469 / 912
Chapter 14 461
Copyright © 2017 Pearson Education, Inc.
7.
chemical shift in ppm
=
downfield from TMS in Hertz
operating frequency in Megahertz
a.
2 ppm
=
x
Hz
300 MHz
b.
2 ppm
=
x
Hz
500 MHz
x
=
600 Hz
x
=
1000 Hz
8.
a.
600 Hz
300 MHz
=
2.0 ppm
b.
The answer is still 2.0 ppm because the chemical shift is independent of the operating frequency of the
spectrometer.
c.
x
Hz
500 MHz
=
2.0 ppm
x
=
1000
1000 Hz downfield from TMS
9.
a.
The chemical shift is independent of the operating frequency. Therefore, if the two signals differ by
1.5 ppm
in a 300 MHz spectrometer, they differ by
1.5 ppm
in a 100 MHz spectrometer.
b.
Hz
MHz
=
ppm
90 Hz
300 MHz
=
0.3 ppm
x
Hz
500 MHz
=
0.3 ppm
x
=
150 Hz
They differ by 150 Hz.
10.
Magnesium is less electronegative than silicon. (See Table 11.1 on page 509 of the text.) Therefore, the
peak for
1
CH
3
2
2
Mg
would be upfield from the TMS peak.
11.
a.
and
b.
1.
CH
3
CH
2
CH
2
Cl
most
shielded
least
shielded
2.
CH
3
CH
2
COCH
3
most
shielded
least
shielded
O
3.
CH
3
CHCHBr
Br Br
most
shielded
least
shielded
(because it is
attached to 2
bromines)