19.5 Families of Organic Molecules – Functional Groups

Learning Objectives

By the end of this section, you will be able to:

  • Identify and describe functional groups in organic molecules.

Organic molecules can be classified into families based on structural similarities. Within a family, molecules have similar physical behavior and often have predictable chemical reactivity. The structural components differentiating different organic families involve specific arrangements of atoms or bonds, called functional groups. If you understand the behavior of a particular functional group, you can describe the general properties of that class of compounds.

The simplest organic compounds are in the alkane family and contain only carbon–carbon and carbon–hydrogen single bonds but do not have any specific functional group. Hydrocarbons containing at least one carbon–carbon double bond, (denoted C=C), are in the alkene family. Alkynes have at least one carbon–carbon triple bond (C≡C). Both carbon–carbon double bonds and triple bonds chemically react in specific ways that differ from reactions of alkanes and each other, making these specific functional groups.

In the next few chapters, we will learn more about additional functional groups that are made up of atoms or groups of atoms attached to hydrocarbons. Being able to recognize different functional groups will help to understand and describe common medications and biomolecules such as amino acids, carbohydrates, and fats. Table 19.5a. below list several of the functional groups to become familiar with as you learn about organic chemistry.

The table here summarizes the structures discussed in this chapter:

Table 19.5a. Summary of the Classification of Organic Compounds.

This table provides compound names, structures with functional groups in red, and examples that include formulas, structural formulas, ball-and-stick models, and names. Compound names include alkene, alkyne, alcohol, ether, aldehyde, ketone, carboxylic acid, ester, amine, and amide. Alkenes have a double bond. A formula is C subscript 2 H subscript 4 which is named ethene. The ball-and-stick model shows two black balls forming a double bond and each is bonded to two white balls. Alkynes have a triple bond. A formula is C subscript 2 H subscript 2 which is named ethyne. The ball-and-stick model shows two black balls with a triple bond between them each bonded to one white ball. Alcohols have an O H group. The O has two pairs of electron dots. A formula is C H subscript 3 C H subscript 2 O H which is named ethanol. The ball-and-stick model shows two black balls and one red ball bonded to each other with a single bond. There are four white balls visible. Ethers have an O atom in the structure between two R groups. The O atom has two sets of electron dots. A formula is ( C subscript 2 H subscript 5 ) subscript 2 O which is named ethanal. The ball-and-stick model shows two black balls bonded to a red ball which is bonded to two more black balls. All bonds are single. There are five white balls visible. Aldehydes have a C atom to which a double bonded O and an H and an R are included in the structure. The O atom has two sets of electron dots. A formula is C H subscript 3 C H O which is named Ethanal. The ball-and-stick model shows two black bonds bonded to two red balls. The ball-and-stick model shows two black balls bonded with a single bond and the second black ball forms a double bond with a red ball. There are three white balls visible. Ketones show a C atom to which a double bonded O is attached. The left side of the C atom is bonded to R and the right side is bonded to R prime. The O atom as two sets of electron dots. The formula is C H subscript 3 C O C H subscript 2 C H subscript 3 and is named methyl ethyl ketone. The ball-and-stick models shows four black balls all forming single bonds with each other. The second black ball forms a double bond with a red ball. There are five white balls visible. Carboxylic acids have a C to which a double bonded O and an O H are included in the structure. Each O atom has two sets of electron dots. A formula is C H subscript 3 C O O H which is named ethanoic or acetic acid. The ball-and-stick model shows two black balls and one red ball forming single bonds with each other. The second black ball also forms a double bond with another red ball. Three white balls are visible. Esters have a C atom which forms a double bond with an O atom and single bond with another O atom which has an attached hydrocarbon group in the structure. Each O atom has two sets of electron dots. A formula is C H subscript 3 C O subscript 2 C H subscript 2 C H subscript 3 which is named ethyl acetate. The ball-and-stick model shows two black balls, a red ball, and two more black balls forming single bonds with each other. The second black ball forms a double bond with another red ball. There are five white balls visible. Amines have an N atom in the structure to which three hydrocarbon groups, two hydrocarbon groups and one H atom, or one hydrocarbon group and two H atoms may be bonded. Each n has a single set of electron dots. A formula is C subscript 2 H subscript 5 N H subscript 2 which is named ethylamine. The ball-and-stick model shows two black balls and one blue ball forming single bonds with each other. There are five white balls visible. Amides have a C to which a double bonded O and single N incorporated in a structure between two hydrocarbon groups. One hydrocarbon group is bonded to the C, the other to the N. Amides can also have a H atom bonded to the N. The O atom as two sets of electron dots, and the N atom has one set. A formula is C H subscript 3 C O N H subscript 2 which is named ethanamide or acetamide. The ball-and-stick model shows two black balls and one blue ball forming single bonds with each other. The second black ball forms a double bond with one red ball. There are four white balls visible.
Source: Summary of the Classification of Organic Compounds. (credit: Chemistry (OpenStax), CC BY 4.0).

Exercise 19.5a

Exercise 19.5a (text version)

Organic Functional Groups: Match the organic structure (1-10) with its functional group.

Structures:

  1. CH3CH3
  2. CH2=CH2
  3. CH≡CH
  4. CH3OH
  5. CH3COCH3
  6. CH3CHO
  7. CH3COOH
  8. CH3COOCH3
  9. CH3CONH2
  10. CH3NH2

Functional Group List:

amide, alkane, carboxylic acid, alkene, alcohol, ketone, alkyne, amine, aldehyde, ester

Check Your Answers:[1]

Source: Exercise 19.5a by Samantha Sullivan Sauer is licensed under CC BY-NC 4.0

Exercise 19.5b 

Exercise 19.5b (text version)

Organic Functional Group Naming: Match the organic structure (1-10) with its functional group name.

Structures:

  1. CH3CH3
  2. CH2=CH2
  3. CH≡CH
  4. CH3OH
  5. CH3COCH3
  6. CH3CHO
  7. CH3COOH
  8. CH3COOCH3
  9. CH3CONH2
  10. CH3NH2

Functional Group Names List:

-amide, -ane, -oic acid, -ene, -ol, -one, -yne, -amine, -al, -oate

Check Your Answers:[2]

Source: Exercise 19.5b by Samantha Sullivan Sauer is licensed under CC BY-NC 4.0

Spotlight on Everyday Chemistry: Doping in Sports

Doping in sports continues to make headlines as some athletes have turned to various drugs to enhance their performance against their opponents. Regulating bodies of professional sports monitor doping closely. The infographic looks at the major drugs used in doping.

Infographic 19.5a:  Read more about “A Brief Guide to Doping in Sports” by Andy Brunning / Compound Interest, CC BY-NC-ND, or access a text-based summary of infographic 19.5a [New tab].

Links to Enhanced Learning

Explore two infographics Functional Groups in Organic Chemistry (first infographic) and Functional Groups in Organic Chemistry (second infographic) by Compound Interest for an extensive summary of functional groups.

Complex molecules have multiple functional groups within them. Explore the infographics from Compound Interest for a comprehensive look at:

Attribution & References

Except where otherwise noted, this page is adapted by Adrienne Richards from:

  1. 1. alkane 2. alkene 3. alkyne 4. alcohol 5. ketone 6. aldehyde 7. carboxylic acid 8. ester 9. amide 10. amine ↵
  2. 1. -ane 2. -ene 3. -yne 4. -ol 5. -one 6. -al 7. -oic acid 8. -oate 9. -amide 10. -amine ↵
definition

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Organic and Biochemistry Supplement to Enhanced Introductory College Chemistry Copyright © 2024 by Gregory Anderson; Caryn Fahey; Adrienne Richards; Samantha Sullivan Sauer; David Wegman; and Jen Booth is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

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