The general rules for naming alkenes and alkynes are similar to those for alkanes, using the alkyl prefixes and ending with -ene or -yne respectively.

Cycle formation isn’t the possible result of dehydrogenation

Adjacent C’s can double bond, C=C, making an unsaturated alkene

Much more reactive than alkanes

Naming Alkenes

Similar to Alkane naming, with some exceptions

In Alkenes, double bonds take priority over the side chain (meaning you must make it the lowest location #)

If the double bonds don’t indicate a preferred numbering direction, then look at the side chain

If more than one double bond is present, give the position of each and use one of the suffixes (-diene, -triene, etc.)

Voice Notes:

• Alkenes are double bonds!
• Dehydrogenation is loss of hydrogen
• Double and triple bonds are always in the main chain

Alkynes: CnH2n-2

This is also a result of dehydrogenation and contains one or more triple carbon-carbon bonds

THIS IS THE MOST REACTIVE HYDROCARBON

Most reactive because it contains more e- due to the bonding

It has the same naming as Alkenes, except they end in -yne

TEXTBOOK READING: pg 15 - 22

Summary for Naming Alkenes and Alkynes

• Step 1. The parent chain must be an alkene or alkyne, and thus must contain the multiple bond.
• Step 2. When numbering the C atoms in the parent chain, begin with the end closest to the multiple bond.
• Step 3. The location of the multiple bond is indicated by the number of the C atom that begins the multiple bond; for example, if a double bond is between the second and third C atoms of a pentene, it is named 2-pentene.
• Step 4. The presence and location of multiple double bonds or triple bonds is indicated by the prefixes di-, tri-, etc.; for example, an octene with double bonds at the second, fourth, and sixth C atoms is named 2,4,6-octatriene

Unsaturated Aromatics

In naming simple aromatic compounds, we usually consider the benzene ring to be the parent molecule, with alkyl groups named as branches attached to the benzene.

• Alternating single/double bond cycles occur in many organic molecules simultaneously
• This class is called “aromatic” (by virtue of their aroma)
• Benzene’s are compounds containing a Benzene ring
• Aromatic hydrocarbons are used as fuels, solvents, dyes, drugs, pesticides, and herbicides
• Compounds with benzene are called aromatic compounds because of their strong odors
• Two types:
  • Those in which benzene is attached to a carbon chain
  • Those in which other groups are attached to a benzene ring

Naming Aromatic Hydrocarbons

1. If an alkyl group is attached to a benzene ring, the compound is named as an alkylbenzene. Alternatively, the benzene ring may be considered as a branch of a large molecule; in this case, the benzene ring is called a phenyl group.
2. If more than one alkyl group is attached to a benzene ring, the groups are numbered using the lowest numbers possible, starting with one of the added groups

Benzene Attached to a Carbon Chain

When benzene is attached to a carbon chain, it loses one hydrogen and is called a phenyl group (-C6H5)

Groups Attached to a Benzene Ring

Some common compounds in which one hydrogen of benzene is replaced by another atom or group are:

Voice Notes:

• Unsaturated aromatics have a distinct smell that you’ll never forget
• Benzene is C6H6 (drawn like a hexagon with a circle inside of it)
• We don’t need to include a number when naming aromatic compounds that contain only one group