5.6 Numbering

5.6 Numbering

• We are almost ready to start naming things.
• We learned how to identify individual parts of a name, but now we need to know how the pieces are connected.
• We need to find a way to identify where all of the pieces are on the parent chain.
• The numbering system comes in here.
• First, we will learn how to number the parent chain, and then we will learn how to apply those numbers in each part of the name.

• There are only two ways to number it, right to left or left to right.

• Pick the parent chain and number it correctly.

• We need to see how to apply the numbers from the parent chain to the different parts of the name.

• The number is placed in front of the suffix.
• The number does not need to be placed in the name if the functional group appears at the number 1.
• The functional group is thought to be at the number 1 position because of the absence of a number.
• The number should be placed at the beginning of the parent.
• The same thing can be said for 2-hexanol and hexan-2-ol.
• Both names are acceptable.

• The lower the number of the two carbon atoms, the more bonds are made.

• The double bond is between C2 and C3.
• The example is 2-hexene.
• We treat triple bonds the same.

• If there are two double bonds in the molecule, we need to indicate them.
• The double and triple bonds must be numbered.

• In front of the substituent is the number of the substituent.

• We must alphabetize the substituents in the name if there are more than one.

• There are four types of substituents in this example.
• They have to be alphabetized (c, e, f, m).

• The letters and numbers are separated by dashes.

• Stereocenters are placed in parentheses.
• When we learn about stereocenters in the upcoming chapters, we will see more of this.

• No one ever said it would take 10 minutes to learn, but with enough practice, you should be good at it.

• The five parts of the name are backwards.
• We begin by looking for a func tional group.
• This compound is a ketone.
• The end of the name will be one.

• We look for unsaturation.
• There is a double bond here.

• The parent needs to be named next.
• The longest chain includes the functional group and double bond.
• It is an obvious choice.
• The parent has seven carbon atoms.

• We are looking for substituents.
• There are two groups of chlorine atoms.
• It will be dichlorodimethyl if we alphabetize and c comes before m.

• Stereoisomerism is next we look for.

• We must assign numbers now that we have figured out all of the pieces.
• In this example, the numbering will go from left to right because we need to number the parent to give the lowest number.
• The functional group is at the number 2 position, the double bond at the 4 position, the chlorine atoms at 4 and 5, and the methyl groups at 6.