What you should remember from the last lecture

Transcription

1 What you should remember from the last lecture Carboca'on rearrangements. When carboca4ons are produced (like in E1/S N 1 reac4ons), rearrangements can occur. ydride shibs and alkyl shibs can occur, par4cularly if a more stable ca4on can result. C 3 C 3 C 3 C 3 C 3 C 3 C 3 C 3 C 3 C 3

2 What you should remember from the last lecture Conversion of alcohols into alkyl halides. These transforma4ons are usually accomplished with SOCl 2 /pyridine (conversion to chlorides) or PBr 3 (conversion to bromides). Alkenes undergo addi'on reac'ons and are weak nucleophiles. As such, they will react with strong electrophiles. With strong acids ( + as electrophile), carboca4ons are formed. If water akacks the ca4on, an alcohol is produced (net result: hydra4on of the C=C bond). If - X is used, X - akacks and the net result is addi4on of - X across the C=C bond.

3 Some typical faky acids CO 2 Stearic Acid (18 carbons): a saturated faky acid CO 2 Oleic Acid (18 carbons): an unsaturated faky acid Linolenic Acid (18 carbons): a polyunsaturated faky acid CO 2

4 Some interes4ng alkenes β- Carotene C 2 O Vitamin A O Re4nal

5 Some interes4ng alkenes Squalene Form 2,3-epoxide O Lanosterol synthase Lanosterol, the parent of the steroids O

6 What to do before the next lecture Read and do exercises within Chapter 10, sec4ons 10.1 through O 1. NC 3 2. SOCl 2 O 1. PBr 3 2. S

7 O 1. NC 3 2. SOCl 2 Cl N O N O SC 2 C 2 C 3 1. PBr 3 2. S

8 What to do before the next lecture Finish reading Chapter 10, comple4ng the problems as you go. Read the few designated parts of Chapter 11 (11.1, 11.11). What you should ALREADY be able to do Br C 3 Br Br 2 Br Br

9 What you should remember from the last lecture Addi'on of - X to Alkenes. These reac4ons involve a ca4on intermediate, and the regiochemistry is driven by ca4on stability. There are many varia4ons on this theme, including hydra4on of alkenes with strong acid in water. Markovnikov s Rule summarizes the regio- chemistry as (roughly speaking) In the addi4on of X to an alkene, X bonds to the most highly subs4tuted carbon. Addi'on of X 2 to alkenes. These reac4ons involved bridged bromonium ion intermediates, and result in an4 addi4on of X 2 across the alkene.

10 As we head toward Exam 4 If you have 3 finals on one day, the highest numbered class must offer an alternate 4me. CE 230 (all sec4ons) is scheduled at 8:30 PM on Wednesday December 12. This is in direct conflict with MA 113! If you have either a direct conflict OR you have 3 exams on December 12, please me, giving me the specific circumstance AND your complete final exam week schedule. I will try to iden4fy a workable 4me for you to take the exam. Exam 4 is just like the other exams: 50 minutes, 100 points, 25% of the final grade. See the syllabus for details.

11 A likle prac4ce. Br Br Br

12 And some halogena4on. via Cl O

13 What you should do before the next What to do before lecture the next lecture Read Chapter 12, comple4ng the problems as you go. SKIP SECTIONS 6, 12B, AND What you should ALREADY be able to do 1. B O 2, NaO C 3 O

14 What you should remember from the last lecture Addi'on of X 2 to alkenes. These reac4ons involved bridged halonium ion intermediates, and result in an4 addi4on of X 2 across the alkene. If X 2 is dissolved in a nucleophilic solvent (water or alcohol), the solvent can act as the nucleophile and a halohydrin results. ydrobora'on/oxida'on. These reac4ons use borane (B 3 ) followed by an oxida4on ( 2 O 2, NaO), and result in the an4- Markovnikov of alkenes. The an4- Markovnikov regiochemistry is a result of boron being the electrophile rather than hydrogen. Steric effects reinforce the regiochemistry.

15 ydrobora4on is syn- addi4on 1. B O 2, NaO C 3 O ydrobora4on is syn addi4on across the C=C bond! Stereospecific!

16 A likle prac4ce. C 3 C 3 C 3 C 3 1. B O 2, NaO O C 3 C 3 α- pinene

17 A likle more mid- day prac4ce.

18 ydrogena4on of small molecules

19 Par4al ydrogena4on of Fats A trans fat

20 What you should remember from the last lecture Mass Spectrometry. The array of ions produced by ioniza4on and fragmenta4on of a molecule, separated by mass. The Parent Ion the ionized but otherwise intact molecule. The mass corresponds to the molecular weight of the compound. This mass can be used to generate prospec4ve molecular formulae. The Base Peak The tallest peak in the spectrum corresponds to the most common ion formed in the fragmenta4on. OBen is the most stable ion produced. Fragment ions - These are the common pieces that are formed as the parent breaks up. The Nitrogen Rule Odd M + means an odd number of N s are present. Otherwise, M + is even and fragments are odd.

21 What you should know about the final Time: 8:30 PM 9:20 PM, Wednesday December 12. Place: CP- 139 (right here) Coverage: Everything (as always). Realis4cally, the exam will be dominated by the material we have covered since the 3 rd exam, but knowledge of everything from day 1 is needed. Some earlier topics may be addressed explicitly, and will be needed implicitly in the more recent material.

22 Some take- home prac4ce problems 1. TsCl, pyr O 2. (C 3 ) 2 S 2, Pd/C 1. O 3 2. Zn, Cl

23 3340 cm - 1 C 3 O 2945 cm - 1 Fingerprint region

24 O O C 3

25 N cm cm cm - 1

26 exane C stretch

27 1- exene sp 2 C- sp 3 C- C=C 1642 cm - 1

28 C 6 12 hexene or cyclohexane? 1460 cm - 1

29 2120 cm - 1 C C 3311 cm - 1

30 C cm - 1

31 O C 3 C cm - 1

32 O 1686 cm - 1

33 O N C 3 C cm - 1

34 1718 cm- 1

35 Candidates: m/e = 43 O O C 6 C 5 12 C 4 8 O O Loss of 29 M + = 72

36 What you should remember from the last lecture Infrared Spectroscopy. You should remember that the posi4on of vibra4onal bands depends on the atoms involved and on the strength of a bond. Bonds between heavy atoms (C- C, etc) have vibra4onal bands at lower frequency than bonds between a heavy and a light atom (C- ). Stronger, s4ffer bonds (C=C) have vibra4onal bands at higher frequencies than weaker bonds (C- C). - O ~3400 cm - 1 C- >3000 cm - 1 for sp 2 C-, < 3000 for sp 3 C- C=O 1660 cm - 1 to 1760 cm - 1 C=C 1630 cm - 1 to 1600 cm - 1

37 A Few Notes Office hours moved to 3:00 PM today Exam Conflicts

38 Some take- home prac4ce problems 1. TsCl, pyr O 2. (C 3 ) 2 S SC 3 2, Pd/C O 1. O 3 2. Zn, Cl O

39 What you should remember from the last lecture Infrared Spectroscopy. You should remember that the posi4on of vibra4onal bands depends on the atoms involved and on the strength of a bond. Bonds between heavy atoms (C- C, etc) have vibra4onal bands at lower frequency than bonds between a heavy and a light atom (C- ). Stronger, s4ffer bonds (C=C) have vibra4onal bands at higher frequencies than weaker bonds (C- C). - O ~3400 cm - 1 C- >3000 cm - 1 for sp 2 C-, < 3000 for sp 3 C- C=O 1660 cm - 1 to 1760 cm - 1 C=C 1630 cm - 1 to 1600 cm - 1

40 What you should remember from the last lecture The Nuclear Magne'c Resonance phenomenon. Many nuclei have a spin that leads to a (4ny) magne4c moment. In the presence of a large external magnet (like a BIG superconduc4ng magnet), these 4ny magnets align either with the field or against the field, and these two states differ in energy by a small amount. That (small) energy difference corresponds to a radio- frequency energy (E = hν), and this leads to NMR spectroscopy. The Chemical ShiZ reflects differences in the electronic environment between different protons in a molecule.

41 A few notes Chapter 12 Oxida4on and Reduc4on Reac4ons (read , , 12.12) Sec4on covers the oxida4ons of alcohols, both 2 alcohols (to ketones) and 1 alcohols (to aldehydes or to acids). I WILL hold regular office hours next week

42 C4

43 C 3 O C 3 O C 3 C 3

44

45 O 3 C 2 C 3 2 1

46 Some Links to Spectroscopy Problems hkp://chemserv.centre.edu/muzyka/spectralzoo hkp:// hkp://orgchem.colorado.edu/hndbksupport/spectprob/problems.html A Link to Reac'ons Problems hkp://chemserv.centre.edu/muzyka/reac4onzoo