How to Name Hydrocarbons (IUPAC)

   
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NAMING HYDROCARBONS

HYDROCARBON DESCRIPTION GENERAL FORMULA
Alkane (-ane

ending)

Only single bonds

(C—C)

CnH2n + 2 (linear)

CnH2n (cycloalkane)

Alkene (-ene

ending)

At least one double bond

(C=C)

CnH2n
Alkyne (-yne

ending)

At least one triple bond

(C=C)

CnH2n-2

Interesting fact:  a double bond is more reactive than a single bond as the second covalent bond is weaker, meaning the electrons are held less tightly.  Triple bonds are even more reactive as there are 2 highly reactive weak bonds out of the three.

How to name organic compounds!

Prefix  +  Root +  Suffix

-ane, -ene , -yne or indicate type of functional group (ketone = -one)

# carbons in the main chain; memorize root names

What is attached to the main chain (alkyl group)

How to Name Hydrocarbons:

STEP 1 Find the root: Identify the longest chain or ring in the hydrocarbon.  If the hydrocarbon is an alkene or an alkyne, make sure that you include any multiple bonds in the main chain.  Remember that the chain does not have to be in a straight line.  Count the number of carbon atoms in the main chain to obtain the root.  If it is a cyclic compound, add the prefix –cyclo- before the root.

Dashes separate #’s and words.

Commas separate numbers

Examples:

CH2—CH3

H3—C—CH2—CH3

CH3

H3C—C==C—CH2—CH3

CH3

CH3

STEP 2 Find the suffix: If the hydrocarbon is an alkane, use the suffix –ane.  Use –ene if the hydrocarbon is an alkene.  Use –yne if the hydrocarbon is an alkyne.  If more than one double or triple bond is present, use the prefix di-(2) or tri-(3) before the suffix to indicate the number of multiple bonds.

Example;

HC==CH—CH2—CH3

CH3—C==C—C==C—CH3

STEP 3 Give a position to every atom in the main chain. Start from the end that gives you the lowest possible position number for the double or triple bond, if there is one.  If there is no double or triple bond, number the compound so that the branches have the lowest possible position numbers.

Example;

STEP 4 Find the prefix: Name each branch as an alkyl group, and give it a position number.  If more than one branch is present, write the names of the branches in alphabetical order.  Put the position number of any double or triple bonds after the position numbers and names of the branches, just before the root.  This is a prefix.  Note:  Use the carbon atom with the lowest position number to give the location of a double or triple bond.

Example:

CH3

HC—CH—CH2—CH3

H3C—C

CH3

Step 5 Put the name together: prefix  +  root + Suffix.

 

Citation


St. Rosemary Educational Institution. "How to Name Hydrocarbons (IUPAC)." http://schoolworkhelper.net/. St. Rosemary Educational Institution, Last Update: 2014. Web. Retrieved on: Friday 25th April 2014. http://schoolworkhelper.net/how-to-name-hydrocarbons-iupac/.
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