Organic Chemistry

1. Organic Chemistry Introduction to Organic Chemistry Alkanes

2. What is Organic Chemistry? • What do you think of when you hear the word organic? Inorganic? • Organic Chemistry is the study of carbon containing compounds • Inorganic Chemistry is the study of the rest of the elements

3. What is Organic Chemistry? • Historically, organic compounds were obtained naturally from plants and animals • We now have found ways of synthesizing these organic compounds (with the desirable properties of the natural compounds)

4. Why is Carbon so Special? • The unique characteristics of carbon allow for large number of organic compounds • Carbon forms a total of four covalent bonds • Thus it can bond to itself or many different atoms • Forms single, double or triple bonds

5. Representing Structures • There are a number of different ways to draw our compounds

6. Structural Formula • Shows all the atoms in a structure and how they are bonded to one another • Are 2-D drawings of 3-D objects thus they are not totally accurate

7. “—” A single line represents one pair of electrons (a single bond) “=” A double line represents two pairs of electrons (a double bond) “≡” A triple line represents three pairs of electrons (a triple bond)

8. Condensed Structural Formula • Shows the kind and number of atoms present • Only shows bonds between carbon atoms • The bond between hydrogen and carbon is assumed to be present

9. Expanded Molecular Formula • Shows the kind and number of atom present in the compound • Does not show the actual bonds that occur, however they are assumed to be present • When written as a molecular formula, the above example becomes C3H8

10. Skeletal Formula • The end of each line, and the points where lines meet, represent carbon atoms • Hydrogen atoms are assumed to be present in the correct number • You may see this in some books and online etc but we will not focus on this!

11. Terms • Saturated: organic compounds in which each carbon atom is bonded to the maximum number of hydrogen atoms, thus containing only single bonds • Unsaturated:organic compounds in which the carbon atoms do not have the maximum number of hydrogen atoms and thus have double or triple bonds

12. Terms • Hydrocarbons: organic compounds consisting of only carbon and hydrogen • Straight Chain: all C bonded to only 2 other C eg. C-C-C-C • Branched Chain: one or more C bonded to 3 or 4 other C’seg. C | C – C – C | C

13. Classifying Hydrocarbons Look at the following compounds. If you were to classify them, how would you do it?

14. Single Bond Compounds These are called Alkanes!

15. Double Bond Compounds These are called Alkenes!

16. Triple Bond Compounds These are called Alkynes!

17. Classifying Hydrocarbons • These are the three groups of hydrocarbons • Alkane • Alkene • Alkyne • We will now look at these further

18. Alkanes Single Bonds C—C • Are saturated hydrocarbons • Each molecule differs from the next by the structural unit –CH2– • This is a homologous series – when each member increases by the same structural unit • The General formula for an alkane is CnH2n+2

19. Properties of Alkanes • Non-polar • Thus are soluble in non-polar solvents and not soluble in polar solvents Remember: Like Dissolves Like • Have relatively low boiling points • Boiling points, melting points and densities of straight-chain alkanes increase with increasing chain length

20. Naming Straight-Chain Alkanes • All alkanes end with the suffix –ane • Root of the name is based on the number of carbons in the chain • Examples: Methane 1 Carbon Ethane 2 Carbon What is the molecular formula of each?

22. What is the name of this compound? CH3—CH2—CH2—CH2—CH3 • Draw the structure for this compound. Octane

23. Naming Branched-Chain Alkanes • These molecules have side chains (branches) that can be made up of alkyl groups or halogens • We name these based on their parent chain (longest alkane) and side chains • Naming follows the general formula: Prefix + Root + Suffix

24. Prefix: the branches attached to the parent chain • Root: the longest continuous chain in the hydrocarbon (the parent chain) • Suffix: for all alkanes, the suffix is –ane

25. Alkyl Branches • Alkyl groups are alkanes with one less hydrogen • They are named as alkanes are, with the ending –yl • Eg. Alkane: Propane CH3CH2CH3 Alkyl Group: Propyl CH3CH2CH2

26. Halogen Branches • Halogen branches are given names based on their element name, with any ending removed • Eg. Br Bromo ClChloro

27. Naming the branches • Prefixes are numbered based on their position along the parent chain – these numbers are always given such that the branch has the lowest possible number! • When putting prefixes together in the name: • Numbers are put in ascending order • Hyphens separate numbers and words • Commas separate numbers

28. How does this go together? CH3–CH–CH2–CH3 | CH3

29. Steps for Naming • Find the root – locate the parent alkane • Find position numbers – number the parent chain starting with the end closest to the branch • Find the prefix – name the branches • Put it together! Prefix + Root + Suffix

30. Try One More Cl | CH3–CH—CH—CH2CH3 | CH2–CH3

31. Recap of Naming • Find the root – locate the parent alkane (the longest carbon chain – it is not always a straight line!) • Find position numbers – number the parent chain starting with the end closest to the branch • Find the prefix – name the branches • Put it together! Prefix + Root + Suffix

32. When putting a name together… • Commas separate numbers from numbers • Hyphens separate numbers from letters • Numbers are put in ascending order ie. 1,2,3

33. When putting a name together… • Branch names are placed in alphabetical order Except!!!! When using di and tri for multiple branches, we order by the branch name and not the prefix eg. dimethyl - order by the “m” not the “d”