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- Alkenes- Alkynes

Mr. Shields Regents Chemistry U16 L03

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AlkenesAlkenes Like the alkanes, the Alkenes form another Like the alkanes, the Alkenes form another

homologous hydrocarbon serieshomologous hydrocarbon series

Each member contains Each member contains oneone double covalent double covalent bond between two C atoms.bond between two C atoms. So alkenes are So alkenes are unsaturated hydrocarbonsunsaturated hydrocarbons..

General formula = General formula = CCnnHH2n 2n (2H less than the Alkanes)(2H less than the Alkanes)

What was the general formula for the Alkanes?What was the general formula for the Alkanes?

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Saturated vs UnsaturatedSaturated vs Unsaturated

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Saturation vs. UnsaturationSaturation vs. Unsaturation

Simply put, a saturated Simply put, a saturated hydrocarbon has no hydrocarbon has no double bonds between double bonds between the Carbon atoms (ex. the Carbon atoms (ex. alkanes)alkanes)

Unsaturated has Unsaturated has one or one or moremore double or triple double or triple bonds between carbons bonds between carbons (alkenes, alkynes)(alkenes, alkynes)

CC C

C

H

H

H

H

HH

H

H

H

H

CH3(CH2)2CH3

CH

CH3 CH

CH3

CH3C C

CH3

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Physical properties of the AlkenesPhysical properties of the Alkenes

-Alkenes have properties similar to the alkanes

- Insoluble in water- But very soluble in organic solvents

- Less dense than water (density of water = 1.0)

- B.P. and M.P increase w/ increasing carbon #- Slightly lower than the corresponding alkane- As with alkanes B.P rises about 20-30 C per carbon- Hexane b.p. 69 C; 1-Hexene b.p. 63.5 C- Heptane b.p. 98 C; 1-Heptene b.p. 93 C

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Naming AlkenesNaming Alkenes

Names are derived using the same prefix used Names are derived using the same prefix used to name the alkane chain with the same number to name the alkane chain with the same number of C atoms.of C atoms.

Replace the –ane ending of the alkane name Replace the –ane ending of the alkane name with –ene.with –ene.

1st member is C2H4, ethene.

H HH HCC==CC

H HH H

Why 1st ?

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Naming AlkenesNaming Alkenes Location of double bond is specified by numbering Location of double bond is specified by numbering

C atoms in longest C backbone. Give double C atoms in longest C backbone. Give double bond the lowest possible number.bond the lowest possible number. Do not use a # if there is only 1 possible locationDo not use a # if there is only 1 possible location

H H H C=C–C–C–HH H H H

C4H8

CH2CHCH2CH3

H H H HH–C–C=C–C–H H H

C4H8

CH3CHCHCH3

1-butene (not 3) 2-butene

Structural Formula

Chemical formula

CondensedStructural formula

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Alkene Homologous SeriesAlkene Homologous Series(w/ C1-C2 double bond)(w/ C1-C2 double bond)

EtheneEthene PropenePropene 1-Butene1-Butene 1-Pentene1-Pentene 1-Hexene1-Hexene 1-Heptene1-Heptene 1-Octene1-Octene 1-Nonene1-Nonene 1-Decene1-Decene

C=CC=CC-C=CC-C=CC-C-C=CC-C-C=CC-C-C-C=CC-C-C-C=CC-C-C-C-C=CC-C-C-C-C=CC-C-C-C-C-C=CC-C-C-C-C-C=CC-C-C-C-C-C-C=CC-C-C-C-C-C-C=CC-C-C-C-C-C-C-C=CC-C-C-C-C-C-C-C=CC-C-C-C-C-C-C-C-C=CC-C-C-C-C-C-C-C-C=C

What is the name of this alkene? C-C-C=C-C-C-CC-C-C=C-C-C-C

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Naming AlkenesNaming Alkenes Once double bond is numbered specify substituents Once double bond is numbered specify substituents

alphabetically by carbon numberalphabetically by carbon number Do not use a number if there is only 1 possible locationDo not use a number if there is only 1 possible location

Use di, tri and tetra for multiple substituents of the same Use di, tri and tetra for multiple substituents of the same groupgroup

C=C–C–C C C

C6H12

CH2C(CH3)CH(CH3)CH3

Structural Formula(w/o the H)

Chemical formula

CondensedStructural formula

2,3-dimethyl-1-butene

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Problems:Problems: Draw the following alkenes:Draw the following alkenes:

2-Butene2-Butene methylpropenemethylpropene 4–Methyl–2-pentene4–Methyl–2-pentene 3,3-Dimethyl-1-butene3,3-Dimethyl-1-butene

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Name this Compound:

4-ethyl-5-methyl-4-octene (why? What is thelongest C chain?

And“E” before “M”

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AlkynesAlkynes Homologous series of unsaturated Homologous series of unsaturated

hydrocarbons that contain one triple hydrocarbons that contain one triple bond.bond.

Each member contains one triple Each member contains one triple carbon-carbon bond.carbon-carbon bond.

Alkynes are unsaturated.Alkynes are unsaturated.

General formula = CGeneral formula = CnnHH2n-22n-2

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Alkyne Homologous SeriesAlkyne Homologous Series(w/ C1-C2 triple bond)(w/ C1-C2 triple bond)

EthyneEthyne PropynePropyne 1-Butyne1-Butyne 1-Pentyne1-Pentyne 1-Hexyne1-Hexyne 1-Heptyne1-Heptyne 1-Octyne1-Octyne 1-Nonyne1-Nonyne 1-Decyne1-Decyne

C CC CC-C CC-C CC-C-C CC-C-C CC-C-C-C CC-C-C-C CC-C-C-C-C CC-C-C-C-C CC-C-C-C-C-C CC-C-C-C-C-C CC-C-C-C-C-C-C CC-C-C-C-C-C-C CC-C-C-C-C-C-C-C CC-C-C-C-C-C-C-C CC-C-C-C-C-C-C-C-C CC-C-C-C-C-C-C-C-C C

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Ethyne

(Common name)

A common use of one of the alkynes:The Acetylene torch

What is the IUPAC name for this compound?

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Hydrocarbon TableHydrocarbon Table

Notice that eachOf the hydrocarbonFamilies differsFrom the next By 2 hydrogen

Alkanes share 1pr e-

Alkenes share 2pr e-

Alkynes share 3pr e-

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Naming AlkynesNaming Alkynes

Use the corresponding name from the alkane Use the corresponding name from the alkane series and change the –ane to –yne.series and change the –ane to –yne.

If necessary, number the carbon atom at which If necessary, number the carbon atom at which the triple bond occurs with the lowest number.the triple bond occurs with the lowest number.

Use the same naming process you used for Use the same naming process you used for naming Alkenesnaming Alkenes

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H–CC–H C2H2 ethyne CHCH

HH–CC–C–H C3H4 propyne CHCCH3

H

H HH–CC–C–C–H C4H6 1-butyne CHCCH2CH3

H H

H HH–C–CC–C–H C4H6 2-butyne CH3CCCH3

H H

Structural Chemical Name CondensedFormula Formula Structural formula

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Can you name this compound?

3-ethyl-1-pentyne

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ProblemsProblems

Name this alkyne:

5,7-diethyl-3-methyl-4-decyne

CC-C-C=C-C-C-C-CC C C C C C