Ch11_Organic_1 - 1 ORGANIC CHEMISTRY 2 Isomerism Types of...

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Unformatted text preview: 1 ORGANIC CHEMISTRY 2 Isomerism Types of Organic Compounds 3 • Isomers have identical composition but Isomers have different structures • Two forms of isomerism • Vast majority of over 20 million known compounds are based on C: organic organic compounds. • Generally contain C and H + other elements • Great variety of compounds – Constitutional (or structural) – Stereoisomerism • Constitutional – Same empirical formula but different atomto-atom connections • Stereoisomerism – Same atom-to-atom connections but different arrangement in space. 4 Structural Isomers 5 6 Stereoisomers: Optical Stereoisomers: Geometric Geometric isomers can occur when there is a C=C double bond. • Optical isomers are molecules with non-superimposable mirror images. superimposable mirror Such molecules are called CHIRAL Such CHIRAL Pairs of chiral molecules are Pairs molecules enantiomers . • Chiral molecules in solution can rotate Chiral molecules the plane of plane polarized light. • • Cis-2-butene Trans-2- butene 1 Chiral Compounds and Chiral Compounds Polarized Light 7 8 Stereoisomers Isomers Stereoisomers Isomers 9 Chirality generally occurs when a C atom has 4 different groups attached. Lactic acid isomers are nonsuperimposable Lactic acid Chirality: Handedness in Nature 10 Chirality: Handedness in Nature 11 Stereoisomers in Nature 12 Right- and lefthanded seashells These molecules are non-superimposable mirror images. These amino acids are nonsuperimposable mirror images. The DNA here is right-handed 2 13 Hydrocarbons 15 17 18 Hydrocarbons • Alkanes have the general formula Alkanes have CnH2n+2 • CH4 = methane • C2H6 = ethane • C3H8 = propane • C4H10 = butane butane 10 • C5H12 = pentane • Compounds of C and H • Subgroups: – Alkanes : C-C single bonds – Alkenes : C=C double bonds – Alkynes : carbon-carbon triple bonds – Aromatic: based on benzene 16 Methane Hydrate, CH4(H2O)x 14 Methane Hydrate, CH4(H2O)x Methane Hydrate, CH4(H2O)x Gas hydrates have been known for many years, and combustion of a sample of methane hydrate is seen on the front cover. Recently, however, vast deposits of methane hydrate were discovered deep within sediments on the floor of the world’s oceans. How these deposits were formed is a mystery. But what is important is their size. It is estimated that the global methane hydrate deposits contain approximately 1013 tons of carbon, or about twice the combined amount in all reserves of coal, oil, and conventional natural gas. Now if scientists and engineers could only solve the problem of extracting the methane conveniently and safely! 3 CH3CH2 CH2CH2 CH3 Pentane CH3 Hydrocarbons 19 & Structural Isomerism CH3CHCH2CH3 Isomers of C 5H12? 2-Methylbutane CH3 H3CCCH3 CH3 2,2-Dimethylpropane Note names of isomers C5H12 has 3 structural isomers. C6H14 has 5 C7H14 has 9 20 Hydrocarbons: Alkanes Hydrocarbons: Alkanes 34 CH2CH3 1 C H 1 C 2 C H H 1-butene H 2 C 3 CH3 1 H 3C 2 C CH3 2-methylpropene (isobutene) H 3 C 4 CH3 2 C H cis-2-butene 1 H3 C 4 H H 3 H 1 H 1 H 6 5 H HH 3 H H H 2 H H H H H 4 H H H H Boat form 5 H H 4 H 3 H H 1 6 H HH 2 H H H Chair form Reactions of Alkenes: Reactions Alkenes ADDITION REACTIONS 24 H2O add to the double bond add H C C + Br2 H H H trans-2-butene 6 • Alkenes are unsaturated — more Alkenes more bonds can form to the C atoms • Molecules such as Br 2, H2, HCl, HBr, and HCl HBr 3 C H H 2 H Equatorial H atom H 5 23 4 CH3 H Axial H atom HH Chair form • How many isomers are possible for a compound with the formula C 4H8? H All compounds are flexible. Cyclohexane , C6H12, has interconverting has interconverting “chair” and “boat” forms. Alkanes are colorless gases, liquids, Alkanes are and solids Generally unreactive (but undergo Generally (but combustion) Not polar (or low polarity) and so are not soluble in water. 22 Alkenes: Compounds with C=C Double Bonds 21 Hydrocarbons: Cycloalkanes Hydrocarbons: Cycloalkanes Alkenes— Many Occur Naturally Br Br HC CH HH 1,2-dibromoethane 4 An Addition Reaction 25 Fat placed in Br2 vapor An Addition Reaction 26 • Fats can be “hydrogenated” with H2. Fat placed in Br2 vapor • The fat in bacon is partially unsaturated. The fat adds Br 2 to the C=C bonds. • Fats can be “hydrogenated” with H2. Alkynes • Alkynes have carbon-carbon triple bonds. Alkynes have • C2H2: common name = acetylene systematic name = ethyne systematic ethyne Preparation: CaC2(s) + H2O(liq) --> 2 2O(liq) C2H2 (g) + Ca(OH) 2(s) 22 2 o Hffo(C2H2, g) = +226.7 kJ/ mol kJ/mol 22 Hrxn for C2H2 + O2 rxn 22 2 = –1300 kJ/mol kJ/mol 27 An Addition Reaction Peanut butter has partially hydrogenated vegetable oil. 28 29 30 Resonance in Benzene Aromatic Compounds • Benzene, C 6H6, in the top 25 chemicals produced in the U.S. • Starting point for hundreds of other compounds. • C6H6 has two resonance structures with alternating double bonds. electrons are delocalized over the ring. delocalized over • The The H C HC H C C H H H CH H C C C H C C H C H CH Resonance structures of benzene, C 6 H6 H C HC H C C H C H CH Abbrev iated representation of resonance structures 5 31 Resonance in Benzene 32 Other Aromatic Hydrocarbons Benzene Derivatives 33 • CC bond order is _______________ • C–C single bond = 154 pm C–C pm C=C bond = 134 pm C=C pm • CC bonds in benzene = 139 pm CC pm electrons delocalized delocalized Toluene Naming Benzene Derivatives Cl 1 6 2 3 5 34 Phenol C6H5NH2 TNT trinitrotoluene C6H5OH C6H4CH3(NO2)3 35 Reactions of Aromatics • Substitutions — not additions — are typical. Ortho to Cl CH3 Meta to Cl + CH3Cl 4 Aniline Naphthalene AlCl3 + HCl Para to Cl 1,4-dimethylbenzene Common name: Para-xylene AlCl3 is a catalyst. Catalysts typically used in aromatic substitutions. 6 ...
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This note was uploaded on 10/19/2011 for the course CHM 2210 taught by Professor Mcquade during the Fall '08 term at FSU.

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