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

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Unformatted text preview: ORGANIC CHEMISTRY 1 2 Types of Organic Compounds • 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 Isomerism • Isomers have identical composition but different structures • Two forms of isomerism – Constitutional (or structural) – Stereoisomerism 3 • Constitutional – Same empirical formula but different atomto-atom connections • Stereoisomerism – Same atom-to-atom connections but different arrangement in space. 4 5 6 Structural Isomers Stereoisomers: Geometric Stereoisomers: Geometric isomers can occur when there is a C=C double bond. Stereoisomers: Optical Stereoisomers: • Optical isomers are molecules with are non-superimposable mirror images. non-superimposable Such molecules are called CHIRAL CHIRAL Pairs of chiral molecules are enantiomers . • Chiral molecules in solution can rotate the plane of plane polarized light. • • Cis-2-butene Cis-2-butene Trans-2-butene Trans-2-butene 1 Chiral Compounds and Polarized Light 7 8 Stereoisomers Isomers Chirality generally occurs when a C atom has 4 different groups attached. Lactic acid Stereoisomers Isomers 9 Lactic acid isomers are nonsuperimposable Chirality: Handedness in Chirality: Nature 10 Chirality: Handedness in Chirality: 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 14 15 Hydrocarbons • Compounds of C and H • Subgroups: – Alkanes: C-C single bonds Alkanes: – Alkenes: C=C double bonds Alkenes: – Alkynes: carbon-carbon triple Alkynes: bonds – Aromatic: based on benzene Hydrocarbons • Alkanes have the general formula CnH2n+2 • CH4 = methane methane • C2H6 = ethane ethane • C3H8 = propane propane • C4H10 = butane butane • C5H12 = pentane pentane 16 Methane Hydrate, CH4(H2O)x Methane Hydrate, CH4(H2O)x 17 18 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 CH 3 Pentane CH3 CH3CHCH2CH3 2-Methylbutane Hydrocarbons 19 & Structural Isomerism Isomers of C 5H12? C5H12 has 3 has structural isomers. C6H14 has 5 has C7H14 has 9 has 20 Hydrocarbons: Alkanes Alkanes are colorless gases, liquids, and solids Generally unreactive (but undergo combustion) Not polar (or low polarity) and so are not soluble in water. Hydrocarbons: Cycloalkanes All compounds are flexible. Cyclohexane, C6H12, has interconverting Cyclohexane, “chair” and “boat” forms. Axial H atom 21 CH3 H3CCCH3 CH3 2,2-Dimethylpropane HH 4 5 3 H H 2 6 1 Equatorial H atom H 4 H 1 5 6 H H H H H 5 4 H H H H H H 3 2 H 3 H 6 H 1 H H H H H H H 2 H HH H H Boat form H HH H Note names of isomers Chair form Chair form Alkenes: Compounds with Alkenes: C=C Double Bonds • How many isomers are possible for a compound with the formula C 4H8? H 1 C H 1-butene 2 C H H 34 CH2CH3 H 1 C 2 C CH3 H 3 CH3 1 H3C 2 C 3 C H 1 H3 C 4 CH3 H 2 C 3 C 22 23 Reactions of Alkenes: Alkenes: ADDITION REACTIONS • Alkenes are unsaturated — more unsaturated more bonds can form to the C atoms • Molecules such as Br 2, H2, HCl, HBr, and HCl, HBr, 24 4 CH3 H2O add to the double bond add to H 2-methylpropene (isobutene) cis-2-butene trans-2-butene Alkenes— Alkenes— Many Occur Naturally H C C + Br2 H H H Br Br HC CH HH 1,2-dibromoethane 4 An Addition Reaction Fat placed in Br2 vapor vapor 25 An Addition Reaction Fat placed in Br2 vapor vapor 26 An Addition Reaction • Fats can be “hydrogenated” with H2. 27 • The fat in bacon is partially unsaturated. The fat adds Br 2 to the C=C bonds. to • Fats can be “hydrogenated” with H2. Peanut butter has partially hydrogenated vegetable oil. Alkynes • Alkynes have carbon-carbon triple bonds. • C2H2: common name = acetylene systematic name = ethyne Preparation: CaC2(s) + H2O(liq) --> O(liq) 2 2O(liq) C2H2 (g) + Ca(OH) 2(s) (g) 22 2 o Hffo(C2H2, g) = +226.7 kJ/mol kJ/mol 22 Hrxn for C2H2 + O2 rxn for 2 2 2 = –1300 kJ/mol –1300 kJ/mol 28 29 30 Aromatic Compounds • Benzene, C 6H6, in the top 25 chemicals produced in the U.S. • Starting point for hundreds of other compounds. Resonance in Benzene • C6H6 has two resonance structures with has alternating double bonds. • The H C H C C C H electrons are delocalized over the ring. delocalized over H H H C C C H H C C H H C H C C C H H HC CH CH 6 H6 HC CH Resonance structures of benzene, C Abbreviated representation of resonance structures 5 31 32 Resonance in Benzene • CC bond order is _______________ • C–C single bond = 154 pm C=C bond = 134 pm • CC bonds in benzene = 139 pm electrons delocalized Other Aromatic Hydrocarbons Benzene Derivatives 33 Toluene Naphthalene Aniline C6H5NH2 Phenol C6H5OH TNT trinitrotoluene C6H4CH3(NO2)3 Naming Benzene Derivatives Cl 1 6 5 4 2 3 Ortho to Cl Meta to Cl 34 35 Reactions of Aromatics • Substitutions — not additions — are typical. CH3 + CH3Cl AlCl3 + HCl Para to Cl 1,4-dimethylbenzene Common name: Para-xylene AlCl3 is a catalyst. Catalysts typically used in is aromatic substitutions. 6 ...
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