Organic Chemistry

1. Organic Chemistry CH. 25

2. Definitions • Organic means “based on carbon” • Hydrogen, oxygen, and other elements are sometimes present • Inorganic means all those compounds without carbon • Exceptions: Diamond, graphite, carbon dioxide

3. What’s So Special About Carbon? • It can form 4 covalent bonds • With other carbon atoms • With other elements • Forms long chains (straight or branched) • Rings and hoops

4. Types of Carbon Atoms • Primary carbon (1o) • a carbon bonded to one other carbon • Secondary carbon (2o) • a carbon bonded to two other carbons • Tertiary carbon (3o) • a carbon bonded to three other carbons

5. Some organic chemicals • Medicines • Active Pharmaceutical Ingredients • Excipients DNA Fuels Materials Essential oils Pigments

6. Hydrocarbons • Compounds which contain only carbon and hydrogen • Obtained from petroleum distillation • Fuels, solvents, lubricants, waxes, paving materials • Starting materials for countless other products

7. Hydrocarbons- Types • Aliphatic Long chains (can be branched) • Alicyclic Rings or hoops

8. Aliphatic Hydrocarbons • 2 Types • Saturated (only single bonded carbons) • Unsaturated (can contain double or triple bonded carbons)

10. Saturated Hydrocarbons:Alkanes • All end in –ane • Only single bonds • Generic formula CnH(2n+2) • Known as a homologous series (add CH2 unit each time) • Methane CH4 (Natural Gas) • Propane C3H8 (common fuel gas) • Butane C4H10 (common fuel gas) • Gasoline (A mixture of liquid hydrocarbons from heptane C7H16 to Decane C10H22

11. Alkanes

12. The First 10 “Normal” Alkanes C1 - C4 are Gases at Room Temperature Name Formula M.P. B.P. # Structural Isomers • Methane CH4 -183 -162 1 • Ethane C2H6 -172 -89 1 • Propane C3H8 -187 -42 1 • Butane C4H10 -138 0 2 • Pentane C5H12 -130 36 3 • Hexane C6H14 -95 68 5 • Heptane C7H16 -91 98 9 • Octane C8H18 -57 126 18 • Nonane C9H20 -54 151 35 • Decane C10H22 -30 174 75 C5 - C16 are Liquids at Room Temperature

13. Prefixes for # of Carbons

14. IUPAC Rules for Naming Branched Alkanes • Find and name the parent chain in the hydrocarbon - this forms the root of the hydrocarbon name • Number the carbon atoms in the parent chain starting at the end closest to the branching • Name alkane branches by dropping the “ane” from the names and adding “yl”. A one-carbon branch is called “methyl”, a two-carbon branch is “ethyl”, etc… • When there are more than one type of branch (ethyl and methyl, for example), they are named alphabetically • Finally, use prefixes to indicate multiple branches

16. Branched- Chains • Designate the location (number of the carbon on the parent chain) for each attached group 2-methyl 1 2 3 4 5

17. Some Simple Alkanes • 2-methylpentane • 3-ethylhexane • 2,2-dimethylbutane • 2,3-dimethylbutane

18. 2 4 1 3 5 Example 1: 2,2-dimethylpentane • The parent chain is indicated by the ROOT of the name - “pentane”. This means there are 5 carbons in the parent chain. • “dimethyl” tells us that there are TWO methyl branches on the parent chain. A methyl branch is made of a single carbon atom. • “2,2-” tell us that BOTH methyl branches are on the second carbon atom in the parent chain.

19. 2 4 1 3 5 6 7 Example 2: 3-ethyl-2,4-dimethylheptane • The parent chain is indicated by the ROOT of the name - “heptane”. This means there are 7 carbons in the parent chain. • “2,4-dimethyl” tells us there are TWO methyl branches on the parent chain, at carbons #2 and #4. • “3-ethyl-” tell us there is an ethyl branch (2-carbon branch) on carbon #3 of the parent chain.

20. 3 5 4 6 2 7 1 8 5 3 2 4 6 7 1 8 Example 3: 2,3,3-trimethyl-4-propyloctane • The parent chain is indicated by the ROOT of the name - “octane”. This means there are 8 carbons in the parent chain. • “2,3,3-trimethyl” tells us there are THREE methyl branches - one on carbon #2 and two on carbon #3. • “4-propyl-” tell us there is a propyl branch (3-carbon branch) on carbon #4 of the parent chain.

21. 4 3 5 5-ethyl- 3,4-dimethyl octane Example 4: Name the molecules shown! • parent chain has 5 carbons - “pentane” • two methyl branches - start counting from the right - #2 and #3 • 2,3-dimethylpentane • parent chain has 8 carbons - “octane” • two methyl branches - start counting from the left - #3 and #4 • one ethyl branch - #5 • name branches alphabetically

22. Isomers • Straight chain alkanes: An alkane that has all its carbons connected in a row. • Branched chain alkanes: An alkane that has a branching connection of carbons.

23. Structural Isomerism • Structural isomers are molecules with the same chemical formulas but different molecular structures - different “connectivity”. • They arise because of the many ways to create branched hydrocarbons. n-pentane, C5H12 2-methlbutane, C5H12

24. Isomers • Isomers - organic molecules that have: • Identical molecular formulas, but • Differing internal arrangement of atoms

25. Different isomers are completely different compounds. They have different structures, different physical properties such as melting point and boiling point, and may have different physiological properties.

26. Isomers: carbons in butane (C4H10) can be arranged in two ways; four carbons in a row (linear alkane) or a branching (branched alkane). These two structures are two isomers for butane.

27. Learning Check • Draw all possible structural isomers of C5H12

28. Unsaturated HydrocarbonsAlkenes • 1 Double Bond • Homologous Series remains the same, add CH2 each time • Generic formula CnH2n • Ethene (C2H4) common name ethylene • Butene (C4H8) • 2 double bonds are called Dienes • 3 double bonds are called Trienes

29. Unsaturated HydrocarbonsAlkynes • Contains a triple bond • Names end in -yne • Generic formula CnH(2n-2) • Most Familiar example is ethyne • Common name acetylene C2H2 • Welding fuel kept dissolved in acetone

30. Naming Alkenes and Alkynes When the carbon chain has 4 or more C atoms, number the chain to give the lowest number to the double or triple bond. 1 2 3 4 CH2=CHCH2CH3 1-butene CH3CH=CHCH3 2-butene CH3CCCH32-butyne

31. Naming Alkenes and Alkynes When the carbon chain has 4 or more C atoms, number the chain to give the lowest number to the double or triple bond. 1 2 3 4 CH2=CHCH2CH3 1-butene CH3CH=CHCH3 2-butene CH3CCCH3 2-butyne

32. Alicyclic Hydrocarbons • 2 types • Saturated rings • Cyclohexane C6H12 • Aromatic rings • Benzene C6H6

33. Alkanes - Cycloalkanes • A cycloalkane is made of a hydrocarbon chain that has been joined to make a “ring”. • Note that two hydrogen atoms were lost in forming the ring! • What is the general formula for a cycloalkane?

34. Cycloalkanes Cycloalkanes: An alkane that contains a ring of carbon atoms. Ring sizes from 3 carbons to 30 or higher are known.

35. Drawing and Naming Cycloalkanes Cycloalkanes are represented by polygons. A triangle represents cyclopropane, a square represents cyclobutane, a pentagon represents cyclopentane, and so on.

36. Line structure: A shorthand way of drawing structures in which atoms aren’t shown; instead a carbon atom is understood to be at each corner and hydrogens are “understood”.

37. Additional Rules for Naming Cyclics • Step 1: Use the cycloalkane name as the parent chain. • Step 2: Number the substituents starting at the group that has alphabetical priority, and proceed around the ring in the direction that gives the second substituent the lower possible number.

38. Cycloalkanes with Side Groups

39. Learning Check Write the IUPAC name for each of the following unsaturated compounds: A. CH3CH2CCCH3 CH3 B. CH3C=CHCH3 C.

40. Learning Check

41. Name those alkenes... cis-4-methyl-2-pentene 2-methyl-2-hexene trans-2-bromo-3-methyl- 2-pentene cyclopentene cis-3-heptene

42. Cis and Trans Isomers • Double bond is fixed • Cis/trans Isomers are possible CH3 CH3 CH3 CH = CH CH = CH cis trans CH3

43. Cis- and Trans- terminology If alkenes have two different substituents at each end of the C=C then they can exist as stereoisomers because there is restricted rotation of the double bond.

44. In cis isomers, two methyl groups are close together on the same side of the double bond.

45. In trans isomer, two methyl groups are far apart on opposite side of the double bond. • Both cis and trans isomers have the same formula and connections between the atoms but have different three dimensional structures because the way the groups are attached to the carbons.

46. Cis-trans isomerism occurs in an alkene whenever each double bond carbon is bonded to two different substituent groups. Cis-trans isomerism is not possible if one of the double bond carbons is attached to two identical groups.

47. Name These

49. Aromatic Compounds and Benzene Aromatic compounds contain benzene. Benzene, C6H6 , is represented as a six carbon ring with 3 double bonds. Two possible resonance structures can be drawn to show benzene in this form.

50. Experimental evidence suggest that all six carbon-carbon bonds in benzene are identical. • The properties, including the above one, of benzene can only be explained by assuming that the actual structure of benzene is an average of the above two possible equivalent structures-known as resonance. • Simple aromatic compounds like benzene are non-polar, insoluble in water, volatile, and flammable. • Unlike alkenes, several aromatic hydrocarbons are toxic. Benzene itself is implicated as a cancer causing chemical.