1. Drawing Chemical Structures Condensed structures: C-H and C-C and single bonds aren't shown but understood –If C has 3 H’s bonded to it, write CH 3 –If C has 2 H’s bonded to it, write CH 2 ; and so on. Sometimes bonds between carbons aren't shown in condensed structures—here the CH 3, CH 2, and CH units are simply drawn next to one another, but some bonds are added for clarity The compound called 2-methylbutane, for example, is written as follows:

2. Constitutional Isomers Isomers that differ in how their atoms are arranged in chains are called constitutional isomers Compounds other than alkanes can be constitutional isomers of one another They must have the same molecular formula to be isomers

3. Alkanes and Alkane Isomers Alkanes: Compounds with C-C single bonds and C-H bonds only (no functional groups) Connecting carbons can lead to large or small molecules The formula for an alkane with no rings in it must be C n H 2n+2 where the number of C’s is n Alkanes are saturated with hydrogen (no more can be added They are also called aliphatic compounds

4. Alkane Isomers CH 4 = methane, C 2 H 6 = ethane, C 3 H 8 = propane The molecular formula of an alkane with more than three carbons can give more than one structure –C 4 (butane) = butane and isobutane –C 5 (pentane) = pentane, 2-methylbutane, and 2,2-dimethylpropane Alkanes with C’s connected to no more than 2 other C’s are straight- chain or normal alkanes Alkanes with one or more C’s connected to 3 or 4 C’s are branched- chain alkanes

7. Names of Small Hydrocarbons No. of Carbons Formula Name(C n H 2n+2 ) 1MethaneCH 4 2EthaneC2H6C2H6 3PropaneC3H8C3H8 4ButaneC 4 H 10 5PentaneC 5 H 12 6HexaneC 6 H 14 7HeptaneC 7 H 16 8OctaneC 8 H 18 9NonaneC 9 H 20 10DecaneC 10 H 22

8. Alkane Structures Planarzig-zag condensed-linecondensed

9. A perfect 3-D zig-zag for n-butane

10. Isomers: butane (C 4 H 10 )

11. Isomers: pentane (C 5 H 12 )

12. Which are isomeric?

13. To tell the isomers apart you can (should): Count total # of carbons and classify them as 1°, 2°, 3°, or 4°. (sometimes isomers give same count! but this is quick and dirty.) Build models (must practice!) Name (foolproof!).

14. General Nomenclature Rules. 1. Find a parent chain (longest continuous). 2. Number the main chain atoms so as to start nearer to the first branch. 3. Name substituents and assign numbers appropriate to their positions along the main chain. 4. Write a name as a single word. 5. Complex (branched) substituents are named as if they were a compound.

15. Details of Nomenclature Rules. 1a. Find a parent chain (longest continuous). Always try all possible permutations!

16. Details of Nomenclature Rules. 1b. Find a parent chain (longest continuous). Maximize the number of branch points, i.e. avoid substituents that are branched (if possible).

17. Details of Nomenclature Rules. 2a. Number the main chain atoms so as to start nearer to the first branch.

18. Details of Nomenclature Rules. 2b. Number the main chain atoms so as to start nearer to the first branch. If the substituents are at the same distances from chain ends give lower number to the substituent with the alphabetical priority of the first letter.

19. Details of Nomenclature Rules. 2c. Number the main chain atoms so as to start nearer to the first branch. If there are more than two substituents, begin numbering at the end nearer to the two closest branch points.

20. Details of Nomenclature Rules. 4a. Write a name as a single word. Pay attention to hyphens and commas.

21. Details of Nomenclature Rules. 4b. Write a name as a single word. Branched substituents are named as a separate molecule. The numbering within the name always starts nearest to the attachment point of the complex substituent.