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Experiment 1:. STRUCTURE, INTERMOLECULAR FORCES AND SOLUBILITY. OBJECTIVES. To learn how to identify which intermolecular forces (IMF) exist between organic compounds. To investigate the relationship between structure, intermolecular forces and solubility using solubility testing. ROLE OF IMF.

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Experiment 1

Experiment 1:

STRUCTURE, INTERMOLECULAR FORCES AND SOLUBILITY


Objectives
OBJECTIVES

  • To learn how to identify which intermolecular forces (IMF) exist between organic compounds.

  • To investigate the relationship between structure, intermolecular forces and solubility using solubility testing.


Role of imf
ROLE OF IMF

  • Physical state

    • solid, liquid & gas

  • Distillation

    • difference in BP

  • Extraction

    • difference in solubility

  • Chromatography

    • different IMF between analyte and stationary vs. mobile phase

  • Biology

    • secondary structure of proteins

    • DNA and DNA-RNA base pairing


Types of imf
TYPES OF IMF

  • London Dispersion Forces

  • Dipole-Dipole Forces

  • Hydrogen Bonding

    • Acceptors

    • Donors

  • Ion-dipole Forces


London dispersion forces

d -

--------------

d -

d +

LONDON DISPERSION FORCES

  • London Dispersion Forces (LDF) = weakest intermolecular force.

  • Temporary attractive force.

  • Electrons are in constant motion, and are at times distributed unevenly about the nucleus. This results in the formation of a temporary dipole.

  • A second atom/molecule can be distorted by the appearance of the dipole in the first atom/molecule (electrons repel one another). This leads to an electrostatic attraction between the two atoms or molecules.

d +


London dispersion forces1
LONDON DISPERSION FORCES

  • Dispersion forces are present between all molecules, whether they are polar or nonpolar.

  • The larger/heavier an atom is, the stronger the dispersion forces are.

  • Compounds which contain carbons and hydrogens ONLY possess LDF ONLY.

LESS LDF

MORE LDF


Dipole dipole forces
DIPOLE - DIPOLE FORCES

  • Dipole moment(m):Electrostatic attraction between polar molecules.

  • Dipole moment = a measure of the unevenness of electron density in a bond or molecule.

  • It depends on both electronegativityof atoms and on molecular geometry.


Dipole dipole forces1
DIPOLE - DIPOLE FORCES

  • Dipole-dipole forces are present only in polar molecules.

  • They occur when the d+ end of one polar molecule is attracted to the d- end of another.


Hydrogen bonding
HYDROGEN BONDING

  • Hydrogen bonds are a result of the large difference in electronegativity between H and N, O, or F.

  • They occur when the H of one molecule attached to an O or N is attracted to an O or N of a different molecule.

  • Some compounds have a H to donate to hydrogen bonding, while others can only accept a H from other compounds to form hydrogen bonds.


Hydrogen bonding1
HYDROGEN BONDING

*** Notice that compounds containing an O or N with a H DIRECTLY bound to it are donors and acceptors!***


Ion dipole
ION-DIPOLE

  • An ion-dipole force exists between an ion and the partial charge on the end of a polar molecule.

  • They are especially important for solutions of ionic substances in polar solvents, such as NaCl in water.


Overview
OVERVIEW

  • A: Test solubility of compounds in hexane and water.

  • B: Test solubility of organic liquids in water.

  • C: Test solubility of alcohols in hexane and water.

  • D: Test solubility of organic solids in diethyl ether, water, acidic and basic solutions.


Table 1 1
Table 1.1

Use the following abbreviations:

LDF = London Dispersion

DD = dipole-dipole

HA = Hydrogen bond acceptor

HD = Hydrogen bond donor

*************************Always indicate if a molecule is a hydrogen bond DONOR, or a hydrogen bond ACCEPTOR ONLY! Do not just write “hydrogen bonding” here!

*************************





Imf flow chart
IMF FLOW CHART

Interacting molecules

or ions

NO

NO

YES

NO

Are polar molecules involved?

Are ions involved?

Are polar

molecules and ions both present?

YES

DIPOLE-DIPOLE

Ex: CH3Cl

YES

NO

YES

Are hydrogen atoms bonded to N, O, or F atoms?

IONIC BONDING

Ex: NaCl

LDF

ONLY

Ex: CH3CH3

ION-DIPOLE

Ex: NaCl in H2O

NO

YES

HYDROGEN BOND

Acceptor

Ex: CH3OCH3

HYDROGEN BOND

Donor

Ex: H2O, NH3


Safety concerns
SAFETY CONCERNS

  • All solvents used in today’s lab are volatile. Wear safety goggles at all times, and use fume hoods.


Waste disposal
WASTE DISPOSAL

  • Pour all liquid waste from this experiment into the container labeled “LIQUID ORGANIC WASTE”.

  • Do NOT pour any waste down the drain!


Laboratory notebook pre lab
LABORATORY NOTEBOOK(Pre-lab)

  • OBJECTIVE (Must clearly state…)

    • What you will evaluate

    • How you will evaluate it

  • TABLE OF PHYSICAL DATA (Complete the following table using MSDS sheets from a site listed on WWW Links ONLY. Wikipedia is unacceptable)

  • REFERENCE TO PROCEDURE (Must include…)

    • Full title including edition and authors

    • page numbers where actual procedure can be found


Laboratory notebook in lab
LABORATORY NOTEBOOK(In-lab)

  • DATA/CALCULATIONS

    • Not applicable for this experiment. All observations will be recorded directly onto the Final Lab Report.

  • EXPERIMENTAL PROCEDURE

    • In paragraph form, briefly describe the procedure that you actually followed during the lab.

    • Paragraph must be written in PAST TENSE, PASSIVE VOICE.

    • Include any mistakes, accidents or observations if necessary.