1. Chem. 1B – 12/3 Lecture

2. Announcements I Lab Final –On Wed./Thurs. Next Week –Will be 25 questions, multiple choice –Bring green type scantron (sorry, don’t have # yet) –Questions will be similar to quiz questions, pre-lab questions, and post-lab questions Make Up Quiz –First 10 to 15 min. on December 8 th –Optional, will replace lowest quiz score (if higher)

3. Announcements II Class Grading –Blackboard score – I’m getting lab instructors to report zeros in place of no score, so this will cause some Blackboard scores to go down to their actual scores Today’s Lecture –Organic Chemistry (Chapter 20) Carbon – carbon bonds Alkanes Alkenes

4. Chapter 20 Organic Chemistry Introduction –Organic Chemistry is a major area of study (we offer 7 organic chemistry classes at the undergraduate level) –In ~1 week, we only have time to introduce basic principles of organic chemistry

5. Chapter 20 Organic Chemistry Overview –Nature of Carbon – Carbon Bonds –Hydrocarbons (structure, naming and isomers) –Reactions –Aromatic Hydrocarbons –Functional Groups

6. Chapter 20 Organic Chemistry Nature of Carbon – Carbon Bonds –Carbon is one of the few elements that form fairly stable bonds with itself –Most alkanes (hydrocarbons with only single bonds), while combustible in air (more stable as CO 2 + H 2 O), have negative  G f º –Carbon “likes to” form 4 bonds ([He]2s 2 2p 2, but mostly forms sp to sp 3 hybrid bonds)

7. Chapter 20 Organic Chemistry Nature of Carbon – Carbon Bonds –Simplest hydrocarbon is CH 4, methane, in which sp 3 hybridization occurs (tetrahedral geometry) –As carbon – carbon bonds are common, in alkanes, they also occur with sp 3 hybridization (tetrahedral for each C atom)

8. H Chapter 20 Organic Chemistry Nature of Carbon – Carbon Bonds –Example alkane with a carbon – carbon bond is ethane: CH 3 CH 3 –All bonds are sigma bonds in alkanes –This means constituents may rotate about bond C H H C H H H H C H H C H H H

9. Chapter 20 Organic Chemistry Nature of Carbon – Carbon Bonds –Hydrocarbons containing double bonds are known as alkenes –Hybridization is sp 2 (see ethene structure below – drawn in 3D) so all atoms in one plane C H H C H remaining p orbital forms  bond Because of  bond, rotation about C-C axis doesn’t occur at room temperature H

10. Chapter 20 Organic Chemistry Hydrocarbon Structures –Linear alkanes: CH 3 (CH 2 ) n CH 3 –Carbon skeleton structure –Example butane = –Only bonds shown as lines and carbons as kinks (Hs omitted) No. Carbons name 1Methane 2Ethane 3Propane 4n-Butane 5n-Pentane

11. Chapter 20 Organic Chemistry Hydrocarbon Structures –Branched structures: –Example isobutane = CH 3 CHCH 3 CH 3 –Butane and isobutane are “structural isomers” (have the same number of Cs and Hs, but are structurally different) –Branched compounds have greater volatility than their linear isomers

12. Chapter 20 Organic Chemistry Hydrocarbon Structures –Optical Isomers As was mentioned in Chapter 24, tetrahedral structures with 4 different constituents (CWXYZ with C in center) will have optical isomers Hydrocarbon example (3-methyl hexane) “Chiral” carbon (carbon with 4 different constituents) shown with star

13. Chapter 20 Organic Chemistry Hydrocarbon Structures –Optical Isomers – cont. Two different (3D) structures can be drawn of 3- methyl hexane corresponding to mirror images Each “enantiomer” (version) will have identical properties except for ability to rotate light and ability to interact with other chiral compounds Reactions in living organisms typically produce only one of two mirror images (also known as enantiomers), while synthetic reactions often produce both isomers (known as racemic mixtures)

14. Chapter 20 Organic Chemistry Alkanes –Sources: Plant/animal products (mostly historic) Petroleum (main source) Synthesis from coal, natural gas, or biomass –Structures: Linear Branched Cyclic Cyclopentane in C skeleton structure Note: cyclopentane (C 5 H 10 ) is NOT an isomer of n-pentane or isopentane (C 5 H 12 ) as it has 2 fewer Hs

15. Chapter 20 Organic Chemistry Example of Contract for Alkane Research with Sacramento Based Alternative Fuel Company Company (Greyrock Energy) is working to produce diesel fuel from agricultural waste or “stranded” gas (natural gas normally vented in oil operations) They produce diesel in the following process: C n H 2n O n + heat CO(g) + H 2 (g) and CO(g) + H 2 (g) + catalyst H 2n+2 C n (various) + H 2 O(l)

16. Chapter 20 Organic Chemistry Contract Research Example My job (or that of students working for me) was to determine H 2n+2 C n (various) + other impurities (benzene, alkenes, alcohols) Four phases produced (liquid water, gas alkanes – methane to butane – used to generate power, hydrocarbon liquid or crude synthetic diesel, and wax or solid hydrocarbons) Q. Does structure of hydrocarbons matter? A. Yes. Linear alkanes generally best for diesel, while branched alkanes are good for gasoline but poor for diesel (increases octane rating)

17. Chapter 20 Organic Chemistry How did we determine the composition of the diesel fuel?Gas chromatography (similar to paper chromatography lab) Chromatogram (each peak = 1 compound) Major constituents were-alkanes (biggest peaks) This sample had relatively high branched alkanes (some alkenes too) Other significant constituents are alkenes

18. Chapter 20 Organic Chemistry Alkanes – Naming compounds –Linear Alkanes (see table in text – should know methane to decane) –Branched alkanes Example Start with longest possible chain Assign numbers to each carbon Add branching constituents – name based on number of carbons added (methane becomes methyl for –CH 3 ) – order is alphabetical

19. Chapter 20 Organic Chemistry Questions 1.What is the name of CH 3 CH 2 CH 3 ? Does it have a branched isomer? 2.What is the name of CH 3 CHCH 3 ? CH 2 CH 3 3.Determine the name and formula of the compound given its carbon skeleton structure below: 4.Does the compound in 3) have optical isomers? 5.Give the number of Hs attached to Cs at A and B A B

20. Chapter 20 Organic Chemistry Alkenes –Contain at least 1 carbon-carbon double bond –Naming (replace –ane ending with –ene with number referring to end of double bond closest to the #1 carbon) –Example: CH 3 CH=CHCH 3 is 2-butene Other isomer (CH 3 CH 2 CH=CH 2 ) is 1-butene

21. Chapter 20 Organic Chemistry Alkenes –Effects of double bonds: structural effect – increases melting point temperatures makes compounds more reactive/less stable –Examples in fats, oils and biodiesel –Fats and oils are triglycerides containing three fatty acids (alkane or alkene in nature)

22. Chapter 20 Organic Chemistry Alkenes – Fatty Acid Examples –Fatty acids are linear hydrocarbons with a carboxylic acid terminus –Size is typically 12 to 22 carbons in length (18 most common) with 0 to 3 double bonds –Animal fats mostly have 0 double bonds and are solids at room temperature –Used in biodiesel, these compounds have high “cloud point” temperatures (gel in fuel tanks at low temperatures)

23. Chapter 20 Organic Chemistry Alkenes – Fatty Acid Examples –Most plant fats have fatty acids with double bonds (cis- isomer) and are liquids at room temperature –Biodiesel made from plant fats has minimal cloud point problems (but does have some oxidation problems) –Why? “Kink” from double bonds reduces van der Waals attractions between neighboring hydrocarbon chains, decreasing melting point temperatures

24. Chapter 20 Organic Chemistry Alkenes – Cis – Trans Isomers –Because double bond is a barrier to rotation, cis- and trans- isomers occur for alkenes –Example 2-butene can be either cis- or trans- C H CH 3 C H cis-2-butene trans-2-butene C CH 3 C H H

25. Chapter 20 Organic Chemistry Alkenes – Cis – Trans Isomers –Are there differences between cis- and trans- isomers? –Large differences in melting points for example between natural plant fatty acids (almost always cis-) and trans- fatty acids formed as a bi-product of hydrogenation (partial conversion from alkenes to alkanes) –Trans- forms have very small kink vs. cis- fatty acids (and are also known to be unhealthy) cis-trans-

26. Chapter 20 Organic Chemistry Alkenes – In Synthetic Diesel –1- and 2-dodecene (C12) shown –Why 2 peaks for 2-alkenes and 1 for 1- alkene? 1-alkene 2-alkenes