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Identifying an Unknown Substance using Infrared Spectroscopy (IR), Carbon-13 Nuclear Magnetic Resonance (13C NMR), and Proton Nuclear Magnetic Resonance (1H NMR)
Identifying an Unknown Substance using Infrared Spectroscopy (IR), Carbon-13 Nuclear Magnetic Resonance (13C NMR), and Proton Nuclear Magnetic Resonance (1H NMR)
By: Veronica Partridge
Table of Contents v
Table of Contents
Table of Contents .................................................................................................................................................................... v
Introduction ........................................................................................................................................................................... vii
Symbols used in this manual ............................................................................................................................................. vii
What is this experiment about .......................................................................................................................................... viii
How are the points distributed ......................................................................................................................................... viii
Infrared Spectroscopy (IR)...................................................................................................................................................... 3
What is IR used for ............................................................................................................................................................. 3
Example of an IR spectra .................................................................................................................................................... 3
Table of IR values ............................................................................................................................................................... 4
Identifying Functional Groups using IR ............................................................................................................................. 5
Carbon-13 Nuclear Magnetic Resonance (13C NMR) ............................................................................................................. 9
What is 13C NMR used for .................................................................................................................................................. 9
Example of a 13C NMR spectra ........................................................................................................................................... 9
Table of 13C NMR values .................................................................................................................................................. 10
Identifying Function Groups from 13C NMR peaks .......................................................................................................... 11
Labeling Carbons using 13C NMR .................................................................................................................................... 12
Proton Nuclear Magnetic Resonance (1H NMR) .................................................................................................................. 15
What is 1H NMR used for ................................................................................................................................................. 15
Example of a 1H NMR spectra .......................................................................................................................................... 15
Table of 1H NMR values ................................................................................................................................................... 16
Identifying 1H NMR peaks ............................................................................................................................................... 17
Labeling Protons using 1H NMR ...................................................................................................................................... 18
Drawing a Structure using 1H NMR ................................................................................................................................. 19
Identifying the Unknown ...................................................................................................................................................... 23
Calculating the degree of unsaturation .............................................................................................................................. 23
Drawing the structure ........................................................................................................................................................ 25
Putting the data together ................................................................................................................................................... 26
Common Problems ................................................................................................................................................................ 33
The Values for IR, 13C NMR, or 1H NMR do not Match up Perfectly ........................................................................... 33
There is only one Signal on the 1H NMR spectra ............................................................................................................. 33
There is a Break in my 1H NMR spectra ........................................................................................................................... 33
There is no Split on a peak for 1H NMR spectra ............................................................................................................... 33
I can’t see how many splits there are in the 1H NMR spectra ........................................................................................... 33
vi Identifying an Unknown Substance using IR, 13C NMR, & 1H NMR The peak has 1H next to it but no peak ............................................................................................................................. 33
Does this atom affect the degree of unsaturation? ............................................................................................................ 33
Index ..................................................................................................................................................................................... 35
Introduction vii
NOTE
The data used to give an example on how to identify an unknown substance will not be the same as the data given to you, so you will not get the same compound as shown in this manual. The data given to you will be unique to that student and no two students will have the same data or substance.
Introduction This manual is for students in the Organic Chemistry I Lab who have at least a beginners understanding of organic chemistry. This manual is meant to guide the student through the identification of an unknown substance using Infrared Spectroscopy (IR), Carbon-13 Nuclear Magnetic Resonance (13C NMR), and Proton Nuclear Magnetic Resonance (1H NMR)
This manual is organized by each part of the experiment:
1. Infrared Spectroscopy (IR) 2. Carbon-13 Nuclear Magnetic Resonance (13C NMR) 3. Proton Nuclear Magnetic Resonance (1H NMR) 4. Identifying the Unknown
It also includes a section for common problems when doing this experiment.
Symbols used in this manual
Table 1 shows the symbols used in this manual and what they mean.
Table 1
Symbol Means ≡ Triple Bond = Double Bond - Single Bond > Connected to a Carbon Skeleton -R Connected to any Other Molecule 1° Primary 2° Secondary 3° Tertiary -X Connected to a Halogen (F, Cl, Br, I, At) π Double or Triple bond
viii Identifying an Unknown Substance using IR, 13C NMR, & 1H NMR What is this experiment about
In this experiment you will be using Infrared Spectroscopy, Carbon-13 Nuclear Magnetic Resonance, and Proton Nuclear Magnetic Resonance to identify an unknown substance. While doing this experiment, please keep in mind that due to acidic functional groups your IR, 13C NMR, or 1H NMR values may be somewhat off.
How are the points distributed
In order to get the full 20 points on this experiment you must
• Identify the peaks in the IR spectra and what functional groups they can relate to. (2 pts.) • Identify the peaks in C NMR and how that shows what the carbon atom is attached to. (4 pts.)
o Label the carbons with which peak they relate to. • Identify the peaks in H NMR and how it shows how many hydrogen atoms are attached to a carbon atom. (10 pts.)
o Label the hydrogen with which peak they relate to. o Create fragments of the compound using the spectral data.
• Identify the compound. (4 pts.) o Write the number of the unknown substance at the top of your paper. o Draw the structure.
All hydrogen must be drawn out. o Find the degree of unsaturation.
List a table with all possible rings and π bonds.
Infrared Spectroscopy (IR)
Carbon-13 Nuclear Magnetic Resonance 3
Infrared Spectroscopy (IR)
In this section you will use the IR chart and table to identify the functional groups of an unknown substance.
This section
• Explains what IR is for • Gives an example of an IR spectra • Gives a table of IR values • Shows how to identify functional groups using IR
What is IR used for
IR is used to identify any functional groups the organic substance may have which can help predict how the compound will react with other substances.
Example of an IR spectra
Figure 1 is the IR spectra of an unknown substance.
Figure 1
4 Identifying an Unknown Substance using IR, 13C NMR, & 1H NMR Table of IR values
Table 2 below shows what values go with the functional groups.
Table 2
Compounds Functionl Group
Fragments Giving IR Signals
Typical IR Signals (cm-1)
Terminal Alkyne Alkynyl (C≡C) Alkynyl Hydrogen (≡C-H)
2100-2260 ~3300
Internal Alkyne Alkynyl (C≡C) 2100-2260
Alkene Alkenyl (C=C) 1620-1680
Aldehyde Carbonyl (>C=O) 1710-1780
Ketone Carbonyl (>C=O) 1680-1750
Carboxylic Acid Carbonyl (>C=O) Hydroxy (-O-H)
1680-1750 3200-3600
Ester Carbonyl (>C=O) Alkoxy (-OCH3)
1735-1750 1000-1280
Amide Carbonyl (>C=O) Amino (-NH2)
1630-1690 3000-3500
1° Amine Primary Amino (-NH2) C-N
3200-3500 (2 signals) 1020-1360
2° Amine Secondary Amino (>N-H) C-N
3200-3500 (1 signal) 1020-1360
3° Amine Tertiary Amino (>N-) C-N
No signal 1020-1360
Alcohol Phenol
Hydroxy (-O-H) Hydroxy (-O-H)
3200-3600 3200-3600
Ether Alkoxy (-O-R) 1000-1280
Aromatic Aromatic (C-H) Phenyl (C=C)
~3300 1500-1700
Carbon-13 Nuclear Magnetic Resonance 5
A
B
C
Identifying Functional Groups using IR
In order to identify functional groups using IR you will need to refer to the IR spectra given in the experiment hand out and the table on the previous page.
Follow the steps below to identify the functional groups in an unknown substance using IR:
1. Eliminate impossible functional groups by looking at the molecular formula on the handout. 2. Look for distinct functional group signals like an alcohol or an amine. 3. Label as many peaks as you can. 4. List all possibilities for the peak. 5. Compare the possibilities of the functional groups from the IR to the possibilities of the functional groups from
the 13C NMR and 1H NMR.
Below is an example for identifying functional groups using the IR spectra
The possibilities for this unknown based on Figure 2 are
• The letter A could be an alcohol, phenol, or carboxylic acid • The letter B could be a ketone, phenyl, or carboxylic acid • The letter C could be an ether or normal carbon
Figure 2
Carbon-13 Nuclear Magnetic Resonance (13C NMR)
Carbon-13 Nuclear Magnetic Resonance 9
Carbon-13 Nuclear Magnetic Resonance (13C NMR)
In this section you will use the 13C NMR spectra and table to identify the functional groups of an unknown substance and label carbons.
This section
• Explains what 13C NMR is for • Gives an example of an 13C NMR spectra • Gives a table of 13C NMR values • Shows how to identify functional groups using 13C NMR • Shows how to label carbons using a 13C NMR spectra
What is 13C NMR used for
13C NMR is used to determine how the carbons in a substance are put together and how close they are to other functional groups.
Example of a 13C NMR spectra
Figure 3 is the 13C NMR spectra for an unknown substance.
Figure 3
10 Identifying an Unknown Substance using IR, 13C NMR, & 1H NMR Table of 13C NMR values
Table 3 shows what values go with what type of carbon.
Table 3
Type of carbon Atom Structure Chemical Shift Value (ppm) 1° Alkyl
0-40
2° Alkyl
10-50
3° Alkyl
15-50
Alkyl halide
10-65
Amine (1°, 2°, and 3°)
10-65
Alcohol
50-90
Ether
50-90
Alkyne (Terminal and Internal)
60-90
Alkene
100-170
Aryl (Phenyl)
100-170
Nitrile
120-130
Amide
150-180
Carboxylic acid
160-185
Ester
160-185
Aldehyde
182-215
Ketone
182-215
Carbon-13 Nuclear Magnetic Resonance 11
1 2
3 4
6 7
5
8
Identifying Function Groups from 13C NMR peaks
In order to identify functional groups using 13C NMR you will need to refer to the 13C NMR spectra given in the experiment hand out and the table on the previous page.
Follow the steps below to identify the functional groups in an unknown substance using 13C NMR:
1. Eliminate impossible functional groups by looking at the molecular formula. 2. Look for distinct functional group signals like an aldehyde or a ketone. 3. Label all the peaks with a number. 4. List all possibilities for the peak. 5. Compare the possibilities of the functional groups from the 13C NMR to the possibilities of the functional groups
from the IR and 1H NMR.
Below is an example for identifying function groups using 13C NMR
The possibilities for this unknown based on Figure 4 and the possibilities of the IR spectra are
• The number 1 could be a carboxylic acid • The number 2 could be an outside carbon on a aryl ring • The number 3 could be an aryl • The number 4 could be an aryl • The number 5 could be an aryl • The number 6 could be a 3° Alkyl • The number 7 could be a 2° Alkyl • The number 8 could be a 1° Alkyl
Figure 4
12 Identifying an Unknown Substance using IR, 13C NMR, & 1H NMR
1 2
3 4
6 7
5
8
1 OH R
O
2
3
3 4
4
5
5 R O
6 R
R
R 7 R R R 8
Labeling Carbons using 13C NMR
In order to label carbons using 13C NMR you will need to refer to the 13C NMR spectra given in the experiment hand out and the table on the previous page (10). You will need to identify the functional groups before labeling.
Follow the steps below to label the carbons with what signal they show:
1. Identify the functional groups of the substance. 2. Label the 13C NMR spectra with numbers. 3. Draw the structures of each functional group. 4. Label the carbons in the structures with the letter or number that goes with the signal. 5. Label the carbons in the final structure after you identify it.
Below is an example for labeling carbons using 13C NMR where the orange numbers represent carboms
Figure 5 uses the information from Figure 4 to create the structures you see.
Figure 5
Figure 4
Proton Nuclear Magnetic Resonance (1H NMR)
Proton Nuclear Magnetic resonance 15
Proton Nuclear Magnetic Resonance (1H NMR)
In this section you will use the 1H NMR spectra and table to identify the functional groups of an unknown substance, figure out how a structure is put together, and label hydrogen (protons) with the peak they show on a 1H NMR spectra.
This section
• Explains what 1H NMR is for • Gives an example of a 1H NMR spectra • Gives a table of 1H NMR values • Shows how to identify functional groups using 1H NMR • Shows how to predict a structure using 1H NMR • Shows how to label hydrogen using a 1H NMR spectra
What is 1H NMR used for
1H NMR is used to determine how the substance is put together. It is useful to help figure out which carbons have protons and how many protons they have. This is helpful in putting together parts of a structure of a substance into the final structure.
Proton signals are “split” when there are nearby protons which make the signal appear to have bumps. The number of bumps is equal to the number of nearby hydrogen + one.
The number above the signal is the number of unique protons that are connected to a single carbon.
Example of a 1H NMR spectra
Figure 6 is the 1H NMR spectra of an unknown substance.
Figure 6
16 Identifying an Unknown Substance using IR, 13C NMR, & 1H NMR Table of 1H NMR values
Table 4 shows what values go with what type of proton.
Table 4
Type of proton Structure Chemical Shift Value (ppm) 1° Alkyl
0.8-1.2
2° Alkyl
1.2-1.5
3° Alkyl
1.4-1.8
Allylic (alkene)
1.6-1.9
Ketone
2.1-2.6
Benzylic
2.2-2.5
Acetylenic
2.5-3.1
Alkyl iodide
3.1-3.3
Ether
3.3-3.9
Alcohol
3.3-4.0
Alkyl bromide
3.4-3.6
Alkyl chloride
3.6-3.8
Vinylic (a)
4.6-5.0
Vinylic (b)
5.2-5.7
Aromatic
6.0-8.5
Aldehyde
9.5-10.5
Alcohol hydroxyl
0.5-6.0
Amino
1.0-5.0
Phenolic
4.5-7.7
Carboxylic
10-13
Proton Nuclear Magnetic resonance 17
Identifying 1H NMR peaks
In order to identify functional groups using 1H NMR you will need to refer to the 1H NMR spectra given in the experiment hand out and the table on the previous page.
Follow the steps below to identify the functional groups in an unknown substance using 1H NMR:
1. Eliminate impossible functional groups by looking at the molecular formula. 2. Look for distinct functional group signals like a carboxylic. 3. Label all the peaks with a letter. 4. List all possibilities for the peak. 5. Compare the possibilities of the functional groups from the 1H NMR to the possibilities of the functional groups
from the IR and 13C NMR.
Below is an example for identifying function groups using 1H NMR
The possibilities for this unknown based on Figure 7 and the possibilities of the IR spectra and 13C NMR are
• The letter A could be a carboxylic acid • The letter B could be an aromatic • The letter C could be an aromatic outside • The letter D could be a 2° Alkyl • The letter E could be a 3° Alkyl • The letter F could be a 1° Alkyl
Figure 7
F
A
B C D
E
18 Identifying an Unknown Substance using IR, 13C NMR, & 1H NMR
F
C OA R
O
C
C
C C
C
C
C R O
C F
F
F C E E
B B
B B
B
C
R R
R
C R D
R
R
Labeling Protons using 1H NMR
In order to label protons using 1H NMR you will need to refer to the 1H NMR spectra given in the experiment hand out and the table on the previous page (16). You will need to identify the functional groups before you can label the protons.
Follow the steps below to label protons in an unknown substance using 1H NMR:
1. Identify the functional groups of the substance. 2. Label the 1H NMR spectra with letters. 3. Draw the structures of each functional group. 4. Label the protons in the structures with the letter or number that goes with the signal. 5. Label the protons in the final structure after you identify it.
Below is an example for labeling protons using 1H NMR where the orange letters are protons
Figure 8 uses the information from Figure 7 to create the structures you see.
A
B C D
E
Figure 8
Figure 7
Proton Nuclear Magnetic resonance 19
F
C
C B B
B B B
C F
F
F
C
E
E
C
D
C
B
B
B B
B
OA O
Drawing a Structure using 1H NMR
In order to draw a structure using 1H NMR you will need to refer to the 1H NMR spectra given in the experiment hand out and the table on the previous page (16).
When drawing structures using 1H NMR it is important to know that
• The number of “splits” or bumps is equal to the number of nearby protons + one. • The number near the peak is the number of unique protons on the carbon.
o Equivalent protons will only show as one signal such as in aromatic structures.
Follow the steps below to draw a structure using 1H NMR:
1. Identify the functional groups of the unknown. 2. Label all the peaks with a letter. 3. Label the hydrogen with the peak they show. 4. Use the number of hydrogen by the peak to start the structure. 5. Use the number of “splits" to put the pieces together.
Below is an example for drawing a structure using 1H NMR with the orange letters representing hydrogen
Figure 9 uses the information from Figure 7 to create the structure you see.
A
B C D
E
Figure 9
Figure 7
Identifying the Unknown
Identifying the Unknown 23
NOTE
The numbers used here are the numbers given from the molecular formula on the experiment handout.
Identifying the Unknown
In this section you will put the information gathered from the previous sections and identify the unknown. You must have already completed the previous sections before you can do this section.
This section
• Shows how to calculate the degree of unsaturation • Shows how to draw the structure • Explains how to put the data together
Calculating the degree of unsaturation
The degree of unsaturation has to do with how many rings and/or double (π) bonds a substance has. The rings and π bonds only relate to carbons.
The formula for calculating the degree of unsaturation is below.
Degree of Unsaturation = 2C+2+N-X-H2
• C=Number of Carbon • N=Number of Nitrogen • X=Number of Halogens (F, Cl, Br, I) • H=Number of Hydrogen
Follow the steps below to calculate the degree of unsaturation:
1. Look at the molecular formula. 2. Times the number of carbon by two. 3. Add two. 4. Add the number of nitrogen. 5. Subtract the number of halogens. 6. Subtract the number of hydrogen. 7. Divide by two. 8. Figure out the number of possible rings or π bonds.
24 Identifying an Unknown Substance using IR, 13C NMR, & 1H NMR
NOTE
Rings count as one degree of unsaturation.
Double bonds count as one degree of unsaturation.
Triple bonds count as two degrees of unsaturation.
Below is an example on how to calculate the degree of unsaturation
The molecular formula used for this example is C10H12O2.
2(10)+2 + 0 – 0 − 122
= 5
The degree of unsaturation for this substance is 5.
Follow the steps below to calculate the number of rings or π bonds in a substance:
1. Calculate the degree of unsaturation. 2. Make a table. 3. List the possible number of rings. 4. List the possible number of double bonds. 5. List the possible number of triple bonds.
Below is an example of how to calculate the number of rings or π bonds in a substance
The molecular formula used for this example is C10H12O2.
The degree of unsaturation for this substance is 5. Table 5
Table 5 shows the possible combination based on the degree of unsaturation.
Table 5
Degree of unsaturation Possible combinations of rings or π bonds 5 Number of Rings Number of double
bonds Number of triple bonds
5 0 0 4 1 0 3 2 0 3 0 1 2 3 0 2 1 1 1 4 0 1 2 1 1 0 2 0 3 1 0 1 2
Identifying the Unknown 25
C
H H H
H H H
C H
H
H
C
H
H
C
H
C
H
H
H H
H
OH O
C OH R
O
C
C
C C
C
C
C R O
C C
R R
R
C R
R
R
Drawing the structure
This section is to show you how to draw the structure of the unknown substance based on the IR, 13C NMR, and 1H NMR spectra.
Before attempting to draw the structure make sure
• You have identified the functional groups. • You have drawn the fragments of the structure using the 13C NMR and 1H NMR spectra.
Follow the steps below to draw the structure of the unknown substance:
1. Identify the functional groups. 2. Draw the fragments of the structure using the 13C NMR and 1H NMR spectra. 3. Piece the fragments together using the 1H NMR spectra. 4. Draw the final structure with all hydrogen.
Below is an example on how to draw the structure of an unknown substance
The functional groups in this unknown are a carboxylic acid and an aromatic ring.
Figure 10 shows the fragments to be put together based off of the 13C NMR and 1H NMR spectra.
Figure 11 shows the final structure with all hydrogen showing.
Figure 10
Figure 11
26 Identifying an Unknown Substance using IR, 13C NMR, & 1H NMR
Putting the data together
This section is to help you put all your data together. To get full points you should be sure to include all information listed in this section.
Follow the steps below to put your data together:
1. Write the number of your unknown at the top of the paper. 2. Find the degree of unsaturation. 3. Identify the functional groups using IR, 13C NMR, and 1H NMR.
a. Label the IR with what function groups they are. 4. Draw the structure with all hydrogen drawn out.
a. Draw the fragments using the 1H NMR data with labeled protons. 5. Draw the final structure.
a. Label the hydrogen and carbon with the peaks that they show on the spectra.
Below is an example on how to put your data together and how you should set up your lab report
1. Unknown 070j 2. The molecular formula used for this example is C10H12O2.
2(10)+2 + 0 – 0 − 122
= 5
The degree of unsaturation for this substance is 5.
Degree of unsaturation Possible combinations of rings or π bonds 5 Number of Rings Number of double
bonds Number of triple bonds
5 0 0 4 1 0 3 2 0 3 0 1 2 3 0 2 1 1 1 4 0 1 2 1 1 0 2 0 3 1 0 1 2
Identifying the Unknown 27
A
B
3. A and B in are signals from a carboxylic acid.
28 Identifying an Unknown Substance using IR, 13C NMR, & 1H NMR
C
H H H
H H H
C H
H
H
C
H
H
C
H
C
H
H
H H
H
OH O
F
C OA R
O
C
C
C C
C
C
C R O
C F
F
F C E E
B B
B B
B
C
R R
R
C R D
R
R
4. The fragments below are to be combined using the 1H NMR spectra
This is the final structure with hydrogen showing:
A
B C D
E
Identifying the Unknown 29
2
C B B
B B B
6 F
F
F
7
E
E
8
D
1
B
B
B B
B
OA O
5 3
3 5
4
4
-
=
1 2
3 4
6 7
5
8
F
5. The structure below is labeled using the 13C NMR spectra and the 1H NMR spectra
A
B C D
E
Common Problems
Common Problems 33
Common Problems In this section are common problems when trying to identify the unknown substance.
The Values for IR, 13C NMR, or 1H NMR do not Match up Perfectly
If the values are not spot on do not fret. This is likely due to an impurity of sorts. So long as the values are in the general area and you can prove that the substance is without a doubt the compound you found it to be it will be fine.
There can be a lot of shifting due to highly acidic functional groups such as carboxylic acids.
There is only one Signal on the 1H NMR spectra
This is how substances that are symmetrical show up. This is also known as the hydrogen all being “equal”
For example benzene will only have one peak on the 1H NMR spectra because it is completely symmetrical.
There is a Break in my 1H NMR spectra
This is because there are no peaks between the number last shown and the number listed after it.
There is no Split on a peak for 1H NMR spectra
This means that all the hydrogen on the nearby carbon are “equal” or symmetrical.
I can’t see how many splits there are in the 1H NMR spectra
This is because there are more than three protons on a nearby carbon.
The peak has 1H next to it but no peak
This means that the nearby carbon has no hydrogen.
Does this atom affect the degree of unsaturation?
The only atoms that affect the degree of unsaturation are carbon, hydrogen, halogen, and nitrogen.
Index 35
Index13C NMR, 7, 9, 10, 11 1H NMR, 15, 16, 17 example, 3, 9, 11, 15, 17, 18, 19, 33 Example, 3, 9, 15 Identifying, 5, 11, 17, 23
IR, viii, 3, 4, 5, 11, 17, 18, 19 NOTE, vii, 23, 24 Problems, 33 unsaturation, viii, 23, 24, 26 values, 4, 11, 17
