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Aromatics

Aromatics. No branching = strong M + . Often see M ++ . m/z 77, 51 = phenyl (monosubst benzene) Most prominent peaks are due to beta cleavage of branches to benzylic (really tropylium.). Alcohols. Weak M + . Often nonexistent for 2 º , 3 º . M-18 (water) (rearrangement using δ H?)

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Aromatics

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  1. Aromatics • No branching = strong M+. Often see M++. • m/z 77, 51 = phenyl (monosubst benzene) • Most prominent peaks are due to beta cleavage of branches to benzylic (really tropylium.)

  2. Alcohols • Weak M+. Often nonexistent for 2º, 3º. • M-18 (water) (rearrangement using δH?) • M-33 (water + methyl) (1º) • β cleave largest branch to oxonium

  3. Ethers • Homologous series is +2 (31, 45, 59….) • β cleave to oxonium • C-O cleavage to R+ • Acetals β cleave to very stable oxonium with 2 res structures  no M+ seen

  4. Carbonyl Compounds • α cleave to acylium ion (vs 43, 57, 71 peak) • McClafferty rearrangement if γ H is present (neutral or pos alkene fragment) • M-28, M-42, M-56 • 28, 42, 56…

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