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Fragmentation of Amines in EI-MS

Fragmentation of Amines in EI-MS. Primary:. α - cleavage. Secondary:. onium reaction. liberation of neutral molecules (alkenes) from iminium ion involves H-rearrangement (R must be C 2 or longer). Aliphatic Amines. Examples of Aromatic Amines (Aniline Derivatives).

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Fragmentation of Amines in EI-MS

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  1. Fragmentation of Amines in EI-MS Primary: α-cleavage Secondary: onium reaction liberation of neutral molecules (alkenes) from iminium ion involves H-rearrangement (R must be C2 or longer)

  2. Aliphatic Amines

  3. Examples of Aromatic Amines (Aniline Derivatives)

  4. Fragmentation of Aliphatic Ethers in EI-MS Primary: α-cleavage C-O cleavage elimination of neutral fragment(H-rearrangement) H Secondary: onium reaction

  5. Fragmentation of Aryl Ethers in EI-MS C-O bond cleavage H-rearrangement and loss of neutral molecule

  6. Examples of Aromatic Ether Cleavages

  7. Fragmentation of Alcohols and Phenols in EI-MS α-cleavage H-rearrangement

  8. Examples of Aliphatic Alcohols

  9. Examples of Aromatic Alcohols (Phenols)

  10. Fragmentation of Halides in EI-MS

  11. Examples of aromatic halides

  12. Fragmentation of Ketones and Aldehydes in EI-MS α-cleavages to an acylium ion and subsequent loss of CO H-rearrangement (McLafferty rearrangement)

  13. Notable features of the McLafferty rearrangement • Related fragmentation reactions occur in other C+X systems. • Secondary hydrogen atoms in the γ-position are more readily abstracted than are primary. • Methyl groups do not rearrange when substituted for hydrogen; the reaction does not occur in compounds that lack γ-hydrogens. • An analogous process occurs in even-electron ions. • If both alkyl groups can undergo the McLafferty rearrangement, the more abundant product is due to reaction from the larger group. Also, the product of two successive alkene eliminations usually appears as an abundant ion.

  14. Fragmentation of Carboxylic Acids in EI-MS Molecular ions are of moderate abundance and the most typical fragmentation pathways are the McLafferty rearrangement as well as C-C-bond cleavage some distance from the functional group. Aromatic acids, in contrast, yield benzoyl ions by HO. loss. Fragmentation of Esters in EI-MS Molecular ions of esters are of moderate abundance and fragment by routes characteristic of both ethers and ketones. Fragmentation at the ether oxygen gives acylium ions (RCO+) that subsequently undergo CO loss. Fragmentation of Amides in EI-MS The molecular ions are usually of high intensity since the C-N bond resists cleavage except in N-arylamides, where the cleavage is accompanied by H-rearrangement. Amides undergo α-cleavage, McLafferty rearrangement and other rearrangements depending on the number and length of the aliphatic rests. Typical fragment ions are OC-NH2+, R-C(=O)NH2, and CH3C(=O)NRR. Fragmentation of Hydrocarbons in EI-MS Aliphatic hydrocarbons display characteristic ions in CnH2n+1 series separated by 14 Da (successive methylene loss). Aromatic hydrocarbons show few abundant fragments such as C7H7+ at 91 m/z.

  15. Example of an aliphatic ketone

  16. Example of an aromatic ketone

  17. Example of an aliphatic aldehyde

  18. Example of an aliphatic ester

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