OCHEM_I_UNIT_13 - OCHEM I UNIT 13: ALK E NES A....

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Unformatted text preview: OCHEM I UNIT 13: ALK E NES A. INTRODUCTION 1. DEFINITION-Alkenes belong to the second class of hydrocarbons. -Alkenes are unsaturated hydrocarbons that contain at least one C-C double bond.-Alkenes are also called olefins . 2. GENERAL MOLECULAR FORMULA OF ALK E NES C n H 2n n = number of carbon atoms in molecule. Note: -have a homologous series. Ex: n = 1 n = 2 n = 6 3. GENERAL MOLECULAR FORMULA OF CYCLOALK E NES: 1 CYCLIC ALK E NES C n H 2n-2 Ex: C 6 H 10 cyclohexene-For cycloalkenes with less than 8 carbons , only cis isomers have been isolated because the trans isomers are too strained to exist. However, for higher cycloalkenes, both isomers exist. 4. TYPES OF ALK E NES: 2 types a. Terminal Alkenes 1-butene b. Internal alkenes 2-butene 5. PROPERTIES OF THE C-C DOUBLE BOND Recall: The -C Ž C- is a very rigid bond. Therefore, it cannot be rotated like a single bond. This gives rise to 2 stereoisomers: cis and trans . 2 Ex: Do problem 10.1 page 362. Note: The cis isomer is less stable than the trans . Why? See Table 10.1 page 362. Read pages 361 - 362. B. DEGREE OF UNSATURATION (DOU) 1. DEFINITION The degree of unsaturation of an unsaturated compound or a cyclic compound is the number of rings and/or multiple bonds (double and triple) in the compound. Ex: 3 1 degree of unsaturation 2 degrees of unsaturation 2 degrees of unsaturation 3 degrees of unsaturation Recall: The general formula of an alkane is: C n H 2n+2 Ex: 2. CALCULATING DEGREES OF UNSATURATION Ex: C 5 H 10 3. SOME POSSIBILITIES DOU = # of missing hydrogens in corresponding alkane 2 4 4. DOU FOR COMPOUNDS CONTAINING HALOGENS-Add the number of halogens to the number of hydrogens. Ex 1: Calculate the DOU of C 5 H 8 Cl 2 . Ex 2: Calculate the DOU of C 7 H 8 Br 4 . #missing Hs DOU possibilities 2 1-1 ring-1 double bond 4 2-2 rings-2 double bonds-1 triple bond-1 ring and 1 double bond 6 3-3 rings-3 double bonds-1 triple bond and 1 double bond, etc. 5 5. DOU FOR COMPOUNDS CONTAINING C, H, AND O-Ignore the number of oxygens. Ex: Calculate the DOU of C 6 H 8 O. 6. DOU FOR COMPOUNDS CONTAINING C, H, AND N-Subtract the number of nitrogens from the number of hydrogens. Ex: Calculate the DOU of C 5 H 9 N. 7. A SUMMARY ON DOU FOR COMPOUNDS CONTAINING HETEROATOMS....
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This note was uploaded on 04/19/2011 for the course CHEMISTRY 2423 taught by Professor Kay during the Spring '08 term at Dallas Colleges.

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OCHEM_I_UNIT_13 - OCHEM I UNIT 13: ALK E NES A....

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