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UNIT 2: ALKANES, ALKENES AND ALKYNESPART 2: ALKENES & ALKYNES A “functional group” is a segment of an organic molecule that has unique physical and chemical properties. The simplest type of functional group is a pi bond, or a pair of delocalized electrons. Like alkanes, alkenes and alkynes contain only hydrogen and carbon. However, alkenes and alkynes are unsaturated, or do not contain the maximum number of hydrogens possible due to the presence of double (alkene) and triple (alkyne) bonds.1. MOLECULAR FORMULA AND NAMING OF ALKENES:a. Each molecule below is an alkene. Write the molecular formula for each molecule in the space provided. __________________ _________________ ________________________propene (propylene) 2-butene (but-2-ene) 2-pentene pent-2-ene (2-butylene)b. Study each molecular formula that you wrote. Write a generic formula for alkenes.c. Use the formula you found above to try to predict the molecular formula of an alkene with 7 carbon atoms:d. The name for each of the molecules is given below the diagrams. Notice that the “ene” suffix replaces the “ane” that was used for alkanes. Why do you think the number 2 is included in the name for 2-pentene and 2-butene? Why isn’t included for propene? NOTE: The names “2-pentene” and “pent-2-ene” are both IUPAC and commonly used today. Ethylene and butylene are named in the “common naming system”, but are not IUPAC names. You need to be familiar with this form, but the correct IUPAC names are propene and ethene. 2. NAMING ALKENES:The steps for naming alkenes are given below.1. Find the longest continuous carbon chain that contains the double bond, and number from the end nearer the double bond.2. Write the alkane name corresponding to the number of carbons, changing the –ane to –ene.3. Identify by number the lower-numbered carbon atom containing the double bond, followed by a hyphen directly before the alkene name.4. If substituent groups are present, they should precede the name of the alkene in the usual way.EXAMPLE: Name the following molecule: STEPS 1 & 2 : hexene STEP 3: 2-hexene STEP 4: 4-ethyl-5-methyl-2-hexene hex-2-ene 4-ethyl-5-methyl-hex-2-enePRACTICE: Name the following molecules: 3. NAMING POLYUNSATURATED ALKENES:A polyunsaturated alkene has more than one double bond. The molecule below is a diene. To name a diene;List the lower numbered carbons containing the double bonds, separated by a comma.After the alkane name, -di- is used to signify 2 double bonds, followed by –ene. 4. MOLECULAR FORMULAS AND NAMING FOR ALKYNES: CnH2n-2Alkynes are unsaturated hydrocarbons that contain a triple bond. To name alkynes, follow the same process you used for naming alkenes except substitute the suffix –yne.TRY: Name the molecules below. Use the prefix chloro- to indicate the presence of a chlorine atom. Then check your answers: b. c. a.Answers: 1-butyne; 4-methyl-2-pentyne; 3-chloro-4-methyl-1-pentyne but-1-yne; 4-methyl-pent-2-yne; 3-chloro-4-methyl-pent-1-yne5. CYCLIC ALKANES, ALKENES & ALKYNESCycloalkanes, cycloalkenes and cycloalkynes have ring structures. The prefix “cyclo” is used in the name. Numbering begins at the multiple bond and moves in the direction toward the nearest branch, the goal being to assign the lowest numbers possible to the branch. All other naming rules are followed.EXAMPLES:center000Name the following molecules: Write the molecular formula for each molecule. How does it compare with a noncyclic molecule containing the same number of carbon atoms?COMMON BRANCH NAMES: ISO-, TERT- & SEC-Number of C Atoms in groupLine DrawingName3isopropylThree carbon branch coming off of a chain; attached at the middle carbon4isobutylFour carbon branch coming off of a chain, attached at the second carbon4sec-butylSame as iso-4tert-butylFour carbons coming off of a chain, in a “methyl propyl” arrangement5isopentyl5-carbon branch coming off of a chain, attached at the second carbon5sec-pentylSame as iso-Examples:4-isopropyl nonane secbutyl cyclopentane 4-tertbutyl-cyclohexeneTRY: 3-tertbutyl -4-propyl-2-octeneLOTS OF PRACTICE & CONDENSED FORMULAS: Complete the charts below. Leave the condensed formula column blank. We will work on it together.:NAMESTRUCTURAL DIAGRAMCONDENSED FORMULA4,4 dimethyl-2-pentene3-methyl-4-propyl-1-heptene3-isopropyl cyclo-octyne4-ethyl-2-hexyneALKENES/ALKYNES – HOMEWORK 1NAME:DATE:1. Name each of the alkenes/alkynes below. b. c. 4,4 dimethyl 2 hexene4-secbutyl-2-octyne2-bromo-3-methyl-2-pentene d. e. f. 2,4-dimethyl-2-pentene4-ethyl-2-fluoro(2,4) hexadiene4-propyl cyclohexyne3. Draw and name each molecule below based on its condensed formula: CH2CHCH2CH(CH3)2b. (CH3)3CCCCH2CH2CH2Cl4. Draw the molecules listed below:2,3 dichloro-3-hepteneb. 3-hexene 5. Complete the chart:CONDENSED FORMULASTRUCTURAL FORMULANAMECH3CH2CHCHCH(CH3)22-methyl-3-hexeneCHC(CH2)5CH2Cl(CH3)3CCHCH(CH2)2CHCH27,7-dimethyl-(1,5) octadiene ................
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