Hydrocarbon isomers
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Transcript of Hydrocarbon isomers
Hydrocarbon isomers
by Nathan Hickey & André Gagnier
Curricular expectations (SCH 4U): B. Organic Chemistry 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. 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.
Less interesting, (but crucial) stuff first...
… now the more interesting stuff.
You have 2 minutes:
In groups of two, Use a molecular kit and
build C6H14
in as many different ways as you can.
Then draw your results.
GO!
Challenge! (the hook, targeting the students’ competitive natures)
Follow-up question: Are these the same?
What is their chemical formula?
C3OH8 and C3OH8
They both have the same chemical formula!
So again, are they the same?
How about these?
They're all C5H12.
So are they all the same? All different?In groups of 2,use a molecular kit
to discover.
• Begin with the Isomer Challenge on slide #3 followed by the questions on the next three slides. (Inquiry-based learning)
• Between every new question will be in-class discussions
where the students must propose hypotheses and take a stand.
• Following this is an introduction to the term "isomer“ and the
theory of constitutional isomers. • End the period with the on-line Isomer Construction Set,
with a few questions assigned as homework.
Day 1: Introduction to constitutional isomers
To demonstrate that isomers have different physical and chemical properties, the students will evaluate the boiling point and density of the following compounds: • Propanol• Isopropanol
After the labs, the rest of the period will be spent discussing why it is that isomers react differently (different electron density, different polarity, etc.).
Day 2: Lab
Using molecular kits, explore the nature of stereoisomers.
Practice exercises are posted on the class Wiki.
Students are also asked to determine whether alkynes also have stereoisomers.
Day 3: Alkene isomers (stereoisomers)
PROBLEM SOLUTION
Students may think that changing the shape (ie.
rotating a C-C bond) means a new isomer is created.
Using molecular models, show that for it to be an isomer,
bonds need to be broken and replaced. Rotations do not
create isomers.Understanding that cis- and
trans- geometric isomers are, in fact 2 different substances.
Using pictures and molecular models to allow students to see
the 3D configuration.Students think that isomers are always members of the same class of compound. (eg. the student can think that any
isomer of an alcohol must also be an alcohol, when in fact it
could be an ether).
Using inquiry-based discovery, students will have to construct all the possible isomers. Using
pictures of 2 molecules (alcohol and ether) and asking students to count the atoms. They will realize that the formulae are
the same.
Potential Student Difficulties
• the Bunsen burners used to determine the compounds' boiling points (obvious fire and burn hazards). Proper care must be taken and safety goggles must always be worn.
• the organic compounds that we handle will have to be
dealt with carefully. Some of them are toxic and all of them are flammable! Proper disposal must be ensured afterwards.
Safety Concerns
Evaluations
Assessment FOR learning
•Questioning based on answers given during isomer identification challenge
Assessment AS learning
•Group-based work during isomer identification challenge and online activity
Assessment OF learning
•Homework: Problem sets•Laboratory: Properties of
different isomers.
Cis- and trans- fatty acids in foods◦ trans-fatty acids are generally associated with health risks
including coronary heart disease ◦ The mechanisms through which these compounds contribute to
these health risks are under investigation
Octane rating of gasoline◦ Simply, this rating can be used as a rough measure of the
isomeric content in the fuel
Chiral drug industry◦ Exploiting isomers in pharmaceuticals to gain better efficacy.◦ Not to be discussed in depth as it includes classes of isomers
outside the scope of the class
Practical Applications and Societal Implications
References:•http://www.flatworldknowledge.com/pub/basics-general-organic-and-bio/421680#web-421674
(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
(A more advanced site with information on organic chemistry)
•http://antoine.frostburg.edu/cgi-bin/senese/tutorials/isomer/index.cgi
(A web-based isomer tutorial. This site contains the virtual isomer construction set)
•www.a-levelchemistry.co.uk/(The isomerism exercises were obtained from this site)