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

Aliphatic Amines

Examples of Aromatic Amines (Aniline Derivatives)

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

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

Examples of Aromatic Ether Cleavages

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

Examples of Aliphatic Alcohols

Examples of Aromatic Alcohols (Phenols)

Fragmentation of Halides in EI-MS

Examples of aromatic halides

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

Fragmentation of Amides in EI-MS Fragmentation of Esters in EI-MS Fragmentation of Hydrocarbons 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- NH 2 +, R-C(=O)NH 2, and CH 3 C(=O)NRR. 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. 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. Aliphatic hydrocarbons display characteristic ions in C n H 2n+1 series separated by 14 Da (successive methylene loss). Aromatic hydrocarbons show few abundant fragments such as C 7 H 7 + at 91 m/z.

Example of an aliphatic ketone

Example of an aromatic ketone

Example of an aliphatic aldehyde

Example of an aliphatic ester