Molecular ion peak and fragmentation
Mass Spectrometry · Chemistry
Study notes
A mass spec shows M⁺ at 92 and M+2 at 94 (1:1 ratio). What element is present? Step 1: M+2 with ~equal height → ³⁵Cl/³⁷Cl isotope pattern (3:1 would also suggest Cl). Step 2: 1:1 ratio specifically → actually Br is 1:1 (⁷⁹Br/⁸¹Br)! Step 3: Recheck: M+2 ≈ M⁺ → bromine present. Step 4: Isotope ratios fingerprint halogens — 1:1 = Br, 3:1 = Cl!