Aldehydes - Structure and Nomenclature

In this article we will discuss about Structure and Nomenclature of Aldehydes in organic chemistry. Aldehydes are the organic compounds with one carbonyl group and general formula is RCHO. 

Aldehydes are the organic compounds which consist of an alkyl / aryl group and one hydrogen atom bonded to a carbonyl group. IUPAC nomenclature of aldehydes is described herein.

Key words: Aldehyde, Carbonyl compounds, Common Names and IUPAC nomenclature of Aldehydes.

Introduction

The aldehyde has general formula R-CHO; where R = alkyl / aryl group. The CHO group also known as formyl group.

Common Names of Aldehydes

Carboxylic acid	Structure	Name of Aldehyde	Structure
Formic acid		Formaldehyde
Acetic acid		Acetaldehye
Propionic acid		Propionaldehyde
Butyric acid		Butyraldehyde
Valeric acid		Valeraldehyde
Caproic acid		Caproaldehyde
Enanthic acid		Enanthaldehyde
Caprylic acid		Caprylic aldehyde
Pelargonic acid		Pelargonaldehyde
Capric acid		Caprinaldehyde

IUPAC Nomenclature

According to IUPAC nomenclature system the names of aldehydes are given based on the corresponding alkanes. There are certain steps we need to follow for writing name of the aldehyde.

Step 1: Select longest carbon chain which includes carbonyl group.

Step 2: Count number of carbons in the chain and assign name of corresponding alkane.

Step 3: Omit “e” from the alkane and add “al” to the name.

Step 4: If any substituents are present on the carbon chain. Then write them in alphabetical order along with the carbon number.

Sr. No.	Compound	Number of carbons in chain and name of alkane	Name of Aldehyde
1.		1; methane	methanal
2.		2; ethane	ethanal
3.		3; propane	propanal
4.		4; butane	butanal
5.		5; pentane	pentanal
6.		6; hexane	hexanal
7.		7; heptane	heptanal
8.		8; octane	octanal
9.		9; nonane	nonanal
10.		10; decane	decanal

   

Let’s see some more examples with substituting groups.

How to write name of the compound 1?

Firstly, select the longest carbon chain which consists of carbonyl group. Here longest carbon chain has 5 carbon atoms. So the name of alkane will be pentane and root name of aldehyde is pentanal. Give carbon number 1 to carbonyl carbon.

In this compound there is ethyl substituent at carbon number 3 and methyl group at carbon number 4. Write these groups as suffix in alphabetical order. So it will be 3-ethyl-4-methyl

Hence correct name of the above compound is 3-ethyl-4-methyl pentanal.

Now write name of the compound 2

It has 7 carbon atoms in the chain therefore name of the alkane is heptane. And root name of the aldehyde will be heptanal. Here there are three substituting groups present on the carbon chain. The bromo substituent is bonded to C-2, ichloro substituent is at C-4 and methyl group is attached to C-4. Hence the name of compound is 2-bromo-4-chloro-4-methylhepatane.

In case there are similar groups present in the molecule, then prefix like “di” , “tri” or “tetra” should be used. For example compound 3 has six carbons chain so root name will be hexanal. Since there are three methyl groups bonded to main carbon chain at C-2, C-3 and C-4; hence name of the compound is 2,3,4-trimethyl hexanal.

Examples for practice:

           

  

That's all for this topic. If you have any questions please feel free to ask me in the comment box. Thank you..!