You are commenting using your Google account. You are commenting using your Twitter account. You are commenting using your Facebook account. Notify me of new comments via email. Notify me of new posts via email. Skip to content. Introduction of Alkene Alkenes are a family of hydrocarbons compounds containing carbon and hydrogen only containing a carbon-carbon double bond. Physical Properties 1. Soluble in water but not inorganic solvents.
Held by weak van der Waals forces of attraction between covalent bonds. It is difficult to get enough oxygen to the flame to ensure complete combustion, so carbon appears in the flame which is seen as black specks. It also gives the flame its characteristic yellow colour. If a compound burns with a yellow flame it provides good evidence that the compound is unsaturated. Complete combustion would give carbon dioxide and water, although complete combustion clearly does not occur in this case:.
Alkenes rapidly decolourise acidified potassium manganate VII , and this is often used as a test for an alkene. With insufficient acid, a brown precipitate may form rather than decolourisation taking place.
Practically, this just means it requires more oxygen to burn cleanly because there are more C-C bonds with the double bond present to have to break up. You can use bromine water to test for alkenes : When an alkene solution is added to bromine water, the brown color of the bromine solution will go colorless. We say that alkenes decolorize bromine water. The brown color caused by bromine water disappears because bromine Br2 is being reacted away.
The double bond in the alkene molecule reacts with a bromine molecule and opens up in an addition reaction, using both reactant molecules up. A colorless dibromoalkane product forms in their place. Using the nomenclature in Organic chemistry introduction , we can name simple alkenes. See the table below for the first five alkenes.
Identify which carbon in the chain the alkene begins at, and use this number with '—ene' as the suffix. In simpler compounds, you can also add the number before the root for the carbon chain length, so butene could be 1-butene.
See the examples below: Remember that some alkenes have implicit numbering. Propene can only have the double bond between carbons 1 and 2. If it was between 2 and 3, the numbering would reverse. So propene is just propene. See the example: Compounds with more than one double bond have the '-ene' suffix changed to show which carbon atoms in the chain the double bonds are found at, and a prefix to say how many double bonds there are. Remember that alkenes with more than one double bond won't have the same general formula as simple alkanes!
Just like with branches in alkanes, the naming of such alkanes is done systematically: Two double bonds in the molecule: -diene Three double bonds in the molecule: -triene Four double bonds in the molecule: -tetraene See the example below: In more complicated compounds that have branched alkyl chains and double bonds, numbering your carbon chain should be done to give the alkene double bond the lowest numbering possible. This is because an alkene is a higher order functional group more on this later than alkyl chains, so the carbon chain 'starts' with the alkene.
See the example: Having a double bond changes the geometry of carbon atoms in a few ways: Carbon atoms with a double bond only bond to three atoms in total — two of its valence of four is used in the double bond, so only two other bonds are made.
This makes the molecule around the double bond flat. This double bond cannot freely rotate , unlike single covalent bonds which can. This part of the molecule is flat and locked in position , there is no rotation of the double bond like there is for single bonds.
This restricted rotation leads to Another type of hydrocarbon that is unsaturated are alkynes. The definition of an alkyne is an unsaturated hydrocarbon containing at least one carbon-carbon triple bond. Alkenes: introduction. Definitions, properties and uses of alkenes. Reactions and testing of alkenes.
Naming alkenes. Geometric E-Z isomers of alkenes. Alkynes: definition and properties. Recall the general formula of alkenes. Study the following chemical formulae and identify which fit the general formulae of an alkene. Recall the test to distinguish alkenes and alkanes.
A student has solutions of two simple hydrocarbons, chemical A and B, and adds them separately to two identical test tubes containing a solution of bromine water.
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