While finding out the IUPAC names of organic compounds, should I count the number of the carbon atoms which is attached to the functional group and having the bond in the very same direction in which I counted the former (i.e., the attachment of the functional group)? I am facing this confusion while solving questions based on the IUPAC nomenclature.

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To name Organic compound the functional group priority must be followed. For which below is the Priority Table : enter image description here

enter image description here

Follow the function group priority. Count from the carbon of highest priority such that lowest locant number are given to every carbon. Denote the low priority groups as their corresponding prefixes and the greatest priority group is included in the name of the parent chain.


First of all, alkenes are hydrocarbons. So they do not contain any functional group except the double bond, '='(though i prefer to regard and call it as bond and not functional group). By reading the details of your question, i presume that you are facing difficulties in writing the IUPAC names of organic compounds in general and not only hydrocarbons since you use the word "bond" as well as the phrase "functional group".

To write the IUPAC name for any organic compound in general proceed as below:

1.First, inspect the molecule of the compound for functional groups, multiple bonds and substituent groups.

If more than one type of functional group is present, then, from the seniority table of functional groups find out which of the functional group(s) present in the compound is the located highest in the table. That functional group is known as the primary functional group and the rest are known as secondary functional group(s).

If only one type of functional group is present then that functional group is the primary functional group and there is no secondary functional group.

2.Then, find out the longest carbon atom chain (in the molecule of the organic compound) which contains (if they are present) the maximum number of functional groups (including the primary functional group), multiple bonds and substituent groups.

3.If functional group(s) are present then the carbon atoms are numbered from such an end that the sum of the position numbers of the primary functional group is the least.

If functional group(s) are not present but multiple bonds are present then between the double bond and triple bond whichever multiple bond is nearest to an end, numbering is done from that end. If, different multiple bonds occupy equal position numbers from both ends, then, the double bond gets greater priority over the triple bond and the numbering is done from the end to which the double bond is the nearest.

If both functional group(s) and multiple bond(s) are absent but substituent groups are present, then the numbering is done from an end corresponding to which the sum of the position numbers of the substituent groups is the lowest.

(In this rule, i have used the sum of locants rule which is actually a wrong generalization of the first point of difference rule but it works in most of the cases)

Note that priority(functional group)>priority(bond)>priority(substituent group)

4.Find out the number of carbon atoms in this chain.

5.A typical IUPAC name has the following structure-

$\ce{secondary prefix + primary prefix + word root + primary suffix + secondary suffix}$


The complete secondary prefix consists of the name(s) of the substituent group(s) along with its(their) position numbers and the secondary functional group(s) along with its (their) position numbers arranged in alphabetical order.


The primary prefix indicates whether the compound is cyclic or not. If it is cyclic, the secondary prefix is cyclo otherwise it is left blank.


The word root indicates the number of carbon atoms in the longest carbon atom chain.

If it is 1 use meth, if 2 use eth, if 3 use prop, if 4 use but, for 5 or more use greek names for numbers, that is, pent, hex, etc.


The complete primary suffix consists of ane, if the compound has no multiple bonds.

If multiple bonds are present then it consists of

position number(s) + (di/tri and so on)ene for double bonds and position number(s) + (di/tri and so on) yne for triple bonds.(If the number of double bonds or triple bonds is more than 1 then correspondingly di, tri and so on is added before ene and yne) ( Note that the double bond part is written before the triple bond part)


The secondary suffix consists of the following :

position number(s) + (di/tri and so on)name used for primary functional group

6.Use '-' to separate a letter and a number and ',' to separate two numbers. If two vowels occur in succession drop the the second vowel.

Here is the seniority table for functional groups. enter image description here


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