Nomenclature of alkanes

Reactions with halogens[ edit ] Main article: Free radical halogenation Alkanes react with halogens in a so-called free radical halogenation reaction.

Nomenclature of alkanes

We have borrowed the rules from there to explain further.

Number of Hydrogen to Carbons

Finding the parent hydrocarbon Find and name the longest continuous carbon chain. Use this name Nomenclature of alkanes the parent name of the molecule.

A sample problem below will make it easier to understand. What is wrong with finding the longest continuous carbon chain in alkane B? IUPAC rule 1 Alkane A has 9 carbon atoms in the longest continuous chain with a substituent on carbon numbers 3 and 6. Finding the longest continuous carbon chain can be tricky as illustrated by the above structures.

Notice that both the structures are same but if you choose to take the wrong lane while counting the carbon atoms from one end to another, you can end up naming the structure with a wrong name. IUPAC Nomenclature of alkanes 1 If there are two or more longest chains of equal length, the one having the largest number of substituents is chosen.

The alkane shown in the figure 4 has 10 carbon atoms in the longest continuous chain counting from both branches at carbon number 5.

Nomenclature of alkanes

However, the green branch has 2 more substituents at carbon number 3 and 4. Therefore, the longest continuous chain chosen in this case is the branch highlighted in green color. Numbering the carbon chain Number the chain consecutively, starting at the end nearest a substituent group.

Now, the question is where to start the numbering. IUPAC second rule tells us to start numbering from the end where we first meet a substituent. Hence, the green way is the right way to number the carbon atoms. Subrule 2 If both ends of the root chain have equidistant substituents: Begin numbering at the end nearest a third substituent, if one is present.

Begin numbering at the end nearest the first cited group alphabetical order. Subrule 2a In case you encounter substituents equidistant from both ends of the longest continuous chain of carbon atoms, the third substituent can now play a crucial role.

According to IUPAC subrule 2a, we have to start numbering from the end nearest to this third substituent. In figure 6, the methyl group, highlighted in red, is nearest to the right end of the molecule as drawn. Therefore, the carbon atom attached to it should get the number 4 and not 6.

If the methyl group highlighted in red were not there, both ends would be equivalent. A sample problem would make things easier to understand. IUPAC subrule 2b may help. Subrule 2b When we have substituents equidistant from both ends of a structure, IUPAC subrule 2a tells us to choose the end nearest to the third substituent.

Naming alkanes

According to the subrule 2b, between the equidistant substituents, the one which precedes the other in alphabetical order will get the priority. Assigning the prefix and the locant Designate the location of each substituent group by an appropriate number and name.

In this page, we are discussing only about alkanes and therefore we have only alkyl groups as the primary functional groups.

Notice, we are also following the rules 1 and 2. Sample problem 3 The longest continuous carbon chain is highlighted in green and the only substituents are the methyl groups at carbon number 3. We have to use as many numbers as there are substituents.

So, we have to name both the methyl groups. As they are both on carbon number 3, they are both given the name 3-methyl.Nomenclature of alkanes Naming straight-chain alkanes Naming of straight chain alkanes (alkanes that do not branch) is a straightforward process.

In chemical nomenclature, the IUPAC nomenclature of organic chemistry is a systematic method of naming organic chemical compounds as recommended by the International Union of Pure and Applied Chemistry (IUPAC). Jan 04,  · Are you confused by IUPAC nomenclature?

Let Professor Dave help! First I'll explain what line notation represents, and then I'll introduce the basic rules for naming alkanes.

Naming branched alkanes. The nomenclature becomes more complex if the alkane branches. In such a case, there are several rules that you must follow to give the alkane the correct name.. Find the longest chain of carbons in the molecule. Alkanes - saturated hydrocarbons The names of the straight chain saturated hydrocarbons for up to a 12 carbon chain are shown below.

The names of the substituents formed by the removal of one hydrogen from the end of the chain is obtained by changing the suffix -ane to -yl. Rules for Naming Alkanes The parent name of the molecule is determined by the number of carbons in the longest chain.

In the case where two chains have the same number of carbons, the parent is the chain with the most substituent s.

Nomenclature of Alkanes - Chemistry LibreTexts