HOME PAGE * KS3 SCIENCES * GCSE BIOLOGY  CHEMISTRY  PHYSICS * ADVANCED LEVEL CHEMISTRY

Advanced Level Organic Chemistry: 15.2.2 Uses-applications of infrared spectroscopy

Scroll down and take time to study the content and/or follow links or [Use the website search box]

Doc Brown's Advanced Organic Chemistry: PART 15.2 Infrared Spectroscopy

Doc Brown's Chemistry Advanced Level Pre-University Chemistry Revision Study Notes for UK IB KS5 A/AS GCE advanced A level organic chemistry students US K12 grade 11 grade 12 organic chemistry courses Spectroscopic methods of analysis and molecular structure determination

All my advanced A level organic chemistry notes

SPECTROSCOPY INDEXES

email doc brown

Use your mobile phone or ipad etc. in 'landscape' mode

This is a BIG website, you need to take time to explore it [SEARCH BOX]

15.2.1 Theory of infrared absorption spectra and how an infrared spectrometer works

15.2.3 Index of infrared spectra (on this page, and added links to relevant organic section indexes)

Some simple NMR-IR problem solving questions


15.2.2 Examples of the applications and uses of infrared spectroscopy

Sub-index for this page

(a) Identification of organic molecules (from the fingerprint pattern)

(b) Following a polymerisation reaction

(c) Measuring alcohol levels in blood samples


(a) Identification of organic molecules (from the fingerprint pattern)

The complex infrared spectra of most organic molecules produces a unique fingerprint pattern, particularly in the 1500 to 400 cm-1 region. Also specific functional group stretching vibrations can help too.

Infrared fingerprinting is used in forensic science.

Some infrared spectrometers can immediately compare the spectrum with a computer database of thousands of compounds.

In the example below you can see significant differences in the fingerprint region and also the lack of the strong O-H absorption in the ether.

Comparing the infrared spectra of the three isomers of C3H8O

NOTE: The images are linked to their original detailed spectral analysis pages AND can be doubled in size with touch screens to increase the definition to the original propan-1-ol, propan-2-ol and methoxyethane image sizes.

infrared spectrum of ethoxyethane wavenumbers cm-1 functional group detection fingerprint pattern identification of diethyl ether doc brown's advanced organic chemistry revision notes I wasn't able to obtain an infrared spectrum for methoxyethane, so I've added the infrared spectrum of ethoxyethane to enable a few comparisons with two aliphatic alcohols

Comparing the infrared spectra of propan-1-ol, propan-2-ol and methoxyethane

Propan-1-ol, propan-2-ol and methoxyethane are structural isomers of molecular formula C3H8O

Propan-1-ol, propan-2-ol and methoxyethane exemplify infrared spectra of the lower members of the homologous series of aliphatic alcohols and ethers

INFRARED SPECTRA (above): There are, as expected, differences in the fingerprint region at wavenumbers 1500 to 400 cm-1, but most absorptions for all three molecules are the various C-O and the many C-H vibrational modes. However, there is one characteristic distinguishing absorption only present in the infrared spectra of alcohols, but not in ethers, that is the broad O-H stretching vibration peaking at ~3350 cm-1. There is also another broad absorption band (origin?) peaking at ~650 cm-1 in the alcohol spectra, but not in the ether spectra.


TOP OF PAGE and sub-indexes


(b) Following a polymerisation reaction

By measuring at a specific frequency over time, you can monitor and measure changes in the character or quantity of a particular bond in an organic molecule.

This is very useful for measuring the degree of polymerisation in polymer manufacture.

The progress of formation of an epoxy resin being hardened by an amine cross linking agent can be monitored by observing the appearance of a hydroxy group in the spectrum of a polymerising sample (or by the disappearance of an epoxy group).

The C-O stretching vibration in the triangular C-O-C epoxy group decreases, at wavenumbers, 1260-1240 cm-1.

The O-H group in the resin increases as it 'cures', O-H stretching vibration measured at ~3600 cm-1.

Both absorptions can be measured relative to each other from the intensity of the two peaks.

use of infrared spectroscopy to monitor the cross linking hardening of epoxy resins with an amine


(c) Measuring alcohol levels in blood samples

An infrared spectroscopy technique can be used to measure the concentration of ethanol ('alcohol') in blood e.g. in a suspected drunk driver.

A portable 'handy' instrument to do this is called a breathalyzer.

A beam of infrared radiation is passed through a sample of the suspect's breath and the absorption at a particular frequency is measured - a series of filters is used to select the intensity (transmittance) of specific analytical wavenumbers used for the alcohol vapour analysis

C-H and C-O stretching vibrations are used.

C-H absorption at 2940 cm-1 and the C-O bond gives a double peak at 1102 and 1055 cm-1 (spectrum below).

The concentration of alcohol in the breath can be related to the concentration of alcohol in the bloodstream.

beathalyzer infrared spectrum of alcohol ethanol vapor vapour

SPECTROSCOPY INDEXES

All Advanced Organic Chemistry Notes

[WEBSITE SEARCH BOX]

TOP OF PAGE and sub-indexes

KS3 BIOLOGY QUIZZES ~US grades 6-8 KS3 CHEMISTRY QUIZZES ~US grades 6-8 KS3 PHYSICS QUIZZES ~US grades 6-8 HOMEPAGE of Doc Brown's Science Website EMAIL Doc Brown's Science Website
GCSE 9-1 BIOLOGY NOTES GCSE 9-1 CHEMISTRY NOTES and QUIZZES GCSE 9-1 PHYSICS NOTES GCSE 9-1 SCIENCES syllabus-specification help links for biology chemistry physics courses IGCSE & O Level SCIENCES syllabus-specification help links for biology chemistry physics courses
Advanced A/AS Level ORGANIC Chemistry Revision Notes US K12 ~grades 11-12 Advanced A/AS Level INORGANIC Chemistry Revision Notes US K12 ~grades 11-12 Advanced A/AS Level PHYSICAL-THEORETICAL Chemistry Revision Notes US K12 ~grades 11-12 Advanced A/AS Level CHEMISTRY syllabus-specificatio HELP LINKS of my site Doc Brown's Travel Pictures
Website content Dr Phil Brown 2000+. All copyrights reserved on revision notes, images, quizzes, worksheets etc. Copying of website material is NOT permitted. Exam revision summaries & references to science course specifications are unofficial.

 Doc Brown's Chemistry 

*

TOP OF PAGE and sub-indexes