Functional Groups: Classification of Organic Compounds (DP IB Chemistry: SL): Exam Questions

Organic compounds are classified into families called a homologous series.

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

The table below shows the boiling points of the first five members of the alkane family.

 On the axes below, 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. 

Estimated boiling point of hexane : ________ ^oC

i) State the general formula for an alkyne.

[1]

ii) Give the molecular formula and name of the fifth member of the alkyne family.

[1]

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.

The molecular formula C₈H₁₀ corresponds to four aromatic isomers which all contain a single benzene ring.

One isomer is ethylbenzene. The other three are positional isomers of dimethylbenzene.

Draw the skeletal formula for ethylbenzene and 1,4-dimethylbenzene.

State the IUPAC name for the other two positional isomers of dimethylbenzene.

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.  

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

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.

Unsaturated carboxylic acids are a class of organic compounds found widely in nature.

The structure of oleic acid is shown below.

State the molecular formula and the empirical formula of oleic acid.

Crotonic acid, C₄H₆O₂, is a simpler unsaturated carboxylic acid.

Draw the displayed formula of the two positional isomers of butenoic acid.

Draw the displayed formula of a branched-chain isomer of butenoic acid.

A chemist is analysing the four compounds shown in the table.

Compound	Structure
1
2
3
4

i) Determine the molecular formula of Compound 1.

[1]

ii) Determine the empirical formula of Compound 4.

[1]

State the IUPAC name for Compound 2 and Compound 3.

A student suggests using acidified potassium dichromate(VI) to distinguish between Compound 1 and Compound 3.

i) Explain why this test would not distinguish between the two compounds.

[1]

ii) Describe a different simple chemical test that would distinguish between the two compounds, stating the expected observation for each.

[2]

Describe a chemical test, other than using bromine water, that would distinguish Compound 2 from Compound 4. State the expected results for both compounds.

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.

Isomers are molecules with the same molecular formula but different structural formulas. The properties and classification of isomers depend on their structure.

The molecular formula C₆H₁₄ corresponds to several alkane isomers.

i) Deduce the number of structural isomers of C₆H₁₄.

[1]

ii) State the IUPAC name of two branched-chain isomers of C₆H₁₄.

[2]

The formula C₆H₁₂ represents a different homologous series.

i) Draw the skeletal formula of one cyclic isomer of C₆H₁₂.

[1]

ii) State the general formula for a non-cyclic alkene.

[1]

Draw the structural formula and state the IUPAC name for a branched-chain isomer of C₆H₁₂ that has the parent name "-pent-1-ene".

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

Identify the class of amine for the two amine functional groups, labelled x and y, present in the molecule

Determine the molar mass of clenbuterol. Show your working

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

Illustrate the types of isomerism shown by C₃H₆O₃.