B. Hydrocarbon chains with double bonds.
These are considered to be “unsaturated” hydrocarbon chains where alkanes are considered to be “saturated” because of the number of hydrogens.
Straight Chain Alkenes
1. Name chain according to number of carbons.
2. If there is at least one double bond between two CARBONS end name with –ene instead of –ane.
Straight Chain Alkynes
1. Name chain according to number of carbons.
2. If there is at least one triple bond between two CARBONS name with –yne instead of –ane.
Hydrocarbon
/Formula
alkanes
/CnH2n+2
alkenes
/CnH2n
alkynes
/CnH2n-2
Alkenes
Formula
/Name
/Structure
/Condensed-Formula
C2H4
/ethene
(ethylene)
/ /H2C=CH2
C3H6
/propene
/ /H2C=CHCH3
C4H8
/butene
/ /H2C=CHCH2CH3
C5H10
/1-pentene
/ /H2C=CHCH2CH2CH3
C5H10
/2-pentene
/ /H3CCH=CHCH2CH3
Alkynes
Formula
/Name
/Structure
/Condensed-Formula
C2H2
/ethyne
(acetylene)
/ /HCCH
C3H4
/propyne
/ /HCCCH3
C4H6
/butyne
/ /HCCCH2CH3
C5H8
/pentyne
/ /HCCCH2CH2CH3
To indicate where the double bond or triple bond occurs, indicate the number of the carbon where the double or triple bond occurs.
Names of carbon chains:
Number of C atoms / Alkane Name / Alkene Name / Alkyne Name1 / Methane / ------/ ------
2 / Ethane / Ethene / Ethyne
3 / Propane / Propene / Propyne
4 / Butane / Butene / Butyne
5 / Pentane / Pentene / Pentyne
6 / Hexane / Hexene / Hexyne
7 / Heptane / Heptene / Heptyne
8 / Octane / Octene / Octyne
9 / Nonane / Nonene / Nonyne
10 / Decane / Decene / Decyne
Cyclic Hydrocarbons
1. If a structure contains a ring of carbons instead of being a straight chain the name contains the prefix “cyclo”.
Cyclohexane