<< Chapter < Page Chapter >> Page >

Naming the alkenes

Give the IUPAC name for each of the following alkenes:

  1. CH 2 CHCH 2 CH 2 CH 3
  2. CH 3 CHCHCH 3

The properties of the alkenes

The properties of the alkenes are very similar to those of the alkanes, except that the alkenes are more reactive because they are unsaturated. As with the alkanes, compounds that have four or less carbon atoms are gases at room temperature, while those with five or more carbon atoms are liquids.

Reactions of the alkenes

Alkenes can undergo addition reactions because they are unsaturated. They readily react with hydrogen, water and the halogens. The double bond is broken and a single, saturated bond is formed. A new group is then added to one or both of the carbon atoms that previously made up the double bond. The following are some examples:

  1. A catalyst such as platinum is normally needed for these reactions H 2 C = C H 2 + H 2 H 3 C - C H 3 ( [link] )
    A hydrogenation reaction
  2. C H 2 = C H 2 + H B r C H 3 - C H 2 - B r ( [link] )
    A halogenation reaction
  3. C H 2 = C H 2 + H 2 O C H 3 - C H 2 - O H ( [link] )
    The formation of an alcohol

The alkenes

  1. Give the IUPAC name for each of the following organic compounds:
    1. CH 3 CHCH 2
  2. Refer to the data table below which shows the melting point and boiling point for a number of different organic compounds.
    Formula Name Melting point ( 0 C) Boiling point ( 0 C)
    C 4 H 10 Butane -138 -0.5
    C 5 H 12 Pentane -130 36
    C 6 H 14 Hexane -95 69
    C 4 H 8 Butene -185 -6
    C 5 H 10 Pentene -138 30
    C 6 H 12 Hexene -140 63
    1. At room temperature (approx. 25 0 C), which of the organic compounds in the table are:
      1. gases
      2. liquids
    2. In the alkanes...
      1. Describe what happens to the melting point and boiling point as the number of carbon atoms in the compound increases.
      2. Explain why this is the case.
    3. If you look at an alkane and an alkene that have the same number of carbon atoms...
      1. How do their melting points and boiling points compare?
      2. Can you explain why their melting points and boiling points are different?
    4. Which of the compounds, hexane or hexene, is more reactive? Explain your answer.
  3. The following reaction takes place: C H 3 C H C H 2 + H 2 C H 3 C H 2 C H 3
    1. Give the name of the organic compound in the reactants.
    2. What is the name of the product?
    3. What type of reaction is this?
    4. Which compound in the reaction is a saturated hydrocarbon?

The alkynes

In the alkynes, there is at least one triple bond between two of the carbon atoms. They are unsaturated compounds and are therefore highly reactive. Their general formula is C n H 2 n - 2 . The simplest alkyne is ethyne ( [link] ), also known as acetylene. Many of the alkynes are used to synthesise other chemical products.

Ethyne (acetylene)

Interesting fact

The raw materials that are needed to make acetylene are calcium carbonate and coal. Acetylene can be produced through the following reactions:

C a C O 3 C a O

C a O + 3 C C a C 2 + C O

C a C 2 + 2 H 2 O C a ( O H ) 2 + C 2 H 2

An important use of acetylene is in oxyacetylene gas welding. The fuel gas burns with oxygen in a torch. An incredibly high heat is produced, and this is enough to melt metal.

Naming the alkynes

The same rules will apply as for the alkanes and alkenes, except that the suffix of the name will now be -yne.

Give the IUPAC name for the following compound:

  1. There is a triple bond between two of the carbon atoms, so this compound is an alkyne. The suffix will be -yne. The triple bond is at the second carbon, so the suffix will in fact be 2-yne.

  2. If we count the carbons in a straight line, there are six. The prefix of the compound's name will be 'hex'.

  3. In this example, you will need to number the carbons from right to left so that the triple bond is between carbon atoms with the lowest numbers.

  4. There is a methyl (CH 3 ) group attached to the fifth carbon (remember we have numbered the carbon atoms from right to left).

  5. If we follow this order, the name of the compound is 5-methyl-hex-2-yne .

Got questions? Get instant answers now!

The alkynes

Give the IUPAC name for each of the following organic compounds.

  1. C 2 H 2
  2. CH 3 CH 2 CCH

Questions & Answers

Is the normal force always 0
Mpilo Reply
define the term rate of reaction in word
David Reply
I think it a chemical process in which substance act mutually on each other.
how many bones are in the human body?
what is wave lengh
mama Reply
is the de broglie wavelength of the particle
calcium and magnesium, which one can displace aluminum from its compound?
Markia Reply
how is aluminum ion formed?
molecules with the same molecular formula but different chain
Malaza Reply
what will be the answer
chain isomer
what does the newton's law says?
there are 3 newtons laws which are newton's law of universal gravitation, law of cooling, law of motion
Did the feather or leaf hit the ground first?
Shaloom Reply
2 to 30 minut long distance race 20 km what's the avarage speed for the race
Jamilla Reply
what is meaning of covalent bonds
Lungani Reply
bonds that exists between non metal atoms. each atom contribute electron(s) which will form a bond joining the two atoms. electrons in the bond now belongs to both atoms
how do we name haloalkanes
Thobeka Reply
how do we name haloalkanes
what are examples of haloalkanes
haloalkanes are compounds that consist of the halogen group chlorine bromine flourine and so on like 2-bromobutan
give an example of calculating work
Nwabisa Reply
what is chain Isomer?
Christian Reply
chain isomer ar compounds with the same molecular formular but different chain length
Where does the functional group of ketone in carbons belong
Keletso Reply
how can I find the structural formulae and IUPAC names of hexane?
Matshidiso Reply
@Matshidiso identify your compound which is an alkane..the general formula for alkane is CnH2n+2... hex-6 substitute n with 6 implying that you'll have 6 carbons and 14 Hydrogens then you can draw your structural formula *NB* every carbon has to have 4 bonds
what are disadvantages of primary cells and advantage of secondary cells?
Thabang Reply

Get the best Siyavula textbooks: gr... course in your pocket!

Source:  OpenStax, Siyavula textbooks: grade 12 physical science. OpenStax CNX. Aug 03, 2011 Download for free at http://cnx.org/content/col11244/1.2
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Siyavula textbooks: grade 12 physical science' conversation and receive update notifications?