Two-Dimensional NMR and Assigning a Whole Structure · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Maps of connected signals

Science · Chemistry · ages 21-22
Name ______________________   Date ____________

  1. On a COSY map you walk from proton A to B to C through cross-spots. What did you trace?

    • A path through the carbon skeleton only
    • The order of chemical shifts
    • A chain of coupled protons

  2. What does each off-diagonal spot on a 2D map tell you?

    • The two signals overlap in one spot
    • Two signals are connected
    • One signal is an impurity

  3. A one-bond map pairs each proton with the carbon holding it.

    Circle one:   True   False

  4. Two fragments sit on either side of a carbon with no protons. Which experiment joins them?

    • Another COSY walk across the gap
    • A long-range correlation map
    • A one-bond correlation map

  5. Your COSY walk gives a chain of four protons, and the one-bond map pairs each with a carbon. What do you hold now?

    • A four-carbon fragment
    • The full structure with every bond proven
    • A single quaternary carbon

  6. An assignment rests on a COSY chain backed by twenty spots and on one lone long-range spot. Which part of the argument is best supported?

    • The lone long-range spot
    • Both are equally supported
    • The COSY chain

  7. A student assigns the whole structure from one long-range spot and ignores a COSY chain that contradicts it. What is the error?

    • Using too many experiments
    • Trusting the weakest link
    • Reading the carbon spectrum first

  8. Two candidate structures both fit the COSY and one-bond data, differing only at one quaternary centre. What decides between them?

    • The long-range spots across that centre
    • A one-bond map of that quaternary carbon
    • More COSY spots along the chains
LightMySky · lightmysky.comW1-mt_UEC4dilKT9-s1

Answer key

For grown-ups. Fold this page away before handing over the rest.

Maps of connected signals W1-mt_UEC4dilKT9-s1

  1. A chain of coupled protons · COSY spots chain neighbours together proton by proton.
  2. Two signals are connected · Off-diagonal spots are links between signals.
  3. True · That pairing is exactly the map's job.
  4. A long-range correlation map · Long-range spots bridge silent centres that COSY cannot cross.
  5. A four-carbon fragment · Chain plus holders yields one placed fragment, not the whole molecule.
  6. The COSY chain · Support follows the number of agreeing spots, and twenty outweigh one. The lone spot is the weakest link.
  7. Trusting the weakest link · A lone spot is the weakest link and cannot overrule a supported chain.
  8. The long-range spots across that centre · Only links across the silent centre touch the disputed joint.
Worksheet · LightMySky