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Infrared Spectroscopy (IR) Lab

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. 33 - 44 Pavia – pp. 851 – 885` (Infrared Spectroscopy)

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Infrared Spectroscopy (IR) Lab

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  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. 33 - 44 • Pavia –pp. 851 – 885` (Infrared Spectroscopy) – pp. 941 - 959 (Mass Spectrometry) –pp. 719 - 729 (Simple Distillation) • Solomons –Sec. 2.16; 9.12 - 9.14 • Lecture Slides (Dr. Schornick Web Site) URL: http://classweb.gmu.edu/jschorni/irlecture.ppt

  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 E-Mailed by Instructor • Due Date to be Determined

  3. Infrared Spectroscopy (IR) Lab • Physical Properties of Spectroscopy Unknown • Boiling Point & Purification via Simple Distillation • Physical Description of Purified Unknown • Solubility Relative to Water • Density Relative to Water • Refractive Index (Corrected for Temperature) • Infrared Spectrum Analysis • Analysis of Results & identification of Unknown • Unknown List – Slayden Manual, Appendix 3, p. 125-127 • Verify physical properties with appropriate literature citation (Merck, CRC, etc.). • The literature citation for a compound must include the item number, if applicable, and page number

  4. 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

  5. Infrared Spectroscopy (IR) Lab • Simple Distillation – Background • Note: The Distillation process (Simple and Fractional) will be formally introduced in a later experiment • Simple Distillation will be introduced here as part of the Spectroscopy experiment to purify the sample and determine its Boiling Point • Distillation, like Spectroscopy, Melting Point, Refractive Index, etc. is one of the tools we introduce you to in the Organic I & II courses • Boiling point and purification of a sample by Simple Distillation is one of several physical properties – solubility & density relative to water, refractive index, melting point – that you will determine routinely on sample unknowns

  6. 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 sequentialvaporization-condensation cycles would produce increasingly pure substances, but this is a very tedious process

  7. 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), 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 = 0.98692 atmospheres = 14.5038 psi (pounds per square inch) = 29.53 in Hg (inches of mercury) = 750.06 mm

  8. Infrared Spectroscopy (IR) Lab • Simple Distillation – Procedure Note: The temperature range you obtain for your boiling point may be inaccurate for three (3) reasons 1. The atmospheric pressure in the lab may not be: 1 bar (0.98692 atm) 2. The thermometers used in the lab may not reflect the actual temperature 3. 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 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

  9. Infrared Spectroscopy (IR) Lab • Typical Distillation Setup

  10. 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

  11. 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

  12. 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

  13. 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 1.4000

  14. Infrared Spectroscopy (IR) Lab • Refractive Index (Con’t) • Release 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 switch on left down and read value to 4 decimal places • Ex. 1.5523

  15. Infrared Spectroscopy (IR) Lab • Refractive Index (Con’t) • The following equation adjusts the raw Refractive Index value to 20oC: ND20 = NDRm Temp + (Rm Temp – 20) * 0.00045 Ex: For an observed value of 1.5523 at 16oC, the correction is: ND20 = 1.5523 + (16 – 20) * 0.00045 = 1.5523 + (-4) * 0.00045 = 1.5505 Light Half 1.5500 1.5523 1.5550 1.5580 1.5600 Dark Half

  16. Infrared Spectroscopy (IR) Lab • Infrared Spectroscopy • 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

  17. 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

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