Unsaturated Compounds (2024) PDF

10/20/2024 Unsaturated compounds By: Dr. Zahra Kassem 20 October 2024 1 Objectives Alkenes: To understand different methods for naming of organic compounds. Provide both IUPAC and com...

10/20/2024 Unsaturated compounds By: Dr. Zahra Kassem 20 October 2024 1 Objectives Alkenes: To understand different methods for naming of organic compounds. Provide both IUPAC and common name for Alkenes. Recognize the most important methods of Alkenes synthesis. To know different reactions of Alkenes: 1. Hydrogenation (Reduction) of Alkene (addition of H₂) 2. Electrophilic Addition of Alkenes: Markovnikov’s Rule Anti-Markovnikov’s Rule 3. Oxidation of alkenes 20 October 2024 2 1  10/20/2024 Objectives Alkynes To understand different methods for naming of organic compounds. Provide both IUPAC and common name for Alkynes. Recognize the most important methods of Alkynes synthesis. To know different reactions of Alkynes Conjugated dienes 20 October 2024 3 Unsaturated compounds can be classified into: 1. Alkenes 2. Alkynes 3. Conjugated dienes 1. Alkenes (Olefins) 20 October 2024 4 2  10/20/2024 Nomenclature IUPAC Nomenclature 1. The –ane suffix of alkane is replaced by –ene. 2. Determine the parent name by selecting the longest chain that contains the double bond and change the ending of the name of the alkane of identical length from: ane to ene. 3. The number assigned is that of that of the lower numbered carbon involved in the double bond, the number is chosen so as to give the double bond the lowest number possible. 4. Indicate the location of the substituent groups by the numbers of the carbon atoms to which they are attached. 20 October 2024 5 20 October 2024 6 3  10/20/2024 4. If there is more than one double bond in a compound , the location of each is designated using the same principle. 5. A number designates the first carbon involved in each double bond. The number of double bonds is indicated by inserting di-(2=) tri(3=) before the –ene suffix. CH2=CH-CH2-CH=CH2 1,4-pentadiene 1 2 3 4 5 CH2=CH-CH=CH2 1,3-butadiene 1 2 3 4 20 October 2024 7 20 October 2024 8 4  10/20/2024 Preparation of Alkenes 1. By the action of concentrated sulfuric acid at 160-170°C on primary alcohols. The acid acts as a dehydrating agent, removing one molecule of water from the alcohol to from the olefin. 2. By the action of ethanolic potassium hydroxide on mono- halogen derivatives of the paraffins. 3. By the action of zinc dust on methanolic solutions of dihalogen derivatives: 20 October 2024 9 Chemical reactions of Alkene I- Hydrogenation (Reduction) of Alkene (addition of H₂): 20 October 2024 10 5  10/20/2024 II- Electrophilic Addition of Alkenes: ( A )- the most important reaction of alkenes is the addition of electrophilic reagents to the electron-rich double bond. 20 October 2024 11 Mechanism (Ionic Reaction) The addition reaction proceeds via initial attack of the alkene on the H+ of HX forming a carbocation. The formed carbocation is attacked by X ¯,in this case we use the symmetrical olefins. 20 October 2024 12 6  10/20/2024 For Asymmetrical Alkene ( Markovnikov’s Rule) 20 October 2024 13 Markovnikov’s Rule In the addition of HX to an alkene, the H+ adds to the carbon atom of the double bond that already has the greater number of hydrogen atoms. Question: give the structural and name of the product that would be obtained from Markovnikov’s addition of HCl to propene and 2-Methylpropene. 20 October 2024 14 7  10/20/2024 Radical Addition to Alkene (Markovnikov’s Rule) (A)- Addition of hydrogen halide in presence of peroxide. This reaction proceeds under free radical condition (Anti Markovnikov’s Rule): 20 October 2024 15 (B)- Addition of Halogens Cl₂/CCl₄ or Br₂/CCl₄: This can be accomplished under both free radical (light, high temp )and ionic condition(polar solvent, low temp). The reaction of reddish-brown bromine with alkenes is used as a qualitative test for the presence of C=C, if we add Br₂ ( brown) to an alkene, the color of bromine disappears. 20 October 2024 16 8  10/20/2024 (C)- addition of water to Alkenes: (Hydration) This reaction is an Acid-catalyzed hydration ,and it follows Markonikov’s Rule: 20 October 2024 17 Mechanism N.B. This reaction is acid-catalyzed the acid is not consumed 20 October 2024 18 9  10/20/2024 III-Oxidation of alkenes (A) Oxidation with potassium permanganate (KMnO₄): The purple color of KMnO₄ disappears, this distinguishes between alkanes and alkenes. This reaction is Syn-addition of two hydroxyl groups; the attacks on the 2C atoms of C=C takes place from the same side. 20 October 2024 19 2.Alkynes (Acetylenes) M.F.= CnH2n-2 The simplest member of the series is acetylene and hence this homologous series is often referred to as the “acetylene series”. Alkynes are named in the same way as alkenes; start with the parent alkane name corresponding to the carbon chain containing the triple bond, and replace the suffix –ane with the suffix –yne. The chain is numbered to give the carbon atoms of the triple bond the lowest possible numbers. Radicals : alkyne →alkynyl 20 October 2024 20 10  10/20/2024 20 October 2024 21 Preparation of Alkynes (1)-By the action of ethanolic KOH on ethylene bromide(vicinal di-halide) The reaction proceeds in two steps: 20 October 2024 22 11  10/20/2024 (2)- By the action of KOH/EtOH on ethylidene chloride (Geminal dihalide): (3)- Using Sodamide in liquid ammonia 20 October 2024 23 Reactions of Alkynes (1)-The Acidity of terminal alkynes: 20 October 2024 24 12  10/20/2024 N.B. Acetylene and terminal alkynes also form metal derivatives with silver and cupper (in ammonical solution). This reaction can be used to differentiate between terminal alkynes and non terminal alkynes ( no reaction). 20 October 2024 25 (2)- Addition of H₂/Pt: 20 October 2024 26 13  10/20/2024 (3)- Addition of Cl₂ or Br₂ (4)- Addition of HBr or HCl 20 October 2024 27 3.Conjugated dienes Alkenes having more than one double bond in their structure are referred to as dienes (two), trienes (three), tetraenes (four). There are three different classes of dines: 20 October 2024 28 14  10/20/2024 Conjugation means that there is an alternating pattern of double and single bonds with the molecule (-C=C-C=C). 20 October 2024 29 Preparation of alkadienes: Stability of conjugated dienes - Conjugated dienes are more stable than isolated dienes. 20 October 2024 30 15  10/20/2024 Reactions of conjugated dienes (1)-Addition reaction Conjugated dienes undergo abnormal addition reactions: the unexpected 1,4-addition and the expected 1,2- addition. 20 October 2024 31 Mechanism Reaction of 1,3-butadiene with HBr: At very low temperature (-80°C), resonance is slow so that the 1,2-product could be predominant. 20 October 2024 32 16  10/20/2024 1.2-versus 1.4-addition Addition of HBr to 1,3-Butadieneyields both the 1,2- and the 1,4-products; the proportions in which they are obtained are affected by the temperature at which the reaction is carried out. o At low temperature, 1,2-product is formed faster than 1,4- product (Kinetically control). o At high temperature, 1,4-product is more stable than 1,2- product (thermodynamically control) Stability of carbocation 20 October 2024 33 (2)-Diels Alder reaction (Cycloaddition reaction) It is type of 1,2-addition reaction of butadiene proceeding by the cis conformation via a cyclic transition state to yield a cyclic product (Adduct). The reaction is promoted by the presence of electron withdrawing substituents in the dienophile. 20 October 2024 34 17  10/20/2024 Examples of dienophiles 20 October 2024 35 List of References Essential Books (Text Books): - Textbook of Organic Medicinal and Pharmaceutical Chemistry, Wilson and Gisvold's, 12th Ed., International Edition, Philadelphia : Lippincott Williams & Wilkins, 2011. - Textbook of Organic Medicinal and Pharmaceutical Chemistry, Wilson and Gisvold's, 11th Ed., Philadelphia : Lippincott Williams & Wilkins, 2004. - Organic Chemistry ,T. W. Graham Solomons, Craig B. Fryhle, 9th Ed., N.Y.: John Wiley & Sons, Inc., 2006. - Organic Chemistry, T. W. Graham Solomons, Craig B. Fryhle, 8th Ed., N.Y.: John Wiley & Sons, Inc., 2004. - March's Advanced Organic Chemistry,: Reactions, Mechanisms, And Structure, Michael B. Smith and Jerry March, 6th Ed., New Jersey : John Wiley and Sons, Inc., 2007. - Organic Chemistry, John McMurry, 7th Ed., Australia : Thomson Brooks/Cole, 2008. 20 October 2024 36 18