Organic molecules

Table of Contents

1. Organic molecules
2. Hydrocarbons
   1. Names and structures of hydrocarbons
3. Reactions of hydrocarbons
   1. Substitution reactions
   2. Addition reactions
4. Functional groups
   1. Identifying functional groups
5. Alcohols
   1. Structure of alcohols
   2. Physical properties of alcohols
6. Reactions of alcohols
   1. Oxidation reactions
   2. Carboxylic acids
   3. Alcohols, carboxylic acids and esters
   4. Identification of alcohols
7. Nitrogen in organic molecules
   1. Amines
   2. Amino acids
8. Determination of formulae and structures
   1. Empirical formulae
   2. Molecular mass and formula

1. Additional resources:
   1. Glossary
   2. Print content

Oxidation reactions

The concepts that you will need to use in this section are shown here:

• oxidation and reduction in terms of electrons
• oxidants (oxidising agents) and reductants (reducing agents)
• half-equations.

You may want to revise some of these areas at this point, especially how to combine half-equations.

What happens when alcohols are oxidised?

The best way to consider the oxidation of an alcohol molecule is the loss of two hydrogen atoms from the molecule. These are the hydrogen atom from the OH group and another hydrogen atom from the alcoholic carbon atom. Look out for this when watching the animations in the following sections.

This activity is in three parts, each part relating to a different alcohol.

[+] Expand all items

Primary alcohols

1

Oxidation products Complete the following sentences by filling in the blanks. The product from this reaction is an . In this case the name of the product is . This is an process because are being lost. Word bank: aldehyde, electrons, oxidation, propanal The product from this reaction is an aldehyde. In this case the name of the product is propanal. This is an oxidation process because electrons are being lost.

The redox reaction

This reaction will of course not happen without an oxidant (oxidising agent) being present. Common oxidants, such as permanganate (MnO₄^-) dichromate (Cr₂O₇^2-) can be used.

Can you write the overall equation for the reaction of potassium permanganate solution with propan-1-ol? Write the equation in your notes.

Use this link to access hints if required.

1. The half-equation for permanganate can be found on your data sheet.
2. When you combine the two half-equations, multiply the permanganate half-equation by two and the propan-1-ol half-equation by five so that the electrons cancel out.
3. Cancel out any hydrogen ions that appear on both sides of the equation.

When you have completed the equation check your answer here.

5 CH₃CH₂CH₂OH + 2 MnO₄^- + 6 H⁺ → 5 CH₃CH₂CHO + 2 Mn²⁺ + 8 H₂O

Note that the product of this reaction is an aldehyde. Aldehydes themselves can be oxidised and you will learn more about the oxidation of aldehydes later.

Secondary alcohols

From the video, write a two-dimensional representation of the process, and then show it as a simple half-equation.

The redox reaction

Can you write the overall equation for reaction of sodium dichromate (Na₂Cr₂O₇) solution with propan-2-ol?

Write the equation into your notes and then check the answer.
Check your version against the redox equation here.

(oxidation of propan-2-ol) CH₃CHOHCH₃ → CH₃COCH₃ + 2 H⁺ + 2 e^-

(reduction of dichromate) Cr₂O₇^2- + 14 H⁺ + 6 e^- → 2 Cr³⁺ + 7 H₂O

(Overall equation) 3 CH₃CHOHCH₃ + Cr₂O₇^2- + 8 H⁺ → 3 CH₃COCH₃ + 2 Cr³⁺ + 7 H₂O

2

Oxidation products Complete the following sentences by filling in the blanks. The product from this reaction is a . In this case the name of the product is . The colour changes observed in this reaction would be from caused by the ion to caused by the ion. Word bank: chromium(III), dichromate, green, ketone, orange, propanone The product from this reaction is a ketone. In this case the name of the product is propanone. The colour changes observed in this reaction would be from orange caused by the dichromate ion to green caused by the chromium(III) ion.

Have a look at the structure of the product of this oxidation of a secondary alcohol. There are no 'available' hydrogen atoms bonded to the carbon atom that was attached to the -OH functional group. This means that no further oxidation reaction of the ketone can take place. (This is different to the product of the oxidation of a primary alcohol, which can be oxidised further.)

Tertiary alcohols

3

Which of the following best explains why tertiary alcohols are not oxidised? a) The carbon chain is too short. b) Tertiary alcohols do not contain the -OH functional group. c) There is no hydrogen atom on the alcoholic carbon atom. d) They will require a stronger oxidising agent. Correct, well done.Incorrect. Two hydrogen atoms need to be lost from the molecule when the alcohol is oxidised.Your answer has been saved.