Chemistry 231L/232LFirst 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 ExperimentChemistry 231L/232LDr. Gergens - SD Mesa College

Name:_______________________________

Section:_____________ Date:____________

Write out the line-angle formula for all 18 isomers with the formula C8H18. Organize the isomers fromdecreasing parent chain length starting with octane. The first three are done for you. Give all isomersan 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 centermarked '* '. Mark all asymmetric centers with a '* '. Finally, answer the questions on the next page.

d ccb aa d ba

a

*

Name: octane Name: 2-methylheptane Name: 3-methylheptane

Name: Name: Name:

Name: Name: Name:

Name: Name: Name:

Name: Name: Name:

Name: Name: Name:

1

Isomers of Octane - Additional QuestionsDr. 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 ExerciseDr. 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. Most drawing and word processing

programs on the market generally have the same generic look and feel. 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. Another

program is Microsoft Word which most already use for general word processing. 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. In general, students can access

ISIS Draw from most computers on campus. 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. If it is not,

link to the QuickTime movie page, download and install the movie player. 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 dgergens@sdccd.cc.ca.us.

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 groupand formula

Re-Drawn Compound & Structure

ethyl butanoate

esterC6H12O2

ethyl butanoate

CH3CH2CH2 C OCH2CH3

O

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 groupand formula

Compound & Structure

esterC6H11BrO2

ethyl 2-bromo-2-methylpropionate

(CH3)2C C OCH2CH3

O

Br

1-phenyl-2-propanone

CH2CCH3

O

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. Use ChemFinder to

obtain a pre-drawn image of caffeine and insert into the box at the right. 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. Afterwards, you will

asked to recall that image and insert it into a word document. 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.

NH2

O

OH

partial structure ofphenylalanine

R –OH added

H's added

Do the same for the following: add a p-orbital, , 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

esterC6H12O2

ethyl butanoate

CH3CH2CH2 C OCH2CH3

O

Ethyl butyrate [105-54-4]

Synonyms: Ethyl Butanoate; Butyric Ether; Butanoic acid ethyl ester; Ethyl n-Butyrate; natural ethyl butyrate;BUTIRATO DE ETILO;

formula: C6H12O2

molar mass: 116.1596melting point: -135.4 °Cdensity: 0.878 g/mLboiling point: 252 °C at 0 mmrefractive index: 1.392solubility in water: 0.68 g/100 mL. InsolubleFlash point: 26 °CComments: 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.

esterC6H11BrO2

ethyl 2-bromo-2-methylpropionate

(CH3)2C C OCH2CH3

O

Br

ethyl 2-bromo-2-methylpropionate

Synonyms: _________

Formula: _________molar mass: _________melting point _________ °Cdensityboiling point _________ °Crefractive index _________solubility in water _________Flash point _________

Comments _________

10

Organic Model Exercise: An Adventure in Structure and BondingDr. Gergens - Mesa College

Introduction

Organic chemistry is the study of compounds that contain the element of carbon; compounds that do not contain carbonare termed inorganic. Carbon is singled out as a branch of chemistry because of the tremendous number of compounds itforms. While there are about 200,000 known inorganic compounds, there are over 6 million known compounds ofcarbon. While organic chemistry is the study of the compounds of carbon, biochemistry is the study of the chemistryof 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 itpossible to classify compounds by reactivity are called functional groups. In this experiment you will familiarizeyourself with the structures of functional groups shown in Chapter 3 of the McMurry text. The use hand-held modelswill aid you in this task. Many studies have shown that tactile (touch) learning far outweighs visual absorption of thissort of information.

Getting Started:

Start by reviewing Chapter 3 in your McMurry text. For this exercise, pay particular attention to the naming of thegeneral 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 three-dimensional 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 inpencil. However, your may be required to turn in your answers to the following questions as a word processeddocument. 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 three-dimensional perspective of organic compounds drawn on a two-dimensional piece of paper. For example, dimethyletherdrawn 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 thisether, 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 asolid black wedge, , and a hashed wedge to represent a 3-D perspective of a bond in three-dimensionalspace. 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 linerepresents bonds lying in the plane of the page. Being able to look at compounds drawn on a two-dimensional piece ofpaper and convert it to a 3-D perspective structure will be an important outcome of this exercise.

A.

C O CH

HHH

H

H 2-DFunctional Group: ether

OHH

H HH H

3-D

11

Part A - Covalencey

The atoms in organic compounds are generally held together by covalent bonding. In contrast, inorganic compounds areusually ionic, though they can have covalent bonds. Since carbon has four electrons in its outer shell, it forms fourcovalent (shared) bonds. These may be single, double or triple bonds as long as the total number of bonds to carbonequals four. Other elements, such as hydrogen and oxygen, are found in organic compounds, making the possibilities forcovalent 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. Wordprocess this image by using the drawing tool in Microsoft Word to add angles, geometric names, and hybridizations.

C

H

CH

H

OH

H

C

H

C

N

H C

H

NH

O

H

H

H

N N N

H

H

H

O

C

H

H

H

C

H

O

geometric name

hybridization

:

::

:

::

::

:

VSEPR = ________ ________ ________ ________ ________Determine the angles between bonds, name the geometry about the central atom and give the its hybridization.

Ideal Geometries

Non-Ideal Geometries

bond angles

bond angles

geometric name

hybridization

geometric name

hybridization

bond angles

On the next page, we will be using ball and stick models to demonstrate the versatility of bonding and thereforestructure 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 writingchemical bonds are highly descriptive and useful. In this exercise, you will be asked to identify and use of a model kitto build each functional group for the compounds below.

Identify each functional group. Construct molecular models for the compounds below. This will greatly assist you invisually seeing the three-dimensional perspective of organic compounds. Notice the tetrahedral carbon has a threedimensional 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-dimensionalrepresentation for each molecule and paste its structure into the table below.

A.

C O CH

HHH

H

H

B.

C ClHH

H

C.

C CH

H

H

H

Functional Group: ether Functional Group: Functional Group:

OHH

H HH H

D.

C C CH

HHH

H

H

OE.

C C OHHH

H

OF.

C C HH

Functional Group: Functional Group: Functional Group:

G.

C C NH2HH

H

OH.

C OHHH

H

I.OH

Functional Group: Functional Group: Functional Group:

J.

C C O CHH

H

OH

HH

K.

C NH2HH

H

L.

C C HHH

H

O

Functional Group: Functional Group: 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 payparticular attention to the existence of isomers. Isomers are prevalent in organic compounds due primarily to carbon'sability 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 three-dimensional 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 samemolecular formulas but different structures. For example, square planar complexes, [PtBr2Cl2]2–.

Cl

Pt Br

Br

Pt Br

Cl

BrCl

Cl

C CH

CH3

H

CH3

C CH

CH3

CH3

H

cis & trans alkenes

trans

cis

chlorine atoms opposite to each otheron opposite sides

chlorine atoms next to each otheron the same side

2-2-

transcis

Alkenes have rigid double bonds that prevent rotation, giving rise to cis- and trans-isomers. Construct the cis andtrans 2-butenes above. Notice the restrictive rotation about a double bond can result in cis-trans geometric isomerismin 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. Ifsubstituents on a cyclic ring point toward the same side, they are cis. If they point toward opposite sides of the ringthey are trans. Note the geometric isomers of 1,2-dimethylcylcohexane cannot inter convert without breaking andreforming bonds.

a. Below are cis- and trans-isomers of 1,2-dimethylcylcohexane. Make models of these compounds to convinceyourself 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

CH3CH3

Cl

Cl

Cl Cl

CH3

CH3

CH3

CH3cis trans

cis trans

transcis

b. Construct a molecular model for each isomer of 1,2-dibromocyclohexane. As seen for 1,2-dimethylcylcohexaneabove, 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? Draw thesame three perspectives for this structural isomer and paste them into the box below.

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 becauseof 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 thathave a nonsuperimposable mirror image. Your hands are nonsuperimposable mirror images, and a pair ofnonsuperimposable 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—amethyl, ethyl, hydroxyl, and hydrogen—thus a chiral carbon. Construct the mirror image of 2-butanol. Note thatboth are isomers—actually stereoisomers (stereo meaning in space).

Me

Et

HOHHO

H

Et

Me

b. Draw the three-dimensional representation using ISIS draw for each optical isomer of 2-butanol and 2-bromobutaneand paste the structure into box at the right. Note these molecules are nonsuperimposable.

CH3

CH2CH3

H

HO

CH3

CH2CH3

Br

H

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 usingChemfinder on the computer. Smell the authentic (-)- and (+)-carvones that are in the hood. What do they smelllike? Can you smell a difference between the odors spearmint and caraway? In the space below, draw theisomers of carvone using ISIS Draw and identify which carvone corresponds to which scent.

16

Intermolecular Nonbonding Forces ExerciseDr. Gergens - SD Mesa College

Introduction

The way electrons orient with respect to each other about atoms or molecules give rise to chemical unions between atomsor 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 intomolecules. The chemical bonds within a molecule are typically quite strong, such that it's usually necessary to heat amolecule to very high energies before the chemical bonds begin to break. A typical covalent chemical bond has a bondenergy 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 atomsor 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 beingnonbonding forces of attractions.

Molecules exist as distinct, separate collections of matter. We commonly think of three classes of forces betweenmolecules. The three classes of forces are:

0.1 kcal/mol1 kcal/mol10 kcal/mol

hydrogen bonding > dipole-dipole (or simply polar) forces > London dispersion forces

A rough estimate of the total amount of energy required to separate molecules very far away from each other is listedwith 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. Your final graphs should appear like Graph 1 for data given in

problem 1. 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

Ch

emic

al a

nd

Ph

ysic

al B

ond

ing

- C

once

pt

Map

Dr.

Ger

gen

s -

SD M

esa

Col

lege

Give at least three examples of each type of bonding:

X = N,O,F

HX

XH

+–

–+

NON-POLAR

molecules

POLAR

molecules

dispersion

dipole-

diople

hydrogen

bonding

attractions between

molecules

Physical

BONDING

••

••

⊕⊕

⊕⊕

⊕⊕

⊕⊕

⊕⊕

⊕⊕

⊕⊕

–+

XXH

HX

H

M+ X– M+

M+ X– M+ X– M+

M+ X– M+

M+ e– M+

M+ e– M+ e– M+

M+ e– M+

electrostatics

sharing of electrons

pure

covalent

(equal sharing)

polar

covalent

(unequal sharing)

ionic

bond

(cations-anions)

metallic

bond

(sea of electrons)

unions between

atoms

Chemical

Physi

cal

Prop

erti

es i

n S

ub

stan

ces

- C

on

cep

t M

apD

r. G

erge

ns

- SD

Mes

a C

olle

ge

X

SUBSTANCES

Non-Molecular

3D array-lattices

between atoms

attractions between

molecules

Molecular

ionic

solids

(cations-anions)electrostatics

M+ X– M+

M+ X– M+ X– M+

M+ X– M+

⊕⊕

⊕⊕

⊕⊕

⊕

hydrogen

bonding

dipole-

diople

dispersion

POLAR

molecules

NON-POLAR

molecules

+–

–+

HX

XH

X = N,O,F

••

••

⊕⊕

⊕⊕

⊕⊕

⊕

M+ e– M+

M+ e– M+ e– M+

M+ e– M+

metallic

solids

(sea of electrons)

network covalent

network

covalent

(atomic solid)

CRYSTALLINE SOLIDS

XX

XXX

XXX

+–+

––

++

–

+–

+–

–+ POLAR

molecules

NON-POLAR

molecules

metallic

solids

(sea of electrons)

ionic

solids

(cations-anions)

network

covalent

(atomic solid)

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 Hydrocarbons

MM bp (°C) MM bp (°C) MM bp (°C)

He 4 -269 F2 38 -188 CH4 16 -161

Ne 10 -246 Cl2 71 -34 C2H6 30 -88

Ar 40 -186 Br2 160 59 C3H8 44 -42

Kr 84 -152 I2 254 184 n-C4H10 58 0

Problem 2 Boiling Points of Polar versus Nonpolar Substances

Polar Substances Nonpolar Substances

hydrogen bonding dipole-dipole dispersion

MM bp (°C) MM bp (°C) MM bp (°C)

NH3 17 -33 CO 28 -192 N2 28 -196

H2O 18 100 PH3 34 -88 SiH4 32 -112

HF 20 20 AsH3 78 -62 GeH4 77 -90

CH3OH 32 65 ICl 162 97 Br2 160 59

Problem 3 Boiling Points for Various Hydrides

Group 4 Group 5 Group 6 Group 7 Group 8

MM bp(°C) MM bp(°C) MM bp(°C) MM bp(°C) MM bp(°C)

CH4 16 -161 NH3 17 -33 H2O 18 100 HF 20 20 He 4 -296

SiH4 32 -112 PH3 34 -88 H2S 34 -60 HCl 36.5 -85 Ne 10 -246

GeH4 77 -90 AsH3 78 -62 H2Se 81 -41 HBr 81 -67 Ar 40 -186

SnH4 123 -47 SbH3 125 -17 H2Te 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

0

100

200

300

0 100 200 300

molar mass

noble gases

halogens

hydrocarbons

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 C3H8, 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. The first is the relationship

between boiling point and molecular weight. 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. PH3 and SiH4 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 H2O, 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 H2O violates the general trend in which a small molecule boils at lower temperature

than a large molecule that is otherwise similar. State why H2O is higher boiling than methanol, CH3OH.

3. In Graph 3, H2Se, AsH3, and GeH4 are about the same size (nearly equal molar mass), and none of them have hydrogen

bonding. State why H2Se 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 CO2 CS2

CH4 CBr4 trimethyl amine n-propyl amine

n-butane n-propane dimethyl ether 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 Nonpolar Substances

hydrogen bonding dipole-dipole dispersion

MM bp (°C) MM bp (°C) MM bp (°C)

butanoic

acid

88 164 butanal 72 76 butane 58 0

pentanoic

acid

102 186 pentanal 86 103 pentane 72 36

hexanoic

acid

116 205 hexanal 100 128 hexane 86 69

heptanoic

acid

130 223 heptanal 114 153 heptane 100 98

octanoic

acid

144 239 ocatanal 128 171 octane 114 126

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

7.

Pred

ict

the

pred

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term

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nbond

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orc

e obse

rved

in e

ach

of

the

follo

win

g c

om

poun

ds, an

d na

me

each

com

poun

d.

8.

Com

ple

te t

he t

able

. If

a b

oili

ng p

oin

t is

mis

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, us

e <

<ch

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erck

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, CRC, or

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rich

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it u

p.

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d N

ame

ΜFo

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bp

(°C

)Com

poun

d an

d N

ame

ΜFo

rce

bp

(°C

)

A.

H2O

18

G.

C

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12

72

36

B.

CH

3N

H2

31

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.

C5H

12

72

C.

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26

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C

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86

69

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3CH

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C

6H

14

86

E.CH

3CO

2H

60

11

8K.

OH

C5H

12O

88

13

8

F.CH

3CO

2N

a8

1m

p 5

8 °

CL.

OH

C

5H

12O

88

9.

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ng P

redic

tions

& E

xpla

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: F

or

each

set

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com

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exp

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lids?

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10

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