SME
Organic Chemistry I · Problem type
What the M + 2 peak says
Use this for “A compound shows peaks at m/z 136 and 138 with heights 100 and 97. Which halogen does it hold?”
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Which halogens does each molecular-ion pattern show?
Tap a card, then tap its group.
Look two units above M: a tiny peak means no Cl or Br, a third of M means one Cl, an equal one means one Br.
Assumptions
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Chlorine is about 76% ³⁵Cl and 24% ³⁷Cl; bromine is about 51% ⁷⁹Br and 49% ⁸¹Br.
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The lowest m/z on each card is the M peak, and each height is a percent of the tallest peak in the group.
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Sulfur’s ³⁴S also adds to M + 2, about 4% for each S; no card here holds sulfur.
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