Chapter 25 & 26 Notes, part II

Alkenes, Alkynes and Cyclic Hydrocarbons

AlkenesUp to now, we have only talked about

carbons that are single bonded. They have been saturated—they have a hydrogen in every possible position.

Alkenes are hydrocarbons that contain at least one double bond in the carbon chain.

Naming AlkenesTo name an alkene, count the number of

carbons in the main chain and use the prefix, then end it in –ene.

If there is more than one spot where a double bond could occur, number it just like you would number a substituent.

The parent chain must include

both carbon atoms

of the double bond

AlkynesAn alkyne is a hydrocarbon that

contains at least one triple bond.

Naming AlkynesTo name an alkyne, count the

number of carbons in the main chain and use the prefix, then end it in –yne.

If there is more than one spot for a triple bond, number it just like you would number a substituent.

Unsaturated HydrocarbonsBoth alkenes and alkynes are considered

unsaturated, because more hydrogens could be added if the double or triple bonds were broken.

Fats are nothing more than large hydrocarbons, so that is what it means to have saturated vs. unsaturated fats.

Cyclic HydrocarbonsUp until now, all carbon chains we

have discussed have been aliphatic, or non ring-containing, hydrocarbons.

If both ends of a hydrocarbon join together, it would be cyclic.

Cyclic HydrocarbonsTo name a hydrocarbon, simply

name as before, except begin the name with cyclo-.

If there are substituents or double/triple bonds to number, begin with the first substituent as 1, and go around the direction that gives you the smallest set of numbers.

Naming rules consolidated

•1. The ene suffix (ending) indicates an

• alkene or cycloalkene. 2. The parent chain must include both

• carbon atoms of the double bond.  3. The root chain must be numbered from

• the end nearest double bond carbon atom.  

•4. The smaller of the two numbers designating the carbon atoms of the double bond is used as the double bond locator.

•5. If more than one double bond is present the compound is named with the prefix indicating the number of double bonds, and each double bond is assigned a locator number.

•1.  The yne suffix (ending) indicates an alkyne or cycloalkyne. 2.   The longest chain chosen for the root name must include both carbon atoms of the triple bond.  3.   The root chain must be numbered from the end nearest a triple bond carbon atom. If the triple bond is in the center of the chain, the nearest substituent rule is used to determine the end where numbering starts. 4.   The smaller of the two numbers designating the carbon atoms of the triple bond is used as the triple bond locator. 5.   If several multiple bonds are present, each must be assigned a locator number. Double bonds precede triple bonds in the IUPAC name, but the chain is numbered from the end nearest a multiple bond, regardless of its nature.

Practice!!