1 2008 Lecture 5 6 7 Alkenes - Chem 2203/2207 Assignments...

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Chem 2203/2207 Assignments and Lecture Notes are posted On http://http-server.carleton.ca/~pbuist/ Lab 2 (IR) will precede Lab 1 this year. New Test Dates: Test 1 Tuesday, Oct 7 , 2008 In class 11:30 – 1:00 Test 2 Tuesday, Nov 4 , 2008 In class 11:30-1:00
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Alkenes Chapters 6 and 7
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Alkenes 1) Introduction 2) Geometry 3) Nomenclature 4) Physical Properties 5) Chemistry
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1) Introduction to Alkenes
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Degrees of unsaturation • All monoalkenes (acyclic) have the same formula (C n H 2n ). Eg. muscalure : C 23 H ?? • You can calculate the degree of unsaturation for any organic molecule using this formula: Degree of unsaturation = ( ) ( ) 2 Hydrogens) of # O ( 2 2 Carbons of Number bs - + ×
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How many degrees of unsaturation does a monoalkene possess? • For a monoalkene, the degree of unsaturation = [(2n + 2 ) – 2n]/2 = 1 • But note: A cycloalkane also has one degree of unsaturation … C 6 H 12
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Using Degrees of Unsaturation to (quickly) derive molecular formulae
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2. Geometry of C=C • sp 2 hybridization – Trigonal planar H sp 3 H H H H sp 2 120 ° vs. H H H
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sp 2 Orbitals • 2 s orbital combines with two 2 p orbitals, giving 3 sp 2 orbitals sp 2 orbitals are in a plane separated by 120° • Remaining p orbital is perpendicular to the plane
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Making Ethene using sp 2 Hybrid Orbitals Add 4 H . C = C H H H H
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Making C=C Bond from 2 sp 2 Hybrid Orbitals and a p orbital • Two sp 2 -hybridized orbitals overlap to form a σ bond p orbitals overlap side-to-side to form a pi ( π ) bond • Electrons in the σ bond are centered between nuclei • Electrons in the π bond occupy regions on either side of a line between nuclei
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Bond Strengths C=C • C=C stronger ( and shorter ) than C-C. • C=C bond strength = 640 kJ/mol (268 from π and 372 from σ ) onds are stronger than onds σ bonds are stronger than π bonds Misleading!
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Systematic Nomenclature for Alkenes • Find longest continuous carbon chain 1-butene not 3-butene • Number carbons in chain so that double bond (vinyl) carbons have lowest possible numbers
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Nomenclature of Alkenes Structure IUPAC name (common name) Ethene (ethylene) Propene (propylene) 1-butene methylpropene (isobutene)
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• Unlike C-C single bonds, cannot rotate around a C=C double bond. Why? • Rotation prevented by
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This note was uploaded on 07/28/2009 for the course CHEMISTRY CHEM 2203 taught by Professor Levin during the Spring '08 term at Indian Institute of Technology, Chennai.

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1 2008 Lecture 5 6 7 Alkenes - Chem 2203/2207 Assignments...

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