91Ó°ÊÓ

Question: How many different types of protons are present in each compound?

Question: How many ¹H NMR signals does each natural product exhibit?

a.

b.

c.

d.

Question: Using a 300 MHz NMR instrument:

a. How many Hz downfield from TMS is a signal at 2.5 ppm?

b. If a signal comes at 1200 Hz downfield from TMS, at what ppm does it occur?

c. If two signals are separated by 2 ppm, how many Hz does this correspond to?

Question: What effect does increasing the operating frequency of a¹HNMR spectrum have on each value: (a) the chemical shift in$\mathrm{δ}$ ;(b) the frequency of an absorption in Hz; (c) the magnitude of a coupling constant J in Hz?

How many ¹H NMR signals does each compound show?

a.

b.

c.

d.

e.

f.

g.

h.

Question: Into how many peaks will the signal for each of the labeled protons be split?

Question: What splitting pattern is observed for each proton in the following compounds?

a.

b.

Question: Label the signals due to H_a ,H_b and H_c in the 1 H NMR spectrum of acrylonitrile (CH₂=CHCN ). Draw a splitting diagram for the absorption due to the proton H_c.

Question: Explain why the carbonyl carbon of an aldehyde or ketone absorbs farther downfield than the carbonyl carbon of an ester in a ¹³C NMR spectrum

Question: How many ¹³C NMR signals do each compound exhibit?