CHEM 2320 Lecture Notes - Lecture 12: Fiji, Chemical Shift, Diamagnetism

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Lecture #13 02.02.17
13
Cchemical shift
Benzene
§
126 Ppm CH3
\135 ppm Mlsonlboppm
Oxygen will donate
:electrons .
gThe electrons donated by oxygen can be found anywhere
.
s
along the ring .
2
←se a
a
Nqcauses
shielding ,
goes up field
Positions With sare shielded =D wpfield .
Electron withdrawing
CCHZ
)pulls CH3
electron
@
t
out ya
of the 7
ring v
+
Positions with St are deshieldea .
=D downfield .
When you have alot of branches in the carbon , it shifts it downfield .Stoic hindrance .
13C NMR shifts of carbonyl groups
Important about carbonyl groups :
09
11
,c-y
,¥
fij
The carbonyl carbon would be moved downfield partly because of the diamagnetic
st
anisotropy .( electrons moving around ).Also more downfield due to e- Withdrawing group .
To demonstrate the Dolan 'tU Of the bond .
It add groups (4) that can donate electron density to The 5, Then that Will shift it more up field Within the carbonyl
range .
aCan split the carbonyl groups into Two main categories :
000
Alkyl groups 11 11
can ornate c- c- c-c- +,,Yfgµ
litter ,
?dfj=
nejtdgnosoitmhwbnut
ketonecaldenud_caar.bg/ulicesteram#
220-190
below ZZOPPM means 175 -165 ppm
that they have some sort
Otcomugation .attached
to them ,like a double Identifying esters from ketone was hard in Ir ,but
bond or a benzene ring .
in Nmr is easier .
Abovezzoppm means that
there is no corrugation .
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Examples of 13C NMA :
b
t
equivalent
8to
a
f. t.ms
noisy baseline due to insensitive method .
Size of The peaks does n't disclose anything .However ,there are three methyl groups that are Three similar methyl
groups so their peak must be taller .
*Quaternary carbons tend to be small .
Br
Br
,
Br µ
www.nnoowx.signas
soyyFFIT¥aEIIi
'
Isham .
Can also identity them based on the number of peaks that arise due to symmetry .
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