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Zumdahl’s Chap. 22

Zumdahl’s Chap. 22. Organic Chemistry. Introduction Alkanes C n H 2n+2 Isomers Nomenclature Cycloalkanes C n H 2n Alkenes C n H 2n Alkynes C n H 2n – 2. Aromatics Functional Groups Alcohols Aldehydes Ketones Carboxylic Acids Esters Amines. Chapter Contents. Organic Chemistry.

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Zumdahl’s Chap. 22

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  1. Zumdahl’s Chap. 22 Organic Chemistry

  2. Introduction Alkanes CnH2n+2 Isomers Nomenclature Cycloalkanes CnH2n Alkenes CnH2n Alkynes CnH2n–2 Aromatics Functional Groups Alcohols Aldehydes Ketones Carboxylic Acids Esters Amines Chapter Contents

  3. Organic Chemistry • Once upon a time … • It was believed that organic chemicals could only arise in life processes … • That they were a product of life’s vitality. • In 1828, German chemist Friedrich Wöhler dispelled that myth when • (Mineral) ammonium cyanate, NH4CNO, heated gave (organic) urea, (NH2)CO(NH2). As if we needed another source.

  4. Modern Views • With the exception of petroleum products, geological and elemental carbon is inorganic carbon. • Other carbon-containing molecules are organic by virtue of carbon’s presence. • There are no end to the combinatorial possibilities since C bonds to C!

  5. Carbon’s Flexibility • sp, sp2, sp3 mean a rich geometry of 180°, 120°, and 109.43° angles in virtually endless chains and branches of organic molecules. The most potent psychotropic chemical cocktail on Earth … CHOCOLATE!

  6. Carbon’s Reactivity • NOT. • With the exception of unsaturated sites (multiple carbon-carbon bonds), it is at the heteroatoms (non-CH atoms, X) in an organic molecule where lies the reactive site. • Common CX combinations are called functional groups and dictate reactivity.

  7. Inorganic Carbon • Elemental carbon • Graphite • Diamond • Buckminsterfullerene • Carbon oxides and halides • Carbonates and carbides • Simple cyano- compounds like HCN.

  8. ALKANES • Saturated hydrocarbons, CnH2n+2. • “Saturated” because they can’t take any more hydrogen atoms! • Straight chains are H3C–(CH2)n–2–CH3 • Gaseous for n<5; solid for n>17 @ STP. • Inert (but for strong oxidizers) • Pathologically nonpolar. • Waxes, oils, & fuel gases as n decreases.

  9. Old Possum’s Naming • After n=4, the prefixanes have Greek numbers as their prefixes. • 5=pent, 6=hex, 7=hept, 8=oct, 9=non, and 10=dec, 20=eicos, 30=triacos • But n4 are named historically • CH4, Methane (“intoxicate” from the Greek) • Ethane, Propane, and Butane for 2,3,4.

  10. Branching & Isomers • After n=3, it’s possible to let some C’s bond with more than 2 other carbons. • But fewer than 5, of course! • The # of structural isomers possible thereby grows exponentially with n. • These isomers have similar chemical and physical properties. • So they’re a bit expensive to separate, and one sees bottles labeled merely “hexanes.”

  11. Isomer Naming • Older conventions would have that as “isooctane,” but a good IUPAC name results from the following: • Name the longest C chain (pentane) • List the side groups in alphabetical order with Greek prefixes (trimethylpentane) • Supply (smallest possible) positional indices (2,2,4 trimethylpentane) • The gasoline power rating standard molecule.

  12. See the C3 and S6 here? Cycloalkanes, CnH2n • If the two end C’s lose 1 H each, they have free valence to close a ring; voila, cyclo(whatever)ane. • Again properties similar to straight chains. • Can now have conformational isomers! • E.g., BOAT cyclohexane versus CHAIR

  13. Obligatory plane seen edge on Alkenes, CnH2n • Cycle formation isn’t the only possible result of dehydrogenation. • Adjacent C’s can double bond, C=C, making an (unsaturated) alkene. • Much more reactive (vulnerable  e– pair) • Rigid  orbitals  rigid planar partners! • E.g., trans-5-methyl-2-hexene

  14. cis for the same side and trans for the opposite cis-2-butene trans-2-butene Alkene Isomers • While an sp3 CX2Y2 has only 1 isomer, • (every X and Y is adjacent to all the others) • the sp2 alkene C2X2Y2 has cis & trans isomers (where X is or isn’t on the same side of = as X). • For longer hydrocarbons, cis & trans refer to the side the chain extends:

  15. propyne Alkynes, CnH2n–2 • sp triple bonding makes a rigid 180° segment in a hydrocarbon. • It too is vulnerable to attack across the multiple bond site. • Double & triple bonds can suffer addition where an AB molecule single bonds A and B to an unsaturated site. H2, HX, and X2 (where X is halogen) are favorites.

  16. bromobenzene anthracene (edge on) Unsaturated Cycles • Earlier we noted the stability lent to benzene, C6H6, by  MOs. • Alternating single/double cycles occur in many organic molecules similarly. • This class is called “aromatic” (by virtue of their aroma). • The  structure is often preserved in their chemical reactions; they don’t add, they substitute instead.

  17. isobutraldehyde or methylpropanal Functional Groups • Organic backbones can bear hetero-atoms as reactive sites. • Alkyl root symbolized as R, a generic hydrocarbon radical(methyl, ethyl, etc.) • Functional groups append R, e.g., R–OH, an alcohol, or R–CHO, aldehyde. R–CO2H, a carboxylic acid, R–NH2, amine.

  18. yeast + 2 2 CO2 ethanol glucose, C6H12O6 Alcohols, R–OH • The –OH makes alcohol polar enough to hydrogen bond.  water soluble • Fermentation product but vulnerable to oxidation to aldehyde and acid.

  19. O C H quinone benzaldehyde, “bitter almond” Aldehydes, R–CHO • Next C oxidation state up from alcohol. • Degradation product in your liver! • If C=O isn’t a chain end substituent, it’s not an aldehyde but a ketone. • Aldehydes are often flavorings, but • Ketones are industrial solvents.

  20. O C O–H butanoic acid “rancid yak butter” ethanol ethyl butyrate “pineapple” water Carboxylic Acids R–CO2H • Usual highest C ox. state in organics. • End product of body’s alcohol degradation. • Weakly acidic but important buffers. • React with alcohols to make highly flavorful esters … a condensation rxn. +  +

  21. Coniine (2ndary) “hemlock” 2-propyl-piperidine Amines, Rn–NH3–n • Come in three varieties, n = 1, 2, & 3. • “Primary” amines, n=1, are at chain end. • “Secondary” amine N bonds to 2 carbons. • “Tertiary” amines bond to 3 C. • Weak base Kb diminishes as n increases. • Alcohols are also primary, secondary, and tertiary. (Primary are on end carbons.) • But this refers to the bonding of the C to which OH is attached.

  22. Mixed Functionality • So H2NCH2CH2OH is an alcohol and an amine; it becomes ethanolamine. • But the monster C9H14N4O3 would be agony to call by its IUPAC name. • So it’s known by it common name, carnosine. How many Ka and Kb are expected? 1 and 4, respectively.

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