Infrared Spectroscopy (IR) Lab

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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.p
  pt

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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

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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

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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

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Infrared Spectroscopy (IR) Lab

• Simple Distillation Background (Cont)
• 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
  (gt100oC)
• Redistilling the distillate from multiple
  sequential vaporization-condensation cycles
  would produce increasingly pure substances, but
  this is a very tedious process.

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Infrared Spectroscopy (IR) Lab

• Simple Distillation Background (Cont)
• Samples of unknown organic compounds that
  students receive in Organic Lab are generally
  pure, but may contain some impurities 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 the impurities that have
  boiling points lower than or higher than the
  compound

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Infrared Spectroscopy (IR) Lab

• Simple Distillation Basics Steps
• Set up Simple Distillation apparatus (next slide)
• Heat sample and collect - in a waste beaker - all
  distillate that comes over while the temperature
  continues to rise.Usually this involves only a
  small amount, if any, of the distillate.
• When the temperature stabilizes over a narrow
  temperature range collect the distillate in a
  small clean container. The bulk of the sample
  will be collected here.
• Stop collecting sample when the temperature
  begins to rise again, i.e., any sample remaining
  at this point would consist of impurities with
  boiling points above that of your unknown sample.

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Infrared Spectroscopy (IR) Lab

• Typical Distillation Setup

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Infrared Spectroscopy (IR) Lab

• Simple Distillation Procedure
• Set up Simple Distillation apparatus
• 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

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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

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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

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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

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Infrared Spectroscopy (IR) Lab

• Refractive Index (Cont)
• 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

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Infrared Spectroscopy (IR) Lab

• Refractive Index (Cont)

• 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

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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

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Infrared Spectroscopy (IR) Lab

• Infrared Spectroscopy Cont
• 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