lecture 5 - CHAPTER 5 Unsaturated Hydrocarbons Unsaturated...

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1 CHAPTER 5 CHAPTER 5 Alkenes: Alkenes: Structure and Structure and Nomenclature Nomenclature Unsaturated Hydrocarbons Unsaturated Hydrocarbons ± Unsaturated hydrocarbon: Unsaturated hydrocarbon: contains one or more carbon-carbon double or triple bonds Unsaturated Hydrocarbons ± Alkene: Alkene: contains a carbon-carbon double bond and has the general formula C n H 2n Ethylene (an alkene) H CC H HH Unsaturated Hydrocarbons Unsaturated Hydrocarbons ± Alkyne : contains a carbon-carbon triple bond and has the general formula C n H 2n-2 Acetylene (an alkyne) . H-C C-H Unsaturated Hydrocarbons Unsaturated Hydrocarbons ± Arenes: Arenes: benzene and its derivatives (Ch 21- 22) Alternative representations for the phenyl group C 6 H 5 -P h - (An arene) Benzene C C C C H H
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2 Structure of Alkenes Structure of Alkenes ± A double bond consists of one sigma bond formed by the overlap of sp 2 hybrid orbitals and one pi bond formed by the overlap of parallel 2 p orbitals the two carbon atoms of a double bond and the four atoms bonded to them lie in a plane, with bond angles of approximately 120° Structure of Alkenes Structure of Alkenes Structure of Alkenes it takes approximately 264 kJ (63 kcal)/mol to break the pi bond in ethylene; that is, to rotate one carbon by 90° with respect to the other so that there is no overlap between 2 p orbitals on adjacent carbons Cis,Trans Isomerism in Alkenes ± Cis,trans Cis,trans isomers: isomers: isomers that have the same connectivity but a different arrangement of their atoms in space due to the presence of either a ring or a carbon-carbon double bond Index of Hydrogen Deficiency Index of Hydrogen Deficiency ± Very useful for determining the number of rings and/or pi bonds from the molecular formula ± Index of hydrogen deficiency (IHD): the sum of the number of rings and pi bonds in a molecule
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3 Index of Hydrogen Deficiency Index of Hydrogen Deficiency ± To determine IHD, compare the number of hydrogens in an unknown compound with the number in a reference hydrocarbon of the same number of carbons and with no rings or pi bonds the molecular formula of the reference hydrocarbon (same as the alkanes )isC n H 2n+2 IDH = 2 (H reference -H molecule ) Index of Hydrogen Deficiency Index of Hydrogen Deficiency (For elements besides C and H in acyclic (For elements besides C and H in acyclic molecules)
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lecture 5 - CHAPTER 5 Unsaturated Hydrocarbons Unsaturated...

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