Alkenes and Alkynes Contain C-C double and triple bonds General alkene formula C n H 2n
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Transcript of Alkenes and Alkynes Contain C-C double and triple bonds General alkene formula C n H 2n
Alkenes and Alkynes• Contain C-C double and triple bonds• General alkene formula Cn H2n
• General alkyne formula Cn H2n-2
• More reactive than alkanes• Known as unsaturated hydrocarbons
CC HHH H
Thermal cracking:Process of breaking the long chain-alkanes found in petroleum into shorter chain alkanes and alkenes.
• Multiple bonds are also formed by removing ahydrogen chemically – dehydrogenation.
C C H
H
H + H2
H
H H
C C HH
H H
C C H
H
H + H2
H
C C HH
Alkenes / Alkynes are converted to alkanes byhydrogenation or addition reaction.
• Find parent chain with the double/triple bond.• Named as total carbons using ending ene / yne
• Show the location of the bond by the carbon number separated with a hyphen. (2-pentene)
• Number carbons from the end that gives the lowest
number to the double or triple bond.
• Name alkyl branches as in alkanes.
Naming Alkenes and Alkynes
ethene CH2= CH2
C = C H
HH
H
ethyne CH ≡ CH
C ≡ C HH
CC HHH H
CC HH
2-hexene CH3CH=CHCH2CH2CH3
3-hexyne CH3CH2C≡CCH2CH3
C - C - C - CC - C = 654321
C ≡ C - C - CC - C - 654321
4-methyl-2-pentene
(4-methylpent-2-ene)
(Note, lowest number goes to the double bond)
CH3CH2CH(CH3)CH=C(C2H5)CH2CH3
3-ethyl-5-methyl-3-heptene
1234567
*Show double/triple bond in condensed formula.
Draw the structural formula for 1-butene.
CH2=CH–CH2–CH3
Draw a condensed for 2,5,5-trimethyl-2-hexene.
CH3C(CH3)=CHCH2C(CH3)2CH34321 5 6
HC≡CCH2C(C2H5)2CH2CH(CH3)CH(CH3)CH3
4,4-diethyl-6,7-dimethyl-1-octyne
1 2 3 4 5 6 7 8
Draw a structural of 2,2,5,5-tetramethyl-3-hexyne.
• Like Alkyl groups (trimethyl), prefixes and numbers must be used to indicate multiple double or triple bonds.
C = C – C = C 1,3-butadiene
3-methyl-1,4-pentadiyne
4321
4321 5
C ≡ C – C – C ≡ C
C
• Alkenes: C=C, CnH2n , –ene.
• Alkynes: C≡C, CnH2n-2 ,–yne.
• Parent chain is numbered to give the double or triple bond the lowest number.
• Draw the parent chain hydrocarbon with the double or triple bonds first.
• Add in alkyl groups and then hydrogen so eachcarbon has 4 bonds.