91Ó°ÊÓ

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: Which of the labeled protons in each pair absorbs farther downfield?

Question: How could you use chemical shift and integration data in ¹H NMR spectroscopy to distinguish between CH₃OCH₂CH₂OCH₃and CH₃OCH₂OCH₃? The ¹H NMR spectrum of each compound contains only singlets.

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

Question: How can you use ¹H NMR spectroscopy to distinguish between CH₂=C(Br)CO₂CH₃ and methyl (E)-3-bromopropenoate, BrCH=CHCO₂CH₃?

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: Draw the four constitutional isomers having molecular formula C₄H₉Brand indicate how many different kinds of carbon atoms each has.