Unsaturated Hydrocarbons Alkenes and Alkynes

ALKENES

ALKENES (Ethylene Series) – CnH2n

➢are HC that contain C-C double bond.

➢the suffix “ene” is used in place of “ane” to identify the family.

➢Are also known as OLEFINS (oil making) because liquids are often obtained by combination of these HC with reagents such as halogens and halogen acids.

NOMENCLATURE

1. Name the parent HC. Find the longest continuous C-chain that contains the double bond, and the compound using the suffix “ene”.

Example:

5 4 3 2 1

CH3-CH2-CH2-CH=CH2 pentene

Note: No need to write 1, If double bond is located in the first carbon.

2. Number the C-atoms in the chain beginning at the end nearer the double bond. If the double bond is equidistant from the two ends, begin numbering at the end nearer the first branch point. This rule ensures that the double bond carbon receives the lowest possible number.

Example:

1 2 3 4 5 6

CH3-CH -CH=CH-CH2-CH3 2-methyl-3-hexene

CH3

3. Write the full name, numbering the substituents according to their position in the chain and listing them alphabetically. Indicate the position of the double bond by giving the number of the first alkene carbon. If more than one double bond is present, give the position of each and use the suffixes - diene, triene and so-on.

1 2 3 4

CH2=C-CH=CH2 2-methyl-1,3-butadiene

CH3

Examples:

2-hexene

4-nonene

5,5-dimethyl-3-heptene

1,4-pentadiene

ALKYNES

ALKYNES ( Acetylene Series) - CnH2n - 2

➢ are HC that contain a C-C triple bond.

➢ are also called as acetylene series, the first member of the series.

➢ change –ene for -yne.

Molecular Formula Structural Formula Acetylene System IUPAC

C2H2 HC≡CH acetylene ethyne

C3H4 CH3C≡CH methyl acetylene propyne

C4H6 CH3CH2C≡CH ethyl acetylene butyne

C5H8 CH3 CH2C≡CCH3 ethyl methyl acetylene 2-pentyne

NOMENCLATURE1. Alkynes are named by general rules similar to those used for alkanes

and alkenes.

2. The suffix –yne is used in the parent HC name to denote an alkyne, and the position of the triple bond is indicated by its number in the chain.

3. Numbering begins at the chain end nearer the triple bond so that the triple bond receives as low a number as possible.

4. Compounds containing both triple and double bonds are called ENYNES. Numbering of the HC chain starts from the end nearer the first multiple bond, whether double or triple. If there is a choice in numbering, double bonds receive lower numbers than the triple bond.

6-ethyl-2-octyne