jpg\" target=\"_blank\" rel=\"noopener\" aria-label=\"Open image fullscreen\">\n<img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/alcohols-halogenoalkanes-spectra-massspectrum.jpg\" alt=\"Mass spectrum of butanone with the molecular ion and fragment ions labelled, and the M and M+2 peaks of chlorine\" data-fullscreen-src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/alcohols-halogenoalkanes-spectra-massspectrum.jpg\">\n<\/a>\n<\/div>\n<div class=\"ols-figure-caption\"><p>The mass spectrum of butanone with its molecular ion and fragment ions labelled, and the M and M+2 peaks that chlorine produces.<\/p><\/div>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Worked example:<\/strong> A spectrum has its molecular ion at m\/z 58 and peaks at 43 and 15. Mr 58 fits C\u2083H\u2086O (propanal or propanone) or C\u2084H\u2081\u2080 (butane).<\/p><p>A strong peak at 43 = CH\u2083CO\u207a with 15 = CH\u2083\u207a and no peak at 29 points to propanone, CH\u2083COCH\u2083, which splits only into CH\u2083CO\u207a and CH\u2083\u2022.<\/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>Check: Using Fragments<\/h2>\n<p>Match fragment peaks to structures that are not the ones above.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-968\" class=\"h5p-iframe\" data-content-id=\"968\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Alcohols, Halogenoalkanes and Spectra Drag: Using Fragments\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">3<\/div>\n<h2>Chlorine and Bromine: M+2 Peaks<\/h2>\n<\/div>\n<p>Chlorine has two isotopes, \u00b3\u2075Cl (75%) and \u00b3\u2077Cl (25%), so a compound with one chlorine atom gives <strong>two molecular ion peaks<\/strong>: M containing \u00b3\u2075Cl and M+2 containing \u00b3\u2077Cl, with heights in the ratio 3 : 1.<\/p><p>Bromine is \u2077\u2079Br and \u2078\u00b9Br in almost equal amounts, so a bromine compound gives M and M+2 peaks of <strong>equal height<\/strong>.<\/p><p>Fragment ions that still contain the halogen show the same pair of peaks; fragments that have lost it do not.<\/p><p>Two chlorine atoms give M, M+2 and M+4 in the ratio 9 : 6 : 1.<\/p>\n\n<div class=\"ols-key-box\">\n<p><strong>Exam focus:<\/strong> Two molecular ion peaks two units apart: 3 : 1 means one chlorine, 1 : 1 means one bromine.<\/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\/09\/alcohols-halogenoalkanes-spectra-mplus2.jpg\" target=\"_blank\" rel=\"noopener\" aria-label=\"Open image fullscreen\">\n<img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/alcohols-halogenoalkanes-spectra-mplus2.jpg\" alt=\"Three simple bar spectra showing the M and M+2 patterns for one chlorine, one bromine and two chlorine atoms.\" data-fullscreen-src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/alcohols-halogenoalkanes-spectra-mplus2.jpg\">\n<\/a>\n<\/div>\n<div class=\"ols-figure-caption\"><p>Two molecular ion peaks two units apart reveal a halogen: a 3 : 1 ratio means one chlorine atom and a 1 : 1 ratio means one bromine atom.<\/p><\/div>\n<\/div>\n<\/article>\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">4<\/div>\n<h2>Common Exam Points<\/h2>\n<\/div>\n<h3>Say<\/h3><p>&#8220;The molecular ion peak at m\/z 72 gives Mr = 72.&#8221; &#8220;The peak at 43 is CH\u2083CO\u207a, formed by loss of a C\u2082H\u2085\u2022 radical.&#8221; &#8220;M and M+2 in a 1 : 1 ratio show one bromine atom.&#8221;<\/p>\n<h3>Do not say<\/h3><p>&#8220;The tallest peak is the molecular ion.&#8221; &#8220;The fragment at 15 is CH\u2083&#8221; without the positive charge.<\/p>\n<h3>Watch for<\/h3><p>Equations for fragmentation must balance in mass and charge: [CH\u2083CH\u2082COCH\u2083]\u207a\u2022 \u2192 CH\u2083CO\u207a + \u2022CH\u2082CH\u2083, with the radical dot on the neutral piece.<\/p>\n<\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Check: Halogens and Fragmentation Equations<\/h2>\n<p>Interpret M+2 patterns and write fragmentation equations for compounds not used above.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"969\"><\/div><\/div>\n<\/section>\n<section class=\"ols-faq-card\">\n<h2>FAQs<\/h2>\n<p>Use these quick answers to check mass spectra.<\/p>\n\n<div class=\"ols-faq-list\">\n<div class=\"ols-faq-item\">\n<h3>Is the molecular ion the tallest peak?<\/h3>\n<p>No. It is the peak with the highest m\/z (ignoring the small M+1 peak) and is often quite small, because most molecular ions fragment before they are detected.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>What is the tiny peak one unit above the molecular ion?<\/h3>\n<p>The M+1 peak, from molecules containing one carbon-13 atom. About 1.1% of carbon atoms are \u00b9\u00b3C, so the more carbons a molecule has, the larger the M+1 peak.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Why are the fragments positive ions?<\/h3>\n<p>When a molecular ion breaks, one piece keeps the positive charge and the other leaves as a neutral radical. Only charged particles are accelerated and detected.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>How can two different fragments both be at m\/z 43?<\/h3>\n<p>CH\u2083CH\u2082CH\u2082\u207a (C\u2083H\u2087\u207a) and CH\u2083CO\u207a both have a mass of 43. The rest of the spectrum, or the infrared spectrum, decides which is present.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>How do I recognise chlorine or bromine?<\/h3>\n<p>Two molecular ion peaks two units apart: heights 3 : 1 for one chlorine atom, 1 : 1 for one bromine atom.<\/p>\n<\/div>\n<\/div>\n<\/section>\n<section class=\"ols-related-card\">\n<h2>Related Topic 10C Spectra Pages<\/h2>\n<p>Use these pages to connect the ideas across spectra and the rest of Topic 10.<\/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-international\/topic-10-alcohols-halogenoalkanes-and-spectra\/10c-spectra\/infrared-spectroscopy\/\">Infrared Spectroscopy<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-10-alcohols-halogenoalkanes-and-spectra\/10c-spectra\/identifying-unknown-compounds\/\">Identifying Unknown Compounds<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-10-alcohols-halogenoalkanes-and-spectra\/10c-spectra\/\">Topic 10C Spectra Overview<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-2-atomic-structure-and-the-periodic-table\/mass-spectrometry\/\">Mass Spectrometry (Topic 2)<\/a>\n<\/div>\n<\/section>\n<section class=\"ols-attribution-card\">\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  \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-international\/topic-10-alcohols-halogenoalkanes-and-spectra\/10c-spectra\/mass-spectra-of-organic-compounds\/#webpage\",\n      \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-10-alcohols-halogenoalkanes-and-spectra\/10c-spectra\/mass-spectra-of-organic-compounds\/\",\n      \"name\": \"Mass Spectra of Organic Compounds | Topic 10C Spectra | Online Learning System\",\n      \"description\": \"Edexcel International A Level Chemistry revision notes on mass spectra of organic compounds: molecular ion, m\/z, fragmentation patterns, common 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