>> View the other Key Equations and Concepts in this chapter

Identifying Functional Groups

The basic organic structure is carbons and hydrogens, all singly bonded to each other. These are called alkanes. Any variation from that basic structure is called a functional group. Knowing the types of functional groups is basic to an understanding of organic chemistry. A list of functional groups is shown in Table I. In this table, R represents a group of carbons and hydrogens not relevant to the functional group. The R groups do not have to be the same.

Name	Condensed Formula	Description
alkene	R2C=CR2	contains a C=C double bond
alkyne	RCCR	contains a CC triple bond
alcohol	ROH	contains O singly bonded to a C and a H
ether	ROR	contains O singly bonded to two C
aldehyde	RCHO	contains C doubly bonded to O and singly to H
ketone	RCOR	contains C doubly bonded to O and singly to two C
hemiacetal	ROCOHR	contains C singly bonded to O of ether and of alcohol
carboxylic acid	RCOOH	contains C doubly bonded to O and singly to O of OH
amine
primary	RNH2	contains N singly bonded to one C and two H
secondary	R2NH	contains N singly bonded to two C and one H
tertiary	R3N	contains N singly bonded to three C
aromatic		contains a flat six-membered ring

>> Example

Identify the functional groups of the following compounds

Solution:

1. This is all carbons and hydrogens, with no double bonds. It has no functional groups and is an alkane.
2. This has an ether (the oxygen in the middle) and an alcohol (the OH group at the end).
3. Although a cyclic compound, this has no functional groups. It is an alkane.
4. There is a double bond between carbons at the top of the ring, an alkene. There is a nitrogen in the ring, so it must be bonded to two carbons, making it a secondary amine. The OH group at the end is an alcohol.
5. The COOH at the end makes this a carboxylic acid.
6. The hexagonal ring with the alternating double bonds makes this an aromatic. The NH₂ group is a primary amine. The carbon with the double bond to an oxygen and a single bond to a hydrogen is an aldehyde.
7. The carbon in the center with the double bond to the oxygen is a ketone.
8. On the back right side of this molecule is a carbon that is bonded to the oxygen of an ether and the oxygen of an alcohol. That makes this a hemiacetal. In addition to the hemiacetal, there are two more alcohol groups, one with the CH₂OH and the other on the bottom left.

>> View the other Key Equations and Concepts in this chapter