solve please Page: 4 10. CH The following questions pertain to the charting or N

Question

solve please Page: 4 10. CH The following questions pertain to the charting or NR spectra. MATCH a term to each description below. Place the letter of the term in the blank to the left of the description. a. TMS b. high-field or upfield side c. MHz d. delta e. low-field or downfield side E. chemical shift g. specific absorption When looking at an NMR chart the right-hand part of the chart is the art is the The exact place on the chart at which a called its_ 12. nuclous absorbs is called its 13. The NMR charts are calibrated using an arbitrary scale that is divided into units. The calibration standard for H and C NMR 14. is: 15. Explain why all protons in a molecule do not absorb rt The following molecules may be prepared using the Diels-Alder dienophile necessary to prepare each molecule and label them. energy at the same frequency. reactions. Write the structures of the starting diene and

Explanation / Answer

11. high field or upfield side

12. chemical shift

13. delta

14. TMS

15.   All nuclei in molecules are surrounded by electron clouds. When a uniform external magnetic field is applied to
a molecule, the circulating electron clouds set up tiny local magnetic fields of their own. These local magnetic fields act in opposition to the applied field, so that the effective field actually felt by a nucleus is a bit smaller than the applied field.

B effective = B applied - B local

This effect is termed shielding. Each nucleus is shielded to a slightly different extent, so each unique kind of proton in a molecule resonates at a slightly different frequency and gives rise to a unique NMR signal.

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