Pharmaceutical Science Exam #2 Lecture 1 (Intermolecular forces)

What are intramolecular forces? Intermolecular forces?

Attractive forces/chemical bonds between atoms within a molecule

Electrical forces between molecules causing one molecule to influence another one

What are three intramolecular forces?

Ionic bonds, covalent bonds, and metallic bonds

What are examples of Intermolecular bonds?

H-bonds, dipole-dipole interactions, Van Der Waals/London dispersion

What properties are influenced by IMF strength?

Melting point, boiling point, and miscibility

What general physical properties can binding forces help explain?

Properties of gases, liquids, solids, surface tension, flocculation, and protein binding/formation

What is cohesion?

Attraction between molecules of the same substance

What is adhesion?

Attraction between molecules of different substances

What causes repulsive forces between molecules? What is the purpose/effect of repulsion?

Molecules get close enough that their outer charge clouds overlap

It protects molecules from structural destruction wen they become too close

What happens when attractive and repulsive forces are equal?

Net potential energy is minimum, equilibrium is established, and the system is most stable

What seven IMF types are there?

Ion-ion, dipole-dipole, dipole-ion, dipole-induced dipole, ion-induced dipole, induced dipole-induced dipole (London), H-bonding

What is an ion-ion interaction?

Electrostatic interaction between closely packed ions of opposite charge

What does Coulomb’s law say about charge and electrostatic force?

Force i directly proportional to the product of the magnitudes of the charges

What does Coloumb’s law say about distance and electrostatic force?

Force is inversely proportional to the square distance between charges

What happens to ion-ion force if ionic charge (q) increases?

Electrostatic attraction or repulsion increases

What happens to ion-ion distance as the distance between ions increases?

The force decreases rapidly

What is H-bonding?

A special case of dipole-dipole interaction between a H atom and a highly electronegative atom (O, N, F)

How does strong H-bonding affect water’s vapor pressure and boiling behavior?

Low vapor pressure + high heat of vaporization → high boiling point

What are examples of hydrogen bonding in biology?

Hold proteins together in secondary structures (Alpha helix and beta sheets)

Help enzymes bind to their substrates

What is a hydrophobic interaction/effect?

The tendency of hydrophobic molecules or molecular regions to avoid water

Where are nonpolar regions of proteins typically located?

Buried inside the protein, away from the aqueous environment

What thermodynamic factor drives hydrophobic interactions?

Entropy

What happens when water forms ordered cages around hydrophobic groups?

System entropy decreases, making the arrangement thermodynamically unfavorable

Why is aggregation of hydrophobic residues thermodynamically favorable?

It frees ordered water molecules, increasing water/system entropy

What does a dipole moment describe?

How electron density s distributed over a molecule

How can electronegativity differences create a dipole?

Electron density shifts toward one side, creating partial negative and partial positive charges

What does a dipole moment quantify?

The polarity of a bond or molecule, is a vector quantity that has both magnitude and direction

What causes dipole-dipole interactions?

Attractions between permanent dipoles in polar molecules

What is an ion-dipole interaction? And where is it most commonly found

Electrostatic attraction between an ion and a neutral polar molecule

In solutions

What increases ion-dipole interactions?

Greater ionic charge and greater dipole magnitude of the polar molecule

What causes London Dispersion Forces?

Variations in electron density create temporary dipoles that induce dipoles in neighboring molecules

What are LDF’s dependent on?

Surface area, become stronger with larger amount of surface contact

What two types of molecules participate in dipole-induced dipole interaction? How is it formed?

One polar molecule and one nonpolar molecule

A permanent dipole distorts/polarizes the electron distribution of a nonpolar molecule, creating a temporary dipoles

What us an ion-induced dipole interaction?

A weak force in which an ion disrupts the electron distribution of a nonpolar atom/molecule, inducing a dipole

Rank the IMFs from strongest to weakest

Ion . Ion-dipole . H-bond . Dipole-dipole . Ion-induced dipole . Dipole-induced dipole . LDF