Teaching a concept Hydrocarbon Isomers by hedongchenchen


									                Teaching a concept:
               Hydrocarbon Isomers
                              SCH4U - Organic Chemistry

André Gagnier and Nathan Hickey

University of Toronto – OISE - EAQ1330Y - Science Senior
Janine Extavour
July 21, 2011

B3. demonstrate an understanding of the structure, properties, and chemical behaviour of
compounds within each class of organic compounds.

B2.3 build molecular models for a variety of simple organic compounds [PR, AI, C]

B3.5 explain the concept of isomerism in organic compounds, and how variations in the properties
of isomers relate to their structural and molecular formulae

Background Information

Isomers are chemical products that have the same formulas but that have different molecular
structures and thus behave differently.

There are two main types of isomers covered in these activities:

      isomers of alkanes (constitutional isomers)
      isomers of alkenes (constitutional isomers and stereoisomers)

Constitutional isomers: isomers differ in the order in which the atoms are connected together so
they contain different functional groups and / or bonding patterns (e.g. branching).

Stereoisomers (geometric only): contain the same functional groups and branching patterns, they
differ only in the arrangement of atoms in space. Stereoisomers across a double bond are usually
designated with the prefixes cis- or trans-.

Teaching a concept: Hydrocarbon Isomers                                                            1
Advance Preparation

Before beginning this part of the organic chemistry unit, we are assuming that the students are
familiar with the following concepts and procedures:

      They must be fully acquainted to the nomenclature of organic chemistry.
      Students need to know how many bonds various atoms can make within a hydrocarbon
       molecule (C=4, O=2, H and halogen =1)
      Students know how to represent molecules using drawings.
      Students must remember that molecules are 3D structures.
      Students will already have experience using molecular models.
      Students will already have experience in lab safety techniques.

Required Materials

      Molecular models                                    Hot plates
      Propanol                                            Beakers
      Isopropanol                                         Graduated cylinders
      Electronic thermometer (probeware)                  Electronic balance
      Ring stand                                          Iron rings and wire gauze
      Bunsen burner

Student Difficulties

                  PROBLEM                                            SOLUTION

Students may think that changing the shape (ie.     Using molecular models, show that for it to be
  rotating a C-C bond) means a new isomer is           an isomer, bonds need to be broken and
                   created.                          replaced. Rotations do not create isomers.

  Understanding that cis- and trans- geometric       Using pictures and molecular models to allow
   isomers are, in fact 2 different substances.          students to see the 3D configuration.

Students think that isomers are always members        Using inquiry-based discovery, students will
of the same class of compound. (eg. the student     have to construct all the possible isomers. Using
  can think that any isomer of an alcohol must      pictures of 2 molecules (alcohol and ether) and
 also be an alcohol, when in fact it could be an     asking students to count the atoms. They will
                      ether).                           realize that the formulae are the same.

Teaching a concept: Hydrocarbon Isomers                                                                 2
     Lesson/Activity Sequence

 Day.                                             Concept                                              Teaching/           Assessment/
Activity                                                                                               Learning             Evaluation

  1.1      Introductory activity (hook):                                                              Inquiry-based      Assessment via
                                                                                                      learning           questioning
                   Identify the Isomers Challenge
                   Introduced as a game (hook)
                   Students are separated into groups and given an empirical formula of a
                    simple alkane (eg. C6H14) and asked to identify with molecular models and         Cooperative        Discussion in between
                    with hand-drawn images as many different molecules as they can that fit that      learning           answers
                   Time limit is given
                   The word “isomer” is not used
                   A small example can be demonstrated on the board if necessary                     Brainstorming
                   Adaptations:
                         o more time
                         o # of molecules is provided
                   Class discusses their answers and students are invited to share in front of the
                   The students are questioned to determine whether they can recognize when
                    two compounds are the same or different. Use of the molecular kits.

  1.2      Discussion of concepts:                                                                    Class discussion   Assessment based on
                   Introduce vocabulary (Isomer, constitutional isomer)                              Socratic episode
                   Discuss characteristics through question and answer
                   Different isomer = different substance                                            Q+A
                   Thus isomers have different characteristics from each other.

  1.3      Online isomer construction activity:                                                       Computer           Assessment of learning
                                                                                                      simulation         (homework)
                   Isomer construction set (click to access the site)
                   Homework:
                        o Using the site as a guide, make a 2-column table. Column A: # of
                            carbons, Column B: # of isomers.
                        o Complete the table up to an alkane with 10 carbon atoms

  2.1      Pre-laboratory discussion                                                                  Class discussion

                   Discussion: review yesterday’s notes and work
                   Introduce set of isomers on board
                   propanol - isopropanol                                                            Q+A
                   Have students build the molecules with models.
                   Isomers have different characteristics

     Teaching a concept: Hydrocarbon Isomers                                                                                  3
               Hypothesize: which would have higher boiling point? Density?

2.2    Laboratory (groups of 2)                                                              Laboratory         Laboratory report

               Investigating boiling point and density of propanol and isopropanol
               Using a simple Bunsen burner setup and an electronic thermometer,
                determine the BP of each compound.
               Using a balance and a graduated cylinder, determine the density.
               Analysis questions:
                     o Why does propanol have a higher BP? Density?
                     o What are the applications of these compounds?
                     o Do these applications exploit their isomeric differences?

3.1    Discussion: return on laboratory results                                              Class discussion   Assessment based on
               Compare results                                                              Q+A
               Discuss questions
               Write possible answers on the board                                          Brainstorming
               Use molecular models to hypothesize why isopropanol boils faster.
               Do structure/ polarity play a role?

3.2    Molecular modeling: Alkenes                                                           Modeling

               All students (and teacher) will have molecular models. (if not, in groups)
               Students follow teachers instructions and will repeat exactly what he/she
                does                                                                         Simulations
               Single bonds can rotate
               Double bonds cannot! Just try!
               We can end up with 2 possibilities:
                                                                                             Socratic episode

       Support these models with pictures:

               These are stereoisomers
               Discussion of isomer applications
                    o see Applications section

  Teaching a concept: Hydrocarbon Isomers                                                                            4
3.3       Homework: Problem set (found on the Wiki)                                   Paper and pencil   Asessment OF
                 “Isomerism exercises.doc”
                 Adaptations                                                                            (exercises)
                 Q’s 1 and 2 only                                                    Problem set
                 heterogeneous grouping
                 Bonus question:
                 Can alkynes have isomers? Why or why not?

  Teaching Ideas and Adaptations

           This is a very visual lesson, auditory learners will have difficulty. However, tactile learners
            will have the benefits of the molecular model kits, despite the fact that these take up more
           Images and drawings made by both the teacher and the students.
           Inquiry-based strategies for students to discover isomers of given formulas on their own.
            (how many can you find?)
           Possible differentiation strategies for isomer-drawing activities
                o giving the # of isomers for a particular formula
                o leading students with a few examples for a given formula
                o (Advanced) Asking students to find trends between the # of isomers and the # of
                    carbons in alkanes.
           Laboratory activity: Investigating boiling points of different isomers.
           As a side mini-lesson, we could lead a discussion touching the etymology of “iso”, “cis”,
            “trans” and “tert” with the goal of providing context to the nomenclature.
                o This has direct applications to fatty acids found in food.
           Problem sets: Homework assignment reviewing the day’s lesson
                o Finding and identifying the isomers for a given formula
                o Naming the isomers
                o Finding and identifying isomers containing different functional groups.
           Post exercises on the Wiki for students to do at home.
                o We could also open one page up to their editing, so that they can have a type of
                    discussion room to post questions and help each other out.

  Evaluation Procedures

           Assessment FOR learning
               o Questioning based on answers given during isomer identification challenge
           Assessment AS learning
               o Group-based work during isomer identification challenge and online activity
           Assessment OF learning

  Teaching a concept: Hydrocarbon Isomers                                                                     5
           o   Homework: Problem sets
           o   Laboratory: Properties of different isomers.

Applications and Societal Issues or Implications

      Cis- and trans- fatty acids in foods
            o trans-fatty acids are generally associated with health risks including coronary heart
            o The mechanisms through which these compounds contribute to these health risks are
               under investigation
      Octane rating of gasoline
            o Simply, this rating can be used as a rough measure of the isomeric content in the fuel
      Chiral drug industry
            o Exploiting isomers in pharmaceuticals to gain better efficacy.
            o Not to be discussed in depth as it includes classes of isomers outside the scope of the

Annotated Internet Addresses/References

These sites would be added to class wiki to help students with their homework.

      http://www.flatworldknowledge.com/pub/basics-general-organic-and-bio/421680#web-
           o (This site has general information on organic chemistry and is very simple and straightforward)
      http://chemed.chem.purdue.edu/genchem/topicreview/bp/1organic/organic.html
           o (A more advanced site with information on organic chemistry)
      http://antoine.frostburg.edu/cgi-bin/senese/tutorials/isomer/index.cgi
           o (A web-based isomer tutorial. This site contains the virtual isomer construction set)
      www.a-levelchemistry.co.uk/
           o (The isomerism exercises were obtained from this site)

Teaching a concept: Hydrocarbon Isomers                                                                    6

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