Lecture 14

Lecture 14 - Chem 11500 Lecture14 (actually half of 13, all...

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Unformatted text preview: Chem 11500 Lecture14 (actually half of 13, all of 14) Reading: Sections 11.1­11.2 (part), 11.3­11.4 (part), pp. 474­485, 496, 500­505 1 Molecules as fuel: what’s in a barrel Molecules of oil? of Almost half of a barrel of oil is gasoline, but there are many other products that we get from oil: The cost of a barrel of oil affects more than just the cost 2 of gasoline A Barrel of Oil: a molecular Barrel perspective perspective Oil is predominantly made of “organic” (carbon containing) molecules 1 – 4 carbon atoms: some fuel, mostly feedstock for plastics and chemical product 5 – 12 carbons: fuel (gasoline), solvents 12 – 16 carbons: fuel (jet fuel) 15 – 18 carbons: diesel fuel 16 – 20 carbons: lubricants (engine oil) > 20 carbons: paraffin, waxes, asphalt What are the molecular structures of these products? 3 Lewis structures of Hydrocarbons: Lewis Isomers Isomers The simplest types of organic molecules are hydrocarbons, which contain only carbon and hydrogen; example C3H8 H H C C C H H H H H H Each carbon forms four covalent bonds, hydrogen forms one covalent bond; indicate a shared (bonding) pair of electrons with a line For hydrocarbons with more than three carbons, more than one Lewis structure is possible; example C4H10 H H H H C C C C H H H H H H H H H linear H C H H C C C H H H H branched Isomers: molecules with the same molecular formula but different structures 4 Shapes of hydrocarbons The carbon atoms are nearly tetrahedral; bond angles (H­C­H, C­C­H, C­C­C) are close to 109.5˚ 109.5˚ Organic molecules with single bonds are not flat! 5 Representing organic structures H Full formula (show all atoms and bonds) H H H Condensed formula (show bonds between carbons, include atoms) Carbon skeleton formula: show only bonds between carbons; carbons are at the vertices C C H H H H H C C C C H H H C H H H H C H3 H3C CH C H2 C H C H3 C H3 6 Multiple bonding between carbon: Multiple alkanes, alkenes, alkynes alkanes, Hydrocarbons that contain only single bonds are known as alkanes Carbon is adept at making multiple bonds with other carbon atoms: alkenes contain a double­bond H H C C C H H H H H H H C C H H3C C H2 C H2 C C H2 C H3 C H H H Alkynes contain a triple bond HHH C C C H H C C C H H H H HC C CH2 C H CH3 CH3 7 Structures around multiple bonds VSEPR predicts: Around double bonds: 3 groups, trigonal planar H Around triple bonds: 2 groups, planar H 120˚ H 120˚ H 180˚ H 8 Names of simple organic molecules Simple organic molecules are named on the basis of their size Molecule Names of simple molecules have two parts: Indicates the number of carbons Number of carbons 1 2 3 4 5 6 etc parent + suffix parent name example methethpropbutpenthex- methane ethane propane butane pentane hexane Indicates the type of molecule: alkanes have suffix “-ane” CH4 CH3-CH3 CH3-CH2-CH3 CH3-CH2-CH2-CH3 CH3-CH2CH2-CH2-CH3 CH3-(CH2)4-CH3 9 CPS Question The combustion quality of automobile gasoline is rated in comparison to “octane”. All of the following structures represent octane except: A B CH3-(CH2)6-CH3 C H3C D C H2 CH2 CH2 CH2 CH2 CH2 CH2 CH3 H HHH HC CCCH HHH HHH HCCCCH HHHH 10 Names of simple alkenes and Names alkynes alkynes To name alkenes and alkynes, we change the suffix carbons 2 Alkenes H H H 3 4 H H H H 5 H CC CC CC CC H Alkynes ethene propene H H CH3 HCCH H C C C H3 ethyne propyne H CH2 CH3 butene H C C CH2 CH3 butyne H CH2 CH2 CH3 pentene H C C CH2 CH2 C H3 pentyne 11 Very large organic molecules: polymers Alkenes can be coupled together to create long chains of “monomers” polymers Free radical polymerization H X + Y. 1. initiation H H X . Y H H H “free radical” H 2. propagation X H . Y H Y 3. termination Y HH ( CH2 X CH XH X H HH H . Y H XH H H + H H X H X . H ). n H X H XH H + XH HH X HH . Y H + Y. H Y ( C H2 X ) CH Y n H 12 CPS question Teflon is a fluorine­containing organic polymer. F FF FF FF FF FF F ( F FF FF FF FF FF F ) What is the alkene monomer in teflon? A B F F F F H F F H H C F F F F H D F F FF F F F F 13 Common polymers Monomer F Polymer ( F F F ( F H Polymer name ) F F polytetrafluoroethylene n F aka PTFE (teflon) tetrafluoroethylene H Cl H H ) Cl H H polyvinylchloride n PVC chloroethene (vinyl chloride) H H H ( H H H ) n polystyrene styrofoam styrene O O methylmethacrylate O O () polymethylmethacrylate PMMA plexiglass 14 Cyclic Hydrocarbons Carbon can bond to form cyclic C CH2 CH H2 2 structures (rings); if it only CH2 contains single bonds, it is a H2C Five membered ring: cycloalkane (cyclic alkane) cyclopentane A cycloalkene is a ring with a double bond in it Cyclic alkynes are known, but generally only in very large rings (C10) (hard to get to a linear geometry) 15 Benzene: a very special cyclic Benzene: alkene alkene = Two equivalent resonance forms Remember: neither is the correct structure of the molecule – it is a hybrid Benzene has very different reactivity from simple alkenes: An example of an aromatic molecule 16 Hydrocarbons as fuel: combustion reactions Combustion involves the reaction with oxygen; hydrocarbons are converted to carbon dioxide and water H3C C H2 C H2 CH C H3 6CO2 + 7H2O + 19 O2 2 C H3 14 CH bonds 5 C-C bonds 19 O-O bonds 12 C=O bonds 14 OH bonds ΔH = -3878 kJ/mol = -45.1 kJ/gram Energy production from other hydrocarbons (kJ/gram) CH4 (natural gas) C3H8 (propane) Benzene (C6H6) Ethanol (CH3CH2OH) -50 -46 -40 -28 17 Oxidation reactions Conversion of carbons in hydrocarbons to CO2 is called oxidation (“creating bonds to oxygen”) Partial oxidation can occur, to create 1, 2, or 3 bonds to oxygen: C H3-C H2-C H3 [O] CH3-CH2-CH2-OH 1 C-O bond [O] O C H3-C H2-C -H 2 C-O bonds [O] O C H3-C H2-C -OH 3 C-O bonds 18 Non-carbon atoms in organic molecules Other types of atoms can be found in organic molecules; see ethanol, which contains a C–O bond H C C H H H H O H H3C CH2 OH OH Organic molecules that contain a C bonded to OH are called alcohols OH Cl Other alcohols include CH3-OH methanol (wood alcohol) OH OH OH Isopropyl alcohol (rubbing alcohol) propylene glycol (in cough syrup) 2-chlorophenol (Chloraseptic) 19 Functional Groups in organic molecules Despite having different numbers of carbons and even very different skeletal structures, organic molecules containing C bonded to OH (alcohols) generally have consistent properties and reactivity; the –OH is called a “functional group” because it’s presence has a large impact on the properties of the molecule A large number of functional groups are known in organic molecules (for a full list, see Table 15.5) Some of the more important to know: Group name type of molecule example -OH hydroxy alcohol CH3OH O C=O carbonyl ketone or aldehyde H3C O CH3 O OH -NH2 carboxylic acid acid amino amine H3C OH CH3CH2NH2 acetone (nail polish remover) acetic acid (vinegar) 20 Question Which of the functional groups listed are present in this molecule a. hydroxy OH b. Amino c. carbonyl d. triple bond 21 Question Which of the functional groups listed are present in this molecule? I. hydroxy II. Amino III. carbonyl IV. triple bond A.I and IV B.I and III C.III and IV D.I, III, and IV 22 Examples of organic molecules Examples with multiple functional groups with morphine novacaine testosterone tetraHydroCannibol (THC) nicotine 23 Summary Oil provides important components for society including fuel and raw materials for production The organic building blocks needed to make plastics (polymers) and drugs come from oil Organic molecules have three dimensional shapes based on the tetrahedron Non­carbon (hetero) atoms are found in organic molecules in functional groups 24 ...
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