Chemistry 211
Fall 2013
Structural Representations of Organic Compounds & The Learning Cycle
Process Learning Goals:
1.
To recognize patterns in different types of structural representations and use them to relate one type of representation to another.
2.
To correctly convert one type of structural representation into another.
Content Learning Goals:
1.
To correctly interpret the most common organic structural representations.
2.
To recognize and label the elements of a Learning Cycle Activity.
Introduction:
1.
Structure-Function Relationships:
From many years of study, organic chemists have developed elaborate theories to explain the structures and the reactivities of molecules. The
consensus from their vast experience is that the behavior of molecules should be directly related to their molecular structure.
Thus, we will begin our consideration of organic chemistry by looking at a range of organic molecular structures and at theories for explaining why
certain structures are more likely to react than are others. Although theories are generally expressed in technical terms, we should recognize that they
simply provide us with models or pictures to use in thinking about structures or processes that are actually invisible. Thus, structural models can be
thought of as:
MACROSCOPIC METAPHORS FOR MOLECULAR STRUCTURES.
2. Representations (Metaphors) for Molecular Structures
(See also, CGW pp. 17-27 & Rev. Gen. Chem. & Math #'s 23->25)
a. Need for Representations:
Before we begin to develop theories to explain properties of molecular structures, we need to have methods for visualizing potential structures
and communicating them to others. Several methods for representing molecular structures are in general use, thus to understand theories that
have been developed and to communicate our own discoveries to others:
WE MUST BE ABLE TO WRITE, READ & UNDERSTAND ALL TYPES OF REPRESENTATIONS
FOR MOLECULAR STRUCTURES
This class group activity is designed to assist you in gaining the ability to interpret and compare the various methods for representing molecular
structures. CGW (pp. 17-27) gives a slightly different, but interesting discussion of why it is important to understand structures and how to deal with
them.
b. Two Dimensional Structural Representations:
Depending upon the aspect of an organic structure that is to be emphasized, organic chemists use various types of structural representations. You
are familiar with some of these representations, but are probably not facile with the use of all of them. Model 1 below illustrates three of the
common structural representation types:
(1.)
Lewis "Dot" Structures
(2.)
Dash Structures
(3.)
Bond-Line Structures (also called Line-bond Structures)
(4.)
Condensed Structures
211-12 Structural Representations
2
Activity
1.
Work together as a group, using only the information available in Table 1, to fill in the missing representations. For each structure you draw be
prepared to provide your explanation (warrant) for how your group devised the structure from the information in Table 1.
2.
How is a chemical bond represented in a Lewis “Dot”
Model 1
structure.
Provide Data from Table 1 and your warrant.
Table 1: Often Used Representations of Organic Molecules
Lewis "Dot"
H
Condensed
Bond-Line
:
:
H
:
H
Dash
H : C : C :C :H
:
:
:
H
H
H
:
::
:
:
:
H
H
What does a line in a Dash structure represent?
Provide Data from Table 1 and your warrant.
4.
What does the vertex in the first Bond-Line structure
represent? Provide Data from Table 1 and your warrant.
5.
What does C6H5 in the last condensed structure
represent? Provide Data from Table 1 and your warrant.
6.
Where are hydrogen atom symbols shown in BondLine structures? Provide Data from Table 1 and your
warrant.
H :O: H
H :O : H
H : C :C : C :H
3.
H
C
C
C
H
H
CH3COCH3
H
H
H
H
C
H
H
H
H
:
:
:
H
CH3CHCH2
C
C
O
:
H
H
H
: :
H
C C
H C
Cl
C
C C
H
H
C
C H
H H H
C6H5CHClCH3
N
:
CH3NHCH3
:
:
H
:
:
H
:
H : C : C :O:H
211-12 Structural Representations
7.
structure for the following compound:
H
C
C
H
Draw a bond-line 8.
CH3C6H4CH2OCH3
H
C
Draw Dash and Bond-
Line structures for
H
N
H
H
:
H
3
H
H
Provide your group’s warrant based on your experience in this Provide your group’s warrant based on your experience in this activity.
activity.
9.
Draw Dash and
Condensed structures for
10.
:
: Br:
Answer the following
questions about the structure below and provide your warrant based on your
experience in this activity.
a.
How
many carbon atoms are there in the compound?
Your group’s warrant:
Provide your group’s warrant based on your experience in this activity.
b.
atoms are attached to each of the carbon atoms?
Write the number next to each carbon atom.
How many hydrogen
Warrant:
11.
a.
:
Work together as group to add the molecular formula and a dash structure below each of the following structures:
b.
c.
d.
e.
H
H
H
H H
CH3OCH2CH2NHCH3
(CH3)2CHC(CH3)2CHOHCH3
O
H C
H
N
H : C : C :O: C:C H
Mol. Form.
Mol. Form.
O
H
H H
Dash
Dash
Mol. Form.
Mol. Form.
Dash
Mol. Form.
Dash
:
: ::
:
:
:
:
:
:
:
:
:
:
:
Dash
211-12 Structural Representations
12.
Sometimes structure types are mixed in order to emphasize particular aspects of a structure. Note also that lone pair electrons are not always
included if they are not important to the discussion.
a. Consult as a group and then, below each mixed structure, draw a bond-line structure including any lone pair electrons that might be present.
b. For each mixed type structure, circle the part of the structure that is being emphasized. Provide your warrant cite specific data.
H
O
H
C
H
13.
4
O
C
CH3
H
C
CH2
H
As a group, decide which type of structure each of the following statements best describes it and provide your warrant:
a. Provides the most explicit information about the structure. (Requires the least interpretation.)
Warrant:
b. Is the easiest to draw.
Warrant:
Three Dimensional Structure Representations: Molecular Models:
Actual three-dimensional representations of three-dimensional structures.
(See the instruction manual for your molecular model kit. Atoms are represented by variously colored and shaped plastic pieces and bonds are represented by various plastic rods.)
Reading Assignments: Rev. Gen. Chem. & Math #'s 23->25, CGW pp. 17-27
211-12 Structural Representations
5
The Learning Cycle
Model 2
POGIL activities are written using the “Learning Cycle”, which enhances learning through:
1.
Exploration (E) of a model; using guiding questions to examine data and develop evidence from the model.
2.
Invention of a concept (I) through making sense of the evidence from the model to draw out the concepts.
3.
Application (A) of the new concepts to new situations through higher order thinking skills.
Figure 1
LEARNING CYCLE1,2,3
(Karplus, Piaget, Abraham)
Karplus and Thier. A New Look at Elementary school Science. Chicago rand McNally (1967)
Piaget, J. J. Res. Sci. Teach. 1964.2.176
3 Abraham, M.R.; Renner, J.W. “The sequence of learning cycle activities in high school chemistry”, J. Res. Sci. Teach. 1986, 23, 121-143.
1
2
1. What does the E stand for in Figure 1? Provide your group’s warrant.
2. What might be introduced during the Concept Invention portion of the Learning Cycle? Provide your group’s warrant.
3. What type of questions would be found at the deductive end of the Learning Cycle? Provide your group’s warrant.
4. Working together, go back to the “Structural Representations of Organic Compounds” section and label each question with an E for Exploration,
an I for concept Invention or an A for Application. It is possible that some questions could be E & I or I & A. Be prepared to provide your
group’s warrant for each designation.
5. How do your designations of questions in the activity correspond to the sequence presented in Figure 1?
211-12 Structural Representations
6
Reflector’s Report Discussion
As a group, summarize what you believe to be the most important points of the two sections of this activity, Structural Representations of Organic
Compounds and The Learning Cycle.
Structural Representations of Organic Compounds:
The Learning Cycle
Have your group members fulfilled the learning goals (See p. 1). Explain.
Strategy Analyst’s Report Discussion
As a group, analyze the sequence of the models and questions in this activity. Note how the logic outlined in the activity helped your group reach the
conclusions summarized in the Reflector’s Report Discussion. Summarize your group’s conclusions.