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Different Types of Organic Molecules

Naming Organic Molecules

Shaping of Organic Molecules

Practice Problems



Naming Organic Molecules

Organic Chemistry requires lots of memorization and in naming different organic compounds, there are lots of rules to remember. Most of these rules involve changing a suffix. Each classification of organic molecule, listed on the previous page, has a specific way to systematically name the compound. For example, a hydrocarbon with a double carbon-carbon bond is an alkene, so its systematic name will end with -ene. On this page is a list of the different classes of organic molecules and how to name them.

Alkanes:
    All organic compounds are bases on simple alkanes. The following is a list of alkanes and their molecular formulas.

Molecular
Formula   		 Name
 State at
Room Temp.               		 Molecular
Formula      		 Name
 State at
Room Temp.
CH4 Methane    gas C11H24 Undecane liquid
C2H6 Ethane gas C12H26 Dodecane liquid
C3H8 Proane gas C13H28 Tridecane liquid
C4H10 Butane gas C14H30 Tetradecane liquid
C5H12 Pentane liquid C15H32 Pentadecane    liquid
C6H14 Hexane liquid C16H34 Hexadecane liquid
C7H16 Heptane liquid C17H36 Heptadecane solid
C8H18 Octane liquid C18H38 Octadecane solid
C9H20 Nonane liquid C19H40 Nonadecane solid
C10H22 Decane liquid C20H42 Eicosane solid

As seen from the chart, alkanes are named by counting the number of carbon atoms, applying the appropriate base word, and adding the suffix -ane. You might see a name such as n-butane. The n in this case means "normal." This is the most common, most "normal" form of butane.

Cyclic alkanes:
    In naming cyclic alkanes, the rules for naming normal alkanes apply, only the term cyclo is added as a prefix for the name. For example, when hexane is in cyclic form, it becomes cyclohexane.

Alkenes and Alkynes:
    For alkenes and alkynes, names are derived by changing the ending of the name of the corresponding alkane to -ene or -yne, respectively. Since alkenes and alkynes have double and triple bonds, this plays a part in their names. A number written in front of the name indicates where the special bond is located. Counting carbons along the chain until you reach a carbon that shares a double or triple bond will give you this number. You always want to have the smallest number possible, so you want to start from the end where the double or triple bond is closest. Thus, "2-pentene" means you have a pentene molecule (C5H10) and the double bond is located between the second and third carbon atoms. The same rules apply to alkynes. When more than one double bond is present, the name includes multiple numbers. "1,3-propadiene" means you have three carbon molecule with two double bonds; one between the first and second carbon atoms, and one between the second and third carbon atoms.

You might find an organic molecule sometime with what appears to be two names in one. 2-ethyl pentane, for example. What is happening here is an ethyl group and a pentane chain are bonded on the second carbon in the five carbon pentane molecule. When different groups branch off eachother, they are named by first, identifying the longest carbon chain. The smaller carbon groups are then identified and this is named first with the number of the carbon it's attatched to, and then the longer group is named. More examples include 1,2-dibromoethane where two bromine atoms are bonded to the two carbons in ethane. 2,3-diethylhexane means an ethyl group is bonded to the second and third carbons in a hexane molecule. 2,2,4-trimethylpentane tells us there are two methyl groups bonded to the second carbon atom of a pentane chain, and a third methyl group bonded to the fourth carbon in the chain.

Alcohols:
    Naming alcohols involves taking the name of the corresponding alkane, and replacing the -e with -ol. When a compound has two -OH groups, the ending becomes -diol and with three, it becomes -triol. Alcohols can be primary alcohols, secondary alcohols, or tertiary alcohols. With primary alcohols, the carbon that is bonded to the -OH group is also bonded to two other hydrogen atoms. For a secondary alcohol, the carbon is bonded to a hydrogen atom and another carbon. For a tertiary alcohol, the carbon bonded to the -OH group is also bonded to two other carbon atoms.

Aldehydes and Keytones:
    For aldehydes, the appropriate suffix for the alkane base is -al. Oft times, however, the suffix -aldehyde is simply included in the common name. For keytones, the suffix for the alkane base is -anone. The term keytone is in the common name of most keytones.

Carboxylic Acids:
    Naming carboxylic acids involves dropping the -e from the methane name, and adding -oic acid. Examples include Methanoic acid, and Butanoic acid.

Esters:
    Since esters are simply the combination of an alcohol and a carboxylate group, their names consist of a combination of these. Normally, the names of esters come in the form of "alkyl carboxylate." Ethyl acetate and and butyl buanoate are both esters.

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