C-13 nmr spectrum of propan-2-ol analysis of chemical shifts ppm interpretation of C-13 chemical shifts ppm of 2-propanol C13 13-C nmr doc brown's advanced organic chemistry revision notes

Advanced Organic Chemistry: Carbon-13 NMR spectrum of propan-2-ol CH₃CH(OH)CH₃

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Interpreting and explaining the 13C NMR 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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C-13 NMR spectroscopy - spectra index * A couple of basic practise questions

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Introductory note on the 13C NMR spectrum of propan-2-ol (2-propanol)

Students and teachers please note that my explanation of the carbon-13 NMR spectrum of propan-2-ol is designed for advanced, but pre-university, chemistry courses.

The description does not involve the chemical shift δ spin-spin coupling effects for propan-2-ol and the relative size of the carbon-13 NMR shifts does not give the ratio of the carbon atoms in the different non-equivalent chemical environments of the propan-2-ol molecule.

The most common solvent used for investigating the C13 NMR spectrum of compounds like propan-2-ol, is CDCl₃ and other deuterated solvents.

C-13 nmr spectrum of propan-2-ol analysis of chemical shifts ppm interpretation of C-13 chemical shifts ppm of 2-propanol C13 13-C nmr doc brown's advanced organic chemistry revision notes

TMS is the acronym for tetramethylsilane, formula Si(CH₃)₄, whose ¹³C atoms are arbitrarily given a chemical shift of 0.0 ppm. This is the 'standard' in ¹³C NMR spectroscopy and all other ¹³C shifts, called chemical shifts, depend on the individual (electronic) chemical environment of the ¹³C atoms in an organic molecule - propan-2-ol here.

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

The molecular structure and naming of aliphatic alcohols and ethers

Interpreting the C-13 NMR spectrum of propan-2-ol (2-propanol, isopropyl alcohol)

As you can see from the diagram above there are 2 different chemical shift lines in the C-13 NMR spectrum of propan-2-ol indicating 2 different chemical environments of the 3 carbon atoms.

(CH₃)₂CHOH or CH₃CH(OH)CH₃

(Note the 2 colours indicating the 2 different chemical environments of the carbon atoms in propan-2-ol).

The carbon atoms of the methyl groups i.e. inhabit the same ¹³C chemical environment in propan-2-ol observed as:

¹³C NMR shifts (a) for the carbon atoms of the two methyl groups, which are equivalent to each other, and,

(b) for the central carbon atom of the CHOH group.

Note the decreasing effect on the chemical shift as the carbon atom is further from the highly electronegative oxygen atoms of propan-2-ol.

The carbon-13 NMR spectra a provides direct evidence of 2 different carbon atom environments in the propan-2-ol molecule from 2 different chemical shifts (ppm).

Note that adding D₂O to the CDCl₃ solution of propan-2-ol has no effect on the 13C NMR spectrum, 13C NMR does not detect proton resonances!

Questions

Some basic practice exam questions based on the 13C NMR spectrum of propan-2-ol.

Jot down your responses and check out the answers

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.

Answer with as much reasoning as possible.

Q1 How many principal 13C NMR chemical shifts would you expect for propan-2-ol?

Q2 How would the ¹³C NMR spectrum of the C₃H₈O isomers propan-1-ol and methoxyethane compare with propan-2-ol?

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 13C NMR chemical shift lines (the methyl carbon atoms are in equivalent chemical environments in the propan-2-ol molecule). You would need other spectral data to distinguish propan-1-ol and methoxyethane.

Key words & phrases: 2-propanol isopropyl alcohol Interpreting the C-13 NMR spectra of propan-2-ol, C-13 nmr spectrum of propan-2-ol, understanding the carbon-13 nmr spectrum of propan-2-ol, explaining the line pattern in the high resolution C-13 nmr spectra of propan-2-ol, revising the C-13 nmr spectrum of propan-2-ol, ppm chemical shifts of the C-13 nmr spectrum of propan-2-ol, how to construct the diagram of the C-13 nmr spectrum of propan-2-ol, how to analyse the chemical shifts in the carbon-13 NMR spectrum of propan-2-ol deducing the chemical environment of all the carbon atoms in propan-2-ol examining the c13 nmr spectrum of propan-2-ol analysing the 13-c nmr spectrum of propan-2-ol how do you sketch and interpret the C-13 NMR spectrum of propan-2-ol 2-propanol isopropyl alcohol isomer of molecular formula C3H8O Molecular structure diagram of the carbon-13 NMR diagram for the 13C NMR spectrum of propan-2-ol 2-propanol. Deducing the number of different chemical environments of the carbon atoms in the propan-2-ol 2-propanol molecule from the 13C chemical shifts in the carbon-13 NMR spectrum of propan-2-ol 2-propanol. Revision notes on the carbon-13 NMR spectrum of propan-2-ol 2-propanol. Matching and deducing the structure of the propan-2-ol 2-propanol molecule from its 13C NMR spectrum. Carbon-13 NMR spectroscopy of aliphatic alcohols, 13C NMR spectra of propan-2-ol 2-propanol, an isomer of molecular formula C3H8O Explanatory diagram of the 13C C-13 carbon-13 NMR spectrum of the propan-2-ol 2-propanol molecule in terms of its molecular structure. Listing data of all the chemical shift peaks in ppm in the carbon-13 NMR spectrum of propan-2-ol 2-propanol. How to explain the C-13 NMR spectrum of propan-2-ol 2-propanol. How to deduce the number of different carbon atom environments in the propan-2-ol 2-propanol molecule from its carbon-13 NMR spectrum to help work out the molecular structure of the propan-2-ol 2-propanol molecule. The uses and distinctive features of the carbon-13 NMR spectrum of the propan-2-ol 2-propanol molecule explained. What does the c-13 carbon-13 NMR spectrum tell us about the propan-2-ol 2-propanol molecule? How do you interpret the chemical shifts of the C-13 NMR spectrum of propan-2-ol How to interpret the C-13 NMR spectrum of propan-2-ol Explanatory diagram of the 13C C-13 carbon-13 NMR spectrum of the number of different carbon atom environments in the propan-2-ol molecule from its carbon-13 NMR spectrum to help work out the molecular structure of the propan-2-ol molecule? The uses and distinctive features of the carbon-13 NMR spectrum of the propan-2-ol molecule explained. What do the number and values of the chemical shifts from the c-13 carbon-13 NMR spectrum tell us about the propan-2-ol molecule? explaining the decoupled carbon-13 NMR spectrum of propan-2-ol with a detailed interpretation diagram of all the C-13 chemical shifts and intensities

Links associated with propan-2-ol

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

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

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

C-13 NMR spectroscopy index

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ANSWERS to the practice exam questions based on the 13C NMR spectrum of propan-2-ol.

Q1 How many principal 13C NMR chemical shifts would you expect for propan-2-ol?

ANSWER: Two different ¹³C chemical environments, CH₃CH(OH)CH₃

Q2 How would the ¹³C NMR spectrum of the C₃H₈O isomers propan-1-ol and methoxyethane compare with propan-2-ol?

ANSWER: CH₃CH₂CH₂OH would show three principal 13C NMR chemical shifts and CH₃OCH₂CH₃ also three.

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

The C-13 NMR spectrum of Propan-1-ol

and The C-13 NMR spectrum of methoxyethane

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