Functional Groups: Classification of Organic Compounds (HL IB Chemistry)

Organic compounds are classified into families called a homologous series.

State three features of members belonging to the same homologous series.

Table 1 shows the boiling points of the first five members of the alkane family.

 Table 1

On the axes below in Figure 1, draw a graph of boiling point against the number of carbon atoms in the alkanes. Estimate the boiling point of the next member of the homologous series, hexane, C₆H₁₄, and show on your graph how you arrived at your estimated boiling point. 

Figure 1

Estimated boiling point of hexane : ________ ^oC

State the general formula for an alkyne and give the molecular formula and name of the fifth member of the alkyne family.

The boiling point of ethyne, C₂H₂, is -84 ^oC.

State with, with a reason, whether the boiling point of ethyne would be expected to be higher or lower than the boiling point of ethane, C₂H₆.

Geraniol is a colourless component of rose oil whose structure is shown in Figure 1.

 Figure 1

Butan-2-ol is an organic compound used industrially to make butanone.

Draw and name all the branched-chain isomers of butan-2-ol.

State, with a reason, the class of alcohols which butan-2-ol belongs to.

The formulae of four organic compounds are given in Table 1. Write the names of the compounds in the second column.

Table 1

Which of the compounds in part (a) are structural isomers of each other and what type of isomerism do they show?

Propofol is a drug used to reduce consciousness during medical procedures. The skeletal structure of propofol is given in Figure 1.

Figure 1

Valeric acid, C₅H₁₀O₂, is a straight chain carboxylic acid found in the plant Valeriana officinalis.

Draw and name all the possible isomers of C₆H₁₄.

Figure 1 below shows a three-dimensional structure of a molecule.                                                  

Figure 1 

Often, scientists will use analytical techniques such as infrared spectroscopy to determine if a desired reaction has taken place.    Outline how infrared spectroscopy generates useful information about an organic molecule.

A chemist uses infrared spectroscopy to distinguish between two organic molecules, a primary alcohol, and an aldehyde. 

Use section 20 of the data booklet to state, with a reason, how the chemist could use the IR spectra produced to distinguish between these two molecules.

The chemist fully oxidized the alcohol from part (b) and used IR spectroscopy to prove that the reaction had taken place. 

State how the chemist could use infrared spectroscopy to determine that the reaction had taken place. Use section 20 of the data booklet to support your answer.

Toluene is a common organic chemical with many industrial and commercial applications. Toluene is also known as methylbenzene. 

Draw the molecular structure of toluene.  

State the number of ¹H NMR signals that would be seen on the NMR spectrum of toluene and state the ratio of the area under the peaks in which they would appear.  

Another derivative of benzene has the molecular formula C₈H₁₀. 

Draw the structures of the four possible isomers of this derivative.

Infrared spectroscopy is a common analytical tool used in chemistry, to identify or distinguish between different organic compounds. These could be compounds such as toluene which contain a benzene ring, or any other organic compound. IR is often used alongside other analytical tools, such as mass spectrometry, to help identify the unknown. 

An organic molecule, J, has the following composition by mass.  

            62.1% carbon

            10.3% hydrogen 

            27.6% oxygen

In the mass spectrum of J, the molecular ion peak has a value of m/z = 116. 

The analytical instruments used for identification of organic compounds are constantly being improved.            

 Mass spectroscopy is one such analytical tool which provides key information used to identify an unknown compound. 

An unknown compound has the empirical formula C₂H₄O, and its mass spectrum has a molecular ion peak at m/z 84.

Deduce the molecular formula of the compound.  

Figure 1 below shows the IR spectrum of the unknown compound in part (a). 

Identify the bonds which are causing peak X and peak Y on the spectrum, using section 20 of the data booklet.

Figure 1

The unknown compound is a carboxylic acid. Deduce the two possible carboxylic acid structural isomers.  

For each of the isomers drawn in part (c), state the number of signals which would be seen in an ¹H NMR spectrum and the ratio of the areas under the peaks.

A group of students are asked to distinguish between four samples of different organic compounds.            

The four samples are as follows: 

• A primary alcohol 
• A tertiary alcohol 
• An aldehyde 
• A carboxylic acid

Describe how the group of students could distinguish between the two different alcohols.

One of the students wanted to distinguish between three compounds using mass spectrometry alone. The three compounds are shown below in Figure 1 and the mass spectrum for one of the compounds is shown in Figure 2.

Figure 1

Figure 2

Explain, using Figure 2,  why determining the exact mass using mass spectrometry alone would not help in distinguishing between the samples of X, Y and Z shown in Figure 1.

The three compounds from Figure 1 in part (b) were analysed using IR spectroscopy. 
 The spectrum of one of the compounds is shown below: 

Figure 3

Identify which of the three compounds X, Y or Z this spectrum belongs to. Justify your choice. 

State, with a reason, how infrared spectroscopy would be used to distinguish between the compounds X and Y from Figure 1 in part (b).

A molecule of oleic acid is shown.

Oleic acid is a fatty acid which occurs naturally in different animals and plants.

Oleic acid exhibits stereoisomerism. Explain the meaning of this term and identify why oleic acid has stereoisomers.

Crotonic acid is another fatty acid which has a similar structure to oleic acid. The molecular formula of crotonic acid is C₄H₆O₂. 

A chemist is analysing a collection of organic compounds. The structural formulae of these compounds are shown.

Give the IUPAC name for the compounds to complete the table.

This question refers to the compounds in the table in part (a)

2-methylbut-2-ene can be converted into 2-methylbutan-2-ol, a liquid that smells of camphor. 

State the reagents needed to convert 2-methylbut-2-ene into 2-methylbutan-2-ol.

The reaction in part (a) produces a small amount of an isomeric co-product, X, which is optically active. 

What does optical activity indicate about the structure of X?

Explain how optical activity can be detected using a polarimeter

Dichloroethene exists as two stereoisomers. Draw the structures of these isomers. 

Explain why dichloroethene has stereoisomers.

Draw the structures of the stereoisomers of 1-bromo-1-chloroethane, C₂H₄BrCl, and show the relationship between them.

Explain the differences in chemical and physical properties between the isomers of C₂H₄BrCl

Ethane-1,2-diol, C₂H₆O₂, can be distinguished from ethanedioic acid,C₂H₂O₄, by a number of analytic techniques including MS, IR and NMR 

The MS of these molecules is shown below. 

Which spectrum belongs to each molecule? Justify your answer.

 

Spectrum A

Spectrum B

The IR spectra of ethane-1,2-diol, C₂H₆O₂, and ethanedioic acid dihydrate, C₂H₂O₄.2H₂O, are shown in spectrum C and D. Use Section 20 of the Data Booklet to answer this question.

Spectrum CSpectrum D

Which spectrum belongs to each molecule? Justify your answer.

The ¹H NMR spectrum of ethane-1,2-diol is shown in spectrum E. Explain the significance of the spectrum.

Predict the number of ¹H NMR signals and splitting pattern for ethanedioic acid. 

During the production of a 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.

 [1]

Four isomers of C₆H₁₂O₂ are shown below.

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

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.  

Using Sections 20 and 21 from the Data Booklet, deduce the structure of compound X. Justify each of your deductions.

State the IUPAC names for the isomers of C₅H₁₂O that are primary alcohols.

State the IUPAC name for the following primary alcohols.

Draw the displayed formula for a straight chain isomer of CH₂(Br)CH(CH₃)CH₂OH.

The empirical formula of the compound in part b) i). 

Phenacetin is a pain killer though the use of this was banned as it was found to cause harm to kidney function.

Deduce the molecular formula of phenacetin. 

Identify the names of the three functional groups present in phenacetin.

Aspirin is a common pain killer and has the following structure.

State the empirical formula of aspirin.

Aspirin is formed from ethanoic anhydride and compound A. State the IUPAC name of compound A.

State the IUPAC names of two branched isomers of C₅H₁₀ that contain a π bond. 

An alcohol can be prepared by hydrolysing the halogenoalkane C₂H₅CHBClCH₃ with aqueous sodium hydroxide. The infrared spectrum for C₂H₅CHClCH₃  is shown below with the C–Cl bond absorption labelled.

Using section 20 of the data booklet deduce how IR spectroscopy will change as a result of the above reaction.

The mass spectrum of (CH₃)₂CHCH₂OH is shown below.

Deduce which ion is responsible for the peak with the greatest relative intensity.

Alcohol X has the following percentage composition by mass. Carbon = 68.2%, hydrogen = 13.6%, oxygen = 18.2%. The molecular ion peak in the mass spectrum for alcohol X occurs at m/z = 88.

The mass spectrum of alcohol X has a major peak at m/z = 45.

Clenbuterol, shown below, is considered a performance enhancing drug and is believed to increase short term work rate and cardiovascular output.

Deduce the functional groups marked x and y and state to which class they belong to.

Determine the m/z value of the molecular ion, M⁺, of clenbuterol. Justify your answer.

Two students, P and Q, were provided with the mass spectrum of an alkane, shown in below. Student P analysed peaks a and b and concluded that the alkane was one of two structures. Student Q analysed peaks a, b and c and was able to identify one possible alkane structure.

Four samples containing isomeric alcohols with molecular formula C₄H₁₀O, were studied using ¹H NMR spectroscopy

Draw structural formulas of the alcohols and deduce the number of peaks in the NMR spectrum of each alcohol

Two of the alcohols produce the same number of peaks in an ¹H NMR spectrum. Suggest how they may be distinguished, by further spectroscopy analysis.

Compound A can be converted into compound B via an intermediate species.

Suggest how you would be able to determine the difference between Compounds A and B by analysis of their ¹H NMR spectra.

Malonic acid, C₃H₄O₄, is naturally occurring and found in many fruits and vegetables. It contains only carbon, hydrogen and oxygen.

The MS of malonic acid is show below.

Determine the relative molecular mass of malonic acid from the spectrum and account for the peak at m/z 45, using section 22 of the Data booklet to support your answer.

The ¹H NMR spectrum of malonic acid is shown below. Use section 21 of the Data booklet to help you with this question.

Suggest the identity of the proton environments seen in the spectrum and comment on the type of signals shown.

The IR spectrum of malonic acid is shown below:

Draw a displayed structure for malonic acid.

An organic compound, Q, of molecular formula C_xH_yO_z, has the following MS. Use section 22 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 peak 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?

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 21 of the Data booklet.

Predict three absorptions you would expect to see in the IR spectrum of oseltamivir. Use section 20 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 20 of the data booklet. 

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

Cholesterol, shown below, is a fatty chemical used by the body to build healthy cells.

State the number of chiral carbons in the cholesterol structure.

A student suggested that cholesterol could be tested with plane polarised light to show that it contains chiral centres.

Is the student correct? Justify your answer.

Limonene, shown below, is a naturally occurring hydrocarbon with the molecular formula C₁₀H₁₆ and is commonly found in the rinds of citrus fruits such as grapefruit, lemon, lime and oranges.

Limonene exists as a pair of enantiomers; one enantiomer is responsible for a strong orange smell while the other is thought to smell like lemons.

Draw 3D representations of the two enantiomers of limonene.

Lactic acid has the molecular formula of C₃H₆O₃, and the structural formula of CH₃CHOHCOOH.

Illustrate the types of isomerism shown by C₃H₆O₃.

The general structure of polylactic acid is shown below:

Draw two possible structures formed from two repeating units. 

Your answer should keep the main polymer chain in the same plane but show the 3D representation of the chiral carbons.

State, why the polymer formed from the uncontrolled condensation polymerisation of lactic acid, is not a racemate.