Alkenes 12/1/2018 Dr seemal Jelani

Alkenes Ethene (ethylene) C2H4 C3H6 Propene C4H8 Butene C5H10 Pentene Name Alkenes Molecular formula Ethene (ethylene) Propene Butene Pentene C2H4 C3H6 C4H8 C5H10 12/1/2018 Dr seemal Jelani

Alkenes are also called olefins. Alkenes contain a carbon—carbon double bond. Terminal alkenes have the double bond at the end of the carbon chain Internal alkenes have at least one carbon atom bonded to each end of the double bond. Cycloalkenes contain a double bond in a ring. 12/1/2018 Dr seemal Jelani

12/1/2018 Dr seemal Jelani

The double bond consists of a  bond and a  bond. Each carbon is sp2 hybridized and trigonal planar, with bond angles of approximately 120°. 12/1/2018 Dr seemal Jelani

Terpenes 12/1/2018 Dr seemal Jelani

12/1/2018 Dr seemal Jelani

12/1/2018 Dr seemal Jelani

12/1/2018 Dr seemal Jelani

Terpenes Any of a large group of volatile unsaturated hydrocarbons found in the essential oils of plants, especially conifers and citrus trees. They are based on a cyclic molecule having the formula C10H16. 12/1/2018 Dr seemal Jelani

Alkenes and alkene derivatives are responsible for the odor of many plants Structure is based on a five-carbon diene called Isoprene (2-methyl-1,3-butadiene) 12/1/2018 Dr seemal Jelani

The isoprene structural unit is encountered in Terpenes in several variant forms that differ in location and in number of double bonds 12/1/2018 Dr seemal Jelani

The number of carbon atoms present on a Terpene is always a multiple of the number 5(10.15,20…….) 12/1/2018 Dr seemal Jelani

β-carotene Responsible for yellow color of carrots Structure is 40 carbon atoms Many isoprene 8 isoprene unit 12/1/2018 Dr seemal Jelani

Beta-carotene serves as a precursor for vitamin A Splitting of beta carotene molecule produces two vitamin A molecules It also function as an antioxidant 12/1/2018 Dr seemal Jelani

Two isoprene unit 12/1/2018 Dr seemal Jelani

α -Phellandrene ( eucalptus) Myrcene 12/1/2018 Dr seemal Jelani

Geranoil 12/1/2018 Dr seemal Jelani

α- Farnesene (natural apple coating) Zingiberene (ginger) α- Farnesene (natural apple coating) 12/1/2018 Dr seemal Jelani

Menthol 12/1/2018 Dr seemal Jelani

Physical properties Insoluble in water Soluble in non polar solvent Physical properties similar to alkanes Alkenes with 1-4 carbon atoms are gases at room temperature 5-17 carbon atoms are liquids at room temperature Above 17-all are solids 12/1/2018 Dr seemal Jelani

Chemical Properties of Alkenes Addition Reactions Combustion Reactions 12/1/2018 Dr seemal Jelani

Addition Reactions Why do alkenes undergo addition reactions? Carbon-carbon double bonds in alkenes are reactive. readily undergoes addition reactions 12/1/2018 Dr seemal Jelani

Unsaturated hydrocarbon Addition Reactions + Unsaturated hydrocarbon Saturated organic compound In an addition reaction, carbon-carbon double bonds become single bonds. This means that an unsaturated hydrocarbon becomes a saturated organic compound. 12/1/2018 Dr seemal Jelani

Types of Addition Reactions General Equation: Reaction with ethene Reaction Conditions Equation (Write it yourself) Bromination (Addition of bromine) - Hydrogenation (Addition of hydrogen) 200 °C, nickel catalyst Hydration (Addition of steam) phosphoric(V) acid catalyst, 300 °C, 60 atm C H Br + Br2 C H + H2 C H OH + 12/1/2018 Dr seemal Jelani

Explanation C-c double bond has σ-bond component and a π- bond component The π- bond is weaker than the σ-bond and can be broken while the σ-bond remains intact This happens in alkenes addition reactions 12/1/2018 Dr seemal Jelani

Classification of addition reaction Symmetrical addition Unsymmetrical addition Example: Hydrogenation and Halogenation Hydrohalogenation Hydration 12/1/2018 Dr seemal Jelani

Types of Addition Reactions General Equation: Reaction with ethene Reaction Conditions Equation (Write it yourself) Bromination (Addition of bromine) - Hydrogenation (Addition of hydrogen) 200 °C, nickel catalyst Hydration (Addition of steam) phosphoric(V) acid catalyst, 300 °C, 60 atm C H Br + Br2 C H + H2 C H OH + 12/1/2018 Dr seemal Jelani

Five addition reactions of cyclohexene 12/1/2018 Dr seemal Jelani

Hydrogenation Involves addition of a hydrogen atom to each carbon of the double bond It is done by heating alkene and H2 in the presence of catalysis 12/1/2018 Dr seemal Jelani

12/1/2018 Dr seemal Jelani

The identity of the catalyst used in the hydrogenation is specified by writing it above the arrow in the chemical equation The hydrogenation of vegetable oils is very important commercial process today Vegetable oils from sources as soyabeans and cottonseeds are composed of long chain organic molecules that contain double bonds On hydrogenation these oils are converted to low-melting solids that are used in margarines 12/1/2018 Dr seemal Jelani

Halogenation of alkenes It involves the addition of a halogen atom to each carbon of the double bond It involves chlorination and bromination No catalysis is needed Product is always a dihalogenated alkene derivative 12/1/2018 Dr seemal Jelani

Bromine in water or CCl4 is reddish brown Bromination often used to test for the presence of C=C double bonds in organic substances Bromine in water or CCl4 is reddish brown The dibromides formed from symmetrical addition of bromine to an organic compound are colorless The decolrization of a bromine solution indicates the presence of C=C 12/1/2018 Dr seemal Jelani

Unsymmetrical Additions Hydrohalogenation Hydration Addition of HCl, HBr or HI to a C=C No catalyst is required Hydrohalogenation—Markovnikov’s Rule With an unsymmetrical alkene, HX can add to the double bond to give two constitutional isomers, but only one is actually formed: 12/1/2018 Dr seemal Jelani

The rule states that, with the addition of HX to an alkene, the hydrogen (H) becomes attached to the carbon with fewer alkyl substituents, and the halide (X) group becomes attached to the carbon with more alkyl substituents 12/1/2018 Dr seemal Jelani

Transversely, the hydrogen atom is added to the carbon with the greater number of hydrogen atoms while the X component is added to the carbon with the least number of hydrogen atoms 12/1/2018 Dr seemal Jelani

12/1/2018 Dr seemal Jelani

Markovnikov’s rule States that in the addition of HX to an unsymmetrical alkene, the H atom adds to the less substituted carbon atom—that is, the carbon that has the greater number of H atoms to begin with. 12/1/2018 Dr seemal Jelani

Halogenation—Addition of Halogen Halogenation is the addition of X2 (X = Cl or Br) to an alkene to form a vicinal dihalide(“X” on adjacent Carbon) 12/1/2018 Dr seemal Jelani

Example of Markovnikov’s Rule Hydration—Addition of H-OH Hydration of 1-propene to form 2-propanol (major) and 1-propanol (minor) 12/1/2018 Dr seemal Jelani

More than one C=C dienes, trienes Addition occurs at every C=C bond but amount is as per double bonds CH2 =CH-CH2-CH2-CH2CH3 + H2---------CH3-(CH2)4-CH3 12/1/2018 Dr seemal Jelani

Polymerization A Polymerization reaction is a reaction in which the repetitious combining small molecules produces a very large molecule The large unit is called Polymer It’s a large molecule composed of many identical repeating units The small repeating units are called Monomers 12/1/2018 Dr seemal Jelani

Addition polymers An addition polymer is a polymer in which the monomers simply “add together” with no other products formed besides the polymer The monomers for addition polymers are most often alkenes or substituted alkenes π- bond bonds present in the alkene monomers are broken Electrons involved in π- bond make σ-bond with C-C between the monomers 12/1/2018 Dr seemal Jelani

How are these formed The π- bonds of alkenes are broken The electrons are now involved in carbon-carbon bonds between the monomers 12/1/2018 Dr seemal Jelani

12/1/2018 Dr seemal Jelani

Applications Telecom Ducts Containers Folding tables and chairs Chemical-resistant, heat-resistant pipes The exact formula for a polymer cannot be written because the length of the carbon chain varies from polymer molecule to polymer molecule Formula of polyethylene 12/1/2018 Dr seemal Jelani

Addition Polymers Copyright © Houghton Mifflin Company. All rights reserved.