�+�qW*-�7s�K\�IN�Z��7���g�ҠKT�h�h63���{�f�uu�R4҉�J���G���X U~�+O��0�X��Z��qZ�Ӳ�x���Ӿ�@g�/`(������U�3�A�8����#� ��j7O��g���F*�k�3����T�r*�şN�����-�^y�%Xuo How to Identify Molecular Fragmentation Patterns in Mass Spectrometry, Organic Chemistry I For Dummies Cheat Sheet, How to Predict the Equilibrium Direction of an Acid-Base Reaction. In these two spectra, this is probably the most dramatic example of the extra stability of a secondary carbocation. �D ј�f.#� �\0B�"��@r2� 0000035257 00000 n When the vaporised organic sample passes into the ionisation chamber of a mass spectrometer, it is bombarded by a stream of electrons. If you remember, the m/z = 57 peak in pentane was produced by [CH3CH2CH2CH2]+. (The figure shows an example of tertiary and primary cations.) 9992 19 F 19 100 18.9984 28 Si 28 92.2 27.9769 29 Si 29 4.7 … What about 4? }�5�M�*��g�۵�\��Պ���Oc�7I��]�9���о�@[��T#/C�cD�6�g��)K��F�3L�Y���"��!hu���@� r�j��]`m�Q:S�1��;[v[���� �ڧ�p�q�o�R~�W�oV`UӇ�k���P'��� ��YM��Z�/SF��l�u��/v~����h~��h5�f��L)��>&��!҆����@��kd'�A�9�l�VkeNe�-Vʥ�(0u�e�!&���v�-�-���`8~*�Ŵ��Hr�%3����`ccdi��6poy�5����@O�n�}�.�\#@�'�$��ȄJE�-�?XNQK�G�!����؜���E��$�Y K���=�����v/���e6���?� ��t�D$b˲�V*},4���P��s�H9!�����|cue^=f@��{.,�Ѣ���કvM�Gyi��w�R9���8��/`�B�E�I���ٍ�}��@m3US (TG8 With a compound, each line represents a different fragment produced when the molecular ion breaks up. As such, it is relatively stable. 6502 0 obj <> endobj xref Energy sufficient to break chemical bonds: radical cation will usually break into a neutral radical and a cation. Alkanes generally break apart to make the most highly substituted cation. The fragmentation patterns have characteristic features in mass spectrum signals, due to which qualitative characterization of … It's important to realise that the pattern of lines in the mass spectrum of an organic compound tells you something quite different from the pattern of lines in the mass spectrum of an element. The mass spectrum of pentan-3-one This time the base peak (the tallest peak - and so the commonest fragment ion) is at m/z = 57. 0000085088 00000 n Summarizing the most important conclusion from the page on carbocations: Applying the logic of this to fragmentation patterns, it means that a split which produces a secondary carbocation is going to be more successful than one producing a primary one. When the vaporised organic sample passes into the ionisation chamber of a mass spectrometer, it is bombarded by a stream of electrons. How about C4H9+ then? %���� This peak in 2-methylbutane is caused by: The ion formed is a secondary carbocation - it has two alkyl groups attached to the carbon with the positive charge. With pentan-3-one, you would only get one ion of this kind: In that case, you would get a strong line at 57. An extremely useful result of EI ionization in particular is a phenomenon known as fragmentation. A common fragmentation pattern for larger carbonyl compounds is called the McLafferty rearrangement: The mass spectrum of 2-hexanone shows a 'McLafferty fragment' at m/z = 58, while the propene fragment is not observed because it is a neutral species (remember, only cationic fragments are observed in MS). 0000004868 00000 n The simplest case is that a molecular ion breaks into two parts - one of which is another positive ion, and the other is an uncharged free radical. The molecular ion in a mass spectrum is always a radical cation, but the fragment ions may either be even-electron cations or odd-electron radical cations, depending on the neutral fragment lost. In mass spectrometry, the sample that needs to be analyzed undergoes ionization by the bombardment of electrons, leading to the formation of fragments of the sample. The peak at m/z = 57 is much taller than the corresponding line in pentane. Let's look at the mass spectrum of 2-methylbutane. Ions are sometimes characterized by loss of a specific neutral fragment from the molecular ion. In addition to alpha cleavage, alcohols readily lose a water molecule to form an alkene (a carbon-carbon double bond), as shown in the next figure. 0000006615 00000 n 0000067992 00000 n 0000008192 00000 n For example, breaking the C-C bond next to an alcohol group creates a resonance-stabilized carbocation. 0000010609 00000 n This page looks at how fragmentation patterns are formed when organic molecules are fed into a mass spectrometer, and how you can get information from the mass spectrum. Arthur Winter is a graduate of Frostburg State University, where he received his BS in chemistry. Table 4. If this is the first set of questions you have done, please read the introductory page before you start. �t�T�A����р�[-9�b�4�c&C%&i`�Rc�O��q �b)����YF= �1H��cS�e2�}c3#aCh|��c�� The base peak is the tallest peak because it represents the commonest fragment ion to be formed - either because there are several ways in which it could be produced during fragmentation of the parent ion, or because it is a particularly stable ion. 0000002527 00000 n The base peak, at m/z=57, is due to the [CH3CH2CO]+ ion. If you look at the structure of pentan-3-one, it's impossible to get that particular fragment from it. But this isn't produced by the same ion as the same m/z value peak in pentane. You can often predict what peaks will be observed in the mass spectrum simply by looking at a molecule’s structure and seeing which pieces would be easy to break off to make stable cations. Common Isotopes Nominal Abundance, Isotope Mass % Exact Mass 1H 1 99.985 1.0078 2H (or D ) 2 0.015 2.0141 12 C 12 98.9 12.0000 13 C 13 1.1 13.0034 14 N 14 99.64 14.0031 15 N 15 0.36 15.0001 16 0 16 99.8 15.9949 17 O 17 0.04 16.9991 18 O 18 0.2 17. That leaves 9 to make up a total of 57. This ion is called the molecular ion - or sometimes the parent ion. Suppose you had to suggest a way of distinguishing between pentan-2-one and pentan-3-one using their mass spectra. This is generally the simplest thing you can be asked to do. 0000005386 00000 n The line at m/z = 43 can be worked out similarly. :/9�6��q��l� �BO���Nd 0000058380 00000 n Use the BACK button on your browser to return quickly to this page. The ionizer makes the molecules into radical cations (cations with an unpaired electron), which then generally break apart into a cationic piece (which is seen by the detector) plus a neutral radical piece (not seen by the detector). 0000009653 00000 n 6502 44 The m/z = 29 peak is produced by the ethyl ion - which once again could be formed by splitting the molecular ion either side of the CO group. © Jim Clark 2000 (modified February 2014). 0000019444 00000 n Ion mass and charge questions . This is caused by a different ion than the corresponding peak in the pentane mass spectrum. This same pattern of alpha cleavage is observed with amines, as shown in the next figure. This time the base peak (the tallest peak - and so the commonest fragment ion) is at m/z = 57. He received his PhD at the University of Maryland in 2007. ��.�!ê�����ʄ$ܝ��,��+��3��"�#'8&�*�̅��b�� P$F��O+�Q�)�s��Ҍ��;��@AG�YPKp�ˈk+G,�Y-3�\��!�!s]%���6��cTR��eQ/� �L��B�ӤXё��l�j(��C���'%K�<4����E1Ys8n����c'�Rrp]�|�5}�tGW���H��a�LE{��ėmT+�I`�h���Gჽ�(�盡Y2�����}ŏ�T�� A split producing a tertiary carbocation will be more successful still. Let's have another look at the mass spectrum for pentane: How many carbon atoms are there in this ion? You will find a link at the bottom of the page. These electrons have a high enough energy to knock an electron off an organic molecule to form a positive ion. With an element, each line represents a different isotope of that element. 0000005844 00000 n Alkenes: 55 / 41 Per fluorinated hydrocarbons: 69 Aromatics: 75-78, /130-138. Using mass spectra to distinguish between compounds. >> Mass spectral fragments of common hydrocarbons Mass Spectral peaks can be identified to have originated from the fragmentation of specific hydrocarbon sources including: Alkanes: 57 / 43. ���葠(�b�I�FN:���4��`b�!u��:���� c��c%(��FCq�#!�4�A�(s#!��]r �=��4��L��"���h�و8�ܻ�B2C�uA��� ���I"��d+e��L��� '�or,I\3��DB�]���� ��1���|7�@�4�p�����3��X�P��\l�4��q��e8���t֊jS�EW} �Q�f��F���P8�3>K�m��9��!�����j��� ��C��5C��u���d���b=�2�p�FA�6��6�]n��7�p���c�yˌ���Xk�'D��St��kI��{�7�y��/. ֕iY|ɢ.�9��e�b���P�Y���ʔIBh(�`��o�ΓQ�B�O��)�"�����Q��/(���s�L:J��D9��~:uNe#t Check past exam papers to find out whether you are likely to need to know about other possibilities. 0000081720 00000 n 0000006256 00000 n You will need to use the BACK BUTTON on your browser to come back here afterwards. In the stick diagram showing the mass spectrum of pentane, the line produced by the heaviest ion passing through the machine (at m/z = 72) is due to the molecular ion. "Automated Data Massaging, Interpretation, and E-Mailing Modules for High Throughput … 0000053100 00000 n %PDF-1.4 %���� Mass Spectrometry - Fragmentation Patterns Alcohol. 4 x 12 = 48. 0000047501 00000 n 0000001198 00000 n 0000001819 00000 n It will be useful in solving the problems. 0000008694 00000 n 0000010047 00000 n 0000085129 00000 n Provided you have a computer data base of mass spectra, any unkown spectrum can be computer analysed and simply matched against the data base. This page looks at how fragmentation patterns are formed when organic molecules are fed into a mass spectrometer, and how you can get information from the mass spectrum. FRAGMENTATION PATTERNS IN THE MASS SPECTRA OF ORGANIC COMPOUNDS. More complicated break-ups are beyond the scope of A'level syllabuses. 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In these two spectra, this is probably the most dramatic example of the extra stability of a secondary carbocation. �D ј�f.#� �\0B�"��@r2� 0000035257 00000 n When the vaporised organic sample passes into the ionisation chamber of a mass spectrometer, it is bombarded by a stream of electrons. If you remember, the m/z = 57 peak in pentane was produced by [CH3CH2CH2CH2]+. (The figure shows an example of tertiary and primary cations.) 9992 19 F 19 100 18.9984 28 Si 28 92.2 27.9769 29 Si 29 4.7 … What about 4? }�5�M�*��g�۵�\��Պ���Oc�7I��]�9���о�@[��T#/C�cD�6�g��)K��F�3L�Y���"��!hu���@� r�j��]`m�Q:S�1��;[v[���� �ڧ�p�q�o�R~�W�oV`UӇ�k���P'��� ��YM��Z�/SF��l�u��/v~����h~��h5�f��L)��>&��!҆����@��kd'�A�9�l�VkeNe�-Vʥ�(0u�e�!&���v�-�-���`8~*�Ŵ��Hr�%3����`ccdi��6poy�5����@O�n�}�.�\#@�'�$��ȄJE�-�?XNQK�G�!����؜���E��$�Y K���=�����v/���e6���?� ��t�D$b˲�V*},4���P��s�H9!�����|cue^=f@��{.,�Ѣ���કvM�Gyi��w�R9���8��/`�B�E�I���ٍ�}��@m3US (TG8 With a compound, each line represents a different fragment produced when the molecular ion breaks up. As such, it is relatively stable. 6502 0 obj <> endobj xref Energy sufficient to break chemical bonds: radical cation will usually break into a neutral radical and a cation. Alkanes generally break apart to make the most highly substituted cation. The fragmentation patterns have characteristic features in mass spectrum signals, due to which qualitative characterization of … It's important to realise that the pattern of lines in the mass spectrum of an organic compound tells you something quite different from the pattern of lines in the mass spectrum of an element. The mass spectrum of pentan-3-one This time the base peak (the tallest peak - and so the commonest fragment ion) is at m/z = 57. 0000085088 00000 n Summarizing the most important conclusion from the page on carbocations: Applying the logic of this to fragmentation patterns, it means that a split which produces a secondary carbocation is going to be more successful than one producing a primary one. When the vaporised organic sample passes into the ionisation chamber of a mass spectrometer, it is bombarded by a stream of electrons. How about C4H9+ then? %���� This peak in 2-methylbutane is caused by: The ion formed is a secondary carbocation - it has two alkyl groups attached to the carbon with the positive charge. With pentan-3-one, you would only get one ion of this kind: In that case, you would get a strong line at 57. An extremely useful result of EI ionization in particular is a phenomenon known as fragmentation. A common fragmentation pattern for larger carbonyl compounds is called the McLafferty rearrangement: The mass spectrum of 2-hexanone shows a 'McLafferty fragment' at m/z = 58, while the propene fragment is not observed because it is a neutral species (remember, only cationic fragments are observed in MS). 0000004868 00000 n The simplest case is that a molecular ion breaks into two parts - one of which is another positive ion, and the other is an uncharged free radical. The molecular ion in a mass spectrum is always a radical cation, but the fragment ions may either be even-electron cations or odd-electron radical cations, depending on the neutral fragment lost. In mass spectrometry, the sample that needs to be analyzed undergoes ionization by the bombardment of electrons, leading to the formation of fragments of the sample. The peak at m/z = 57 is much taller than the corresponding line in pentane. Let's look at the mass spectrum of 2-methylbutane. Ions are sometimes characterized by loss of a specific neutral fragment from the molecular ion. In addition to alpha cleavage, alcohols readily lose a water molecule to form an alkene (a carbon-carbon double bond), as shown in the next figure. 0000006615 00000 n 0000067992 00000 n 0000008192 00000 n For example, breaking the C-C bond next to an alcohol group creates a resonance-stabilized carbocation. 0000010609 00000 n This page looks at how fragmentation patterns are formed when organic molecules are fed into a mass spectrometer, and how you can get information from the mass spectrum. Arthur Winter is a graduate of Frostburg State University, where he received his BS in chemistry. Table 4. If this is the first set of questions you have done, please read the introductory page before you start. �t�T�A����р�[-9�b�4�c&C%&i`�Rc�O��q �b)����YF= �1H��cS�e2�}c3#aCh|��c�� The base peak is the tallest peak because it represents the commonest fragment ion to be formed - either because there are several ways in which it could be produced during fragmentation of the parent ion, or because it is a particularly stable ion. 0000002527 00000 n The base peak, at m/z=57, is due to the [CH3CH2CO]+ ion. If you look at the structure of pentan-3-one, it's impossible to get that particular fragment from it. But this isn't produced by the same ion as the same m/z value peak in pentane. You can often predict what peaks will be observed in the mass spectrum simply by looking at a molecule’s structure and seeing which pieces would be easy to break off to make stable cations. Common Isotopes Nominal Abundance, Isotope Mass % Exact Mass 1H 1 99.985 1.0078 2H (or D ) 2 0.015 2.0141 12 C 12 98.9 12.0000 13 C 13 1.1 13.0034 14 N 14 99.64 14.0031 15 N 15 0.36 15.0001 16 0 16 99.8 15.9949 17 O 17 0.04 16.9991 18 O 18 0.2 17. That leaves 9 to make up a total of 57. This ion is called the molecular ion - or sometimes the parent ion. Suppose you had to suggest a way of distinguishing between pentan-2-one and pentan-3-one using their mass spectra. This is generally the simplest thing you can be asked to do. 0000005386 00000 n The line at m/z = 43 can be worked out similarly. :/9�6��q��l� �BO���Nd 0000058380 00000 n Use the BACK button on your browser to return quickly to this page. The ionizer makes the molecules into radical cations (cations with an unpaired electron), which then generally break apart into a cationic piece (which is seen by the detector) plus a neutral radical piece (not seen by the detector). 0000009653 00000 n 6502 44 The m/z = 29 peak is produced by the ethyl ion - which once again could be formed by splitting the molecular ion either side of the CO group. © Jim Clark 2000 (modified February 2014). 0000019444 00000 n Ion mass and charge questions . This is caused by a different ion than the corresponding peak in the pentane mass spectrum. This same pattern of alpha cleavage is observed with amines, as shown in the next figure. This time the base peak (the tallest peak - and so the commonest fragment ion) is at m/z = 57. He received his PhD at the University of Maryland in 2007. ��.�!ê�����ʄ$ܝ��,��+��3��"�#'8&�*�̅��b�� P$F��O+�Q�)�s��Ҍ��;��@AG�YPKp�ˈk+G,�Y-3�\��!�!s]%���6��cTR��eQ/� �L��B�ӤXё��l�j(��C���'%K�<4����E1Ys8n����c'�Rrp]�|�5}�tGW���H��a�LE{��ėmT+�I`�h���Gჽ�(�盡Y2�����}ŏ�T�� A split producing a tertiary carbocation will be more successful still. Let's have another look at the mass spectrum for pentane: How many carbon atoms are there in this ion? You will find a link at the bottom of the page. These electrons have a high enough energy to knock an electron off an organic molecule to form a positive ion. With an element, each line represents a different isotope of that element. 0000005844 00000 n Alkenes: 55 / 41 Per fluorinated hydrocarbons: 69 Aromatics: 75-78, /130-138. Using mass spectra to distinguish between compounds. >> Mass spectral fragments of common hydrocarbons Mass Spectral peaks can be identified to have originated from the fragmentation of specific hydrocarbon sources including: Alkanes: 57 / 43. ���葠(�b�I�FN:���4��`b�!u��:���� c��c%(��FCq�#!�4�A�(s#!��]r �=��4��L��"���h�و8�ܻ�B2C�uA��� ���I"��d+e��L��� '�or,I\3��DB�]���� ��1���|7�@�4�p�����3��X�P��\l�4��q��e8���t֊jS�EW} �Q�f��F���P8�3>K�m��9��!�����j��� ��C��5C��u���d���b=�2�p�FA�6��6�]n��7�p���c�yˌ���Xk�'D��St��kI��{�7�y��/. ֕iY|ɢ.�9��e�b���P�Y���ʔIBh(�`��o�ΓQ�B�O��)�"�����Q��/(���s�L:J��D9��~:uNe#t Check past exam papers to find out whether you are likely to need to know about other possibilities. 0000081720 00000 n 0000006256 00000 n You will need to use the BACK BUTTON on your browser to come back here afterwards. In the stick diagram showing the mass spectrum of pentane, the line produced by the heaviest ion passing through the machine (at m/z = 72) is due to the molecular ion. "Automated Data Massaging, Interpretation, and E-Mailing Modules for High Throughput … 0000053100 00000 n %PDF-1.4 %���� Mass Spectrometry - Fragmentation Patterns Alcohol. 4 x 12 = 48. 0000047501 00000 n 0000001198 00000 n 0000001819 00000 n It will be useful in solving the problems. 0000008694 00000 n 0000010047 00000 n 0000085129 00000 n Provided you have a computer data base of mass spectra, any unkown spectrum can be computer analysed and simply matched against the data base. This page looks at how fragmentation patterns are formed when organic molecules are fed into a mass spectrometer, and how you can get information from the mass spectrum. FRAGMENTATION PATTERNS IN THE MASS SPECTRA OF ORGANIC COMPOUNDS. More complicated break-ups are beyond the scope of A'level syllabuses. 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%PDF-1.2 Again a secondary carbocation is formed - this time, by: You would get the same ion, of course, if the left-hand CH3 group broke off instead of the bottom one as we've drawn it. Common Observed and Predicted Background Ions in ESI Positive Mode Compounds and Species Ions Mass of ions Fragment from acetonitrile CN-26.0036 Formic acid HCOO-44.9982 Acetic acid CH SO-59.0139 Phosphoric acid, and oligonucleotides or phosphopeptides PO 3-78.9591 Sulfuric acid and other sulfated materials SO-79.9574 If you haven't got past papers, follow the link on the syllabuses page to find out how to get hold of them. �ټŖOȃA�v���x���B?f���=ҵ�5y{%��-�d2@P�&4j�$*P��䓁DҚ�. As you've seen, the mass spectrum of even very similar organic compounds will be quite different because of the different fragmentations that can occur. The ionizer makes the molecules into radical … 0000008077 00000 n Two are isomeric hexanes and the third is cyclohexane. 0000001979 00000 n h���A 0ð4,~\Gc���������z�C. By Arthur Winter . In the pentan-2-one case, there are two different ions like this: That would give you strong lines at m/z = 43 and 71. You don't need to worry about the other lines in the spectra - the 43, 57 and 71 lines give you plenty of difference between the two. The formation of molecular ions. Examples involving carbocations (carbonium ions). With a small amount of patience, you'll eventually find [CH3CH2CO]+ - which is produced by this fragmentation: You would get exactly the same products whichever side of the CO group you split the molecular ion. Look first at the very strong peak at m/z = 43. �p��QF�2��E7�P��� �;NוR���0��OT�L����R�P�W#̫���W�� �� �D>)BY�P��G��.N�)��s^��:�'�e+��ҿ��Wi��vz��j(��q&+65���de`�"/��3\�%u�q���{AU`u{�(�ҩ��i� �W�;c� tOP���(hm�'zvQ�-oj�L�K$���>�+�qW*-�7s�K\�IN�Z��7���g�ҠKT�h�h63���{�f�uu�R4҉�J���G���X U~�+O��0�X��Z��qZ�Ӳ�x���Ӿ�@g�/`(������U�3�A�8����#� ��j7O��g���F*�k�3����T�r*�şN�����-�^y�%Xuo How to Identify Molecular Fragmentation Patterns in Mass Spectrometry, Organic Chemistry I For Dummies Cheat Sheet, How to Predict the Equilibrium Direction of an Acid-Base Reaction. In these two spectra, this is probably the most dramatic example of the extra stability of a secondary carbocation. �D ј�f.#� �\0B�"��@r2� 0000035257 00000 n When the vaporised organic sample passes into the ionisation chamber of a mass spectrometer, it is bombarded by a stream of electrons. If you remember, the m/z = 57 peak in pentane was produced by [CH3CH2CH2CH2]+. (The figure shows an example of tertiary and primary cations.) 9992 19 F 19 100 18.9984 28 Si 28 92.2 27.9769 29 Si 29 4.7 … What about 4? }�5�M�*��g�۵�\��Պ���Oc�7I��]�9���о�@[��T#/C�cD�6�g��)K��F�3L�Y���"��!hu���@� r�j��]`m�Q:S�1��;[v[���� �ڧ�p�q�o�R~�W�oV`UӇ�k���P'��� ��YM��Z�/SF��l�u��/v~����h~��h5�f��L)��>&��!҆����@��kd'�A�9�l�VkeNe�-Vʥ�(0u�e�!&���v�-�-���`8~*�Ŵ��Hr�%3����`ccdi��6poy�5����@O�n�}�.�\#@�'�$��ȄJE�-�?XNQK�G�!����؜���E��$�Y K���=�����v/���e6���?� ��t�D$b˲�V*},4���P��s�H9!�����|cue^=f@��{.,�Ѣ���કvM�Gyi��w�R9���8��/`�B�E�I���ٍ�}��@m3US (TG8 With a compound, each line represents a different fragment produced when the molecular ion breaks up. As such, it is relatively stable. 6502 0 obj <> endobj xref Energy sufficient to break chemical bonds: radical cation will usually break into a neutral radical and a cation. Alkanes generally break apart to make the most highly substituted cation. The fragmentation patterns have characteristic features in mass spectrum signals, due to which qualitative characterization of … It's important to realise that the pattern of lines in the mass spectrum of an organic compound tells you something quite different from the pattern of lines in the mass spectrum of an element. The mass spectrum of pentan-3-one This time the base peak (the tallest peak - and so the commonest fragment ion) is at m/z = 57. 0000085088 00000 n Summarizing the most important conclusion from the page on carbocations: Applying the logic of this to fragmentation patterns, it means that a split which produces a secondary carbocation is going to be more successful than one producing a primary one. When the vaporised organic sample passes into the ionisation chamber of a mass spectrometer, it is bombarded by a stream of electrons. How about C4H9+ then? %���� This peak in 2-methylbutane is caused by: The ion formed is a secondary carbocation - it has two alkyl groups attached to the carbon with the positive charge. With pentan-3-one, you would only get one ion of this kind: In that case, you would get a strong line at 57. An extremely useful result of EI ionization in particular is a phenomenon known as fragmentation. A common fragmentation pattern for larger carbonyl compounds is called the McLafferty rearrangement: The mass spectrum of 2-hexanone shows a 'McLafferty fragment' at m/z = 58, while the propene fragment is not observed because it is a neutral species (remember, only cationic fragments are observed in MS). 0000004868 00000 n The simplest case is that a molecular ion breaks into two parts - one of which is another positive ion, and the other is an uncharged free radical. The molecular ion in a mass spectrum is always a radical cation, but the fragment ions may either be even-electron cations or odd-electron radical cations, depending on the neutral fragment lost. In mass spectrometry, the sample that needs to be analyzed undergoes ionization by the bombardment of electrons, leading to the formation of fragments of the sample. The peak at m/z = 57 is much taller than the corresponding line in pentane. Let's look at the mass spectrum of 2-methylbutane. Ions are sometimes characterized by loss of a specific neutral fragment from the molecular ion. In addition to alpha cleavage, alcohols readily lose a water molecule to form an alkene (a carbon-carbon double bond), as shown in the next figure. 0000006615 00000 n 0000067992 00000 n 0000008192 00000 n For example, breaking the C-C bond next to an alcohol group creates a resonance-stabilized carbocation. 0000010609 00000 n This page looks at how fragmentation patterns are formed when organic molecules are fed into a mass spectrometer, and how you can get information from the mass spectrum. Arthur Winter is a graduate of Frostburg State University, where he received his BS in chemistry. Table 4. If this is the first set of questions you have done, please read the introductory page before you start. �t�T�A����р�[-9�b�4�c&C%&i`�Rc�O��q �b)����YF= �1H��cS�e2�}c3#aCh|��c�� The base peak is the tallest peak because it represents the commonest fragment ion to be formed - either because there are several ways in which it could be produced during fragmentation of the parent ion, or because it is a particularly stable ion. 0000002527 00000 n The base peak, at m/z=57, is due to the [CH3CH2CO]+ ion. If you look at the structure of pentan-3-one, it's impossible to get that particular fragment from it. But this isn't produced by the same ion as the same m/z value peak in pentane. You can often predict what peaks will be observed in the mass spectrum simply by looking at a molecule’s structure and seeing which pieces would be easy to break off to make stable cations. Common Isotopes Nominal Abundance, Isotope Mass % Exact Mass 1H 1 99.985 1.0078 2H (or D ) 2 0.015 2.0141 12 C 12 98.9 12.0000 13 C 13 1.1 13.0034 14 N 14 99.64 14.0031 15 N 15 0.36 15.0001 16 0 16 99.8 15.9949 17 O 17 0.04 16.9991 18 O 18 0.2 17. That leaves 9 to make up a total of 57. This ion is called the molecular ion - or sometimes the parent ion. Suppose you had to suggest a way of distinguishing between pentan-2-one and pentan-3-one using their mass spectra. This is generally the simplest thing you can be asked to do. 0000005386 00000 n The line at m/z = 43 can be worked out similarly. :/9�6��q��l� �BO���Nd 0000058380 00000 n Use the BACK button on your browser to return quickly to this page. The ionizer makes the molecules into radical cations (cations with an unpaired electron), which then generally break apart into a cationic piece (which is seen by the detector) plus a neutral radical piece (not seen by the detector). 0000009653 00000 n 6502 44 The m/z = 29 peak is produced by the ethyl ion - which once again could be formed by splitting the molecular ion either side of the CO group. © Jim Clark 2000 (modified February 2014). 0000019444 00000 n Ion mass and charge questions . This is caused by a different ion than the corresponding peak in the pentane mass spectrum. This same pattern of alpha cleavage is observed with amines, as shown in the next figure. This time the base peak (the tallest peak - and so the commonest fragment ion) is at m/z = 57. He received his PhD at the University of Maryland in 2007. ��.�!ê�����ʄ$ܝ��,��+��3��"�#'8&�*�̅��b�� P$F��O+�Q�)�s��Ҍ��;��@AG�YPKp�ˈk+G,�Y-3�\��!�!s]%���6��cTR��eQ/� �L��B�ӤXё��l�j(��C���'%K�<4����E1Ys8n����c'�Rrp]�|�5}�tGW���H��a�LE{��ėmT+�I`�h���Gჽ�(�盡Y2�����}ŏ�T�� A split producing a tertiary carbocation will be more successful still. Let's have another look at the mass spectrum for pentane: How many carbon atoms are there in this ion? You will find a link at the bottom of the page. These electrons have a high enough energy to knock an electron off an organic molecule to form a positive ion. With an element, each line represents a different isotope of that element. 0000005844 00000 n Alkenes: 55 / 41 Per fluorinated hydrocarbons: 69 Aromatics: 75-78, /130-138. Using mass spectra to distinguish between compounds. >> Mass spectral fragments of common hydrocarbons Mass Spectral peaks can be identified to have originated from the fragmentation of specific hydrocarbon sources including: Alkanes: 57 / 43. ���葠(�b�I�FN:���4��`b�!u��:���� c��c%(��FCq�#!�4�A�(s#!��]r �=��4��L��"���h�و8�ܻ�B2C�uA��� ���I"��d+e��L��� '�or,I\3��DB�]���� ��1���|7�@�4�p�����3��X�P��\l�4��q��e8���t֊jS�EW} �Q�f��F���P8�3>K�m��9��!�����j��� ��C��5C��u���d���b=�2�p�FA�6��6�]n��7�p���c�yˌ���Xk�'D��St��kI��{�7�y��/. ֕iY|ɢ.�9��e�b���P�Y���ʔIBh(�`��o�ΓQ�B�O��)�"�����Q��/(���s�L:J��D9��~:uNe#t Check past exam papers to find out whether you are likely to need to know about other possibilities. 0000081720 00000 n 0000006256 00000 n You will need to use the BACK BUTTON on your browser to come back here afterwards. In the stick diagram showing the mass spectrum of pentane, the line produced by the heaviest ion passing through the machine (at m/z = 72) is due to the molecular ion. "Automated Data Massaging, Interpretation, and E-Mailing Modules for High Throughput … 0000053100 00000 n %PDF-1.4 %���� Mass Spectrometry - Fragmentation Patterns Alcohol. 4 x 12 = 48. 0000047501 00000 n 0000001198 00000 n 0000001819 00000 n It will be useful in solving the problems. 0000008694 00000 n 0000010047 00000 n 0000085129 00000 n Provided you have a computer data base of mass spectra, any unkown spectrum can be computer analysed and simply matched against the data base. This page looks at how fragmentation patterns are formed when organic molecules are fed into a mass spectrometer, and how you can get information from the mass spectrum. FRAGMENTATION PATTERNS IN THE MASS SPECTRA OF ORGANIC COMPOUNDS. More complicated break-ups are beyond the scope of A'level syllabuses.

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