Isomerism
Session 7: Isomerism.
Total Session Time: 60 minutes
Prerequisites
Learning Tasks
By the end of this session students are expected to be able to:
Resources Needed:
SESSION OVERVIEW
|Step |Time |Activity/ |Content |
| | |Method | |
|1 |05 minutes |Presentation |Introduction, Learning Tasks |
|2 |15 minutes |Buzzing |Definition of Isomer and Isomerism |
| | |Presentation | |
|3 |40 minutes |Group |Types of Isomers |
| | |discussion | |
| | |Presentation | |
|4 |40 minutes |Presentation |Importance of Isomerism in Pharmacy |
| | |Brainstorming | |
|5 |10 minutes |Presentation |Key Points |
|6 | | Presentation |Evaluation |
| |10 minutes | | |
SESSION CONTENTS
STEP 1: Presentation of Session Title and Learning Tasks (5 minutes)
READ or ASK students to read the learning tasks and clarify.
ASK students if they have any questions before continuing.
STEP 2: Definition of Isomer and Isomerism (15 minutes).
|Activity: Buzzing (10 minutes) |
| |
|ASK students to pair up and buzz on the following question for 5 |
|minutes |
| |
|What is an isomer? |
|What is isomerism? |
|ALLOW pairs to respond on the question. |
| |
|WRITE their response on the flip chart/board. |
| |
|CLARIFY and SUMMARIZE by using the content in the table 1 below |
structural formula
formula but different structural formula
STEP 3: Types of Isomerism (40 minutes).
|Activity: Small Group Discussion (20 minutes) |
| |
|DIVIDE students into small groups |
| |
|ASK students to discuss in groups on the following questions |
|What are the types of isomerism |
| |
|[pic]REFER Students to Book |
| |
|ALLOW students to discuss for 15 minutes |
| |
|ALLOW each group to present for 5 minutes |
| |
|CLARIFY and SUMMARIZE by using the contents below |
The following are the descriptions of types of isomerism;
o Arises due to restricted rotation across the C-C double bonds.
o Occurs only when two atoms/groups attached to each carbon of the
double bond are different from one another.
o This type of isomerism is also known as cis-trans isomerism.
o The cis-isomer has like groups on the same side of the double bond,
whereas the trans-isomer has like group on opposite sides of the
double bond.
Example,
[pic]
o Cis Butene (the methyl groups are on the same side)
[pic]
o Trans Butene (the methyl groups are on the opposite side)
o Another way to name the cis-trans isomers is to use the Z and E
nomenclature
[pic] E
Zusammen, means together
which means on opposite sides.
o These are Isomers which have the atoms of their molecules linked in a
different order
o The structural isomerism is further subdivided in the following
categories;
Chain Isomerism
different arrangement of carbon chain within the molecule.
boiling point due to different strengths of intermolecular bonding.
[pic]
Positional Isomerism
and same carbon skeleton but differ in the position of attached atoms or
groups or in position of multiple bonds.
usually very similar.
properties.
[pic]
propyl alcohol; I) and propan-2-ol (isopropyl alcohol; II)
attached to an end carbon in the first isomer and to the center carbon in
the second.
increases; for example, the next largest alcohol, named butanol (C4H10O),
has four different structural isomers.
[pic]
Functional Group Isomers
formula but different functional groups.
chemically dissimilar.
[pic]
o Isomers that differ in connectivity are called constitutional
(sometimes structural) isomers.
o They have the same parts, but those parts are attached to each other
differently.
o The bracelets of red and green beads mentioned above are analogous to
constitutional isomers.
o The simplest hydrocarbons—methane (CH4), ethane (CH3CH3), and propane
(CH3CH2CH3)—have no constitutional isomers, as there is no other way
to connect the carbons and hydrogens of these molecules consistent
with the tetravalency of carbon and the univalency of hydrogen.
[pic]
o However, there are two different butanes, C4H10, and these two
molecules, called butane and isobutane, are constitutional isomers.
o They are different molecules with different chemical and physical
properties.
o Butane has its four carbon atoms bonded in a continuous chain.
Isobutane has a branched structure.
o [pic]
o The number of possible constitutional isomers increases greatly with
the number of available atoms.
o There are only two butanes, but there are three pentanes (C5H12), 18
octanes (C8H18), and no fewer than 366,319 constitutional isomers of
the hydrocarbon containing 20 carbon atoms and 42 hydrogens.
o Stereoisomers are isomers that have the same composition (that is, the
same parts) but that differ in the orientation of those parts in space.
o There are two kinds of stereoisomers:
an object and its non-superimposible mirror image, like one’s
hands.
type of a stereoisomer.
compound have different configurations at one or more (but
not all) of the equivalent (related) stereocenters and are
not mirror images of each other.
one stereocenter they are epimers. Each stereocenter gives
rise to two different configurations and thus increases the
number of stereoisomers by a factor of two.
are pairs of stereoisomers that differ in all stereocenters
and are therefore mirror images of one another.
o Enantiomers of a compound with more than one stereocenter are also
diastereomers of the other stereoisomers of that compound that are not
their mirror image.
o Diastereomers have different physical properties (unlike enantiomers) and
different chemical reactivity.
[pic]
Fig. Isomerism
[pic]
STEP 4: The importance of Isomerism in Pharmacy (40 minutes).
|Activity: Brainstorming (5 minutes) |
| |
|Ask students to brainstorm on the following question: |
| |
|What is the importance of isomerism in pharmacy? |
| |
|ALLOW few students to respond |
| |
|WRITE their responses on the flip chart/ board |
| |
|CLARIFY and SUMMARISE by using the content below |
and more effective drug alternatives of the newer as well as existing
drugs.
racemic mixture to one of its isomers.
and safer drug has been made available.
reactions like Quinine has antimalarial activity while quinidine has
an antiarrythmic property.
Levomethorphan is a potent opiod analgesic while dextromethorphan
is a cough suppressant
o R-Thalidomide is sedative while S-Thalidomide has been shown
teratogenic effects;
o R-Naproxen is used for arthralgic pain while S-Naproxen is
teratogenic
found to cause blindness
dopa which has never been used because it causes deficiency of
white blood cells and thus susceptibility to infections.
STEP 5: Key Points (10 minutes).
structural formula.
Constitutional isomerism and Stereoisomerism.
pharmacokinetic and pharmacodyanmic properties which has helped in
introducing safer and more effective drug alternatives of the newer as
well as existing drugs.
STEP 6: Evaluation (10 minutes)
References
States: W.B. Saunders Co.
Morrison R.T and Boyd R N (1997). Organic Chemistry (6th Ed.). New Delhi,
India: Prentice Hall of India
Graham Solomon et al (2014). Organic Chemistry (11th Ed.). New Jeysey,
United States: John Willey and Sons.
Rama Rao Nadendla (2005). Principles of Pharmaceutical Organic Chemistry.
New Delhi, India: MacMillan Publishers
Bruice Y (2013). Organic Chemistry (7th ed.). New York, United States:
Prentice Hall Pearson.
Delgado J. N. Et al (1998). Wilson and Gisvold's Textbook of Organic
Medicinal and Pharmaceutical Chemistry (10th Ed.). California, United
States: Lippincott Williams
Bhassin S.K, Gupta R. (2013). Pharmaceutical organic chemistry (E-book
Kindle edition). New Delhi, India: Elsevier Publishing Services
Unataka kutumiwa notes hizi kupitia WhatsApp?Kwa notes zilizopangiliwa vizuri kwa kusoma offline au PDF, bonyeza kitufe hapa chini. Ujumbe wenye Level, Semester, Module na Topic utaandaliwa moja kwa moja.TUMIWA NOTES WHATSAPP