infrared spectroscopy (ir) lab

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2/26/2015 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 – 88 (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://mason.gmu.edu/~jschorni/irlecture.ppt 1

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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) - PowerPoint PPT Presentation

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Page 1: Infrared Spectroscopy (IR) Lab

2/26/2015 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 – 88 (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://mason.gmu.edu/~jschorni/irlecture.ppt1

Page 2: Infrared Spectroscopy (IR) Lab

2/26/2015 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

2

Page 3: Infrared Spectroscopy (IR) Lab

2/26/2015 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

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Page 4: Infrared Spectroscopy (IR) Lab

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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

Page 5: Infrared Spectroscopy (IR) Lab

2/26/2015 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

Page 6: Infrared Spectroscopy (IR) Lab

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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

Page 7: Infrared Spectroscopy (IR) Lab

2/26/2015 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

Page 8: Infrared Spectroscopy (IR) Lab

2/26/2015 8

Infrared Spectroscopy (IR) Lab Simple Distillation – Background

Boiling PointThe 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 levelAt 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 bar1 bar = 105 Pascals = 0.98692 atmospheres = 14.5038 psi (pounds per square inch) = 29.53 in Hg (inches of mercury) = 750.06 mm

Page 9: Infrared Spectroscopy (IR) Lab

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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 thermal inefficiency of the glassware used for the boiling point determination may result in a lower than expected measured value by as much as2 – 5oC

2. The thermometers used in the lab may not reflect the actual temperature

3. The atmospheric pressure in the lab may not be:

1 bar (0.98692 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

Page 10: Infrared Spectroscopy (IR) Lab

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Infrared Spectroscopy (IR) Lab Typical Distillation Setup

Page 11: Infrared Spectroscopy (IR) Lab

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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

Page 12: Infrared Spectroscopy (IR) Lab

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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

Page 13: Infrared Spectroscopy (IR) Lab

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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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Page 14: Infrared Spectroscopy (IR) Lab

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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

Page 15: Infrared Spectroscopy (IR) Lab

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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. 1.5523

Page 16: Infrared Spectroscopy (IR) Lab

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Infrared Spectroscopy (IR) Lab

The following equation adjusts the raw Refractive Index value to 20oC:

ND20 = ND

Rm 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

Dark Half

Light Half

1.5500 1.5523 1.56001.5550 1.5580

Refractive Index (Con’t)

Page 17: Infrared Spectroscopy (IR) Lab

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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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Page 18: Infrared Spectroscopy (IR) Lab

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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

Page 19: Infrared Spectroscopy (IR) Lab

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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. 125-127

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