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Organic Chemistry
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  1. Organic Chemistry Chapter 25 Chemistry 100

  2. Organic Chemistry • Historically: the chemistry of products from plants and animals • Today: The chemistry of carbon- containing compounds • Wöhler (1828) made urea from ammonium cyanate • Distinction between “natural” and “synthetic” chemicals disappeared.

  3. The world of plenty • The American Chemical Society has a database with more than 11 million organic compounds • Why so many? • Because carbon can make chains and rings, and things

  4. Carbon • Electronic configuration 1s22s22p2 • Needs 4 electrons to complete the shell • Electronegativity 2.5 so it forms covalent bonds with other elements • 2s22p2 makes hybrid orbitalssp3 - tetrahedron

  5. Functional Groups • We look at an organic molecule and ask “what functional groups does it have? • Examples • Alcohols have the OH group • Amines have the NH2 group • Unsaturated compounds have double or triple bonds C=C or CC

  6. Functional groups • Acetic acid CH3COOH is a carboxylic acid - it has the -COOH group • The compound CH3NH2 is methyl amine • An amino acid like glycine (see picture) has both the carboxylate and the amino group

  7. Categorizing organic compounds • There are so many we need a system to name them • Unlike biologists we use English words, but sometimes you would not know this!

  8. Hydrocarbonscontain only C and H • Aliphatic (meaning derived from fats) • Alkanes CnH2n+2 • Alkenes CnH2n • Alkynes CnH2n-2 • Aromatic (yes - they smell) contain one or more benzene rings

  9. Alkanes CnH2n+2 • n = 1 Methane (marsh gas) CH4 • n = 2 Ethane C2H6 • n = 3 Propane C3H8 • n = 4 Butane C4H10 • n = 5 Pentane (liquid) C5H12 • n = 6 Hexane C6H14 • n = 7 Heptane C7H16 • n = 8 Octane C8H18 • n = 9 Nonane C9H20 • n = 10 Decane C10H22

  10. Butane Condensed formula (two forms) Lewis structural formula

  11. Iso-butane A branched chain We may think of this as CH3CH2CH3 with one of the H atoms substituted by a CH3 group

  12. Alkylgroups CH3Cl methyl chloride CH3CH2CH2OH n-propyl alcohol

  13. Naming larger alkanes • Find the longest continuous chain. Use this as the base name • Number the C atoms, starting from the nearest substitution • Name and give location of each substitued group • When more than one group at the same location: use di, tri, tetra, penta if they are the same name in alphabetical order, if different

  14. Naming Example

  15. Petroleum products

  16. Cycloalkanes CnH2n Cyclopropane cyclobutane cyclopentane cyclohexane

  17. Substituted cycloalkanes

  18. Reactions of alkanes • Combustion • Substitution reactions C2H6 + Cl2 C2H5Cl + HCl

  19. Unsaturated hydrocarbons • alkenes CnH2n contain a double bond ethylene or ethene C2H4 propylene or propene C3H6 • alkynes CnH2n-2 contain a triple bond acetylene C2H2 propyne C3H4

  20. C H C H 3 3 2-methyl-2-butene H C H 3 H C C H C H 3 2 3 2-pentene H H C H C H = C H 3 2 Sample alkenes

  21. Geometrical isomers

  22. Addition reactions

  23. Aromatic hydrocarbons

  24. Functional Groups I

  25. Functional Groups II

  26. Alcohols; R-OH • The hydroxyl or alcohol functional group -OH • The OH group is polar; hydrogen bonding makes alcohols more soluble in water than in hydrocarbons • CH3OH methyl alcohol, methanol, “wood alcohol”. Impurity in moonshine; causes blindness • CH3CH2OH ethyl alcohol, ethanol, “alcohol” Prepared by fermentation of sugar-containing plant material.

  27. Reactions with alcohols • The OH group does NOT make alcohols basic. In fact, phenol is weakly acidic. • An important reaction is esterification - the formation of esters when an alcohol reacts with an acid. See notes on carboxylic acids

  28. Ethers R-O-R • The -O- bridge • CH3CH2-O-CH2CH3 is diethyl ether, or “ether”. Used in medicine but not as much as at one time. Very explosive! • Ethers are used industrially as solvents

  29. Aldehydes • Some aldehydes have common names like formaldehyde and acetyaldehyde. • The other way to name them is with the al ending. CH3CH2CHO is propanal or propyl aldehyde

  30. Aldehydes and Ketonesthe carboxyl group C=O

  31. Carboxylic Acids R-COOH

  32. Alcohol Aldehyde  Carboxylic acid

  33. Esters • Carboxylic acid + alcohol  ester + water • For organic chemists, reactions that generate water are called condensation reactions • The condensation reaction is called esterification • Fruity smell. Pentyl acetate (amyl acetate) gives bananas their smell but is very poisonous in large amounts.

  34. Esterification

  35. Hydrolysis of ester • Ester + water  carboxylic acid + alcohol • The reverse of esterification • When done using a base (NaOH, for example), the reaction is called saponification. • Soap was made by reacting fat (esters of stearic acid and glycerin) with NaOH to get sodium stearate.

  36. Amines R-NH2 , R2NH, R3N • Organic chemistry’s base. • Think of amines as substituted ammonia NH3 + R  RNH2  R2NH  R3N • Just as NH3 is an proton acceptor making NH4+ , so amines are proton acceptors. • They also react with carboxylic acids to give amides • Horrid smell. One is called putricine, another cadaverine

  37. Amines

  38. Amidescarboxylic acid + amine  amide

  39. Amino acids • A compound with the carboxylic acid group and the amine group

  40. Peptides &Proteins • The amine group of one acid reacts with the carboxylic acid group of another to make a peptide • When more molecules add on, we get a polypeptide • Certain polypeptides are of biological importance - proteins

  41. Stereoisomers; chirality

  42. Carbohydrates • Have the general formula Cn(H2O)n • The simple sugars glucose and fructose are the basic building units of many carbohydrates. These sugar molecules can make rings. • Disaccharides like table sugar (sucrose) consists of two rings joined together. • When many rings join we get starch or cellulose. The difference is in how the rings are joined. We can digest starch but not cellulose