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Infrared Spectroscopy (IR) Lab

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Evaporate on Salt Plate. Solid Samples Not Soluble in Acetone ... Put Salt Plate sandwich in Plate Holder. Place Plate Holder into Beam Slot of IR Spectrometer ... – PowerPoint PPT presentation

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Title: Infrared Spectroscopy (IR) Lab


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.p
    pt

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
  • 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

5
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.

6
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

7
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.

8
Infrared Spectroscopy (IR) Lab
  • Typical Distillation Setup

9
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

10
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

11
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

12
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

13
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

14
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

15
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

16
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
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