Question

If you know of any way that I can better understand functional groups, please share. I am still having difficulty understanding how to identify them in a compunds. Thank you in advance!

Answer 1

We generally associate functional groups with organic compounds.

In organic chemistry, we have divided organic compounds basically into 2 categories:

1) Acyclic or open chain or aliphatic compounds 2) Cyclic or closed chain compounds

Now basically Aliphatic compounds are again classified into a) Saturated (Alkanes) b) Unsaturated (Alkene or alkynes)

Now, we know know how to identify each of them i.e alkane (C_nH_2n+2) , alkene (C_nH_2n), alkynes (C_nH_2n-2).

where n represents the number of Carbon atoms. This give rise to homologous series.

A functional group is defined as a group of atoms responsible for the characteristic reactions of a particular compound.

.Now, if we replace 1 H atom from any of these alkane/alkene/alkyne and replace with various groups like -OH, -CHO, -COOH, -COCl, -CO-, -NH₂, -CONH₂, -COOR (where R can be any alkyl or aryl group) give rise to a new set of molecules.

e.g CH₄ is methane and CH₃OH is methanol. Look carefully what is the change that has taken place. One H from methane is removed and a -OH is placed instead. Hence, -OH is a functional group. Now properties of CH₃OH is different from CH_4.Methane is a gas used for cooking where as methanol is a solvent (liquid).

Similarly, CH₃CHO is acetaldehyde, One of the H is replaced by -CHO group.

CH₃NH₂ is methyl amine.

One simple way of identifying a functional group may be to see that a functional group doesnot comprise of C and H only. If there is a heteroatom i.e atom other than C and H only in any of your compound, then it is a functional group.

CH₃CH₂CH₂OCH₂CH₃ in this example, it was a normal alkane until 'O' atom is inserted in between them. Thus -O- linkage is called an ether linkage.

CH₃CH₂COCH₃ -- if you write the open structure of this compound then you will find that, although 'O' in this case not the part of the chain but is attached to one of the carbon separating two alkyl groups CH₃CH₂ on the left and CH₃ on the right. Thus it is treated as a functional group and it is known as keto group.

CH₃CH₂Cl --Here one of the H atom from ethane is replace by a Cl atom which is ofcourse an heteroatom i.e not C or H. Hence it is a functional group and is called as halo group (Chloroethane).

Hope this will be helpful