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Unformatted text preview: Chapter 7: Structure and Synthesis of Alkenes 7-1 Introduction Alkene: Hydrocarbons with carbon-carbon double bonds (olefins) Pi bond (double bonds) much less than sigma (single) much more reactive Considered a functional group, relatively reactive 7-2 The Orbital Description of the Alkene Double Bond Lewis Structure (C::C) Pauli Exclusion Principle: Two pairs of electrons can go into same region of space only if each has its own molecular orbital 7-2A Sigma Bond Framework Sp 2 hybridized - 120 angles Carbon-hydrogen sigma bond formed by overlap of sp 2 orbital on carbon (p280) Ethane vs. Ethylene C = C in ethylene is shorter than in Ethane S orbital is closer to the nucleus than the p orbital shorter bonds More S character and 2 bonds are used. 7-2B Pi Orbital Unhybridized p orbitals of carbons overlap to form pi-bonding molecular orbital P orbitals must be parallel. Half o pi-bonding is above C C sigma bond, half below Double bonds do not permit rotation origin of cis-trans isomerism 7-4 Nomenclature of Alkenes CH 2 = CH 2 CH 2 = CH 2 CH 3 IUPAC- ethene IUPAC propene Cyclohexene CN - ethylene CN propylene When chain contains more than three carbon atoms, number used to give location of the double bond. Start number closest to double bond. Double bond is given lower number of two....
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- Spring '08
- Pi Bond