Daley amp Daley Chapter 4 Physical Properties 41 Physical properties of organic molecules Solids liquids amp gases Melting point Boiling point 42 Types of intermolecular interactions ID: 1045185
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1. CHE2060 4: Physical properties & interactionsDaley & DaleyChapter 4:Physical Properties 4.1 Physical properties of organic molecules Solids, liquids & gases Melting point Boiling point4.2 Types of intermolecular interactions van der Waals interactions Dipolar interactions Hydrogen bonding 4.3 Solubility4.4 Surfactants Micelles & emulsionsLabs Melting point determinationViscosity of organic compoundsDistillation of wine
2. SurfactantsAmphipathic lipidsMicelles vs. emulsions
3. SurfactantsSurfactants are a class of molecules with ‘dual’ or ‘two-faced’ physical natures. One end is polar The other end is non-polarD&D p.194-6:O::O:..-1K +1non-polar tailhydrophobicpolarhead grouphydrophilicSo soaps & other amphipathic compounds are able to clean greasefrom objects by making the grease soluble in water. Normally grease & water don’t mix… …but soaps create a molecular bridge between grease & water… surfactants greatly increase solubility!Bile salts are a surfactant that dissolve lipids in body fluid.So these amphipathic molecules are able to interact with (or be soluble in)both polar and non-polar molecules & solvents.Soaps are a good example:
4. Soap scum & ‘advanced’ soapsSo, what’s soap scum? It’s a precipitate formed when metal ions in hardwater interact with the carbonate head group of soap & form a precipitatethat builds up on surfaces.D&D p.194-6Hard water ions: calcium, magnesium, ironLike most precipitates, soap scum is dissolved by acids.. Typical cleaners use HCl.Some surfactants are less likely to form “scum” precipitates because of theirchemical structures & properties.Sodium dodecanyl sulfate (aka sodium lauryl sulfate): :O::O:..Na +1non-polar tailhydrophobicpolarhead grouphydrophilic:O:S:O:SDS doesn’t precipitate with asmany metals…. So less soap scum.
5. Surfactants & lung developmentSurfactants can lower surface tension & this helps allow oxygen to gainaccess to the surface of lung alveoli.D&D p.194-6Animals born prematurely haven’t yet developed the ability to produce DPPC, &without the surfactant their lungs aren’t able to inflate & stay inflated.They can be saved by being given the missing surfactants until they develop their own.non-polar tailspolar headHyaline membrane disease?The inner surface of lungs is coated with a solution of lipid in water.DPPC (dipalmitoylphophatidyl choline) is the lipid of choice.
6. Soap bubblesSoap bubbles are two lipid (soap) monolayers with a layer of water in betweenthem.The non-polar fatty carbon tails point outward into the air, also non-polar.Polar head groups face into the layer of very polar water.
7. Lipid structures in waterWhen mixed with water (or an aqueous solution), amphipathic lipids spontaneously form 3D structures to increase lipid solubility.Salad dressing, hollandase sauce, mayonnaiseNote that the polar heads are hydrophilic & interact with the water, while the hydrophobic non-polar tails interact only with each other or other hydrophobic molecules (hiding from water).non-polarmoleculesMicelles are spherical structures one lipid ‘thick’ with no filling. Liposomes are formed by closing a bilayer to create a hollow sphere filled with aqueous solution. Emulsions are micelles that hold non-polar, hydrophobic molecules in their cores where they are solubilized by the surfactant’s tails.Emulsions
8. Lipids, emulsions and dairy scienceMilk fat droplets have very weird and elaborate structures.Triacylglcyerol core surrounded by a monolayerof phospholipids.All enclosed by a phospholipid bilayerstudded with proteins.Processing, like pasteurization and homogenization, changes the structure of milk.
9. Effect of chain length on physical properties
10. Density of organic compoundsThe density of organic compounds depends on their ratio of “heavy” andlight atoms. For example: C8H18 C8H14Cl4The ability of molecules to pack together well(efficiently) also affects density, but is less important than MW and ratio of heavy to lightatoms. density (g/mL)n-pentane C5H12 0.621-bromobutane C4H9Br 1.27hexane C6H14 0.66cyclohexane C6H12 0.78diethyl ether C4H10O 0.711-butanol C4H9OH 0.81D&D p.197-4McKee p70 more dense, sinksTop: H2O, red food coloring;Bottom: CH2Cl2