Simulate electron-ionization (EI) mass spectrometry: see the molecular ion (M⁺) peak, common fragmentations (alpha-cleavage, tropylium cation, McLafferty rearrangement), and identify the base peak for classic organic molecules.
Electron-ionization mass spectrometry fragments organic molecules in predictable, chemically meaningful ways, and reading the resulting fragmentation pattern to identify a molecule's structure is a genuinely advanced organic chemistry skill covered in IChO and upper-level coursework.
Bombarding a molecule with high-energy electrons knocks out one electron, forming a radical cation called the molecular ion (M+•), whose mass-to-charge ratio directly gives the molecule's molar mass — the single most immediately useful piece of information a mass spectrum provides, assuming the molecular ion peak survives to be detected at all.
The molecular ion is often unstable and fragments further along predictable pathways. Alpha-cleavage — breaking a C-C bond immediately adjacent to a heteroatom (like the oxygen in a ketone or alcohol) — is favored because the resulting fragment can be stabilized by resonance donation from that heteroatom's lone pair, making this one of the most commonly observed fragmentation patterns in oxygen-containing organic molecules.
The tropylium cation, appearing characteristically at m/z = 91, arises when a benzylic C-C bond cleaves and the resulting cation rearranges into the remarkably stable, fully aromatic seven-membered tropylium ring — its distinctive stability means this peak, when present, is often unusually intense and immediately suggests a benzyl-containing structure in the original molecule.
McLafferty rearrangement is a more complex fragmentation specific to carbonyl compounds with a gamma hydrogen: the molecule undergoes an internal hydrogen transfer through a six-membered transition state, cleaving a C-C bond and producing a distinct fragment mass shift that's diagnostic once recognized.
Isotope patterns provide additional structural clues independent of fragmentation: chlorine and bromine each produce a characteristic M+2 peak (from the ³⁷Cl or ⁸¹Br isotope) at roughly the intensity ratio expected from natural isotope abundance, immediately signaling the presence of that halogen even before any other structural analysis.
This simulator shows the molecular ion, common fragmentation pathways, and base peak identification for classic organic molecules, building the pattern-recognition skill mass spectrum interpretation actually requires.