byrd2001

In the Classroom
Learning the Functional Groups: Keys to Success
Shannon Byrd
Francis Marion University, Florence, SC 29536
David P. Hildreth*
Department of Education Studies, Guilford College, Greensboro, NC 27410
One of the major organizational principles of organic
chemistry is functional groups. Functional groups are the
specific groups of atoms attached to a backbone, or framework,
of carbon atoms that influence the chemical and physical
properties of molecules. They are the sites of chemical reactions
in organic compounds. Organic compounds are classified
into a relatively small number of classes of structure by their
functional groups.
In high school and collegiate chemistry courses, textbooks customarily present functional groups in a chart, listing
the class, structure, IUPAC prefix or suffix, and an example
(see Table 1). Students are expected to learn this chart.
The key is dichotomous. At each step, students must choose
one of two yes/no statements, which are the opposite of each other
and together include all possibilities. For example, to distinguish
an alkane from an alcohol, students must choose between
“the molecule is a hydrocarbon” (alkane) and “the molecule
is not a hydrocarbon” (alcohol). By using this “the molecule
is…the molecule is not approach”, students are able to focus
on one characteristic at a time, thereby improving their chances
of correctly using and learning from the key.
Table 1. Part of a Typical Chart of the Functional Groups
Important terms on the key must be defined clearly. For
example, a hydrocarbon is defined as a molecule that contains
only carbon and hydrogen atoms. There must be an answer
key, and additional information about each functional group
should be provided so that as students learn how to identify
the functional groups, they can also learn important facts
about them. For example, an important fact about alkanes
is that their general formula is CnH2n+2. The glossary and
annotated answer key that accompany the example in Figure 1
are given in the Appendix.
Class
Structure
IUPAC Prefix or Suffix
Example
Alcohol
R–OH
-ol
CH3OH
Amine
R–NH2
-amine
CH3CH2NH2
Many students memorize the chart instead of actually
learning to identify the functional groups. (If they are lucky,
they are taught how to identify functional groups in lab, using
infrared spectroscopy or even scanning tunneling microscopy
[1].) If students simply memorize a chart, more often than
not they forget the functional groups shortly after an examination; this precludes their being able to apply the material to
future topics such as chemical reactions, nomenclature, VSEPR
theory, and amino acids.
Textbook authors typically break the functional groups
into three categories: those containing either oxygen, nitrogen,
or sulfur or halogen. A pedagogical aid that could be helpful
in teaching and learning the functional groups is a classification
key. Classification keys are used to sort or identify items on
the basis of their characteristics, usually physical ones. They
are commonly used in biology to classify and identify organisms (2). The use of classification keys helps students not
only to learn the content inherent in the key itself but also
to critically analyze the differences among and between items,
thereby improving their critical thinking abilities.
Important Considerations When Developing a Key
for Classroom Use
Variations
Other common functional groups could have been used,
such as nitrile, ether, or thiol. Functional groups can also be
depicted in generic form (R–COOH), as is typical in textbooks,
or in an example (H3C–COOH), as in the structure below.
H
H
O
C
C
OH
H
One could use just the generic form or a combination of both.
Feedback
Developing and Implementing the Functional Groups
Classification Key
Our classification key was developed to help students,
individually or in groups, learn the functional groups typically
taught in first-year (high school and college) chemistry classes.
Ten common functional groups were selected to represent the
alkane, alkene, alkyne, carboxylic acid, ester, aldehyde, ketone,
alcohol, amine, and amide series. The key was based on the
attributes of molecules that contain a single one of these functional groups. An example of the key and its use is shown in
Figure 1.
The dichotomous classification key was tested on students enrolled in high school, college freshman, and organic
chemistry courses. Students had to respond to sequential pairs
of opposite statements, only one of which could be true. In
this way, they were able to key out the sample molecules and
assign them to the appropriate chemical series. Some of their
comments are summarized below.
Student 1, who had taken high school chemistry the year
before, and Student 2, who had just completed a high school
chemistry course, both agreed that having this classification
key while learning the functional groups would have been
JChemEd.chem.wisc.edu • Vol. 78 No. 10 October 2001 • Journal of Chemical Education
1355
In the Classroom
very helpful when they were taking chemistry. Student 1 said
that when he had to learn the functional groups using the
chart, he just memorized them, not really knowing the difference between them. He stated that the key would help
students to actually learn to identify the functional groups
and not just memorize them. The additional information on
each functional group was also a helpful learning aid, stated
Student 1. Student 2 commented that having actual examples
was better than having the generic form (e.g., R–COOH).
Student 3, who was currently taking general chemistry
in college, commented that the key was easy to follow and fill
in. Student 3 also stated that the additional information on
each functional group was helpful. After Student 4, who had a
bachelor’s degree in Biology, filled in the classification key, she
asked, “Why didn’t you give this to me when I was taking
organic?” Student 5, who was taking organic chemistry, stated
H
H
H
C
H
C
H
C
H
H
H
H
H
O
C
C
H
H
CH3CH2CH3
C
C
A classification key offers teachers an alternative to tables
for teaching the functional groups. In addition, by using a different approach, teachers may be able to better accommodate
students’ various learning styles. As is evident by the comments
provided by students, learning the functional groups with the
aid of a classification key may be a key to success!
Literature Cited
1. Giancarlo, L.; Fang, H.; Avila, L.; Fine, L.; Flynn, G. J. Chem.
Educ. 2000, 77, 66–71.
2. Seevers, E. R. Science Activities 1978, 15 (4), 23–25.
H
H
H
H
CH3COOH
Conclusion
O
H
OH
that the key was a “more helpful way to learn” the functional
groups than learning and memorizing from a chart.
C
H
CHCH
CH3COH
O
C
H
H
C
C
H
H3C
OH
H
C
C
H
H
H
H
O
H
C
C
H
H
H
C
C
N
H
H
H
O
NH2
OH
1
H
CH3CH2NH2
CH3COCH3
OH
O
H
H
H
CH3CHCH2
CH3CH2OH
H
C
2
4
3
5
8
7
6
Classify these ten molecules and write the number of the molecule into the box.
Molecule is a hydrocarbon.
H
Molecule is not a hydrocarbon.
H
O
C
C
H
O
C
H
H
CH3COOCH3
Only
has
single
bonded
carbon
atoms.
Does
not only
have
single
bonded
carbon
atoms.
The carbon atom
bonded to the
nitrogen atom is
also double
bonded to an
oxygen atom.
alkane
2
Has a sp hybridized
carbon.
Does not
have a sp 2hybridized
carbon but
a sphybridized
carbon.
The carbon atom
bonded to the
nitrogen atom is
not also double
bonded to an
oxygen atom.
Does
not
have
two
oxygen
atoms.
Has an
oxygen atom
bonded to a
sp 3- hybridized
carbon atom.
amine
amide
Has an oxygen
atom not
bonded to a
3
sp - hybridized
carbon atom.
alcohol
Has C=O
with an
OH group.
alkene
O
9
Has
two
oxygen
atoms.
Has C=O
without
an OH
group.
alkyne
carboxylic
acid
C atom in
C=O is
bonded to
two other
carbon
atoms.
C atom in
C=O is not
bonded to
two other
carbon
atoms.
ester
ketone
aldehyde
Figure 1. The classification key and exercise for functional groups.
1356
H
H
O
C
C
N
H
H
CH3CONH2
O
O
Does not have a
nitrogen atom.
Has a
nitrogen
atom.
H
Journal of Chemical Education • Vol. 78 No. 10 October 2001 • JChemEd.chem.wisc.edu
NH2
10
H
In the Classroom
Appendix
Glossary
Hydrocarbon—a molecule that contains only hydrogen (H) and
carbon (C) atoms.
sp2-Hybridized—consists of double bonds, e.g. C=C. Only two
of the three p orbitals are used to form sp2 hybrid orbitals; bond angle
is 120°; consists of one sigma (σ) bond and one pi (π) bond.
sp3-Hybridized—consists of single bonds, e.g. C–C. A set of hybrid
orbitals constructed from one s orbital and three p orbitals; bond angle
is 109.5°; consists of one σ bond.
sp-Hybridized—consists of triple bonds, e.g. C≡C. The hybrid
orbital consists of only one of the three p orbitals; consists of one σ bond
and two π bonds; bond angle is 180°.
Hybrid orbitals—orbitals used to describe bonding, obtained by
taking combinations of atomic orbitals of the isolated atoms.
Sigma (σ) bond—has a cylindrical shape about the bond axis.
Formed either when two s orbitals overlap or when an orbital with
directional character, such as a p orbital or a hybrid orbital, overlaps
another orbital along the interatomic axis.
Pi (π) bond—has an electron distribution above and below the bond axis.
OH —hydroxyl group.
C=O —carbonyl group.
–NH2 —amino group.
Annotated Answer Key
A. Alkane
A1. example is propane [C3H8], 1
A2. single-bonded C atoms
A3. saturated C atoms
A4. carbon atoms can be bonded in chains or rings
A5. sp3-hybridized carbon atoms
A6. bonded either to other carbon atoms or to hydrogen atoms
A7. each compound’s name has suffix -ane
A8. have densities between 0.6 and 0.8 g cm᎑3
A9. pure alkanes are colorless, tasteless, and nearly odorless
A10. nonpolar
A11. not soluble in water
A12. general formula CnH2n+2 when bonded in a chain
A13. low-molecular-weight alkanes are gaseous fuels at room
temperature (methane, propane, ethane, butane)
A14. rotate freely when bonded in a chain
A15. undergo halogenation and oxidation reactions
B. Alkene
B1. example is propene (methylethylene) [C3H6 or CH3–CH=CH2], 6
B2. unsaturated carbon atoms
B3. double-bonded carbon atoms
B4. general formula CnH2n
B5. insoluble in water
B6. soluble in nonpolar solvents
B7. each compound’s name has suffix -ene
B8. restricted rotation
B9. geometric isomers
B10. undergo addition of HX to the double bond and hydrogenation
C. Alkyne
C1. example is ethyne [C2H2], 4
C2. each compound’s name has suffix -yne
C3. triple-bonded carbon atoms
C4. sp-hybridized
C5. bond angle 180°
C6. unsaturated carbon atoms
C7. undergo hydrogenation and halogenation
C8. general formula CnH2n–2
D. Amide
D1. example is ethanamide [CH3CONH2], 10
D2. form strong intermolecular hydrogen bonds between the amide
hydrogen atom of one molecule and the carbonyl oxygen atom
of a second molecule, resulting in high melting and boiling points
D3. amides with low molecular weights dissolve in water
D4. nitrogen atom is bonded to an sp2-hybridized carbon atom
E. Amine
E1. example is ethanamine or ethylamine [CH3CH2NH2], 8
E2. derivative of ammonia in which one or more hydrogen atoms
are replaced by alkyl or aryl groups
E3. nitrogen atom is bonded to an sp3-hybridized carbon atom
E4. smells like dead fish
F. Carboxylic acid
F1. example is ethanoic (acetic) acid [CH3COOH], 2
F2. contains carbonyl group and –OH group attached to the
carbonyl carbon
F3. each compound’s name has suffix -oic and term acid
F4. undergo neutralization of base, esterification, and hightemperature decomposition reactions
G. Ester
G1. example is methyl ethanoate [CH3COOCH3], 9
G2. the carbonyl carbon atom is bonded to an alkoxy group such
as –OCH3
G3. undergo acid hydrolysis and saponification reactions
G4. smells sweet
H. Alcohol
H1. example is ethanol [CH3CH2OH], 5
H2. each compound’s name has suffix -ol
H3. organic compound with hydroxyl group bonded to sp3hybridized carbon atom
H4. undergo oxidation to form aldehydes or ketones, dehydration
to form alkenes, formation of esters, conversion to halides
I. Ketone
I1. example is propanone [CH3COCH3], 7
I2. carbonyl group C=O
I3. each compound’s name has suffix -one
I4. undergo reactions with Grignard reagents, HCN, and alcohols
J. Aldehyde
J1. example given is ethanal (acetaldehyde) [CH3CHO], 3
J2. contains carbonyl group
J3. compound’s name has suffix -al
J4. bond angles around the carbonyl carbon atom are approximately 120°; sp2-hybridized C
J5. the lower-molecular-weight compounds dissolve in water in
all proportions
J6. undergo reactions with Grignard reagents, HCN, and alcohols
JChemEd.chem.wisc.edu • Vol. 78 No. 10 October 2001 • Journal of Chemical Education
1357