1. Infrared Spectroscopy (IR) Lab
Infrared Spectroscopy – Identification of Unknown
The use of selected physical properties and Infrared Spectroscopy to determine the identity of an unknown compound
Text Materials
Slayden – pp
Pavia – pp. 851 – 88 (Infrared Spectroscopy)
– pp (Mass Spectrometry)
– pp (Simple Distillation)
Solomons – Sec. 2.16;
Lecture Slides (Dr. Schornick Web Site)
URL:

2. Infrared Spectroscopy (IR) Lab
Elements of the Experiment
1st Week
Lecture on Theory of:
Infrared Spectroscopy
Mass Spectroscopy
Ultraviolet / Visible Spectroscopy
2nd Week
Determination of Unknown Physical Properties
IR Spectrum of Unknown
Spectroscopy Problem Set:
Will be ed by Instructor
Due Date to be Determined

3. Infrared Spectroscopy (IR) Lab
IR Spectroscopy
The following spectrographic techniques are introduced to the Chem 315 and Chem 318 organic lab courses:
Mass Spectrometry
Ultraviolet Spectroscopy
Ultraviolate (IR) Spectroscopy
Nuclear Magnetic Resonance (NMR)
Other Instrumental Techniques
Gas Chromatography

4. Infrared Spectroscopy (IR) Lab
Physical Properties of Spectroscopy Unknown
The following physical properties of organic compounds are routinely determined in various combinations in most experiments
Melting Point
Refractive Index (Corrected for Temperature)
Boiling Point & Purification via Simple Distillation
Physical Description of Purified Unknown
Solubility Relative to Water
Density Relative to Water

5. Infrared Spectroscopy (IR) Lab
Organic Lab – Unknowns, Purification, Boiling Point
Several experiments in Chem 315/318 (Org Lab I & II) involve the identification of an unknown compound
Liquid samples that students receive in Lab may contain some impurities in addition to the unknown compound that could produce ambiguous results when determining the chemical or physical properties of the compound
Simple Distillation is used to purify the sample by separating the pure compound that comes over in a narrow temperature range – corresponding to its boiling point – from impurities that have boiling points either lower than or higher than the compound

6. Infrared Spectroscopy (IR) Lab
Simple Distillation - Background
Distillation, like Spectroscopy, Melting Point, Refractive Index, etc. is one of the tools we introduce you to in the Organic I & II courses
Simple Distillation will be introduced here as a means to purify the unknown sample and to obtain an approximate boiling point of the compound
Simple Distillation and Fractional Distillation will be used in a future experiment as a means of separating compounds in a mixture
Boiling point is one of several physical properties – solubility & density relative to water, refractive index, melting point – that you will determine routinely on sample unknowns

7. Infrared Spectroscopy (IR) Lab
Simple Distillation – Background (Con’t)
Single Vaporization / Condensation cycle of a liquid sample
The Distillate for a mixture is always impure at any temperature range between the range of boiling points of the components
Therefore, it is impossible to completely separate the components in a mixture with simple distillation.
Relatively pure substances can be obtained from a mixture with Simple Distillation, if the boiling points of the components differ by a large amount (>100oC)
Redistilling the distillate from multiple sequential vaporization-condensation cycles would produce increasingly pure substances, but this is a very tedious process

8. Infrared Spectroscopy (IR) Lab
Simple Distillation – Background
Boiling Point
The normal boiling point (also called the atmospheric boiling point or the atmospheric pressure boiling point) of a liquid is the temperature at which the vapor pressure of the liquid is equal to 1 atmosphere (atm), i.e., the atmospheric pressure at sea level
At that temperature, the vapor pressure of the liquid becomes sufficient to overcome atmospheric pressure and allow bubbles of vapor to form inside the bulk of the liquid.
The standard boiling point is now (as of 1982) defined by IUPAC as the temperature at which boiling occurs under a pressure of 1 bar
1 bar = 105 Pascals = atmospheres
= psi (pounds per square inch)
= in Hg (inches of mercury) = mm

9. Infrared Spectroscopy (IR) Lab
Simple Distillation – Procedure
Note: The temperature range you obtain for your boiling point may be inaccurate for three (3) reasons
The thermal inefficiency of the glassware used for the boiling point determination may result in a lower than expected measured value by as much as 2 – 5oC
The thermometers used in the lab may not reflect the actual temperature
The atmospheric pressure in the lab may not be:
1 bar ( atm)
You should take this potential temperature differential into account when you compare your measured results with the list of possible unknowns in lab manual tables

10. Infrared Spectroscopy (IR) Lab
Typical Distillation Setup

11. Infrared Spectroscopy (IR) Lab
Simple Distillation – Procedure
Set up Simple Distillation apparatus (previous slide)
Use 25 mL or 50 mL Distillation flask
Place a Corundum or Teflon boiling chip in the flask
Start gentle water flow through condenser
Put a waste receiving container (small beaker) into an ice water bath – especially for low boiling liquids.
Begin heating sample
Note: The sample may appear to be boiling, but the actual boiling point is not reached until the temperature of the boiling liquid and the vapor surrounding the thermometer bulb reach equilibrium. At this point the vapor will start to condense in the condenser

12. Infrared Spectroscopy (IR) Lab
Simple Distillation - Procedure
Note the temperature when the distillate begins to drip into the waste receiving container
Continue to collect distillate in the waste container until the temperature begins to level off
Remove the waster container and begin collecting the distillate in a small clean Erlenmeyer flask
Note the temperature when you start to collect the purified sample
Continue to collect the sample until the temperature begins to rise again (it may not change before the all of the sample has come over)
Note the temperature just before the temperature begins to change
The first and last temperatures recorded in the narrow boiling range represent the boiling point range of your sample

13. Infrared Spectroscopy (IR) Lab
Solubility & Density Relative to Water
Place about 2 mL Distilled Water in a medium test tube
Add 4-5 drops of the solid or purified liquid unknown
Shake test tube firmly
Observe solubility of Sample in Distilled Water
If sample is insoluble, observe whether sample:
Floats on top of water
Floats in the middle of the water
Sinks to the bottom of the test tube

14. Infrared Spectroscopy (IR) Lab
Refractive Index
Clean prisms of ABBE’ Refractometer with tissues & Methyl Alcohol – BE GENTLE!!
Do not touch prism with fingers or other hard objects, use tissues
Place 3-4 drops of sample on Prism.
Close Prism and raise lamp in front of Prism Portal.
Flip switch on left side to turn on light.
Use large dial on right to bring light/dark image into view.
If image cannot be found, flip switch on left down and use large dial on right to bring the Scale into view around

15. Infrared Spectroscopy (IR) Lab
Refractive Index (Con’t)
itch on left down and read value to 4 decimal placesRelease switch on left and use large dial on right to bring light/dark image into view
Sharpen line of demarcation using Drum dial on front of instrument.
Use Eyepiece to sharpen Cross-Hairs
Align the line of demarcation with the Cross-Hairs
Flip sw Ex

16. Infrared Spectroscopy (IR) Lab
Refractive Index (Con’t)
Dark Half
Light Half
1.5500
1.5523
1.5600
1.5550
1.5580
The following equation adjusts the raw Refractive Index value to 20oC:
ND20 = NDRm Temp + (Rm Temp – 20) *
Ex: For an observed value of at 16oC, the correction is:
ND20 = (16 – 20) * = (-4) * =

17. Infrared Spectroscopy (IR) Lab
Liquid Samples
1 to 2 drops of liquid sample are placed between two single crystals of sodium chloride (Salt Plates)
Note: NaCl plates are water soluble – keep dry
Solid Samples Soluble in Acetone
Dissolve sample in acetone
Evaporate on Salt Plate
Solid Samples Not Soluble in Acetone
Make Potassium Bromide (KBR) pellet
Put Salt Plate sandwich in Plate Holder
Place Plate Holder into Beam Slot of IR Spectrometer

18. Infrared Spectroscopy (IR) Lab
Infrared Spectroscopy – Con’t
Confirm with instructor that “Background” has been scanned in.
Select Memory location (X, Y, or Z)
Press “SCAN” button
Verify No. of Scans is “4”; if not, notify instructor
Press “Execute” (last (far right) “soft” button
If spectrum absorptions bottom out, remove Salt Plate holder and reload Salt Plate with less sample.
Rerun Scan / Execute again
Push “Plot” to produce chart
Remove Cell Holder and disassemble
Clean Salt Plate with acetone and dry with ChemWipe
Place Salt Plate in desiccator

19. Infrared Spectroscopy (IR) Lab
The Laboratory Report
Analyze and label the IR Spectrum to determine the type of compound
Select compounds of similar type from the Unknown List in the Slayden Manual, Appendix 3, p
Analyze the physical property results to narrow down the possible candidates for the compound’s identity
Verify measured physical properties with appropriate literature or online resources - Merck, CRC, etc.
Cite the compound resource in the literature citation section of the report using the format described on slide 27 of the Organic Lab Handout.
Be sure to include the item number, if applicable, and the page number