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Ch6slides - Chapter 6 Alkenes Structure and Stability O OH...

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1 Chapter 6. Alkenes: Structure and Stability Degrees of unsaturation saturated hydrocarbon C n H 2n+2 cycloalkane (1 ring) C n H 2n alkene (1 π -bond) C n H 2n alkyne (2 π -bonds) C n H 2n-2 For each ring or π -bond, -2H from the formula of the saturated alkane Degrees of unsaturation: # of rings and/or π -bonds in a molecule. Information can be obtained from the molecular formula OH O Steric Acid (saturated fatty acid) OH O Linoleic Acid (unsaturated fatty acid) Correction for other elements: For Group VII elements (halogens): subtract 1H from the H-deficiency for each halogen, or add 1H to the molecular formula of each halogen For Group VI elements (O and S) No correction is needed For Group V elements (N and P) add 1H to the H-deficiency for each N or P or subtract 1H from the molecular formula for each N or P N N CH 3 HO Cl C 6 H 6 C 10 H 14 N 2 C 11 H 11 OCl
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2 Naming Alkenes Suffix: -ene Many of the same rules for alkanes apply to alkenes 1. Name the parent hydrocarbon by locating the longest carbon chain that contains the double bond and name it according to the number of carbons with the suffix -ene. H 3 C CH 2 CH 2 C CH 2 CH 2 H 3 C H 3 C CH 2 CH 2 C CH 2 CH 2 H 3 C Parent = pentene not hexene (does not contain double bond) Systematic Nomenclature (IUPAC System) Prefix-Parent-Suffix 2a. Number the carbons of the parent chain so the double bond carbons have the lowest possible numbers. b. If the double bond is equidistant from each end, number so the first substituent has the lowest number. 3. Write out the full name, numbering the substituents according to their position in the chain and list them in alphabetical order. H 3 C CH 2 CH 2 CH CH CH 3 1 2 3 4 5 6 2-hexene H 3 C CH CH CH CH 2 CH 3 1 2 3 4 5 6 2-methyl-3-hexene CH 3
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3 4. Indicate the double bond by the number of the first alkene carbon. 5. If more than one double bond is present, indicate their position by using the number of the first carbon of each double bond and use the suffix -diene (for 2 double bonds), -triene (for 3 double bonds), -tetraene (for 4 double bonds), etc. H 3 C CH 2 CH 2 CH CH CH 3 1 2 3 4 5 6 2-hexene H 2 C CH CH 2 CH CH 2 1 2 3 4 5 1,4-pentadiene H 2 C CH CH CH CH 3 1 2 3 4 5 1,3-pentadiene CH 3 1 2 3 3-methylcyclohexene CH 3 1 2 3 4 5 6 NOT 6-methylcyclohexene 6a. Cycloalkenes are named in a similar way. Number the cycloalkene so the double bond carbons get numbers 1 and 2, and the first substituent is the lowest possible number. b. If there is a substituent on one of the double bond carbons, it gets number 1. CH 3 CH 3 CH 3 CH 3 1 2 3 4 5 1 2 3 4 5 1,5-dimethylcyclopentene NOT 2,3-dimethylcyclopentene
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4 Alkenes as substituents: CH CH 2 ethenyl or vinyl (vinylcyclohexane) CH 2 CH CH 2 2-propenyl or allyl (allylcyclohexane) CH 2 methylene (methylenecyclohexane) HC CH 3 ethylidene (ethylidenecyclohexane) Non-IUPAC Alkenes (Table 6.1, pg. 194) H 2 C CH 2 CH CH 2 H 3 C ethylene (ethene) propylene (propene) C CH 2 H 3 C H 3 C isobutylene (2-methylpropene) C CH H 2 C CH 3 CH 2 isoprene (2-methyl-1,3-butadiene) Squalene (C 30 , 6 isoprene units) β -carotene (C 40
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