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Advanced Organic Chemistry: Infrared spectrum of propan-2-ol

Interpreting the infrared spectrum of propan-2-ol  (2-propanol)

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 involving molecular spectroscopy analysing infrared spectra of propan-2-ol

See also comparing the infrared, mass, 1H NMR and 13C NMR spectra of the 3 isomers of C3H8O

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, alcohols and ether structure and naming (c) doc b , alcohols and ether structure and naming (c) doc balcohols and ether structure and naming (c) doc b , alcohols and ether structure and naming (c) doc b

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.

infrared spectrum of ethanol diagram of intermolecular hydrogen bonding forces between liquid alcohol molecules doc brown A level organic chemistry revision notes R-O–Hδ+llllδ: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 vibration 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.

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.

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.

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


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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