LOGO Course lecturer : Jasmin Šutković 27 th April 2016 Chemistry - SPRING 2016 Lecture 10: Hydrocarbons

Contents International University of Sarajevo 1.Alkanes 2.Properties of Alkanes 3.Alkenes and Alkynes 4.Naming of hydrocarbons 5.Cis-Trans isomers 6.Aromatic compounds

Organic compounds  Organic compounds is the study of carbon containing molecules. Organic compounds ALWAYS contain carbon and hydrogen.  We found Organic compounds everywhere around: common products we use (gasoline, medicine, shampoos, plastics etc), in food we eat (carbohydrates, fats and proteins)

Bonding in Organic compounds  Hydrocarbon: compound made of carbon and hydrogen  Hydrocarbon is saturated where all bonds in the molecule all single bonds  CH4

Alkanes  The simples hydrocarbons are alkanes, having only single bonds (C-C) like CH4, C2H6, C3H8 etc..  The alkanes ethane, propane, and butane contain two, three, and four carbon atoms, respectively, connected in a row or a continuous chain. As we can see, the names for alkanes end in ane.  Such names are part of the IUPAC (International Union of Pure and Applied Chemistry) system used by chemists to name organic compounds.

IUPAC names of Alkanes

Molecular and Structural formulas

Drawing of structural formulas  Page 365, example 11.2  Pentane

Butane

Cycloalkanes  Cyclic or ring structures of alkanes are called cycloalkanes  The simplest is cyclopropane

Alkanes with substituent's  When an alkane has four or more carbon atoms, the atoms can be arranged so that a side group called a branch or substituent is attached to a carbon chain.

Examples

Naming

Haloalkanes

Properties of Alkanes  They make up: different types of fuels and mineral oils and their usage is supported by their physical properties (density and solubility)  The first four alkanes—methane, ethane, propane, and butane—are gases at room temperature and are widely used as heating fuels.  Alkanes having five to eight carbon atoms, pentane, hexane, heptane, and octane, are liquids at room temperature. They are highly volatile, which makes them useful in fuels such as gasoline

Alkenes and Alkynes  Alkenes are hydrocarbons that contain one or more carbon-to-carbon double bonds (C=C).  Double bonds are very reactive, they easily add hydrogen atoms (hydrogenation) or water (hydration) to the carbon atoms in the double bond. Example ethylene (ethene) C2H4

Example : Ethene (Acetylene)

Naming

Cis and Trans isomerism  In any alkene, the double bond is rigid, which means there is no rotation around the double bond.  As a result, the atoms or groups are attached to the carbon atoms in the double bond on one side or the other, which gives two different structures called geometric isomers or cis – trans isomers.

Example

Cis–Trans Isomers for Night Vision  The retinas of the eyes consist of two types of cells: rods and cones.  The rods on the edge of the retina allow us to see in dim light, and the cones, in the center, produce our vision in bright light.  In the rods, there is a substance called rhodopsin that absorbs light. Rhodopsin is composed of cis-11-retinal, an unsaturated compound, attached to a protein.  When rhodopsin absorbs light, the cis-11-retinal isomer is converted to its trans isomer, which changes its shape.  The change from the cis to trans isomer and its separation from the protein generate an electrical signal that the brain converts into an image.

Addition reactions  The most characteristic reaction of alkenes is the addition of atoms or groups of atoms to the carbon atoms in a double bond. Addition occurs because double bonds are easily broken, providing electrons to form new single bonds.  The addition reactions have different names that depend on the type of reactant we add to the alkene, as Table 11.7 shows.

Hydrogenation  In a reaction called hydrogenation, H atoms add to each of the carbon atoms in a double bond of an alkene. During hydrogenation, the double bonds are converted to single bonds in alkanes.  A catalyst such as finely divided platinum (Pt) nickel (Ni), or palladium (Pd) is used to speed up the reaction.  The general equation for hydrogenation can be written as follows:

Examples:

 In hydration, an alkene reacts with water (H-OH).  A hydrogen atom (H-) from water forms a bond with one carbon atom in the double bond, and the oxygen atom in (-OH) forms a bond with the other carbon.  The reaction is catalyzed by a strong acid such as H2SO4.  Hydration is used to prepare alcohols, which have the hydroxyl (-OH) functional group.

Examples

Aromatic Compounds  Benzen – C6H6,1825 isolated by Michael Faraday  Because many compounds containing benzene have fragrant odors, the family of benzene compounds became known as aromatic compounds.