Organic Chemistry Alkene

Organic Chemistry Alkene Nomenclature - Summary

• Identify the longest chain - ane changes to -ene
• Carbon >3, number is used to give the location of the double bond.

          Example: all the same naming for carbon =3

• When there is an alkyl group, double bond is still given preference in numbering. ex: give number "1" to double bond than alkyl group.

         Example : 2 at alkene, 3 on methyl group. -- 3 methyl, 2 pentene.

• If there is an alkene as a substitute ... methylene, vinyl, allyl and phenyl group
• Check whether it is cis or trans. That is based on the same identical group on the two ends of carbon bond. Exclude Hydrogen.   Example below: it is a cis because two methyl group are identical.

   Cis - 3 methyl, 1 pentene. ( This can be named with E even though it is cis. E was assigned by the priority atomic number, different definition from cis. Though, the concept sounds like the same.

   Exclude Hydrogen - no cis or trans. 1 butene.

• when there are 4 different group, use E and Z system.

Alkene Stability

1. More highly substittued double bond are usually more stable

2. Trans alkene more stable than Cis ( because the substituted groups are further apart.)

3. Zaitsev and Hoffman products are based on the substitutions on the double bonds. The most substitutes which are the most stable alkene=> Zaitsev product.

    Circle the alkene, only one substitute.            

Circle the alkene, 3 substitutes

Circle the alkene, 3 substitutes ( do mind the length of the substitute )

4. E2 in cyclohexane must have halide and hydrogne line up on the axial position.