Hydrocarbons

1. Hydrocarbons Objectives Describe the bonding in hydrocarbons . Distinguish between straight-chain alkane and branched-chain alkane .

2. Organic Chemistry Includes the Chemistry of virtually all carbon compounds , regardless of their origin . Before scientists believed that organic compounds could only be sinthesized by organisms , but Friedrich Wöhler (1800-1882) refuted that theory in 1828. Carbon compounds number more than a million , with many valuable properties : One main reason is carbon´s unique bonding ability . The simplest of the organic compounds are the H ydrocarbons .

3. Basic Principle of Carbon Bonding : Carbon has four (4) valence electrons , therefore will always form four covalent carbon-hydrogen bonds . Note: Remembering this will help you complete and correct structures for organic molecules .

4. Types of Formulas: Structural Formulas: Convenient to write . Two -dimensional representations of three -dimensional molecules

5. Molecular Models : Represent shapes of molecules more accurately

6. Carbon has the ability to make stable carbon-carbon bonds and to form chains . This is the main reason for the numerous carbon compounds . Carbon + Hydrogen → Methane C + H 2 CH 4

7. Straight-Chain Alkanes : Contain any number of carbon atoms , one after the other , in a chain They always end in – ane To draw the structural formula for a straight-chain alkane , write the symbol for carbon as many times as necessary to get the proper chain length . Then , fill in with hydrogens and lines representing covalent bonds . Each covalent bond is equivalent to two electrons .

8. Butane

9. Homologous Series: The straight chain of alkanes are an example of a homologous series. A group of compounds form a homologous series if there is a constant increase / increment of change in molecular structure from one compound in the series to the next . The -CH 2 - group is the increment of change in straight – chain alkanes . As the number of carbons in the straight-chain alkane increases , so does the boiling point and their melting point .

10. Molecular Formula: CH 4 Methane Complete Structural Formulas: Show all the atoms and bonds in a molecule . Condensed Structural Formulas: Leave out some bonds and/ or atoms from the structural formula. Although they do not appear , you must understand that these bonds and atoms are there . Complete Structural Formula Condensed Structural Formula

11. Nomenclature / Naming System : IUPAC: International Union of Pure and Applied Chemistry . All the names end in – ane . The root part of an alkane´s name indicates how many carbon atoms it contains . Scientists also rely on a combination of systematic , semisystematic , and common names to identify organic compounds . Some organic compounds are best known for their common names .

12. Basic Alkanes :

13. Branched-Chain Alkanes An alkane with one or more alkyl groups An alkyl group is a hydrocarbon substituent Substituent : an atom or group of atoms that can take the place of a hydrogen atom on a parent hydrocarbon molecule . An alkyl group consists on an alkane with one hydrogen removed. Sometimes referred to as radicals . Change the suffix – ane from the parent structure to - yl

14. Rules f or Naming Branched-Chain Alkanes : Find the longest chain of carbons in the molecule . We consider this the parent structure . 2. Number the carbons in the main chain sequence . Start at the end that will give the groups attached to the chain the smallest numbers . 3. Add numbers to the names of the substituent groups to identify their positions on the chain . These numbers become prefixes to the name of the parent alkane . 4. Use prefixes to indicate the appearance of a group more than once in the structure . Ex. Di-, tri -, tetra-; penta -, etc. 5. List the names of the alkyl substituents in alphabetical order . 6. Use proper punctuation . Commas ( ,) are used to separate numbers , hyphens (-) are used to separate numbers and words . The entire name is written without spaces .

15. 2,3,3-trimethylpentane

16. To draw the formula when given the name : With an alkane name and knowledge of the IUPAC rules, it is easy to reconstruct the structural formula. Steps : Find the root word ( ending in – ane ) in the hydrocarbon name . Number the carbons on this parent chain . Identify the substituent groups . Attach the substituents to the numbered parent chain at the proper positions. Add hydrogens as needed .

17. Properties of Alkanes :

18. Other Properties of Alkanes : They are non-polar Hydrocarbons of low molar mass tend to be gases or low-boiling liquids . Non-polar organic molecules are insoluble in water . Rule: “ Like dissolves like ” Polar dissolves polar and non-polar dissolves non-polar. Non-polar will never mix with a polar.

19. Practice Problems : Name the following compounds

20. Unsaturated Hydrocarbons : Objectives : Explain the difference between unsaturated and saturated hydrocarbons . Differentiate between the structures of alkenes and alkynes .

21. Alkenes Alkanes are said to be saturated compounds because they contain a maximum number of hydrogens . Alkenes and alkynes , on the other hand , contain double and triple bonds respectively . They are said to be unsaturated compounds because they contain fewer number of hydrogens in their structure .

22. IUPAC Naming System for Alkenes : Find the longest chain in the molecule that contains the double bond. This is the parent alkene . As a base, you use the base name of alkanes and change the suffix – ane to –ene. The chain is numbered in the same way that alkanes , except that the carbon atoms of the double bond get the lowest possible numbers . Substituents on the chain are named and numbered in the same way they are for alkanes . Ethene and propene are the simplest alkenes .

23. Ethene 2D: Ethene 3D Prop ene 2D Prop ene 3D

24. Name the following alkenes :

25. Alkynes : Are hydrocarbons containing carbon-carbon triple covalent bonds They are unsaturated compounds They are not plentiful in nature The simplest alkynes are: ethyne , propyne , butyne Ethyne is commonly called acetylene .

26. Name the following compound :