Problem Set Assignments/2009

1. Problem Set Assignments/2009 • May 12 class: Chapt 1 #1,2; Chapt 2#6,8,18; Chapt 3 #3; Chapt 5 #26,30; Chapt 9# 1,14; Chapt 12#1,18 • May 14 class: Chapt 6 #1,8; Chapt 8#1,21 • Answers posted on the course website

2. What will be on quizzes and exam? • Lecture material and PP slides • Problem set material • Explanations etc. from Demo’s • Material covered in “What’s in the News” • Questions: T/F; short answer and multiple choice format

3. 6. Organic Chemistry :an overview “carbon to candles” chapter 6

5. HYDROCARBON COVALENT BONDING H H C H H ×H • •× × • •C• • × ×• • Hydrogen Atom Carbon Atom Carbon with Hydrogen • • • • • C : C • C : : C • • • • Carbon with Carbon C C C C C C triple single double

6. ORGANIC STRUCTURES ( a ‘short hand’) H H H H-C-C-C-H CH3 – CH2 – CH2 or CH3 H H H-C-H H or CH3CH2CH2CH3 or all H’s understood

8. Positional Isomers of the Alkanes # of C’sFormula# of Isomers 1 2 3 4 5 6 7 8 9 101520 CH4 C2H6 C3H8 C4H10 C5H12 C6H14 C7H16 C8H18 C9H20 C10H22 C15H32 C20H42 1 1 1 2 3 5 9 18 35 75 4347 366,319

12. The First 10 Straight - Chain Alkanes NameMolecular Formula Methane Ethane Propane Butane Pentane Hexane Heptane Octane Nonane Decane CH4 CH3–CH3 CH3-CH2-CH3 CH3-CH2-CH2-CH3 CH3-CH2-CH2-CH2-CH3 CH3-CH2-CH2-CH2-CH2-CH3 CH3-CH2-CH2-CH2-CH2-CH2-CH3 CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH3 CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3 CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3

13. More than 10 C’s in the chain • Undecane (11), dodecane (12) tridecane(13),tetradecane(14), pentadecane(15) hexadecane (16) heptadecane (17), octadecane (18), nonadecane(19) • After C19, beyond the scope of CHEM 1003! • C20H42 is eicosane

14. Where to start numbering? • At the end of the chain with the most branches • 3-methylhexane

16. Origin of Hydrocarbons

18. Additional Complications! • Isomers!

20. Optical isomers • Enantiomers: contain one chiral (Gr. “Chiros” =hand) center and are non-superimposable mirror images • Are identical in all respects except for the direction in which they rotate plane polarized light • D and L isomers • Arise from tetrahedral C with 4 different substituents

21. Non-superimposable Mirror images

22. Amino Acids and Chirality • All naturally occuring amino acids are the L –isomers : rotate the plane of polarized light in counterclockwise direction (Why??) • Enzymes: many are chiral and are only active for a specifically handed substrate • Lock and key (hand in glove) mechanism for activity

23. Drug activity and handedness • L-Dopa is active vs. Parkinson’s disease • Its mirror image D-Dopa is inactive • “Chiral synthesis” of pharmaceuticals is a multibillion $ operation • Separations are costly and time consuming

24. Isomers with multiple (n) unique chiral centres • # of isomers possible =2n. • These are diastereomers: have different mp, bp • Cholesterol has 8 chiral centres, hence 28= 256 possible isomers. But only one occurs naturally!

25. Cholesterol : A steroid • 8 chiral centres

26. Geometrical Isomers • Geometrical isomers • Simplest examples are cis-trans isomers • Differ only in the spatial arrangement of atoms

27. Trans fats geometrical isomers of cis fats (cis=same) , trans= opposite

28. Trans fats • Produced by partial hydrogenation of polyunsaturated vegetable oil • Are solids-give longer shelf life to products • Are worse than lard (sat’d fat) for your arteries! • “Banned” in NYC as of Jan 1, 2008

29. Can we totally rid our diet of trans fats? • No, they occur naturally in small amounts in beef tallow, butter, milk • Arise from microbial hydrogenation of polyunsaturated fats in the animals’ digestive system • Ottawa City council has decided against a “ban” (wisely)

30. Organic Nomenclature - Descriptors R C C C C R R R Examples cis- or trans- fatty acids trans cis R PABA = para-amino benzoic acid (in sunscreen) R R R R R ortho- meta- para- hexane butane pentane cyclo = cyclo

31. More Complex Organic Molecules • Contain atoms other than C and H • To understand their properties, they are grouped according to the nature of these atoms and how they are bonded • Classified according to reactivity and function, hence “functional groups”

33. Organic Functional Groups Functnl GrpGeneric‘Suffix’‘Prefix’Examples halocarbon -halide halo- PVC, R – X R – OH R – OR R – NHR perchloro- ethylene alcohol -ol hydroxy menthol, ethanol cholesterol ether -ether alkoxy Methyl-t-butyl ether (MTBE); octane enhancer amineam(ine)amino- adrenaline nicotine cocaine

34. Organic Functional Groups Functnl GrpGeneric‘Suffix’‘Prefix’Examples R – C = O aldehyde -al acyl citronellal retinal formaldehyde H R – C = O ketone -one ----- cortisone acetone testosterone R

35. Organic Functional Groups Functnl GrpGeneric‘Suffix’‘Prefix’Examples R – C = O carboxylic -oic carboxyl acetic acid acid ASA OH fatty acids R – C = O ester -oate ------ phthalates (acid + polyester OR alcohol) ethyl acetate R – C = O amide -amide amido- DEET (acid+ NR2

36. Common Names vs. IUPAC • Acetone (common solvent) is propanone • Acetic acid (in vinegar) is ethanoic acid • Benzene (potent carcinogen) is 1,3,5-cyclohexatriene • Chloroform is trichloromethane

37. Candle Chemistry • Candle waxes are mixtures of solid saturated hydrocarbons (paraffins) and long chain (C16 or more) monoesters. • Combustion in air generates CO2, H2O, heat and light

38. Wax Components (esters) • Oleo Stearin or Oleo Stearate (palm vegetable wax) mp 155-160oF • Stearic acid is the common name for octadecanoic acid (C18) • Oleic acid is same as stearic acid, except for a cis C=C at the C9 position of the chain

39. Dripless candles • Made by “overdipping” a normal candle (wax mp. 135-145 F) with a higher melting (160-170 F) • Candle burns down the middle leaving a hallow rim/tube to hold the melted inner wax • Or, try soaking a normal candle for 24 hours in salt water (2 tbs. salt to 2 cups water) for 24 hours • Demo!!

40. Salted candles don’t drip! • Compare flame intensity

41. Why does salt make a candle burn brighter? • Wick absorbs the NaCl solution • When the wax starts to burn, it excites the sodium electrons to a higher energy level • Visible light (yellow) is given off when these electrons return to a lower E level • Sodium D line at 589 nm (yellow) in visible range of 700 (red) to 400 (violet);3p to 3s

42. Sodium D line • Heat excites 2p electrons to 3p level • Visible light (589 nm wavelength) is emitted when these electrons come down to the 3s level • Recall electron configurations • Na is 1s2, 2s2, 2p6, 3s1. • Na+ has lost the 3s electron

43. Visible light • Red is longest wavelength, violet is shortest

44. Why no drips? • Flame is hotter and stronger with salt present in the wick, hence melted wax on top vaporizes and burns off before it drips down the side!