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An Introduction to Organic Chemistry: Nomenclature and Structure of Hydrocarbons

This chapter provides a comprehensive overview of organic chemistry, focusing on the nomenclature and reactions involving hydrocarbons. It discusses the characteristics of aliphatic and aromatic compounds, introducing the IUPAC system for naming. Learn about the different types of hydrocarbons (alkanes, alkenes, and alkynes) and their structural representations. The chapter covers guidelines for drawing organic structures, functional groups, and reactivity patterns in hydrocarbons, providing a solid foundation for understanding organic molecular structures and nomenclature rules.

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An Introduction to Organic Chemistry: Nomenclature and Structure of Hydrocarbons

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  1. Chapter 24 and Beyond Organic Chemistry: Nomenclature and Reactions

  2. Organic Chemistry • What does this branch of chemistry deal with? • Compounds that contain carbon (and hydrogen), called hydrocarbons • Aliphatic – Chains • Aromatic – Resonating rings of delocalized electrons • Very specific hydrocarbon naming system - IUPAC • Different types are separated according to certain functional groups

  3. Aliphatic Hydrocarbons • What are the three main types of aliphatic hydrocarbons? • Based on the types of bonds: • Alkane – only single bonds • Saturated • i.e. hard to breakdown • Alkene – At least one double bond • Unsaturated • i.e. easy to breakdown • Alkyne – At least one triple bond • Unsaturated

  4. Notes About Drawing • What are the guidelines for drawing organic structures? • Structural Diagrams • Shows all atoms, bonds and structure • Structural Formulas • Shows all atoms and suggests structure CH3CH(OH)CH2CH3 • Skeletal Diagrams

  5. Structural Formula • How are structural formulas different from molecular and empirical? • Structural formulas show the basic structure and location of functional groups • CH3CH2CH2CH3 • Molecular formulas simply show the number of atoms • C4H10 • Empirical formulas are simplified molecular formulas • C2H5

  6. International Union of Pure and Applied Chemistry (IUPAC) • What is IUPAC? • IUPAC is an organization that has determined the internationally adopted way to name chemicals • Nomenclature – fancy word for naming • System is based on the longest hydrocarbon chain and the Greek prefixes

  7. IUPAC Nomenclature for Alkanes • What is the first rule? • Determine the parent chain and name • Find the longest hydrocarbon chain • May not be a straight line • Use the appropriate prefix • Meth – 1 • Eth – 2 • Prop – 3 • But – 4 • Pent – 5 • Hex – 6 • Hept – 7 • Oct – 8 • Non – 9 • Dec – 10

  8. IUPAC Nomenclature for Alkanes • If there are only single bonded carbons use the suffix – ane • Ex.

  9. IUPAC Nomenclature for Alkanes • What is the second rule? • If an alkane has a hydrocarbon (alkyl) group, determine its name and number • Use the suffix -yl • Make sure to assign it so that it has the lowest number possible • Ex.

  10. IUPAC Nomenclature for Alkanes • What is the third rule? • What is the fourth rule? • If more than one alkyl group exists then you must assign the lowest numbers possible • If there is more than one of the same group, use the prefixes di-, tri- and tetra- • Also in alphabetical order! • Ex.

  11. IUPAC Nomenclature for Alkanes

  12. IUPAC Nomenclature for Alkanes • Please name the following compounds.

  13. IUPAC Nomenclature for Alkanes • Please draw the following compounds. • 2-methyl heptane • 4-ethyl-3,4-dimethyl octane • 4-ethyl-2,2-dimethyl hexane • 2,4,4-trimethyl heptane • 3,3-diethyl-2,5-dimethyl nonane • 4-propyl-3-methyl heptane

  14. IUPAC Nomenclature for Alkanes • Please build the following compounds. • propane • 2-methyl butane • 2,2-dimethyl pentane

  15. Alkenes and Alkynes • How do we name hydrocarbons with a double or triple bond? • Double and triple bonds MUST have the lowest number possible • Determine the lowest number where the bond begins and place in or in front of the parent chain • Suffix added to the parent name • Alkenes use the suffix –ene • Alkynes with the suffix –yne • Ex.

  16. IUPAC Nomenclature for Alkanes • What is a functional group? • Functional group Anything that is not a C-C or H-C single bond OR not part of the main chain • Substituent Something that is substituted in for a H • Ex. -Br, -OH, -CH3,etc. • Alkyl Group  A hydrocarbon substituent • Ex. Methyl or ethyl group

  17. Functional Groups • How do we identify and name a(n)... • Alcohol • General Formula: R-OH • Naming: -e at the end of alkane replaced by –ol • Ex. Ethanol • Can also use hydroxy prefix • Halogenoalkane • General Formula: R-X • X=F, Cl, Br, I • Naming: fluoro-, chloro-, bromo-, iodo- place before parent chain • Ex. 2-chloro-propane

  18. Functional Groups • How do we identify and name a(n)... • Aldehyde • General Formula: R-CHO • Naming: -e at the end of alkane replaced by –al • Ex. Propanal • Keytone • General Formula: R-COR’ • Naming: -e at the end of alkane replaced by –one • Ex. 2-Butanone or Butan-2-one

  19. Functional Groups • How do we identify and name a(n)... • Carboxylic Acid • General Formula: R-COOH • Naming: -e at the end of alkane replaced by –oic acid • Ex. Propanoic Acid

  20. Functional Groups How do we identify an... • Amine • General Formula: R-NH2 • Ex. Propyl amine • Ester • General Formula: R-COOR’ • Ex. Ethyl ethanoate

  21. Reactivity of Alkanes • Why are alkanes very unreactive? • Strong C-C and C-H bonds • Very low polarity • Can only undergo combustion and halogen substitution reactions

  22. Combustion of Alkanes • What is required for combustion? • All hydrocarbons burn with large amounts of oxygen • When combusted they produce two products: • Carbon dioxide • Water

  23. Combustion of Alkanes • Why is this reaction exothermic? • C=O and O-H bonds are stronger than C-C and C-H, so energy is released • For this reason, alkanes (natural gases) make very good fuels

  24. Combustion of Alkanes • What happens when there is not enough oxygen? • Incomplete combustion • CO and other harmful chemicals are now made in addition to CO2 and water • Motor vehicles use catalytic converters to minimize this effect

  25. Alkane Substitution Reactions • What is a substitution reaction? • A functional group replaces a hydrogen • In this case, a halogen will replace a hydrogen • Typically Br2 or Cl2 • This cannot happen without a high energy catalyst, ultraviolet light

  26. Mechanism of Chlorination of Methane • What is a mechanism? • Breaks down the different parts of a reaction and shows the movement of electrons • Single electron movement • Electron pair movement

  27. Mechanism of Chlorination of Methane • What are the different types of chemical cleavage? • A bond can break: • Heterolytically • Both electrons go to one atom • Homolytically • One electron goes to each

  28. Mechanism of Chlorination of Methane • What is unique about homolytic cleavage? • It does NOT create ions, but something new called… FREE RADICALS! • Radicals are VERY reactive and are very complicated • NOTE: They play a large part in atmospheric chemistry, global warming and ozone depletion

  29. Mechanism of Chlorination of Methane • What is the mechanism for the chlorination of methane? • Three steps • Initiation • Cl2 homolytically cleaves • Propagation (chain reaction) • Radical Cl removes H from CH4 • Cl2 cleaves and a Cl radical attaches to the methane radical • Termination • Two Cl radicals combine with each other • One Cl radical attaches to the methane radical • Two methane radicals combine with each other

  30. Mechanism of Chlorination of Methane • What can be done with your chloromethane product? • It can continue to be substituted in the same manner to produce dichloromethane, trichloromethane and tetrachloromethane

  31. Mechanism of Chlorination of Ethane

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