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Chem 102 1st Edition Lecture 8Outline of Last Lecture I. Chapter 12Outline of Current Lecture II. Chapter 13: Lesson 2.1 - Unsaturated HydrocarbonsIII.Lesson 2.2 - Characteristics of Alkenes and CycloalkenesIV. Lesson 2.3 - IUPAC Nomenclature of alkenes and CycloalkenesV. Lesson 2.4 - Line-Angle Structural formulas for AlkenesCurrent Lecture2.1 Unsaturated Hydrocarbons• Unsaturated hydrocarbon: a hydrocarbon with one or more carbon–carbon multiple bonds (double bonds, triple bonds, or both). – Physical properties similar to those of saturated hydrocarbons. – Chemical properties are distinct. – Chemically more reactive than saturated hydrocarbons. – Reactivity of unsaturated hydrocarbons is due to carbon–carbon multiple bond(s).Functional Group • Functional group: Part of an organic molecule where most of its chemical reactions takes place. • Unsaturated hydrocarbon functional group: Carbon– carbon multiple bonds. • Subdivided into 3 groups: – Alkenes: Contain one or more carbon–carbon double bonds – Alkynes: contain one or more carbon–carbon triple bonds – Aromatic hydrocarbons: A special type of “delocalized” bonding that involves a six membered carbon ring2.2 Charateristics of Alkenes and Cycloalkenes• Alkenes: An alkene is unsaturated hydrocarbon that contains one or more carbon – carbon double bonds. • Functional group: C=C group.• Naming: Names end with an “-ene” –The -ene ending means a double bond is present. • General molecular formula: CnH2n • Two simplest alkenes are ethene (C2H4) and propene (C3H6).CH2 = CH2EtheneCH2 = CH - CH3Propene• The arrangement of bonds about the carbon atom in alkanes is tetrahedral. • The arrangement of bonds about carbon atoms with double bonds in alkenes is trigonal planar.• Cycloalkenes: A cyclic unsaturated hydrocarbon with one or more carbon– carbon double bonds withinthe ring system. • Cycloalkenes with only one double bond have the molecular formula CnH2n-2. • The simplest cycloalkene: Cyclopropene (C3H4), a three-membered carbon ring system with one double bond.2.3 IUPAC Nomenclature of alkenes and CycloalkenesIUPAC Rules Rule 1: Replace the alkane suffix -ane with the suffix -ene Rule 2: Select as the parent carbon chain the longest continuous chain of carbon atoms that contains both carbon atoms of the double bond. Rule 3: Number the parent carbon chain beginning at the end nearest to the double bond. If the double bond is equidistant from both ends of the parent chain, begin numbering from the end closer to a substituent. Rule 4: Give the position of the double bond in the chain as a single number, which is the lower-numbered carbon atom participating in the double bond.Rule 5: Use the suffixes -diene, -triene, -tetrene, and so on when more than one double bond is present in the molecule. Rule 6: A number is not needed to locate the double bond in unsubstituted cycloalkenes with only one double bond because that bond is assumed to be between carbons 1 and 2. Rule 7: In substituted cycloalkenes with only one double bond, the double-bonded carbon atoms are numbered 1 and 2 in the direction (clockwise or counterclockwise) that gives the firstencountered substituent the lower number.Rule 8: In cycloalkenes with more than one double bond within the ring, assign one double with numbers 1 and 2 and the other double bonds the lowest numbers possible.The parent chain of a compound containing carbon-carbon double bonds end with the suffix? a.) -ane b.) -ene c.) -yne d.) -ayneAlkene Nomenclature• 1) Find the longest continuous chain that includes the double bond. • 2) Replace the -ane ending of the unbranched alkane having the same number of carbons with ene. • 3) Number the chain in the direction that gives the lowest number to the doubly bonded carbon.• 4) If a substituent is present, identify its position by number. The double bond takes precedence over alkyl groups and halogens when the chain is numbered. • The compound shown above is 4-bromo-3-methyl-1-butene. • (or 4-bromo-3-methylbut-1-ene)Alkenyl Groups- Methylene - vinyl - allyl - isopropenylCycloalkene Nomenclature• 1) Replace the -ane ending of the cycloalkane having the same number of carbons with -ene.Common Names (Non-IUPAC Names) • There is no scientific basis for assigning such names therefore one must have to memorize them • Two most common names for alkenes are: CH2=CH2 Ethylene (IUPAC name – Ethene) CH2=CH2-CH3 Propylene (IUPAC name – propene)2.4 Line-Angle Structural formulas for AlkenesLine-angle formulas for the three- to six-carbon acyclic 1-alkenesRepresentative line-angle structural formulas for substituent-bearing alkenesDiene representitives in terms of line-angle structural


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