Transcript Carey_13CNMR.ppt

13.14
13C
NMR Spectroscopy
1H
and 13C NMR compared:
both give us information about the
number of chemically nonequivalent
nuclei (nonequivalent hydrogens or
nonequivalent carbons)
both give us information about the
environment of the nuclei (hybridization
state, attached atoms, etc.)
1H
and 13C NMR compared:
the signal for the NMR of a 13 C nucleus is
10-4 times weaker than the signal for a
hydrogen nucleus
a signal for a 13C nucleus is only about 1% as
intense as that for 1H because of the
magnetic properties of the nuclei, and
at the "natural abundance" level only 1.1% of
all the C atoms in a sample are 13C (most are
12C)
1H
and 13C NMR compared:
13C
signals are spread over a much wider
range than 1H signals making it easier to
identify and count individual nuclei
Check the spectra on the next slides: Figure
13.20 (a) shows the 1H NMR spectrum of 1chloropentane; Figure 13.20 (b) shows the
13C spectrum. It is much easier to identify the
compound as 1-chloropentane by its 13C
spectrum than by its 1H spectrum.
1H
Figure 13.20(a) (page 511)
ClCH2CH2CH2CH2CH3
10.0
9.0
8.0
7.0
6.0
CH3
ClCH2
5.0
4.0
3.0
Chemical shift (d, ppm)
2.0
1.0
0
Figure 13.20(b) (page 511)
Note: in these spectra the peak intensities are
not exactly proportional to the number of
carbon atoms.
13C
ClCH2CH2CH2CH2CH3
a separate, distinct
peak appears for
each of the 5
carbons
200
180
160
140
120
CDCl3
100
80
60
Chemical shift (d, ppm)
40
20
0
13.15
13C
Chemical Shifts
are measured in ppm (d)
from the carbons of TMS
13C
Chemical shifts are most affected by:
• hybridization state of carbon
• electronegativity of groups attached to carbon
Examples (chemical shifts in ppm from TMS)
23
138
sp3 hybridized carbon is more shielded than sp2
Examples (chemical shifts in ppm from TMS)
OH
61
O
202
sp3 hybridized carbon is more shielded than sp2
Examples (chemical shifts in ppm from TMS)
OH
23
61
an electronegative atom deshields the carbon
to which it is attached
Examples (chemical shifts in ppm from TMS)
O
138
202
an electronegative atom deshields the carbon
to which it is attached
Table 13.3 (p 513)
Type of carbon Chemical shift (d),
ppm
RCH3
0-35
R2CH2
15-40
R3CH
25-50
R4C
30-40
Table 13.3 (p 513)
Type of carbon Chemical shift (d), Type of carbon
ppm
Chemical shift (d),
ppm
RCH3
0-35
RC
CR
65-90
R2CH2
15-40
R2C
CR2
100-150
R3CH
25-50
110-175
R4C
30-40
Table 13.3 (p 513)
Type of carbon Chemical shift (d),
ppm
RCH2Br
20-40
RCH2Cl
25-50
RCH2NH2
35-50
RCH2OH
50-65
RCH2OR
50-65
Table 13.3 (p 513)
Type of carbon Chemical shift (d), Type of carbon
ppm
Chemical shift (d),
ppm
O
RCH2Br
20-40
RCH2Cl
25-50
RCH2NH2
35-50
O
RCH2OH
50-65
RCR
RCH2OR
50-65
RCOR
160-185
190-220