Alkanes

1. Alkanes

2. Required background: Thermodynamics from general chemistry Lewis structures Molecular geometry Essential for: 1. Naming organic compounds 2. Recognizing functional groups 3. Stereochemistry 4. Role of alkanes in the economy

3. Outline • Carbon Chains 2. Functional Groups and Classes of Organic Compounds 3. Isomerism and Nomenclature of Alkanes 4. Physical Properties of Alkanes 5. Conformations 6. Cycloalkanes 7. Polycyclic compounds

4. 1. Carbon Chains 2. Functional Groups and Classes of Organic Compounds 3. Isomerism and Nomenclature of Alkanes 4. Physical Properties of Alkanes 5. Conformations 6. Cycloalkanes 7. Polycyclic compounds

5. The idea of carbon chains was introduced in 1858-1860 by Kekule, Couper, Butlerov. The compound with the largest known carbon Chain was described by Bidd and Wittig in 1985: CH3(CH2)388CH3 There are significantly more substances with an even number of carbons, than with an odd number. Nature, 1996, 384, 320 Reasons: 1. Nature utilizes acetate (CH3COO-) as a building block for synthesis. 2. Chemical industry utilizes mostly ethylene (C2H4) as a building block.

6. Carbon Chains 2. Functional Groups and Classes of Organic Compounds 3. Isomerism and Nomenclature of Alkanes 4. Physical Properties of Alkanes 5. Conformations 6. Cycloalkanes 7. Polycyclic compounds

9. Carbon Chains 2. Functional Groups and Classes of Organic Compounds 3. Isomerism and Nomenclature of Alkanes 4. Physical Properties of Alkanes 5. Conformations 6. Cycloalkanes 7. Polycyclic compounds

10. Presentation of structural formulas Hexane Homologuos formula of alkanes: CnH2n+2

11. Branched alkanes Combustion CnH2n+2 + (3n+1)/2 O2 = nCO2 + (n+1)H2O More branched alkanes are slightly more stable, than unbranched alkanes. They have a little smaller heat of combustion.

12. Nubmer of carbons Number of isomers • 1 • 1 3 1 4 2 5 3 7 9 10 75 20 366,319 Consequence: Problem of nomenclature The first set of IUPAC (International Union of Pure and Applied Chemistry) rules was made in 1892 in Geneva. The list of rules takes several book volumes and is updated every few years, so we will not learn the rules in detail. We will consider just some basic principles, which are unlikely to change.

13. IUPAC Principles of Nomenclature 1. Name unbranched alkanes by the number of carbons. 2. For branched alkanes, pick the longest chain of carbons (principal chain)

14. 3. If there is a choice, choose the chain with the greatest number of substituents 4. Number carbons in the principal chain to assign the lower number to the first substituent. Do not number carbons in the substituents.

15. 5. Name each substituent 6. Construct the chemical name

16. 7. For compounds with multiple substituents, each substituents receives its own number. Each substituent has own numbers. Number of substituents: 2(di-), 3(tri-), 4(tetra-), 5(penta-) etc.

17. 8. Substituents are cited in the alphabetical order regardless of their position 9. If the numbering is not resolved by other rules, the first-cited substituent receives the lowest number.

18. Carbon Chains 2. Functional Groups and Classes of Organic Compounds 3. Isomerism and Nomenclature of Alkanes 4. Physical Properties of Alkanes 5. Conformations 6. Cycloalkanes 7. Polycyclic compounds

19. Methane  butane – gases (at 25 oC). Pentane  C12-C15 – liquids Each carbon increases the b.p. by approximately 20-30 oC. More symmetrical molecules generally melt higher. The higher the molecular surface, the large the Van-der-Waals forces of attraction, the higher the boiling point. Consequences: 1. Alkanes with larger molecules boil higher, than alkanes with smaller molecules. 2. Alkanes with unbranched molecules boil higher, than alkanes with branched molecules. 3. Alkanes can be separated by distillation. They are produced in industry by fractional distillation of petroleum and natural gas.

20. Refine petroleum--fractional distillation

21. Carbon Chains 2. Functional Groups and Classes of Organic Compounds 3. Isomerism and Nomenclature of Alkanes 4. Physical Properties of Alkanes 5. Conformations 6. Cycloalkanes 7. Polycyclic compounds

22. Conformations of ethane Newman projections Wedge projections

26. Carbon Chains 2. Functional Groups and Classes of Organic Compounds 3. Isomerism and Nomenclature of Alkanes 4. Physical Properties of Alkanes 5. Conformations 6. Cycloalkanes 7. Polycyclic compounds

29. Carbon Chains 2. Functional Groups and Classes of Organic Compounds 3. Isomerism and Nomenclature of Alkanes 4. Physical Properties of Alkanes 5. Conformations 6. Cycloalkanes 7. Polycyclic compounds