Chapter 18 : Organic Chemistry

1. C Chapter 18 : Organic Chemistry Organic chemistry:The study of the compounds of carbon. • 85% of all known compounds are organic. • Carbohydrates, lipids, proteins, enzymes, nucleic acids, hormones, vitamins, and almost all other chemicals in living systems are organic compounds. < Abundance of the elements in the Earth’s crust.

2. Why is organic chemistry a separate discipline within chemistry? • Vitalism: a “vital force” present in living organisms was believed to be necessary to produce an organic compound. • The experiment of Wöhler in 1828 was the first in a series of experiments that led to the demise of the vital force theory. See reaction below:

3. Why are Organic Compounds and Inorganic Compounds Different? • carbon atoms can do some unique things that other atoms cannot • their bonds are very strong and unreactive • they can attach together in very long chains • they can attach together to form rings • they can form single, double or triple bonds

4. Hydrocarbons • hydrocarbons contain only C & H • two types - aliphatic or aromatic • insoluble in water • no polar bonds to attract water molecules • aliphatic hydrocarbons • may be chains or rings • ring molecules have two less H than chain so that ends can join • straight chain called the “normal” isomer

5. Saturated Hydrocarbons • a saturated hydrocarbon has all C-C single bonds • it is saturated with hydrogens • saturated aliphatic hydrocarbons are called alkanes • chain alkanes have the general formula CnH2n+2

6. Unsaturated Hydrocarbons • unsaturated hydrocarbons have one of more C=C double bonds or CC triple bonds • unsaturated aliphatic hydrocarbons that contain C=C are called alkenes • the general formula of a monounsaturated chain alkene is CnH2n • remove 2 more H for each additional unsaturation • unsaturated aliphatic hydrocarbons that contain CC are called alkynes • the general formula of a monounsaturated chain alkyne is CnH2n-2 • remove 4 more H for each additional unsaturation

7. Hydrocarbons

8. Uses of Hydrocarbons

10. Alkanes • also know as paraffins • aliphatic, saturated • general formula CnH2n+2for chains • very unreactive • CH3 groups at ends of chains, CH2 groups in the middle • chains may be straight or branched • n-alkane = straight chain

11. Alkanes - Physical Properties • nonpolar molecules, intermolecular attractions due to induced dipoles • both boiling points and melting points generally increase as the size of the molecule increases • insoluble in water, commonly used as nonpolar solvents • less dense than water, density increases with size

12. Structural Isomers • isomers are molecules with the same molecular formula but different arrangements of the atoms • different chemical and physical properties • structural isomersare isomers in which the atoms are attached differently • different bonding pattern • structural isomers have different physical properties • structural isomers may give different products in a reaction, though they undergo same types of reactions

13. Structural Isomers of C4H10 Butane, BP = 0°C Isobutane, BP = -12°C

14. Possible Structural Isomers

15. Practice – Draw the 3 structural isomers of pentane

16. Example – Draw all 9 structural isomers of heptane • the prefix hept- means 7, so the molecular formula is C7H16 • Start by drawing the carbon skeleton of the straight chain isomer

17. Example – Draw all 9 structural isomers of heptane • fill in the hydrogens so each C has 4 bonds

18. Alkenes • also known as olefins • aliphatic, unsaturated • C=C double bonds • formula for one double bond = CnH2n • subtract 2 H from alkane for each double bond • trigonal shape around C • flat • much more reactive than alkanes • polyunsaturated = many double bonds

20. Alkynes • also known as acetylenes • aliphatic, unsaturated • CºC triple bond • formula for one triple bond = CnH2n-2 • subtract 4 H from alkane for each triple bond • linear shape • more reactive than alkenes

22.  Aromatics • Benzene • resonance hybrid • does not react like alkenes • Reactions are generally substitutions for H

23. Functional Groups • other organic compounds are hydrocarbons in which functional groups have been substituted for hydrogens • a functional group is a group of atoms that show a characteristic influence on the properties of the molecule • generally, the reactions that a compound will perform are determined by what functional groups it has • since the kind of hydrocarbon chain is irrelevant to the reactions, it may be indicated by the general symbol R CH3—OH R group functional group

24. Functional Groups

25. Alcohols • R-OH • ethanol = CH3CH2OH • grain alcohol = fermentation of sugars • alcoholic beverages • proof number = 2X percentage of alcohol • gasohol • isopropyl alcohol = (CH3)2CHOH • 2-propanol • rubbing alcohol • poisonous • methanol = CH3OH • wood alcohol = thermolysis of wood • paint solvent • poisonous

26. Ethers • R– O – R • ether = diethyl ether = CH3CH2OCH2CH3 • anesthetic • to name ethers, name each alkyl group attached to the O, then add the word ether to the end diethyl ether

27. formaldehyde acetone Aldehydes and Ketones • contain the carbonyl group • aldehydes = at least 1 side H • ketones = both sides R groups • many aldehydes and ketones have pleasant tastes and aromas • some are pheromones • formaldehyde = H2C=O • pungent gas • formalin = a preservative • wood smoke, carcinogenic • acetone = CH3C(=O)CH3 • nail-polish remover

28. Aldehyde Odors and Flavors • butanal = butter • vanillin = vanilla • benzaldehyde = almonds • cinnamaldehyde = cinnamon

29. Ketone Odors and Flavors • acetophenone = pistachio • carvone = spearmint • ionone = raspberries • muscone = musk

30. Carboxylic Acids • RCOOH • sour tasting • weak acids • citric acid • found in citrus fruit • ethanoic acid = acetic acid • vinegar • methanoic acid = formic acid • insect bites and stings

31. methyl butanoate aspirin Esters • R–COO–R • sweet odor • made by reacting carboxylic acid with an alcohol RaCOOH + RbOH  RaCOORb + H2O • name alkyl group from alcohol, then acid name with ate ending • precedence over carbonyls, but not carboxylic acid • number from end with ester group

32. Amines • N containing organic molecules • very bad smelling • form when proteins decompose • organic bases • name alkyl groups attached to the N, then add the word amine to the end putrescine ethylamine ethylmethylamine cadaverine

33. Amines • many amines are biologically active • dopamine – a neurotransmitter • epinephrine – an adrenal hormone • pyridoxine – vitamin B6 • alkaloids are plant products that are alkaline and biologically active • toxic • coniine from hemlock • cocaine from coca leaves • nicotine from tobacco leaves • mescaline from peyote cactus • morphine from opium poppies

34. Macromolecules • polymers are very large molecules made by repeated linking together small molecules • monomers • natural • modified natural polymers • synthetic • plastics, elastomers (rubber), fabrics, adhesives • composites • additives such as graphite, glass, metallic flakes

35. Natural Polymers • polysaccharides • cellulose (cotton) • starch • proteins • nucleic acids (DNA) • natural latex rubber, etc • shellac • amber, lignin, pine rosin • asphalt, tar

36. O O H N ( C H ) N H C ( C H ) C 2 6 2 4 Nylon • polyamides • good physical properties • effected by moisture • very good heat resistance • excellent chemical resistance • excellent wear resistance • nylon 6,6 made by condensing 1,6–hexandiamine, H2N–(CH2)6–NH2, with hexandioic acid, HOOC–(CH2)4–COOH