Chemistry Reference
In-Depth Information
12.23
The chemical shifts suggest that carbon is more electronegative (more electron-
withdrawing) than silicon. Electronegativity generally decreases as one goes down a
column in the periodic table. The Pauling electronegativities of carbon and silicon are
2.5 and 1.8, respectively.
12.24
a.
CH
3
CCl
3
All the protons will appear as a singlet.
CH
2
ClCHCl
2
There will be two sets of peaks, with an area ratio of 2:1.
The former will be a doublet, the latter a triplet.
b.
CH
3
CH
2
CH
2
OH
In addition to the O-H peak, there will be three sets of
proton peaks, with area ratio 3:2:2.
(CH
3
)
2
CHOH
In addition to the O-H peak, there will be only two sets of
proton peaks, with area ratio 6:1.
c.
O
H
3
CO
C
CH
3
The spectrum will show a singlet at about
δ
3.5-3.8 for the O-CH
3
protons
and a singlet at
δ
2.0-2.5 for the other methyl group.
O
HO
C
CH
2
3
The spectrum will show a triplet at about
δ
1.0 for the methyl group, a quartet
near
δ
3.8 for the -CH
2
- group, and a singlet near
δ
9.0 for the -CHO group.
d.
CH
2
CH
O
A one-proton aldehyde peak at
δ
9.5-9.7 ( a triplet) will easily distinguish this
aldehy
d
e from its ketone isomer.
O
C
HC
The aliphatic protons will give a sharp three-proton singlet at about
δ
2.1-2.6.
12.25
The peaks are assigned as follows:
δ
7.15
δ
7.87
HH
O
CH
3
C
O
C
H
3
δ
2.35
H
H
δ
3.82
δ
7.15
δ
7.87
In general, aromatic protons show up at lower field strengths if they are adjacent to
electron-withdrawing substituents. This is the basis for distinguishing between the
two sets of aromatic protons.
12.26
a.
(CH
3
)
2
CHCHO
