Presentation on theme: "Chapter 3 Introduction to Organic Molecules and Functional Groups."— Presentation transcript:
1Chapter 3IntroductiontoOrganic MoleculesandFunctional Groups
2Introduction to Organic Molecules and Functional Groups A functional group is an atom or a group of atoms with characteristic chemical and physical properties. It is the reactive part of the molecule.Most organic compounds have C—C and C—H bonds. However, many organic molecules possess other structural features:Heteroatoms—atoms other than carbon or hydrogen. Bonds—the most common bonds occur in C—C and C—O double bonds.These structural features distinguish one organic molecule from another. They determine a molecule’s geometry, physical properties, and reactivity, and comprise what is called a functional group.
3Introduction to Organic Molecules and Functional Groups Heteroatoms and bonds confer reactivity on a particular molecule.Heteroatoms have lone pairs and create electron-deficient sites on carbon. Bonds are easily broken in chemical reactions. A bond makes a molecule a base and a nucleophile.R : usually saturated hydrocarbon unit (alkyl)Don’t think that the C—C and C—H bonds are unimportant. They form the carbon backbone or skeleton to which the functional group is attached.
4Introduction to Organic Molecules and Functional Groups The hydroxy group makes the properties of ethanol very different from the properties of ethane.
5An Overview of Functional Groups HydrocarbonsHydrocarbons are compounds made up of only the elements carbon and hydrogen. They may be aliphatic or aromatic.
6An Overview of Functional Groups HydrocarbonsAromatic hydrocarbons are so named because many of the earliest known aromatic compounds had strong characteristic odors.The simplest aromatic hydrocarbon is benzene. The six-membered ring and three bonds of benzene comprise a single functional group.When a benzene ring is bonded to another group, it is called a phenyl group.
7There must be smarter way to use these hydrocarbons !! An Overview of Functional GroupsHydrocarbonsAlkanes have no functional groups and very unreactive.They combust (“burn” in air) and the C-C bonds can be broken in the absence of air at very high temperatures (~700 oC) (pyrolysis reactions).There must be smarter way to use these hydrocarbons !!Polyethylene (-[CH2-CH2]n-), a common packaging material, is so resistant to environmental degradation (both chemical and biological) that it persists for years in landfill disposal sites.
8An Overview of Functional Groups Compounds containing C-Z s Bonds
9An Overview of Functional Groups Compounds containing C-Z s BondsThe electronegativity difference between C and Z causes the C-Z bond to be polar:Alcohol : meant “spirit”. anything that was distilled. “spirit of wine” – distilled winei.e. ethanol (ethylalcohol)Ether : originally named for diethylether due to its volatility and anesthetic effect.cf. petroleum ether: low boiling fraction for petroleum
10An Overview of Functional Groups Compounds containing C-Z s BondsExamples
12An Overview of Functional Groups Compounds Containing a C=O GroupThis group is called a “carbonyl group”.The polar C—O bond makes the carbonyl carbon an electrophile, while the lone pairs on O allow it to react as a nucleophile and base.The carbonyl group also contains a bond that is more easily broken than a C—O bond.
13An Overview of Functional Groups Compounds Containing a C=O GroupExamples
14Introduction to Organic Molecules and Functional Groups A functional group determines all of the following properties of a molecule:Bonding and shapeType and strength of intermolecular forcesPhysical propertiesNomenclatureChemical reactivity
15Intermolecular forces (attractive) Ions, ionic moleculesIons, ionic moleculeswith polar compoundpolar compoundIons, ionic moleculeswith nonpolar compoundFigure 13.1nonpolar compoundInduced dipole :Ion induces polarization to generate dipole.dispersion :Instantaneous dipole generated by short time fluctuations in the charge cloudsinduces polarization to generate dipole.
16Introduction to Organic Molecules and Functional Groups Intermolecular ForcesIntermolecular forces are interactions that exist between molecules. Functional groups determine the type and strength of these interactions.Ionic compounds contain oppositely charged particles held together by extremely strong electrostatic inter-actions. These ionic inter-actions are much stronger than the intermolecular forces present between covalent molecules.
17Introduction to Organic Molecules and Functional Groups Intermolecular ForcesThe nature of the forces between molecules depends on the functional group present. There are three different types of interactions, shown below in order of increasing strength:van der Waals forcesdipole-dipole interactionshydrogen bonding
18Introduction to Organic Molecules and Functional Groups Intermolecular Forces—van der Waals Forcesvan der Waals forces are also known as London forces + repulsive interaction.They are weak interactions caused by momentary changes in electron density in a molecule.They are the only attractive forces present in nonpolar compounds.even for methane, CH4Even though CH4 has no net dipole, at any one instant its electron density may not be completely symmetrical, resulting in a temporary dipole. This can induce a temporary dipole in another molecule. The weak interaction of these temporary dipoles constitutes van der Waals forces.
19Introduction to Organic Molecules and Functional Groups Intermolecular Forces—van der Waals ForcesAll compounds exhibit van der Waals forces.The surface area of a molecule determines the strength of the van der Waals interactions between molecules. The larger the surface area, the larger the attractive force between two molecules, and the stronger the intermolecular forces.
20Introduction to Organic Molecules and Functional Groups Intermolecular Forces—van der Waals Forcesvan der Waals forces are also affected by polarizability.Polarizability is a measure of how the electron cloud around an atom responds to changes in its electronic environment.
21Introduction to Organic Molecules and Functional Groups Intermolecular Forces—Dipole-Dipole InteractionsDipole—dipole interactions are the attractive forces between the permanent dipoles of two polar molecules.These attractive forces caused by permanent dipoles are much stronger than weak van der Waals forces.
22Introduction to Organic Molecules and Functional Groups Intermolecular Forces—Hydrogen BondingHydrogen bonding typically occurs when a hydrogen atom bonded to O, N, or F, is electrostatically attracted to a lone pair of electrons on an O, N, or F atom in another molecule.can be extended to p-electrons of a benzene ring.
23Introduction to Organic Molecules and Functional Groups Intermolecular Forces—Hydrogen BondingIntramolecular Hydrogen bonding :reduces intermolecular interactions.Hydrogen bonding in nylon
24Introduction to Organic Molecules and Functional Groups Intermolecular ForcesNote: as the polarity of an organic molecule increases, so does the strength of its intermolecular forces.
25Introduction to Organic Molecules and Functional Groups Physical Properties—Boiling PointThe boiling point of a compound is the temperature at which liquid molecules are converted into gas.In boiling, energy is needed to overcome the attractive forces in the more ordered liquid state.The stronger the intermolecular forces, the higher the boiling point.For compounds with approximately the same molecular weight:
26Introduction to Organic Molecules and Functional Groups Physical Properties—Boiling PointFor two compounds with similar functional groups:The larger the surface area, the higher the boiling point.The more polarizable the atoms, the higher the boiling point.
27Introduction to Organic Molecules and Functional Groups Separation of a mixture : distillationLiquids having different boiling points can be separated in the laboratory using a distillation apparatus.
28Introduction to Organic Molecules and Functional Groups Physical Properties—Melting PointThe melting point is the temperature at which a solid is converted to its liquid phase.In melting, energy is needed to overcome the attractive forces in the more ordered crystalline solid.The stronger the intermolecular forces, the higher the melting point.Given the same functional group, the more symmetrical the compound, the higher the melting point. --- packing effect
29Introduction to Organic Molecules and Functional Groups Physical Properties—Melting PointSymmetry also plays a role in determining the melting points of compounds having the same functional group and similar molecular weights, but very different shapes.A compact symmetrical molecule like neopentane packs well into a crystalline lattice whereas isopentane, which has a CH3 group dangling from a four-carbon chain, does not. Thus, neopentane has a much higher melting point.
30Introduction to Organic Molecules and Functional Groups Physical Properties—SolubilitySolubility is the extent to which a compound, called a solute, dissolves in a liquid, called a solvent.
31Introduction to Organic Molecules and Functional Groups Physical Properties—SolubilityCompounds dissolve in solvents having similar kinds of intermolecular forces.“Like dissolves like.”Polar compounds dissolve in polar solvents. Nonpolar or weakly polar compounds dissolve in nonpolar or weakly polar solvents.Water and organic solvents are two different kinds of solvents. Water is very polar and is capable of hydrogen bonding with a solute. Many organic solvents are either nonpolar, like carbon tetrachloride (CCl4) and hexane [CH3(CH2)4CH3], or weakly polar, like diethyl ether (CH3CH2OCH2CH3).Most ionic compounds are soluble in water, but insoluble in organic solvents.
32Physical Properties—Solubility An organic compound is water soluble only if it contains one polar functional group capable of hydrogen bonding with the solvent for every five C atoms it contains. For example, compare the solubility of butane and acetone in H2O and CCl4.
33Introduction to Organic Molecules and Functional Groups Physical Properties—SolubilityTo dissolve an ionic compound, the strong ion-ion interactions must be replaced by many weaker ion-dipole interactions.
34Introduction to Organic Molecules and Functional Groups Physical Properties—Solubilityethanol is water soluble since it has a small carbon skeleton of five C atoms, compared to the size of its polar OH group.Cholesterol has 27 carbon atoms and only one OH group. Its carbon skeleton is too large for the OH group to solubilize by hydrogen bonding, so cholesterol is insoluble in water.The nonpolar part of a molecule that is not attracted to H2O is said to be hydrophobic. (“water hating”)The polar part of a molecule that can hydrogen bond to H2O is said to be hydrophilic. (“water loving”)
35Introduction to Organic Molecules and Functional Groups Application—VitaminsFat soluble vitamins : vitamin A, D, E, KWater soluble vitamins : vitamin B complex, C
36Fat soluble vitamins : vitamin A, D, E, K vitamin Dvitamin E (tocopherol)vitamin K
37Water soluble vitamins : vitamin B complex, C Vitamin B2(riboflavin)Vitamin B12Vitamin C (ascorbic acid)
38Introduction to Organic Molecules and Functional Groups Application—Soap
39Introduction to Organic Molecules and Functional Groups Application—The Cell Membrane
40Introduction to Organic Molecules and Functional Groups Application—The Cell MembraneTransport Across a Cell Membrane:Polar molecules and ions are transported across cell membranes encapsulated within molecules called ionophores.Ionophores are organic molecules that complex cations. They have a hydrophobic exterior that makes them soluble in the nonpolar interior of the cell membrane, and a central cavity with several oxygens whose lone pairs complex with a given ion.
41Introduction to Organic Molecules and Functional Groups Application—The Cell MembraneTransport Across a Cell Membrane:
42Introduction to Organic Molecules and Functional Groups Synthetic ionophoresCrown ethers are cyclic ethers containing several oxygen atoms that bind specific cations depending on the size of their cavity.They are named using the general format x-crown-y, where x is the total number of atoms in the ring and y is the number of oxygen atoms.Charles Pedersen at DuPont
43Introduction to Organic Molecules and Functional Groups Influence of Functional Groups on ReactivityRecall that:Functional groups create reactive sites in molecules.Electron-rich sites react with electron poor sites.All functional groups contain a heteroatom, a bond or both, and these features create electron-deficient (or electrophilic) sites and electron-rich (or nucleophilic) sites in a molecule. Molecules react at these sites.
44Introduction to Organic Molecules and Functional Groups Influence of Functional Groups on Reactivity
45Introduction to Organic Molecules and Functional Groups Influence of Functional Groups on ReactivityAn electron-deficient carbon reacts with a nucleophile, symbolized as :Nu¯.An electron-rich carbon reacts with an electrophile, symbolized as E+.For example, alkenes contain an electron rich double bond, and so they react with electrophiles E+.
46Introduction to Organic Molecules and Functional Groups Influence of Functional Groups on ReactivityOn the other hand, alkyl halides possess an electrophilic carbon atom, so they react with electron-rich nucleophiles.
47Introduction to Organic Molecules and Functional Groups BiomoleculesBiomolecules are organic compounds found in biological systems.Many are relatively small with molecular weights of less than 1000 g/mol.There are four main families of small molecule biomolecules:Simple sugars—combine to form complex carbohydrates like starchNucleotides—are the building blocks of DNAAmino acids—join together to form proteinsFatty acids—are the building blocks of triacylglycerols, lipids that are stored as fat droplets in adipose tissue.Biomolecules often have several functional groups.
51Preview of Chapter 4 Alkanes What are alkanes?Systematic naming of Alkanes.Conformations of Alkanes.how flexible or rigid are various alkanes- Reactions of Alkanes.
52Assignment for March 4th Class. What is the general molecular formula for an acyclic alkane?What is the general molecular formular for a cyclic alkane with one ring?What is the meaning of conformation?What are eclipsed conformation and staggered conformation?What are angle strain and torsional strain in cycloalkanes?