Download C-NMR Spectroscopy

LSW F03
NMR
isotope used
natural abundance
sensitivity
Time of experiment
Chemical shift range
Peak spread
Reference
Electronegativity
integration
Number of peaks
Splitting patterns
Coupling
Organic Chemistry Exam II notes
13
C-NMR Spectroscopy
H
C
Correlation table of 1H chemical shifts:
Correlation table of 13C chemical shifts:
95
LSW F03
Organic Chemistry Exam II notes
Interpreting C-NMR Spectra
How many types of C ?
What types of C ?
Examples of 13C-NMR spectra:
96
LSW F03
Organic Chemistry Exam II notes
Ultraviolet-visible spectroscopy
Terminology
Absorbance
A, a measure of the amount of radiation absorbed
Band
Describes a UV-vis absorption.
Chromophore
Structural unit responsible for the absorption of light.
Molar absorptivity
ε, absorbance of a 1 molar sample in 1 cm cell.
Extinction coefficicent
An alternative term for the molar absorptivity.
Path length
l, the length of the sample cell in cm.
Concentration
c = moles / litre
Beer-Lambert Law
A = ε.c.l
λmax
The wavelength at maximum absorbance
εmax
The molar absorptivity at λmax
HOMO
Highest Occupied Molecular Orbital
LUMO
Lowest Unoccupied Molecular Orbital
auxochrome
extends conjugation with nonbonding electrons.
bathochromic shift
The shift of absorption to a longer wavelength.
hypsochromic shift
The shift of absorption to a shorter wavelength.
hyperchromic effect An increase in absorption intensity.
hypochromic effect A decrease in absorption intensity
Transmittance
Amount of light which passes through a solution
I
intensity of transmitted light
I0
intensity of incident light
% Transmittance
Beer-Lambert Law
(I / I0) * 100%
Absorbance = -log(I / I0) = εcl
97
LSW F03
Organic Chemistry Exam II notes
Types of electronic transitions
Excitation of ethene:
π*
π
π*
hν171nm
(164kcal/mol)
π
Chromophores
λmax
Chromophore
170 Alkyne
-C≡C
λmax
Transition
π to π∗
Chromophore
160 Nitrile
254
204 Aryl
184
∗
175 Alkene
-C=C-
π to π
180 Alcohol
-OH
η to σ∗
180 Ether
π to π∗
190
∗
290
180
280
Ketone
-COR
η to π
-C≡N
-C6H5
-OR
Aldehyde -COH
Transition
η to π∗
π to π∗
η to σ∗
π to π∗
η to π∗
190 Amine
-NR2
η to σ∗
210 Thiol
-SH
η to σ∗
205 Acid
-COOH
η to π∗
205 Ester
-COOR
η to π∗
271 Nitro
-NO3
η to π∗
280 Nitroso
-NO2
n to pi*
210 Amide
-CON
η to π∗
340 Azo
-N=N-
98
η to π∗
LSW F03
Organic Chemistry Exam II notes
Major factors that alter values of λmax.
Conjugation
As conjugation is extends, what happens to the HOMO-LUMO energy gap?
As conjugation is extended, what happens to the wavelength of absorption?
λmax = 176nm
λmax = 180nm
λmax = 223nm
List these compounds in order of increasing lambda-max:
1,3-octadiene,
1,3,5-hexatriene
1-propene.
99
λmax = 258nm
LSW F03
Organic Chemistry Exam II notes
Alkyl group substitution
λmax = 217nm
Electronegativity:
λmax = 232nm
(Auxochromes)
Auxochromes
Amount of λ shift
Ester
-OC(O)CH3
0
Ether
-OR
6
Halogen
-Cl, -Br
5
Amine
-NR2
60
Thiol or thiol
ether
-SR
30
Natural and Synthetic Dyes
Most organic compounds that are perceived as having color are highly conjugated.
N
N
Malachite
Green
Crystal
Violet
N
O
N
Cl
N
OH
OH
OH
Indigo (blue)
Cl
O
H
N
O2
Alizarin (red)
N
H
N
H
O
O
100
LSW F03
Organic Chemistry Exam II notes
azo dyes
Et
FD&C Green No. 3
(Fast Green FCF)
N
SO3Na
CH2
HO
N
HO
methyl N
orange N
para
red N
SO3Na
SO3
N
H2
C
SO3Na
NO2
N
Et
Phenolphthalein
OH
B
sp
3
sp
colorless
O
2
red
H
(pH 8 - 9.6)
OH
O
CO2
-
+ Base
CO2
O
-
-
+ H-Base + OH
-
Cyanidine
red
absorbs blue and green light
poppies, acidic sap
HO
OH
OH
-
OH
O
OH
blue
absorbs red and green light
cornflower, basic sap
HO
OH
O
H3O+
HO
OH
HO
101
O
LSW F03
Organic Chemistry Exam II notes
Mass Spectrometry
Terminology
Molecular ion The ion obtained by the loss of an electron from the molecule
Base peak
The most intense peak in the MS, assigned 100% intensity
M+
Symbol given to the molecular ion
Radical cation positive charged species with an odd number of electrons
Fragment ions Lighter cations from decomposition of the molecular ion
Mass Spectrometer: http://www.colby.edu/chemistry/OChem/DEMOS/MassSpec.html
All mass spectrometers consist of three distinct regions.
1) Ionizer 2) Ion Analyzer 3) Detector
102
LSW F03
Organic Chemistry Exam II notes
1) Ionizer:
Electron Impact (EI) Ionization
Methanol
CH OH + 1 electron
CH OH
3
.+
3
+ 2 electrons
.
CH OH +
3
+ CH OH+
2
(or) CH OH
.+
.
OH + CH +
3
3
2) Ion Analyzer quadrupole mass analyzer
Ions travel down the path based on their mass to charge ratio (m/z)
3) Detector
Interpreting spectra
1) Assignment of relative abundance
.
2) Highest mass in an EI spectrum
103
H
.
LSW F03
Organic Chemistry Exam II notes
3) Fragmentation:
Alkane: Hexane
C6H14
MW =
H
H
H
H
CH3
CH3
H
Aromatic: Naphthalene
Alcohol:
3-Pentanol
C10H8
C5H12O
H
H
H
MW =
MW =
OH
H
CH3CH2
CH3
H
104
H
LSW F03
Ether:
Organic Chemistry Exam II notes
Ethyl methyl ether
C3H8O
MW =
H
CH3
CH3
O
H
Amines
1o Primary Amine:
n-Butylamine
C4H11N MW =
CH3CH2CH2
2o Secondary Amine: n-Methylbenzylamine C8H11N
H
H
C
H
N
MW =
H
C
H
105
N
H
CH3
H
LSW F03
Organic Chemistry Exam II notes
Carbonyl compounds
Aldehyde:
3-Phenyl-2-propenal
C9H8O
MW =
.
O
H
Ketone:
4-Heptanone
C7H14O
MW =
O
CH3CH2CH2
Carboxylic Acid:
2-Butenoic acid
C4H6O2
CH2CH2CH3
MW =
O
CH3CH
106
CH
OH
LSW F03
Ester:
Organic Chemistry Exam II notes
Ethyl acetate
C4H8O2
MW =
O
CH3
Amide:
3-Methylbutyramide
C5H11NO
H
CH3
Halide:
1-Bromopropane
C3H7Br
Br
107
C
CH2CH3
MW =
H
H
O
NH2
MW =
CH2CH2CH3
LSW F03
Organic Chemistry Exam II notes
4) Relative Isotope Abundance:
Element Isotope
Carbon
Hydrogen
Nitrogen
Oxygen
Sulfur
Chlorine
Bromine
12
C
1
H
14
N
16
O
32
S
35
Cl
79
Br
Relative
Relative
Relative
Isotope
Isotope
Abundance
Abundance
Abundance
13
100
C
1.11
2
100
H
.016
15
100
N
.38
17
18
100
O
.04
O
.20
33
34
100
S
.78
S
4.40
37
100
Cl
32.5
81
100
Br
98.0
What ratios do you expect for a chlorinated compound?
What information can be found in each of the following Mass Spectra?
108
LSW F03
Organic Chemistry Exam II notes
109
LSW F03
Compound
1
2
Organic Chemistry Exam II notes
M
M+2
ratio
base
110
ion
others
ratio
Ion