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Thin Layer Chromatography

Melting Point

Simple Distillation

Column Chromatography

Infrared Spectroscopy

Polarimetry

Solubility Testing

Reflux

Extraction

Gas Chromatography-Mass Spectrometry

Classification Tests-Halides

Fractional Distillation

ChemDraw

 

Infrared Spectroscopy (FT-IR)
Infrared spectroscopy is a technique used to identify various functional groups in unknown substances through the identification of different covalent bonds that are present in the compound. By identifying the different covalent bonds that are present in a compound, you can establish the types of functional groups present. By comparing the absorptions seen in an experimental spectrum to the literature absorptions of various functional groups, you can determine a list of possible identities for the bonds present.

The web tutorial Infrared Spectroscopy and Organic Functional Groups has more information.

Apparatus

IR

Procedure

CHEM 211 students may run IR spectra only during their regularly scheduled laboratory time.

1. If the OPUS software is NOT already running, select ftir_user to get to the desktop. On the desktop, double click on the OPUS 7.0 icon to start the acquisition program. When prompted, log in as student. There is no password, so click on Login to open the program. The ATR-diamond surface should be clean and free of any sample at this point. In the About OPUS window, click on OK. [The program will open and run a performance test on the instrument. You can observe the test in the lower bar of the open window. Do not touch the instrument during this performance check. When the test is completed, you should see a green circle in the bottom right corner of the window. If it is a yellow or red circle, please see an instructor or lab assistant.

2. To obtain an FT-IR spectrum, click on the green test tube icon in the icon menu bar.

3. Enter a sample name. The best sample names include the name of the compound and your initials.

4. To store your data in the correct folder, select the appropriate folder for your data in the path: field by clicking on the on the browse button . Select the correct folder in the C:\Data folder. For Chem. 105, for example, it would be C:\Data\Fall 2012\Chem105\.

5. With a clean and dry ATR-diamond surface, select Start Background Measurement.


6. For liquid samples: place 2-3 drops of your sample on the ATR-diamond and select Start Sample Measurement. After four scans are run on your sample, your FT-IR spectrum should appear in the OPUS window.

For solid samples: place enough solid to easily cover the entire ATR-diamond and lower the plunger with the handle until it snaps into place. NOTE: it is impossible to put too much force on your solid using the plunger since it is calibrated to never apply too much force to the ATR-diamond. Select Start Sample Measurement. After four scans are run on your sample, your FT-IR spectrum should appear in the OPUS window.

7. To label your peaks, click on Evaluate in the upper menu bar and select Peak Picking. Click and drag the box in the middle of the spectrum upwards until you see peak labels on all of the peaks of interest to you. (Typically, we are only concerned with major peaks between 4000-1400cm-1.) Click on Store in the left-hand window to retain the peak labels.

8. To save your spectrum to your USB flash drive. A. Right-click on your spectrum and select, copy all. B. Open the Paint program (if it isn’t already open) and Paste in your spectrum. C. Save your spectrum as a jpeg file on your USB drive.

9. CLEAN UP! Remove your liquid sample with KimWipes or use the vacuum to remove your solid sample from the sample area. Then, use damp ethanol KimWipes to thoroughly clean the sample area and under-side of the plunger.

10. To leave the program ready for the next user, please go to the menu bar, select window in the upper menu bar and New Spectrum Window.

The following is an example data table which you should use to display the data given in your infrared spectra.

Experimental Frequencies (cm-1)

Literature Frequencies (cm-1)*

Possible Peak Assignments

3320-3300

3500-3300

3600-3200

N-H stretch: 2o amine

OH stretch: alcohol, phenol

1730-1710

1730-1625

C=O stretch: carboxylic acid, ketone, aldehyde

(Literature IR frequency absorptions were taken from Table 1 below) 
 

Table 1: Principal IR Absorptions for Certain Functional Groups above 1400 cm-1


Functional Group Names
&
Example Compounds

Absorption Ranges Frequency (cm--1)

[Look for a single absorption in these regions unless stated otherwise.]


Type of Vibration
(causing IR absorption)

Alkanes:


3000-2800

(Note: The absorptions can be seen a several distinct peaks in this region.)

1500-1450


C-H Stretch

 

C-H Bend

Alkenes:


3100-3000

1675-1600


=C-H Stretch

C=C Stretch

Alkynes:


3300-3200

2200-2100


Aromatic Rings:


3100-3000

1600-1580

1500-1450


=C-H Stretch

C=C Stretch

C=C Stretch

Alcohols, Phenols:


3600-3100
(Note: Phenols MUST have Aromatic Ring Absorptions too.)


(1300-1000)


H-bonded O-H Stretch




(
C - O Stretch)

Ketones:

1750-1625

C=O Stretch

Aldehydes:


1750-1625

2850-2800

2750-2700


C=O Stretch

C-H Stretch off C=O

C-H Stretch off C=O

Carboxylic Acids:


3400-2400

(Note: This peak always covers the entire region with a VERY BROAD peak.)

1730-1660


H-bonded O-H Stretch




C=O Stretch

Esters:


1735

(1300-1000)


C=O Stretch

(C - O Stretch)

Ethers:


(1300-1000)


(C - O Stretch)

Amines: Primary


3500-3200
(TWO PEAKS!)

1640-1560


N-H Stretch


N-H Bend

Amines: Secondary


3500-3200
(ONE PEAK!)

1550-1450


N-H Stretch


N-H Bend

Nitriles:


2300-2200


Nitro Groups:


(Note: Both peaks are < 200 cm-1 apart.)


1600-1500

1400-1300


N=O Stretch

N=O Stretch

Amides:


3500-3100

1670-1600

1640-1550


N-H Stretch

C=O Stretch

N-H Bend

Printable Version of FT-IR Literature Table