1. Chapter 3 Alkenes and Alkynes: Structure and Nomenclature

2. 3.1 Introduction to Alkenes and Alkynes Remember from chapter 2. Alkenes are hydrocarbons with at least one carbon-carbon double bond. – Simplest form is Ethene, C 2 H 4 – Also known as ethylene, which is the precursor to polyethylene plastic. – Formula C n H 2n – Use the same prefixes as alkanes but change the ending to “ene.”

3. Alkynes are hydrocarbons that have at least one carbon-carbon triple bond. – Simplest form is Ethyne, C 2 H 2 – Also known as acetylene, which is used in welding. – Formula C n H 2n-2 – Again use the same prefixes while naming but you change the ending to “yne.”

4. Remember the terms saturated and unsaturated hydrocarbons from chapter 2. Alkanes are saturated because all the carbons have four attached atoms. Alkenes and alkyne are unsaturated because not all of their carbons have the maximum number of bonded atoms.

5. 3.2 Nomenclature of Alkenes and Alkynes Use the suffix (ene) for a double bond attached to the Greek # for carbon. Use the suffix (yne) for a triple bond attached to the Greek # for carbon. 1.Identify the longest continuous chain of carbons. If the multiple bond is not in the longest chain you select the longest continuous chain of carbons that includes the multiple bond in it.

6. 2. Change the suffix of carbon chain to represent the correct type of bond. 3. Number the chain so as to give the lowest possible # to the double or triple bond (double bonds take priority over triple bonds if they are equal distance from either end of the carbon chain). 4. Name and # all the substituents connected to the longest chain. Place them at the beginning of the name (use alphabetical order while writing).

7. 5. If there is a double and triple bond in the longest chain of carbons the double bond is written first with the longest chains name (drop the e from the ending) and you use a hyphen and add the number and the word “yne” at the end. Example: CH 2 =CHC≡CCH 2 Br Name: 5-bromo-1-penten-3-yne

8. 6. If there are two or more double or triple bonds in the longest chain you place the proper prefix in the middle of the parent chain name before the suffix “ene” or “yne.” Example: CH 3 CH=CHCH 2 CH=CH 2 Name: 1,4-hexadiene

9. Common Nomenclature Some alkenes are commonly given an “alkylene”-type nomenclature. Two common alkylenes are ethylene and propylene. Once in awhile ethylene and propylene groups are referred to with the prefixes: Vinyl- CH 2 =CH is the this group. Allyl- CH 2 =CHCH 2 is this group. Page 76 gives an example of this.