1. 1 Lecture 2: Discussion on Hydrocarbons Continued Outcome of the One-Minute Paper Needs Clarification  Condensed vs. Expanded vs. Molecular Formula  Naming Cycloalkanes and Alkanes with Substituents  Lewis-dot structures and assigning formal charges  Molecular Polarity  Pace …Rushed through examples at the end Went Well  Naming Alkanes  Group Activities … Retained concepts better  Guided inquiry questions through the lecture

2. 2 Lecture 2: Discussion on Hydrocarbons Continued  Today’s Class Agenda  Revisit Condensed vs. Structural vs. Molecular Formula  Revisit naming alkanes with substituents and cycloalkanes with substituents  Properties of alkanes  Reactions involving alkanes  Combustion  Halogenation  Revisit Lewis-dot structures and Resonance (pages 148-152 and 157-166) We will also do Group Activities, Finish off the ALE 1 and check into lab drawers

3. 3 Revisiting Drawing Structural Formulas for Alkanes Expanded formula: carbons connected in a row … bonds between all atoms shown Condensed formula: carbons connected in a row … bonds of atoms attached to carbon shown as a group, with subscripts showing number of atoms bonded to each carbon atom Molecular formula: carbon and atoms attached to it are shown as a group, with subscripts indicating the number of each atom present

4. 4 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings Structural Formulas for Alkanes TABLE 11.3 Line-bond structure

5. 5 Conformations The groups attached to a C-C single bond Rotate around the bond, Give different relative arrangements called conformations. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

6. 6 Revisiting Naming Alkanes With Substituents 1. How are the names of the cycloalkanes with substituents determined? 2. What about alkanes with substituents? Study the names of the following alkanes and cycloalkanes and then answer the following questions (work in groups to determine the rules):

7. 7 Guide To Naming Alkanes So, to name alkanes, we do the following 1. We find the longest continues chain and write the name of that alkane 2. We number chain from end nearest substituent. 3. We locate substituents and name them in alphabetical order 4. If cylcoalkanes, we use the prefix “cyclo” before the alkane name 5. For Cycloalkanes, numbering starts with the substituents that gives the lowest numbers to the other substituents (thus clockwise or counterclockwise) 6. A hyphen is used between numbers and names, and commas to separate two or more numbers

8. 8 Pause: ALE 1 Lets revisit problems 10-13 of ALE 1. Try it on your own. You have 5 minutes to do all of the problems.

9. 9 Learning Check Write three isomers of C 5 H 12 and name each one (use line- bond formulas Write three isomers of C 5 H 10 and name each one Isomer 1 (and name): Isomer 2 (name): Isomer 3 (name): Isomer #Isomer FormulaName 1 2 3

10. 10 Properties of Alkanes: A Learning Check For the following pairs of hydrocarbon, which one has the higher boiling point? Why? 1. butane or octane 2. hexane or 2,3-dimethylbutane Properties of Alkanes  Nonpolar, flammable in air, less dense than water  1-4 carbons, gas at room temperature; 5-17 carbons, liquid at RT; > 18 carbons, waxy solids at room temp.  Effect of boiling point > increases with increased # of carbons > Decreases for branched alkanes > Increases for cycloalkanes

11. 11 Classification of Carbon Atoms The classification of carbon atoms indicates the number of carbon atoms attached. A primary carbon (1°) bonds to one carbon atom. A secondary carbon (2°) bonds to two carbon atoms. A tertiary carbon (3°) bonds to three carbon atoms. CH 3 | CH 3 —CH 2 —CH 2 —CH 3 CH 3 —CH—CH 3 primary secondary tertiary

12. 12 Reactions of Alkanes: Combustion Alkanes are flammable in air and react with oxygen. Study the following reactions and see if you can figure out what is happening. 1.In each reaction, what products are formed? 2.Are the differences between the reactions? C 5 H 12 + 8O 2  5CO 2 + 6H 2 O + Energy C 3 H 8 + 5O 2  3CO 2 + 4H 2 O + Energy C 7 H 16 + 11O 2  7CO 2 + 8H 2 O + Energy What conclusions can we make about the reaction of alkanes with oxygen?

13. 13 1. Write the combustion reaction for ethane and balance. 2. In the cells of our body, energy is produced by the combustion of glucose (C 6 H 12 O 6 ). There are series of reactions involved, but we can write the overall combustion of glucose in our cells. Write the combustion reaction for glucose and balance. Learning Check

14. 14 Halogenation of Alkanes (Substitution Reaction) Lets review the following reactions between alkanes and halogens. Think about what is happening and propose explanation? (for each reaction to occur, a light or heat is required) CH 3 —CH 3 + Cl 2  CH 3 —CH 2 —Cl CH 3 -CH 2 -CH 3 + Br 2  CH 3 —CH 2 —CH 2 — Br 1.How many Hs were present in the alkanes before reaction happened? 2.How many are present after the reaction happened? 3.What does this tell us about the process of halogenation?

15. 15 Summary: Halogenation of Alkanes When alkanes react with halogens, The reaction is called substitution, one or more H atoms are replaced with a halogen, usually Cl or Br. Light or heat is required. A mixture of halogenated products result, but we write the equation with the monosubstituted product. Example: ethane and chloride light CH 3 —CH 3 + Cl 2 CH 3 —CH 2 —Cl

16. 16 Revisiting Covalent Bonds for Elements in Organic Compounds ElementGroup #Valence Electrons # of electrons need to achieve octet Covalent bond it can form H C N O, S F, Cl, Br, I Fill out the following table for each element?

17. 17 Revisiting Lewis-Dot Structures Lewis-Dot structures give us structural formulas which we can get arrangement of atoms, bond order, and formal charges as well as resonance Rules For Lewis Dots 1. Structure has to agree with formula 2. All atoms have to be attached (molecular skeleton) 3. Structures with maximum octets are preferred 4. Correct # of electrons must be present 5. More electron negative atoms are accommodated first 6. Minimum charge separation preferred

18. 18 Lewis-Dot Structures Central Atom: guess central atom. Some suggestions:  Never H  Most single dots  Least Electronegative  Least Numerous Let’s illustrate this on the board using the following examples: CH 4, NH 3, CO 2 Formula for the # of possible bonds and possible charges: # of bonds = ½ [(sum of valence e- if full) – (sum of val. e-  charge)] # of charges = # val. electrons - [# bonds + 2(unshared pairs)] Lets use CO 2 as an example to illustrate this

19. 19 Examples of Lewis Dot Structures These are done on board CH 4 NH 3 CO 2 CO CO 3 2- NO -

20. 20 Revisiting Molecular Polarity and Shape Know that we know how to figure out bonds between atoms, how does molecular shapes impact molecular polarity?  Predict shape of molecule from Lewis-dot structures  Determine if there is polar bonds  Do dipoles cancel out as a result of the molecule’s shape? If no, than molecule is polar. If dipoles cancel, then molecule is nonpolar  The presence of lone pairs in central atom makes molecules polar Redo Problems 1-4 of ALE 1

21. 21 Resonance Structures (page 152) Resonance Structures: Two or more equivalent structures (actual is intermediate) for the same molecule  Pushing electrons away from one atom and towards another is a movement of the charge  Relative position of all atoms stays unchanged  Equivalent resonance structures contribute equally to resonance intermediate  Arrow connecting resonance structures is double- headed () Example: Draw resonance structures of CO 3 2-

22. 22 Revisiting Functional Groups Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings TABLE 11.9

23. 23