21.1 Spectroscopic Identification of Organic compounds

An organic compound, Q, of molecular formula C_xH_yO_z, has the following MS. Use section 28 of the Data booklet to help you answer this question.

The IR spectrum of Q is shown below. 

Suggest which functional group(s) could be present in Q.

The ¹H NMR spectrum of Q is shown below.

Explain the relative peaks heights and splitting patterns

Suggest the identity of Q, giving your reasons.

Compound A, has molecular formula C₅H₁₀ and occurs as 6 isomers. The table below shows the number of signals in the NMR spectrum of each isomer.

Suggest a structure for A and F.

The IR spectrum of A is shown below.

How does this spectrum distinguish A from the other isomers?

Evaluate whether X-ray crystallography could distinguish between the isomers of A.

Oseltamivir is a drug used to treat and prevent influenza A and influenza B.

Predict the number of different proton environments in the molecule.

Predict the chemical shift and the splitting pattern seen for the hydrogens on the carbon atom circled in the diagram. Use section 27 of the Data booklet.

Predict three absorptions you would expect to see in the IR spectrum of oseltamivir. Use section 26 of the data booklet. 

Ibuprofen is an important painkilling drug. The structure is:

Part of the low resolution ¹H NMR spectrum is shown below.

The high resolution expansion of the peaks in B-F is:

The protons responsible for the peaks are numbered 1-7:

Complete the table to show the assignment of the missing peaks. 

A sample of ibuprofen shows strong absorptions at 1716 cm^-1 and 3345 cm^-1 in an IR spectrum. Suggest the bonds responsible for these absorptions using section 26 of the data booklet. 

A sample of ibuprofen rotates plane polarised light. Identify the feature in ibuprofen responsible for this.

During the production of an ¹H NMR spectrum, tetramethylsilane (TMS) is mixed with the sample. 

Predict the number of peaks in the ¹H NMR spectrum of 1,3-dichlorobenzene.

The structural formula of ethylbenzene is shown below in Figure 1. 

Figure 1  

Predict the splitting patterns of the signals due to the ethyl group found in the ¹H NMR spectrum of ethylbenzene.

Methyl cinnamate, C₁₀H₁₀O₂, is a white crystalline solid used in the perfume industry. A sample of methyl cinnamate was analysed by ¹H NMR spectroscopy.

A simplified spectrum is shown below.

This question is about the use of ¹H NMR spectroscopy to distinguish between isomers of C₆H₁₂O₂. 

Draw the two esters with formula C₆H₁₂O₂ that each have only two peaks, both singlets, in their ¹H NMR spectra. The relative peak areas are 3:1 for both esters.

The high resolution ¹H NMR spectrum of another isomer of C₆H₁₂O₂ is shown below.

The integration values for the peaks in the ¹H NMR spectrum of this isomer, are given below.

Explain why the splitting patterns of these peaks are produced.

Four isomers of C₆H₁₂O₂ are shown below.

Which isomer matches the ¹H NMR spectrum below? Justify your choice.

X- ray crystallography is a spectroscopy technique use to determine structural Information. State two pieces of information found by this technique.

X ray crystallography enables chemists to produce electron density maps for substances, such as sodium chloride, shown below.

Estimate the interionic bond length and state which of the two patterns, A or B, belongs to the chloride ion.

Using Sections 26 & 27 of the Data Booklet and other sources, state three pieces of different spectroscopic evidence that would give structural information to identify benzene.

The ester shown below was analysed by high resolution ¹H NMR spectroscopy.

The ¹H NMR spectrum shown was produced for this ester.

Explain the splitting pattern marked on the spectrum. 

An isomer with the molecular formula C₅H₁₀O₂ was analysed by infrared spectroscopy, to confirm it was a carboxylic acid.

This question is about two aldehydes, 2-aminopropanal and 3-aminopropanal.

Explain how ¹H NMR spectra can be used to distinguish between these two aldehydes. You need to reference the splitting patterns and integration pattern in your answer.

Suggest how the two isomers in part b) could be distinguished using mass spectroscopy.

A compound X has a molecular formula of C₆H₁₄O. The infrared spectrum and ¹H NMR spectrum of compound X are shown below.  

Use Section 26 from the Data Booklet, deduce the structure of compound X. Justify each of your deductions.