Chemistry 231L/232L
First Four Exercises - Fall 2002
Isomers of Octane ..............................................................................................1
Word Processing, Chemical Drawing, and ChemFinder Exercise .......................................4
Organic Model Exercise: An Adventure in Structure and Bonding.....................................11
Intermolecular Nonbonding Forces Exercise ..............................................................17
O-CHEM
Isomers of Octane Experiment
Chemistry 231L/232L
Dr. Gergens - SD Mesa College
Name:_______________________________
Section:_____________ Date:____________
Write out the line-angle formula for all 18 isomers with the formula C8 H18 . Organize the isomers from
decreasing parent chain length starting with octane. The first three are done for you. Give all isomers
an I.U.P.A.C. name. Identify by letter, all equivalent carbon atoms. Use the first three examples as a guideline.
Note, 3-methylheptane has no equivalent carbon atoms because it is asymmetric due to its chiral center
marked '* '. Mark all asymmetric centers with a '* '. Finally, answer the questions on the next page.
a
*
a
b
Name:
c
d
octane
d
c
b
a
a
Name:
2-methylheptane
Name:
Name:
Name:
Name:
Name:
Name:
Name:
Name:
Name:
Name:
Name:
Name:
Name:
Name:
Name:
Name:
3-methylheptane
1
Isomers of Octane - Additional Questions
Dr. Gergens - SD Mesa College
Answer the following questions. Use a molecular model kit to assist you.
1.
Give the total number of each isomer having the following parent chain name. octane ____, heptane ____,
hexane ____, pentane ____, butane ____, propane ____?
2.
How many alkanes have the ethyl— branch in its name ____. Give their IUPAC name:
3.
How many alkanes have the propyl— branch in its name ____. Give their IUPAC name:
4.
How many alkanes have the isopropyl— branch in its name ____. Give their IUPAC name:
5.
How many alkanes have the prefix di in their IUPAC name ____.
6.
How many alkanes have the prefix tri in their IUPAC name ____.
7.
How many alkanes have the prefix tetra in their IUPAC name ____.
8.
How many alkanes have only one chiral carbon center ____ .
A tetrahedral carbon atom that bears four
different substituents is called a chiral center. Give their IUPAC name:
9.
How many alkanes have two chiral centers ____. Give their IUPAC name:
10. Which alkane appears to have six equivalent methyl branches its structure? Give its IUPAC name:
11. Which alkane appears to have three equivalent ethyl branches in its structure. Give its IUPAC name:
12. How many alkanes contain both two equivalent methyl and two equivalent ethyl branches in its structure?
Give their IUPAC name:
2
13. Which alkane appears to have two equivalent sec-butyl branches? (Hint: It is the one with two chiral centers
as well). Give its IUPAC name:
14. Which alkane appears to have two equivalent n-butyl branches in its structure? Give its IUPAC name:
15. Which alkane appears to have two equivalent isobutyl branches in its structure? Give its IUPAC name:
16. Which alkane appears to have two equivalent t-butyl branches in its structure? Give its IUPAC name:
17. Which alkane appears to have two equivalent n-propyl branches in its structure? Give its IUPAC name:
18. Which alkane appears to have two equivalent isopropyl branches in its structure? Give its IUPAC name:
19. Which chiral molecule appears to have a methyl, ethyl, n-butyl branch about its chiral center? Give its IUPAC
name:
20. Which chiral molecule appears to have a methyl, ethyl, t-butyl branch about its chiral center?
Give its IUPAC
name:
21. Which chiral molecule appears to have a methyl, propyl, isopropyl branch about its chiral center?
Give its
IUPAC name:
22. IUPAC stands for_________________________________________________________________
3
Word Processing, Chemical Drawing, and ChemFinder Exercise
Dr. Gergens - SD Mesa College
Purpose
Computer literacy is fast emerging as a basic skill that will be as important to life in the twenty-first century as
reading is now.
The purpose of this exercise is to give students practical experience in computer literacy by
developing some general computer word processing and chemical drawing skills needed for this course.
In particular,
students should be able to draw chemical structures—perhaps using a drawing program like ISIS Draw—import and
edit images, and save and insert images from web based sources into their reports.
In the process, you will be
exposed to the use of chemical data base, www.chemfinder.com, to track down chemical data as well.
Finally,
students will be given the opportunity to learn the basics of scanning data and images, saving the scanned information
to disk, and importing and word processing that information into their report.
To assist you in learning to draw
chemical structures, you will find a tutorial covering some simple basics for drawing chemical structure, and how to
select, resize , and import chemical structure into a word document.
Getting Started
There are several chemical drawing programs available in the laboratory.
programs on the market generally have the same generic look and feel.
Most drawing and word processing
If you are already accustom to using a
drawing program, good for you. In this course, use what ever drawing and word processing programs you are most
familiar and comfortable with in word processing your laboratory reports.
One chemical drawing program commonly used by students in our chemistry department is ISIS Draw.
program is Microsoft Word which most already use for general word processing.
Another
If you're new to ISIS Draw, you
might be terrified. Once you review the tutorial and get going though you'll see you can create professionally great
graphics simply by clicking on your screen. ISIS Draw has a complete set of tools and templates for creating many
different kinds of drawings, but we will use it mainly to draw chemical structures.
ISIS Draw from most computers on campus.
In general, students can access
Students can find access to computers in I-110, K-400, and on the
fourth floor of the Learning Resource Center (LCR) to be most convenient.
ISIS Draw is also available as a free
download through the link http://www.sdmesa.sdccd.net/~dgergens/spectroscopy_links.htm
Exercise
Welcome to ISIS Draw. To start in learning the basics, find a computer with ISIS Draw loaded and that has Internet
access.
Open
ISIS
Draw
and
either
Netscape
or
Explorer.
Access
Dr.
Gergens'
home
page
http://www.sdmesa.sdccd.net/~dgergens/chem231L/index.html and find the ISIS draw tutorial link and click on it.
The ISIS tutorial is a QuickTime movie.
QuickTime Movie Player should be installed on your computer.
link to the QuickTime movie page, download and install the movie player.
If it is not,
I would suggest watching the tutorial first
then mimic the same process using ISIS Draw. Some of you may be even clever enough to resize your viewing screen
so both ISIS Draw and the browser windows are viewable at the same time. In this way, you would be able to watch
the movie and following along using ISIS Draw at the same time.
The tutorial will answer most of your questions
regarding the use of the program. If you have additional questions and/or suggestions regarding the tutorial, you can
e-mail at [email protected].
Download from the same web page the ISIS Draw Assignment.
This is the ISIS Draw Assignment is the word
document that will be word processed and turned in for grading.
An important note on importing images.
When importing or pasting an image from ISIS into a Microsoft Word
document, select and copy the image in ISIS, then paste into Word by selecting <Insert>, <Paste Special>, and select
<Enhanced Meta File>. This is very important to remember.
"A picture is worth a thousand (by a thousand) words"
4
PART A - Cleaning Up Hand Drawn Images
In this exercise, you will be asked to redraw these hand drawn chemical structures by using a chemical drawing
program. It is recommended you use ISIS Draw to redraw and word process these structures. Any drawing program
you are more familiar with, however, could also be used to complete this task and is acceptable as well.
Redraw these chemical structures in ISIS Draw. Please attempt to redraw each hand drawn structure as it is shown.
Then cut and paste each image into the box on the right of each hand drawn image. Resize each image so all eight
structures can fit on this page. Finally, identify the functional group. The ethyl butanoate, an ester, is done for you.
Hand Drawn Compound & Structure
functional group
and formula
Re-Drawn Compound & Structure
ethyl butanoate
ethyl butanoate
ester
C6H12 O2
O
CH3CH2CH2 C OCH2CH3
N-ethylaniline
N-ethylaniline
4-isopropyltoluene
4-isopropyltoluene
2-methylpropanoic acid
2-methylpropanoic acid
polyethylene
polyethylene
3-bromopropyne
3-bromopropyne
adipoyl chloride
adipoyl chloride
5
PART B - Saving and Inserting Web Based Images
In this exercise, you will be asked to use a data base as a source of pre-drawn chemical structures.
Often we will
have to search for physical data (e.g., structure, mp, bp) on a compound using a data base. In our search, the data
base in general will give the structure of the compound as an image. Images can be save to disk to be inserted into a
word document at a later time. This should save us time and effort in having to re-draw each structure.
Use http://www.chemfinder.com to search on the given compounds.
Searching by molecular formula will give a
much broader search result for the given compound. To do a molecular search, be sure that you total the number of
atoms—and hydrogens—are added up correctly. Search by both molecular formula and name. To copy an image from
the internet, place the cursor on the image, mouse click and hold, select <Save Image As.> and save the image to disk.
Recall the image and insert it into the box at the left. When inserting a saved image into a Microsoft Word document,
select <Insert>, <Picture>, <From file>, select the <file name>. If the image does not go into the desired cell in the
table, you may have to copy the image then paste back into Word by selecting <Insert>, <Paste Special>, and select
<Enhanced Meta File>.
We would like the image to fit into the box at the left without having the box expanding larger
than what it is currently.
All eight structures should be resized to fit on this page.
The first one the ester,
ethyl 2-bromo-2-methylpropionate, is done for you.
Web Base Image
functional group
and formula
Compound & Structure
ethyl 2-bromo-2-methylpropionate
ester
C6H11 BrO 2
O
(CH3)2C C OCH2 CH3
Br
1-phenyl-2-propanone
O
CH2CCH3
3,7-dimethyl-6-octenal
H
O
3-methyl-1-butanol
(CH3)2CHCH2CH2OH
2-aminotoluene
NH2
CH3
3-methyl-3-buten-2-one
O
6
PART C - Editing a Chemical Structure
In this exercise, you will be asked to draw in ISIS Draw and import the structure of Tylenol.
Also you will be asked
to use a data base as a source of the pre-drawn chemical structure for caffeine. Afterwards, you will edit the image
in Microsoft word.
For example, cyclohexanone was imported using ChemFinder and was also drawn in ISIS Draw.
Then, while in Microsoft Word, the image was edited by double clicking on the image which opened a tool box. From
the tool box in MS Word an arrow was added to each image.
cyclohexanone
cyclohexanone
O
Use ISIS draw to draw the structure of Tylenol and import its image into the box on the left.
obtain a pre-drawn image of caffeine and insert into the box at the right.
Use ChemFinder to
Finally edit both images by double clicking
on both images while in MS Word and add an arrow and a star to each image.
Compound & Structure
Compound & Structure
Tylenol
(Imported from Chemfinder)
caffeine
(Drawn by ISIS Draw)
7
PART D - Editing a Scanned Image
In this exercise, you will be asked to scan an FTIR spectrum of Nujol oil and save it to disk.
asked to recall that image and insert it into a word document.
Afterwards, you will
Finally, you will be asked to edit the image in
Microsoft Word. For example, the scanned spectrum of Nujol oil was imported and then edited by adding the labels
C-H stretching and C-H bending, and a title was given.
Have available a disk with this assignment document file on it. You will scan an image to this disk.
In the laboratory there is a scanner.
You will need to save the scanned image to the same disk that has this
assignment document file. Obtain a sample FTIR spectrum of Nujol oil from your instructor.
Scan the image of FTIR
spectrum of Nujol oil following the procedures "How to Scan" posted near the scanner. Name the scanned image file
<Nujol.doc> and save the image and file to disk.
Is the <Nujol.doc> image file on the same disk with the file for this
assignment? If so, open the <Nujol.doc> and the file for this assignment. From the <Nujol.doc> document, select and
copy the FTIR spectrum. Do a <Insert>, <Paste Special>, <Enhanced Meta File> to insert the FTIR spectrum for Nujol
into box below for this assignment.
Finally, edit the FTIR spectrum for Nujol by double clicking on the image and adding the labels C—H stretching and C—H
bending, and by giving the spectrum a title. We would like the image to fit into the box below without having the box
expanding larger than what it is currently. Your scanned image should remain on this page.
8
PART E - Use of ISIS Draw Templates
In this exercise, you will be asked to insert pre-drawn images from templates available in ISIS Draw.
Open ISIS Draw and select <Templates> in the menu bar. Select <Beta-D-Sugars> and a menu of several beta-D-sugar
structures appear.
Place the cursor on one of the bonds in the structure for the sugar [ADGLUCO]
which is for
beta-D-glucose and mouse click. After mouse clicking, the structure should appear in ISIS Draw. Using the atom tool
and add hydrogens to all the oxygens except the one in the ring. Import the structure into this document in the
box below.
Compound & Structure
Compound & Structure
[ADGLUCO]
L-phenylalanine
To import phenylalanine derived from the L-Phenylalanyl template, use the select <Templates> in the menu bar,
the <L-Amino Acids>. Place the cursor on one of the bonds in the structure for the amino acid L-Phenylalanyl and
mouse click. After mouse clicking, the structure should appear in ISIS Draw. Using ISIS Draw, add a hydroxyl group
to the carbonyl and add hydrogens to the nitrogen to form complete structure of L-phenylalanine, them select all and
import the entire image of L-phenylalanine into the box on the right above.
partial structure of
phenylalanine
O
R
OH
NH2
Do the same for the following: add a p-orbital,
–OH added
H's added
, and
Bicyclo[2.2.1]heptane
Structure
Compound & Structure
a p-orbital
Bicyclo[2.2.1]heptane
9
PART G - Cutting and Pasting Data from Chemfinder
In this exercise, you will be asked to search on a compound using www.chemfinder.con and cutting pasting that data
into this document. For example, physical data for ethyl butanoate was copied and pasted from chemfinder into the
box below. Try looking up ethyl butanoate by its name and molecular formula to see how chemfinder works.
ethyl butanoate
ethyl butanoate
ester
C6H12 O2
O
CH3CH2CH2 C OCH2CH3
Ethyl butyrate [105-54-4]
Synonyms: Ethyl Butanoate; Butyric Ether; Butanoic acid ethyl ester; Ethyl n-Butyrate; natural ethyl butyrate;
BUTIRATO DE ETILO;
formula:
molar mass:
melting point:
density:
boiling point:
refractive index:
solubility in water:
Flash point:
Comments:
C6 H12 O2
116.1596
-135.4 °C
0.878 g/mL
252 °C at 0 mm
1.392
0.68 g/100 mL. Insoluble
26 °C
Colorless liquid with pineapple odor. Used in perfumes, rum
Now do the same for the ethyl 2-bromo-2-methylpropionate.
Use http://www.chemfinder.com to search on the
given compounds. Searching by molecular formula will give a much broader search result for the given compound. To
do a molecular search, be sure that you total the number of atoms—and hydrogens—correctly.
Search by both
molecular formula and name. If data is not given at the site, write in the word NONE.
ethyl 2-bromo-2-methylpropionate
ester
C6H11 BrO 2
O
(CH3)2C C OCH2 CH3
Br
ethyl 2-bromo-2-methylpropionate
Synonyms:
_________
Formula:
molar mass:
melting point
density
boiling point
refractive index
solubility in water
Flash point
_________
_________
_________ °C
Comments
_________
_________ °C
_________
_________
_________
10
Organic Model Exercise: An Adventure in Structure and Bonding
Dr. Gergens - Mesa College
Introduction
Organic chemistry is the study of compounds that contain the element of carbon; compounds that do not contain carbon
are termed inorganic. Carbon is singled out as a branch of chemistry because of the tremendous number of compounds it
forms. While there are about 200,000 known inorganic compounds, there are over 6 million known compounds of
carbon. While organic chemistry is the study of the compounds of carbon, biochemistry is the study of the chemistry
of living organisms. Organic compounds are found in all living organisms, foods (fats, proteins and carbohydrates),
fuels (petroleum), wood, paper, fabrics, plastics, dyes, paints, cosmetics, drugs, medicines, insecticides, herbicides,
soaps, and detergents.
Organic compounds can be classified according to their structural features. The structural features that make it
possible to classify compounds by reactivity are called functional groups.
In this experiment you will familiarize
yourself with the structures of functional groups shown in Chapter 3 of the McMurry text. The use hand-held models
will aid you in this task. Many studies have shown that tactile (touch) learning far outweighs visual absorption of this
sort of information.
Getting Started:
Start by reviewing Chapter 3 in your McMurry text. For this exercise, pay particular attention to the naming of the
general classification of functional groups. Your instructor will discuss structural isomerism, geometric isomerism,
and chirality for aliphatic and cyclic compounds covered in Chapter 3 in laboratory.
This project is composed of three parts: Part A - covalencey; Part B - functional group classification and their threedimensional representations through the use of hand held models; and Part C - working with structural, geometric,
and optical isomerism. While working on this exercise, you may hand draw the structures and answer questions in
pencil. However, your may be required to turn in your answers to the following questions as a word processed
document. Data sheets to word process this assignment are available for download from the web site at
http://www.sdmesa.sdccd.net/~dgergens/chem231L/index.html
You will use a model kit to build each functional group. This will greatly assist you in visually seeing the threedimensional perspective of organic compounds drawn on a two-dimensional piece of paper. For example, dimethylether
drawn below can be drawn with a 2-D and 3-D perspective. If drawn in 2-D, the molecule appears to be linear.
In actuality, the ether has a bent structure about the oxygen atom. If your were to make a molecular model of this
ether, you would quickly recognize the central oxygen atom as being bent in geometry and the carbons as tetrahedral.
To represent this molecule as having a three-dimensional structure, the tetrahedral methyl carbons are drawn with a
solid black wedge,
, and a hashed wedge
to represent a 3-D perspective of a bond in three-dimensional
space. In the 3-D structure, each black wedge shows bonded atoms pointing towards you, coming out of the page,
whereas each hashed wedge represents bonded atoms pointing away from you, going into the page. Each solid line
represents bonds lying in the plane of the page. Being able to look at compounds drawn on a two-dimensional piece of
paper and convert it to a 3-D perspective structure will be an important outcome of this exercise.
A.
H
H C
H
O
2-D
H
CH
H
Functional Group: ether
H
H
H
O
H
H
H
3-D
11
Part A - Covalencey
The atoms in organic compounds are generally held together by covalent bonding. In contrast, inorganic compounds are
usually ionic, though they can have covalent bonds. Since carbon has four electrons in its outer shell, it forms four
covalent (shared) bonds. These may be single, double or triple bonds as long as the total number of bonds to carbon
equals four. Other elements, such as hydrogen and oxygen, are found in organic compounds, making the possibilities for
covalent combinations to become enormous. In the table below, are the most stable bonding modes for carbon, nitrogen,
and oxygen. For each bonding mode, give the angle, geometric name, and hybridization about the central atom. Word
process this image by using the drawing tool in Microsoft Word to add angles, geometric names, and hybridizations.
VSEPR = ________
________
________
________
________
Determine the angles between bonds, name the geometry about the central atom and give the its hybridization.
Ideal Geometries
H
H
H
bond angles
C
H
H
H
C
C
H
H
C
C H
:
N
N
O
C
O
H
geometric name
hybridization
Non-Ideal Geometries
:
:
:
N
H
H
N
N
:
H
bond angles
H
H
geometric name
hybridization
:
H
:
bond angles
:
O
H
:
H
O
C
H
geometric name
hybridization
On the next page, we will be using ball and stick models to demonstrate the versatility of bonding and therefore
structure in organic compounds. In general, the color correlation of the plastic spheres to elements is as follows:
C - carbon
H - hydrogen
O - oxygen
N - nitrogen
Cl - chlorine
Br - bromine
black
white
red
blue
green
red
12
Part B - Functional Group Classification
Structural features make it possible to classify compounds by functional groups and the methods for the writing
chemical bonds are highly descriptive and useful. In this exercise, you will be asked to identify and use of a model kit
to build each functional group for the compounds below.
Identify each functional group. Construct molecular models for the compounds below. This will greatly assist you in
visually seeing the three-dimensional perspective of organic compounds. Notice the tetrahedral carbon has a three
dimensional array of atoms. For the moment, sketch a hand drawn 3D-chemical structure for each on this handout.
Afterwards, use a computer assisted chemical drawing program (i.e. ISIS) to redraw a three-dimensional
representation for each molecule and paste its structure into the table below.
A.
B.
H
H C
H
O
H
CH
H
Functional Group: ether
H
H
D.
C
Functional Group:
H
CH
H
Functional Group:
O
C
H
I.
H
H C
H
NH2
Functional Group:
OH
OH
Functional Group:
J.
Functional Group:
K.
H
HC
H
O
C
Functional Group:
H
O CH
H
C H
Functional Group:
H.
O
C
OH
Functional Group:
G.
C
H
F.
H
H C
H
Functional Group:
H
H C
H
C
H
E.
H
H C
H
C
H
H
O
H
H
Cl
H
O
H
C.
H
H C
H
L.
H
H C
H
Functional Group:
NH2
H
H C
H
O
C
H
Functional Group:
13
Part C - Structural, Geometric, and Optical Isomerism.
In this laboratory activity, you will be examining molecular models of various organic compounds. You will pay
particular attention to the existence of isomers. Isomers are prevalent in organic compounds due primarily to carbon's
ability to make 4 bonds.
Constitutional isomerism. Two molecules with the same molecular formula but different structures are called isomers.
Using your model kit, construct a model of the requested isomer. Using either ISIS or ChemDraw, draw a threedimensional representation and paste its figure into the table below.
1. an alcohol of compound A.
2. an aldehyde of compound D
3. an ester of compound E.
Geometric cis- trans isomerism is a type of geometric isomerism that arises when two species have the same
molecular formulas but different structures. For example, square planar complexes, [PtBr 2 Cl 2 ]2– .
Br
2-
Cl
2-
cis & trans alkenes
H
Cl Pt Br
Br Pt Br
Cl
Cl
cis
chlorine atoms next to each other
on the same side
trans
C
CH3
chlorine atoms opposite to each other
on opposite sides
H
C
CH3
cis
H
CH3
C
CH3
C
H
trans
Alkenes have rigid double bonds that prevent rotation, giving rise to cis- and trans-isomers. Construct the cis and
trans 2-butenes above. Notice the restrictive rotation about a double bond can result in cis-trans geometric isomerism
in organic molecules; the methyl groups cannot interconvert.
Construct a molecular model and draw the three-dimensional representation for the three isomers of dibromoethene.
Using either ISIS or ChemDraw, draw each isomer and paste its figure into the table below.
cis
trans
neither cis or trans
14
Geometric isomerism is also possible when there is a ring present.
A cycloalkane has two distinct faces.
If
substituents on a cyclic ring point toward the same side, they are cis. If they point toward opposite sides of the ring
they are trans. Note the geometric isomers of 1,2-dimethylcylcohexane cannot inter convert without breaking and
reforming bonds.
a.
Below are cis- and trans-isomers of 1,2-dimethylcylcohexane. Make models of these compounds to convince
yourself that cis- and trans-1,2-dimethylcylcohexane cannot inter convert by simple rotations about the bonds.
Also convince yourself that all three forms draw for cis and for trans
CH3
CH3
CH3
CH3
CH3
CH3
cis
trans
CH3
cis
Cl
CH3
Cl
trans
Cl
Cl
trans
cis
b.
Construct a molecular model for each isomer of 1,2-dibromocyclohexane. As seen for 1,2-dimethylcylcohexane
above, duplicate the three perspectives for 1,2-dibromocyclohexane and paste their images into each box.
c.
Can you construct a molecular model for an isomer of dibromocyclohexane the is neither cis or trans?
same three perspectives for this structural isomer and paste them into the box below.
Draw the
neither cis or trans
15
Optical Isomerism - The Optically Active Tetrahedral Carbon
Optical isomerism is a type of isomerism that is frequently encounter throughout organic chemistry. It occurs because
of the tetrahedral nature of the bonding around a carbon atom.
Molecules may be chiral, or handed; think of your left and right hand. Chiral is derived from the Greek word cheir,
meaning hand. A carbon atom with four different atoms or groups attached to it is referred to as a chiral center,
meaning the carbon is without a plane of symmetry. A chiral center is asymmetric, just like your left and right hand.
A molecule containing such a carbon atom may show optical isomerism. Optical activity is exhibited by molecules that
have a nonsuperimposable mirror image.
Your hands are nonsuperimposable mirror images, and a pair of
nonsuperimposable mirror images are called enantiomers.
a.
Construct a molecule of 2-butanol. Notice the number two carbon, C2 , has four different groups attached to it—a
methyl, ethyl, hydroxyl, and hydrogen—thus a chiral carbon. Construct the mirror image of 2-butanol. Note that
both are isomers—actually stereoisomers (stereo meaning in space).
Me
Me
H
H
HO
b.
OH
Et
Et
Draw the three-dimensional representation using ISIS draw for each optical isomer of 2-butanol and 2-bromobutane
and paste the structure into box at the right. Note these molecules are nonsuperimposable.
CH3
CH3
CH3
CH2
HO
H
CH3
H
CH2
Br
c.
What are the tests or observations you can make on the structure of a molecule to determine whether it is chiral?
d.
Using your models, construct the optical isomers of carvone. You may have to look up the structure using
Chemfinder on the computer. Smell the authentic (-)- and (+)-carvones that are in the hood. What do they smell
like? Can you smell a difference between the odors spearmint and caraway? In the space below, draw the
isomers of carvone using ISIS Draw and identify which carvone corresponds to which scent.
16
Intermolecular Nonbonding Forces Exercise
Dr. Gergens - SD Mesa College
Introduction
The way electrons orient with respect to each other about atoms or molecules give rise to chemical unions between atoms
or physical attractions between molecules and atoms; see the concept map for bonding on the next page.
Forces between atoms in molecules are induced by the way in which the electrons distribute themselves around nuclei.
When the electrons are shared between nuclei and they induce powerful chemical bonding forces that join nuclei into
molecules. The chemical bonds within a molecule are typically quite strong, such that it's usually necessary to heat a
molecule to very high energies before the chemical bonds begin to break. A typical covalent chemical bond has a bond
energy or bond dissociation energy of about 100 kcal/mol (400 kJ/mol).
Even when the electrons don't cause an actual chemical bond to form, they still induce nonbonding forces that cause atoms
or molecules to influence each other. The physical attractive forces between molecules are called intermolecular forces.
Since the forces of attraction are physical, not chemical, sometimes we refer to the forces of attraction as being
nonbonding forces of attractions.
Molecules exist as distinct, separate collections of matter.
molecules. The three classes of forces are:
We commonly think of three classes of forces between
hydrogen bonding > dipole-dipole (or simply polar) forces > London dispersion forces
10 kcal/mol
1 kcal/mol
0.1 kcal/mol
A rough estimate of the total amount of energy required to separate molecules very far away from each other is listed
with the force. Note, the rough estimate is a decrease of ten-percent (10%) total energy is
Purpose
In this experiment, you will use structural and graphical analysis to study the intermolecular forces of various compounds.
Getting Started
a.
Your instructor will present a discussion over intermolecular nonbonding forces. You may also want to review your old
general chemistry notes and textbook covering this topic.
b.
Review the graphing tutorial provided at
http://www.sdmesa.sdccd.net/~dgergens/chem231L/forces/graphing_frame.html
The graphing tutorial covers the steps to graph the data in Problem 1 given in this exercise. You will need to download
and install QuickTime Movie Player if you do not have it on your home computer to view the movie.
This link is
available at the tutorial site as well.
c.
Download the Microsoft Word file <<force.doc>> to your diskette From the same link.
You will need to word process
this assignment, placing your answers into appropriate cells (boxes) in this document.
d.
Graph the data for problems 2 and 3.
Begin by opening the spread sheet program Excel.
Open the Word file
<<force.doc>>.
e.
Select all data in the given cells in problem 2, cut and paste the data into an Excel spread sheet. Review the graphing
steps in the graphing tutorial movie if this is not clear; you should not have to re-input the data into the spread sheet;
be sure to just cut and paste the data from Word to Excel.
f.
Use Excel to graph the data set for problem 2.
problem 1.
Your final graphs should appear like
Graph 1 for data given in
Plot boiling point (y-axis) versus molar mass (x-axis), overlaying each subset of data.
Include
appropriate labels.
g.
Copy and paste your graph for problem 2 into the appropriate table cells in the <<force.doc>> word document.
h.
Repeat this for problem 3.
i.
Save your work.
j.
Once your graphs are created and your work is saved, read the following discussion, and answer the questions.
17
18
ionic
bond
–
+
M
e
–
M
+
⊕ • ⊕
⊕ • ⊕ • ⊕
⊕ • ⊕
e
M
+
M
e
+
e
–
M
–
M
+
M
+
⊕
⊕
⊕
+
M
X
–
M
+
⊕
–
X
M
+
X
–
⊕
⊕
+
M
X
–
M
+
M
⊕
+
+
H
–
X
(unequal sharing)
polar
covalent
X
H
X
H
(equal sharing)
pure
covalent
sharing of electrons
Give at least three examples of each type of bonding:
M
+
+
(sea of electrons) (cations-anions)
metallic
bond
electrostatics
H
X
X = N,O,F
H
X
+
+
–
–
dipolediople
Dr. Gegens © 2002
dispersion
molecules
hydrogen
bonding
NON-POLAR
POLAR
molecules
Physical
attractions between
molecules
Chemical
unions between
atoms
BONDING
Chemical and Physical Bonding - Concept Map
Dr. Gergens - SD Mesa College
19
⊕
⊕
M
+
(cations-anions)
⊕
⊕
M
+
X
–
+
M
(atomic solid)
⊕
⊕
X
⊕
M
–
M
+
X
+
–
–
X
ionic
solids
M
+
+
M
network
covalent
X X X
X X X
X X X
e
M
+
e
–
M
M
+
metallic
solids
⊕ • ⊕
⊕ • ⊕ • ⊕
⊕ • ⊕
CRYSTALLINE SOLIDS
M
–
M
+
e
+
e
–
M
(sea of electrons)
M
+
+
(atomic solid)
–
(sea of electrons)
(cations-anions)
network
covalent
+
metallic
solids
electrostatics
ionic
solids
network covalent
Non-Molecular
3D array-lattices
between atoms
SUBSTANCES
H
H
X
–
+
–
–
Dr. Gegens © 2002
molecules
–
+
NON-POLAR
+
–
–
POLAR
–
+
+
+
+
–
molecules
–
+
X
+
dispersion
molecules
dipolediople
NON-POLAR
POLAR
X = N,O,F
hydrogen
bonding
Molecular
attractions between
molecules
molecules
Physical Properties in Substances - Concept Map
Dr. Gergens - SD Mesa College
Boiling Point Data
The boiling point of a compound is the temperature at which a compound turns from a liquid to a gas or a gas to a liquid.
This temperature is a true measure of the forces of attractions between molecules as molecules separate from one another
when they turn from a liquid to a gas.
Below are boiling point and molar mass data sets of several compounds.
You will
need to graph these data sets.
If you have not done so, watch the tutorial at
http://www.sdmesa.sdccd.net/~dgergens/chem231L/forces/graphing_frame.html
The graphing tutorial covers the steps to graph the data in problem 1 given in this exercise.
The graph for problem 1 is
shown on the next page. Then graph the data for problems 2 and 3. After you have graphed the data for problems 2 and 3,
read through the discussion section and answer the questions.
Word process this exercise using the Microsoft Word file
<<force.doc>> available from the link above.
Problem 1
Effect of Molar Mass on Boiling Points of Molecular Substances
Noble Gases
Halogens
MM
bp (°C)
He
4
-269
Ne
10
Ar
Kr
Hydrocarbons
MM
bp (°C)
F2
38
-188
-246
Cl 2
71
40
-186
Br 2
84
-152
I2
Problem 2
MM
bp (°C)
CH4
16
-161
-34
C2 H6
30
-88
160
59
C3 H8
44
-42
254
184
n-C 4 H10
58
0
Boiling Points of Polar versus Nonpolar Substances
Polar Substances
hydrogen bonding
Nonpolar Substances
dipole-dipole
MM
bp (°C)
NH3
17
-33
H2 O
18
HF
CH3 OH
dispersion
MM
bp (°C)
CO
28
-192
100
PH 3
34
20
20
AsH 3
32
65
ICl
Problem 3
MM
bp (°C)
N2
28
-196
-88
SiH 4
32
-112
78
-62
GeH4
77
-90
162
97
Br 2
160
59
Boiling Points for Various Hydrides
Group 4
Group 5
MM
bp(°C)
CH4
16
-161
SiH 4
32
GeH4
SnH4
Group 6
MM
bp(°C)
NH3
17
-33
-112
PH 3
34
77
-90
AsH 3
123
-47
SbH3
Group 7
MM
bp(°C)
H2 O
18
100
-88
H2 S
34
78
-62
H2 Se
125
-17
H2 Te
Group 8
MM
bp(°C)
MM
bp(°C)
HF
20
20
He
4
-296
-60
HCl
36.5
-85
Ne
10
-246
81
-41
HBr
81
-67
Ar
40
-186
130
-4
HI
128
48
Kr
84
-152
20
Boiling Point Versus Molar Mass Graphs
Problem 1 - Boiling Point vs Molar Mass for
Nonpolar Molecules
300
200
100
noble gases
0
-100
0
100
200
300
halogens
hydrocarbons
-200
-300
molar mass
Select this cell, and paste your Problem 2 Graph.
Select this cell, and paste your Problem 3 Graph.
21
Discussion
Graph 1 shows the relationship between three classes of nonpolar substances; noble gases, halogens, and hydrocarbons.
There are two trends that we can examine in Graph 1.
The first is the relationship between boiling point and molecular
weight. For each class of compound, as molecular weight increases there is a corresponding increase in boiling point.
The
second trend that we can observe in Graph 1 is shown by comparing the boiling points of molecules from different
categories that have similar molecular weight.
Ar, F2 , and C3 H8 , have similar molecular weights, but their respective
boiling points are -186, -188, and -42 °C. To understand the difference in boiling points we must examine the structure
of these molecules and determine the types of intermolecular forces between molecules.
The shape of molecule is also a
factor in determining the magnitude of dispersion forces.
Because the surface between these molecules are different, the
dispersion forces between these molecules will vary.
Molecules that are structurally large have stronger dispersion
forces because the area of contact between molecules in general is greater.
Graph 2 shows the relationship between polar and nonpolar substances and three classes of nonbonding forces; dispersion,
dipole-dipole, and hydrogen bonding. There are two trends that we can examine in Graph 2.
between boiling point and molecular weight.
The first is the relationship
As molecular weight increases there is a corresponding increase in boiling
point. CO, PH3 , AsH3 , and ICl are within the same category with their respective boiling points as -192, -88, -62 and
97 °C.
The second trend that we can observe in Graph 2 is shown by comparing the boiling points of molecules from
different categories that have similar molecular weight. PH 3 and SiH 4 have similar molecular weights, but their respective
boiling points are -62 and -90 °C.
The dispersion force in SiH4 is weaker than the dipole-dipole force in PH3 . The high
boiling points of H2 O, HF, and NH3 violate the trend in which small molecules boil at lower temperatures than larger
molecules that are otherwise similar.
This indicates that for small molecules in particular, hydrogen bonding cause
exceptionally strong intermolecular nonbonding attractions.
Graph 3 illustrates intermolecular nonbonding attractions between various periodic groups of hydrides. The boiling points
of these different groups of hydrides show how dipole-dipole, dispersion forces based on molecular size, and hydrogen
bonding affect intermolecular attractions.
22
Questions:
1.
In Graph 1, the higher boiling points of low molecular weight hydrocarbons violate the general trend. "molecular size is
related to molar mass," in which lower molecular weight molecules boil at lower temperatures than higher molecular
weight molecules.
State the reason why there is a violation in the general trend observed for hydrocarbons.
(Hint: Make molecules of these substances and consider molecular size).
2.
In Graph 2, the high boiling point of H2 O violates the general trend in which a small molecule boils at lower temperature
than a large molecule that is otherwise similar. State why H 2 O is higher boiling than methanol, CH3 OH.
3.
In Graph 3, H2 Se, AsH 3 , and GeH4 are about the same size (nearly equal molar mass), and none of them have hydrogen
bonding. State why H 2 Se is highest boiling of the three.
4.
The Group 4 hydrides all have tetrahedral structures. They are nonpolar, and they have no hydrogen bonding. The only
intermolecular nonbonding force is dispersion. State why CH4 is lowest boiling and SnH4 is highest boiling.
5.
Predict on the basis of molecular shape, molecular size, molecular polarity, and hydrogen bonding, which member of
each set of compounds has the higher boiling point. State the reason for each choice. Assume that molecular size is
related to molar mass.
CO2
SO2
CH4
CBr4
n-butane
n-propane
CO2
trimethyl amine
dimethyl ether
CS 2
n-propyl amine
ethanol
23
6.
The data table shows the relationship between three classes of organic compounds, alkanes, aldehydes, and carboxylic
acids. Graph the given data and paste Graph 4 into this document, and answer the question at the bottom of the page.
Problem 4
Boiling Points of Three Classes of Organic Compounds
Polar Substances
hydrogen bonding
butanoic
Nonpolar Substances
dipole-dipole
MM
bp (°C)
88
164
102
dispersion
MM
bp (°C)
MM
bp (°C)
butanal
72
76
butane
58
0
186
pentanal
86
103
pentane
72
36
116
205
hexanal
100
128
hexane
86
69
130
223
heptanal
114
153
heptane
100
98
144
239
ocatanal
128
171
octane
114
126
acid
pentanoic
acid
hexanoic
acid
heptanoic
acid
octanoic
acid
Graph 4
Select this cell, and paste your Problem 4 Graph.
There are two trends that we can examine. Give a brief written discussion of these two trends.
24
25
C
D
ROW 2 B
ROW 3 C
G
E
D
H
F
E
G
I
G
J
J
I
C5 H12 O
L.
C5 H12 O
OH
K.
C6 H14
F
E
K
I
L
L
88
88
86
86
10.
What is the definition of boiling point?
Give the letters: At room temperature 1) Which compounds are gases? _______; 2) liquids? _______________; 3) solids? _______________
D
ROW 1 A
Boiling Predictions & Explanations: For each set of compounds, circle the letter with the higher boiling point & give a reasonable explanation.
9.
mp 58 °C
118
OH
CH3 CO2 Na
F.
81
60
CH3 CO2 H
E.
J.
C6 H14
46
I.
D. CH3 CH2 OH
65
32
72
CH3 OH
C5 H12
H.
C.
-6
Force
31
72
Μ
CH3 NH2
C5 H12
G.
Compound and Name
B.
bp (°C)
18
Force
A. H2 O
Μ
Complete the table. If a boiling point is missing, use <<chemfinder>>, the Merck Index, CRC, or Aldrich Chemical Catalog to look it up.
8.
Compound and Name
Predict the predominate intermolecular nonbonding force observed in each of the following compounds, and name each compound.
7.
138
69
36
bp (°C)