Pharm Org Chem I Unsaturated Hydrocarbons Lecture BUA Fall 2024 PDF

Pharmaceutical Chemistry Department Pharm. Org. Chem. I (PC 102/102C) Unsaturated Hydrocarbons Lecture 3 1  ALKENES (Olefins) Structure For straight chain alkenes, it is the same basic rules as nomenclature of alkanes except change t...

Pharmaceutical Chemistry Department Pharm. Org. Chem. I (PC 102/102C) Unsaturated Hydrocarbons Lecture 3 1  ALKENES (Olefins) Structure For straight chain alkenes, it is the same basic rules as nomenclature of alkanes except change the suffix to "-ene“. are unsaturated hydrocarbons with the molecular formula: CnH2n , which is also the same molecular formula as cycloalkanes. Hybridization of alkenes is sp2, and the molecule will be with a trigonal planar molecular geometry. 2 sp2 Hybrid orbitals: one 2s orbital combines with two 2p orbitals, giving 3 orbitals (s + pp = sp2). sp2 Hybridized Carbon 3 Trigonal planar geometry  What is the C – C double bond (C = C) mean????? Two sp2-hybridized orbitals overlap to form a sigma (s) bond, and two p orbitals overlap side-to-side to form a pi () bond, resulting in the formation of a double bond. 4 sp2 orbitals are in a plane with 120° angles, where remaining p orbital is perpendicular to the plane. 5 6  Nomenclature 1. Find the longest carbon chain that contains the carbon- carbon double bond. If the double bond is not terminal, then the carbons should be numbered in such a way as to give the first of the two double-bonded carbons the lowest possible number. 1 2 3 4 1 2 3 4 5 6 H2C CH CH2 CH3 H3C HC CH CH2 CH2 CH3 1-butene 2-hexane (not 3-butene) ( not 4-hexene) 7 2. If there is more than one double bond in an alkene, all of the bonds should be numbered in the name of the molecule - even terminal double bonds. The numbers should go from lowest to highest, and be separated from one another by a comma. Deca-1,5-diene: CH2=CHCH2CH2CH=CHCH2CH2CH2CH3 Octa-2,4-diene: CH3CH=CHCH=CHCH2CH2CH3 8 3. Add substituents and their position to the alkene as prefixes (of course remember to give the lowest numbers possible and remember to name them in alphabetical order when citing them). 2 3 4 2 3 4 5 6 1 1 2-methyl-2-butene 2,5-dimethyl-2-hexene (not 3-methyl-2-butene) (not 2,5-dimethyl-4-hexene) 2 4 6 3 1 5 2 1 4 Cl 3 9 5,5-dimethyl-2-hexene 1-chloro-2-butene  Synthesis of Alkenes A) Dehydration of alcohol (Remove H2O molecule) Using heat and a dehydrating agent, such as acids like H2SO4 (conc.), H3PO4 (conc.), in addition to Al2O3 (Alumina) 10 B) Reduction of Alkynes (Hydrogenation) C) Dehydrohalogenation of Alkyl halides (Remove HX molecule) Using bases, such as: Alkoxides (Alcohol + Oxides) 11  Reactions of Alkenes Addition Reactions Nucleophilic Attack by a Nucleophile (Nucleophilic reagent = Electron Donors): are nucleus loving reagents. Heterolytic (unsymmetrical) Bond Fission 12 Examples of Nucleophiles A- Negatively charged Species (Anions) as: OH-, CN-, RO- OH + R X R OH + X B- Neutral molecules having lone pair of electrons R3N: H3N: H2O: R2O: R2S : 13 1. Addition of Mineral Acids Symmetric alkene Asymmetric alkene 14 Markovnikov’s Rule 15 2- Oxidation of Alkenes Oxidation by ozone (ozonolysis of alkenes) 16  Alkynes (Acetylenes) Another class of unsaturated hydrocarbons, with a general molecular formula: CnHn. Characterized by presence of an sp hybridized carbon. 17  What is the C – C triple bond (C ≡ C) mean????? Linear Molecule 18 19 IUPAC Nomenclature Choose the longest chain containing triple bond (functional gp), make numbering to give the prior functional gp least no., and locate and name substituents. 4-methyl-2-pentyne 2,2,10-triiodo-5-methyl-3-decyne 20  Synthesis of Alkynes Elimination Reactions of Dihalides Dehydrohalogenation using strong bases like alkoxides (ROX) and amides (NaNH2 or KNH2) at high temperature. Vicinal dihalides Geminal dihalides 21 22  Reactions of Alkynes 1. Addition Reactions 23 24 25