infrared spectrum of propan-2-ol prominent wavenumbers cm-1 detecting ? functional groups present finger print for identification of 2-propanol image diagram doc brown's advanced organic chemistry revision notes

Advanced Organic Chemistry: Infrared spectrum of propan-2-ol CH₃CH(OH)CH₃

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Interpreting and explaining the infrared spectrum of propan-2-ol CH₃CH(OH)CH₃

[Author © Dr Phil Brown GRIC, PhD: Doc Brown's advanced level organic chemistry exam revision notes suitable for students of UK A level chemistry courses & US K12 grade 11, grade 12 and AP honors chemistry courses: Molecular spectroscopy analysis of propan-2-ol [spectra page updated RE-EDIT]

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Infrared spectroscopy - spectra index * A couple of basic practise questions

Introductory note on the infrared spectrum of propan-2-ol (2-propanol)

Students and teachers please note my explanation of the infrared spectrum of propan-2-ol is designed for advanced, but pre-university, chemistry courses.

Based in the infrared spectrum diagram for propan-2-ol, only some of the most prominent peaks for particular bond vibrations are discussed, particularly if propan-2-ol has a functional group with a particular characteristic wavenumber peak.

The infrared spectrum of propan-2-ol is unique and the whole, or selected wavenumbers, can be used to fingerprint its identity, sometimes analysing a mixture containing propan-2-ol or following its change of concentration in a reaction.

infrared spectrum of propan-2-ol wavenumbers cm-1 functional group detection fingerprint pattern identification of 2-propanol doc brown's advanced organic chemistry revision notes

Spectra obtained from a liquid film of propan-2-ol. The right-hand part of the of the infrared spectrum of propan-2-ol, wavenumbers ~1500 to 400 cm^-1 is considered the fingerprint region for the identification of propan-2-ol and most organic compounds. It is due to a unique set of complex overlapping vibrations of the atoms of the molecule of propan-2-ol.

Propan-2-ol, C₃H₈O, , , , secondary alcohol

The molecular structure and naming of aliphatic alcohols and ethers

Interpretation of the infrared spectrum of propan-2-ol (2-propanol, isopropyl alcohol)

The most prominent infrared absorption lines of propan-2-ol

The most characteristic absorption is the broad O-H stretching vibration band at wavenumbers ~3500 to 3230 cm^-1, the breadth is caused by hydrogen bonding interactions, common to all hydrogen bonded molecules with a hydroxyl group e.g. alcohols and carboxylic acids.

R-O–H^δ⁺llll^δ^–:O-R ... etc.

C-H stretching vibration absorption occurs ~2900 cm^-1, wavenumbers common to any molecule with alkyl groups.

C-C-C skeletal vibrations show absorptions at wavenumbers ~1175 to 1140 cm^-1 and 840 to 790 cm^-1 for a -C(CH₃)₂ grouping in propan-2-ol.

There are C-O stretching vibrations and C-H deformation vibration absorption bands of wavenumbers ~1350 to 1030 cm^-1, common to aliphatic alcohols like propan-2-ol.

The absence of other specific functional group bands will show that particular functional group is absent from the propan-2-ol molecular structure.

Questions

Some basic practice exam questions based on the infrared spectrum of propan-2-ol

Jot down your responses and check out the answers

Answer with as much reasoning as possible.

ANSWERS

If you think there are any errors, please email me asap at chem55555@hotmail.com

I don't mind if students/teachers do a selected printout of these questions and answers.

Q1 Which characteristic vibration would you expect for the infrared spectrum of propan-2-ol? and what wavenumber region?

Q2 What would be an obvious difference in the infrared spectrum of methoxyethane, another isomer of C₃H₈O?

Comparing the infrared, mass, 1H NMR and 13C NMR spectra of the 3 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.

	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.

	Comparing the mass 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 the mass spectra of the lower members of the homologous series of aliphatic alcohols and ethers
MASS SPECTRA (above): The base ion peaks are m/z 45 for propan-2-ol and methoxyethane, but that of propan-1-ol is m/z 31. Many of the fragmentation ions are common to all three spectra. The m/z 45 ion is peak is much smaller in the propan-1-ol spectrum compared to the other two.

	Comparing the 1H proton NMR 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 the 1H proton NMR spectra of the lower members of the homologous series of aliphatic alcohols and ethers
1H NMR SPECTRA (above): The 1H NMR spectra of all three molecules give different integrated proton ratios for the different ¹H chemical environments i.e. the proton ratios are as follows: propan-1-ol 3:2:2:1; propan-2-ol 6:1:1 and methoxyethane 3:2:3. Therefore, all three can be distinguished by their ¹H NMR spectra.

	Comparing the carbon-13 NMR 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 the carbon-13 NMR spectra of members of the lower members of the homologous series of aliphatic alcohols and ethers
13C NMR SPECTRA (above): The ¹³C NMR spectra of propan-1-ol and methoxyethane show three different ¹³C NMR chemical shifts, but propan-2-ol can be distinguished from the other two by exhibiting only two chemical shift lines. You would need other spectral data to distinguish propan-1-ol and methoxyethane.

Key words & phrases: CH3CHOHCH3 2-propanol isopropyl alcohol image and diagram explaining the infrared spectrum of propan-2-ol, complete infrared absorption spectrum of propan-2-ol, comparative spectra of propan-2-ol, prominent peaks/troughs for identifying functional groups in the infrared spectrum of propan-2-ol, important wavenumber values in cm-1 for peaks/troughs in the infrared spectrum of propan-2-ol, revision of infrared spectroscopy of propan-2-ol, fingerprint region analysis of propan-2-ol, how to identify propan-2-ol from its infrared spectrum, identifying organic compounds like propan-2-ol from their infrared spectrum, how to analyse the absorption bands in the infrared spectrum of propan-2-ol detection of alcohol hydroxyl functional groups in the propan-2-ol molecule example of the infrared spectrum of a molecule like propan-2-ol with a functional group ? 2-propanol isopropyl alcohol isomer of molecular formula C3H8O Diagram of absorption of wavenumber peaks in the infrared spectrum of propan-2-ol 2-propanol. Characteristic peak wavenumbers in the infrared spectrum of propan-2-ol 2-propanol. Finger print identification pattern using the infrared spectrum of propan-2-ol 2-propanol. Revision notes on the infrared spectrum of propan-2-ol 2-propanol. Matching and deducing the structure of the propan-2-ol 2-propanol molecule from its infrared spectrum. Infrared spectroscopy of aliphatic secondary alcohols, infrared spectra of propan-2-ol 2-propanol, an isomer of molecular formula C3H8O Explanatory diagram of the infrared spectrum of the propan-2-ol 2-propanol molecule in terms of its molecular structure. Listing data of the prominent main wavenumber peaks troughs in the infrared spectrum of propan-2-ol 2-propanol. How to explain the infrared spectrum of propan-2-ol 2-propanol. Use of the infrared spectrum of propan-2-ol 2-propanol, identification of propan-2-ol 2-propanol from its infrared spectrum - fingerprint wavenumber pattern to identify the propan-2-ol 2-propanol molecule. The uses of the infrared spectrum of the propan-2-ol 2-propanol molecule. The distinctive features of the infrared spectrum of the propan-2-ol 2-propanol molecule explained. explaining the peaks-trough of the transmittance of the infrared spectrum of propan-2-ol 2-propanol what does the infrared spectrum tell you about the structure and properties of the propan-2-ol 2-propanol molecule? How do you interpret the infrared absorption spectrum of propan-2-ol How to interpret the infrared spectrum of propan-2-ol Explanatory diagram of the infrared spectrum of the propan-2-ol molecule in terms of its molecular structure. Listing data of the prominent main wavenumber peaks troughs in the infrared spectrum of propan-2-ol. How to explain the infrared spectrum of propan-2-ol. Use of the infrared spectrum of propan-2-ol, identification of propan-2-ol from its infrared spectrum - fingerprint wavenumber pattern to identify the propan-2-ol molecule. The uses of the infrared spectrum of the propan-2-ol molecule. The distinctive features of the infrared spectrum of the propan-2-ol molecule explained interpretation diagram explaining the peaks-trough of the transmittance of the infrared spectrum of propan-2-ol what does the infrared spectrum tell you about the structure and properties of the propan-2-ol molecule? How is infrared spectrum of propan-2-ol used to identify propan-2-ol?

Links associated with propan-2-ol

The chemistry of ALCOHOLS revision notes INDEX

The mass spectrum of Propan-2-ol (2-propanol, isopropyl alcohol)

The H-1 NMR spectrum of Propan-2-ol (2-propanol, isopropyl alcohol)

The C-13 NMR spectrum of Propan-2-ol (2-propanol, isopropyl alcohol)

Infrared spectroscopy index

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ANSWERS to the practice exam questions based on the infrared spectrum of propan-2-ol.

Q1 Which characteristic vibration would you expect for the infrared spectrum of propan-2-ol? and what wavenumber region?

ANSWER: Around ~3500 to 3200 cm^-1, characteristic of the stretching vibrations of the hydroxyl group of alcohols.

Q2 What would be an obvious difference in the infrared spectrum of methoxyethane, another isomer of C₃H₈O?

ANSWER: No OH stretching vibration, but would still have C-O stretching vibrations.

For more information see Isomers of molecular formula C₃H₈O (M_r = 60)

The infrared spectrum of Propan-1-ol

and The infrared spectrum of methoxyethane

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