1.3 Carboxylic acids, amines and carboxlyic acid derivatives  (Page 2/2)

The carbonyl group

The carbonyl group (-CO) consists of a carbon atom that is joined to an oxygen by a double bond. If the functional group is on the end of the carbon chain, the organic compound is called a ketone . The simplest ketone is acetone , which contains three carbon atoms. A ketone has the ending 'one' in its IUPAC name.

Carboxylic acids, esters, amines and ketones

1. Look at the list of organic compounds in the table below:

   Organic compound	Type of compound
   CH ${}_3$ CH ${}_2$ CH ${}_2$ COOH
   NH ${}_2$ CH ${}_2$ COOH
   propyl ethanoate
   CH ${}_3$ CHO

   1. Complete the table by identifying each compound as either a carboxylic acid, ester, amine or ketone.
   2. Give the name of the compounds that have been written as condensed structural formulae.
2. A chemical reaction takes place and ethyl methanoate is formed.
   1. What type of organic compound is ethyl methanoate?
   2. Name the two reactants in this chemical reaction.
   3. Give the structural formula of ethyl methanoate.

Summary

• Organic chemistry is the branch of chemistry that deals with organic molecules. An organic molecule is one that contains carbon.
• All living organisms contain carbon. Plants use sunlight to convert carbon dioxide in the air into organic compounds through the process of photosynthesis . Animals and other organisms then feed on plants to obtain their own organic compounds. Fossil fuels are another important source of carbon.
• It is the unique properties of the carbon atom that give organic compounds certain properties.
• The carbon atom has four valence electrons , so it can bond with many other atoms, often resulting in long chain structures. It also forms mostly covalent bonds with the atoms that it bonds to, meaning that most organic molecules are non-polar .
• An organic compound can be represented in different ways, using its molecular formula , structural formula or condensed structural formula .
• If two compounds are isomers , it means that they have the same molecular formulae but different structural formulae.
• A functional group is a particular group of atoms within a molecule, which give it certain reaction characteristics. Organic compounds can be grouped according to their functional group.
• The hydrocarbons are organic compounds that contain only carbon and hydrogen. They can be further divided into the alkanes, alkenes and alkynes, based on the type of bonds between the carbon atoms.
• The alkanes have only single bonds between their carbon atoms and are unreactive.
• The alkenes have at least one double bond between two of their carbon atoms. They are more reactive than the alkanes.
• The alkynes have at least one triple bond between two of their carbon atoms. They are the most reactive of the three groups.
• A hydrocarbon is said to be saturated if it contains the maximum possible number of hydrogen atoms for that molecule. The alkanes are all saturated compounds.
• A hydrocarbon is unsaturated if it does not contain the maximum number of hydrogen atoms for that molecule. The alkenes and alkynes are examples of unsaturated molecules. If a double or triple bond is broken, more hydrogen atoms can be added to the molecule.
• There are three types of reactions that occur in the alkanes: substitution , elimination and oxidation reactions.
• The alkenes undergo addition reactions because they are unsaturated.
• Organic compounds are named according to their functional group and its position in the molecule, the number of carbon atoms in the molecule and the position of any double and triple bonds. The IUPAC rules for nomenclature are used in the naming of organic molecules.
• Many of the properties of the hydrocarbons are determined by their molecular structure , the bonds between atoms and molecules, and their surface area .
• The melting point and boiling point of the hydrocarbons increases as their number of carbon atoms increases.
• The molecular mass of the hydrocarbons determines whether they will be in the gaseous, liquid or solid phase at certain temperatures.
• An alcohol is an organic compound that contains a hydroxyl group (-OH).
• The alcohols have a number of different uses including their use as a solvent, for medicinal purposes and in alcoholic drinks.
• The alcohols share a number of properties because of the hydroxyl group. The hydroxyl group affects the solubility of the alcohols. Those with shorter carbon chains are generally more soluble, and those with longer chains are less soluble. The strong hydrogen bond between the hydrogen and oxygen atoms in the hydroxyl group gives alcohols a higher melting point and boiling point than other organic compounds. The hydroxyl group also gives the alcohols both acidic and basic properties.
• The carboxylic acids are organic acids that contain a carboxyl group with the formula -COOH. In a carboxyl group, an oxygen atom is double-bonded to a carbon atom, which is also bonded to a hydroxyl group.
• The carboxylic acids have weak acidic properties because the hydrogen atom is able to dissociate from the carboxyl group.
• An ester is formed when an alcohol reacts with a carboxylic acid.
• The amines are organic compounds that contain an amino functional group, which has the formula -NH ${}_2$ . Some amines belong to the amino acid group, which are the building blocks of proteins.
• The ketones are a group of compounds that contain a carbonyl group , which consists of an oxygen atom that is double-bonded to a carbon atom. In a ketone, the carbonyl group is on the end of the carbon chain.

Summary exercise

1. Give one word for each of the following descriptions:
   1. The group of hydrocarbons to which 2-methyl-propene belongs.
   2. The name of the functional group that gives alcohols their properties.
   3. The group of organic compounds that have acidic properties.
   4. The name of the organic compound that is found in vinegar.
   5. The name of the organic compound that is found in alcoholic beverages.
2. In each of the following questions, choose the one correct answer from the list provided.
   1. When 1-propanol is oxidised by acidified potassium permanganate, the possible product formed is...
      1. propane
      2. propanoic acid
      3. methyl propanol
      4. propyl methanoate
      (IEB 2004)
   2. What is the IUPAC name for the compound represented by the following structural formula?

      

      1. 1,2,2-trichlorobutane
      2. 1-chloro-2,2-dichlorobutane
      3. 1,2,2-trichloro-3-methylpropane
      4. 1-chloro-2,2-dichloro-3-methylpropane
      (IEB 2003)
3. Write balanced equations for the following reactions:
   1. Ethene reacts with bromine
   2. Ethyne gas burns in an excess of oxygen
   3. Ethanoic acid ionises in water
4. The table below gives the boiling point of ten organic compounds.

   	Compound	Formula	Boiling Point ( ${}^0$ C)
   1	methane	CH ${}_4$	-164
   2	ethane	C ${}_2$ H ${}_6$	-88
   3	propane	C ${}_3$ H ${}_8$	-42
   4	butane	C ${}_4$ H ${}_{10}$	0
   5	pentane	C ${}_5$ H ${}_{12}$	36
   6	methanol	CH ${}_3$ OH	65
   7	ethanol	C ${}_2$ H ${}_5$ OH	78
   8	propan-1-ol	C ${}_3$ H ${}_7$ OH	98
   9	propan-1,2-diol	CH ${}_3$ CHOHCH ${}_2$ OH	189
   10	propan-1,2,3-triol	CH ${}_2$ OHCHOHCH ${}_2$ OH	290

   The following questions refer to the compounds shown in the above table.
   1. To which homologous series do the following compounds belong?
      1. Compounds 1,2 and 3
      2. Compounds 6,7 and 8
   2. Which of the above compounds are gases at room temperature?
   3. What causes the trend of increasing boiling points of compounds 1 to 5?
   4. Despite the fact that the length of the carbon chain in compounds 8,9 and 10 is the same, the boiling point of propan-1,2,3-triol is much higher than the boiling point of propan-1-ol. What is responsible for this large difference in boiling point?
   5. Give the IUPAC name and the structural formula of an isomer of butane.
   6. Which one of the above substances is used as a reactant in the preparation of the ester ethylmethanoate?
   7. Using structural formulae, write an equation for the reaction which produces ethylmethanoate.
   ( IEB 2004 )
5. Refer to the numbered diagrams below and then answer the questions that follow.

   

   1. Which one of the above compounds is produced from the fermentation of starches and sugars in plant matter?
      1. compound 1
      2. compound 2
      3. compound 3
      4. compound 4
   2. To which one of the following homologous series does compound 1 belong?
      1. esters
      2. alcohols
      3. aldehydes
      4. carboxylic acids
   3. The correct IUPAC name for compound 3 is...
      1. 1,1-dibromo-3-butyne
      2. 4,4-dibromo-1-butyne
      3. 2,4-dibromo-1-butyne
      4. 4,4-dibromo-1-propyne
   4. What is the correct IUPAC name for compound 4?
      1. propanoic acid
      2. ethylmethanoate
      3. methylethanoate
      4. methylpropanoate
   IEB 2005
6. Answer the following questions:
   1. What is a homologous series?
   2. A mixture of ethanoic acid and methanol is warmed in the presence of concentrated sulphuric acid.
      1. Using structural formulae, give an equation for the reaction which takes place.
      2. What is the IUPAC name of the organic compound formed in this reaction?
   3. Consider the following unsaturated hydrocarbon:

      

      1. Give the IUPAC name for this compound.
      2. Give the balanced equation for the combustion of this compound in excess oxygen.
   (IEB Paper 2, 2003)
7. Consider the organic compounds labelled A to E. A. CH ${}_3$ CH ${}_2$ CH ${}_2$ CH ${}_2$ CH ${}_2$ CH ${}_3$ B. C ${}_6$ H ${}_6$ C. CH ${}_3$ -Cl D. Methylamine

   

   1. Write a balanced chemical equation for the preparation of compound C using an alkane as one of the reactants.
   2. Write down the IUPAC name for compound E.
   3. Write down the structural formula of an isomer of compound A that has only FOUR carbon atoms in the longest chain.
   4. Write down the structural formula for compound B.