Organic Chemistry 2612 Name_________________________Final Lab Exam - sample Encircle your lab section:

MULTIPLE CHOICE. (36 pt). Black in the letter corresponding to the best answer for questions 1-13 on the answer sheet provided.

1. Which of the following compounds serves as the best nmr solvent for most organic compounds? a) CHCl3 b) CH3COCH3 (acetone) c) CDCl3 d) D2O

2. Based on the reaction conditions you utilized, which of the following processes seemed to be the least favorable (required the most energy to run)?

a) SN1 prep of 2-chloro-2-methylbutane b) E1 elimination of cyclohexanol to cyclohexenec) Solvolysis of 2-chloro-2-methylbutane d) Addition of Br2 trans-cinnamic acid

3. The silver nitrate test, R-X + AgNO3 AgX↓ + R+ NO3-, works best for 3o halides. It

likely involves which of the following reaction pathways?

a) SN1 b) SN2 c) addition d) elimination (E1)

4. Which of the following compounds 1-4 gives an infrared spectrum with peaks at 3311 cm-1 (strong peak) and 2120 cm-1 (medium peak)?

5. Which of the following compounds gives a proton NMR spectrum consisting of only a singlet?

a) 1,1-dibromopropane b) 2-bromopropane c) 1,3-dibromopropane d) 2,2-dibrompropane

6. Which of the following combinations of peaks appears in the 1H NMR spectrum of diisopropyl ether, (CH3)2CHOCH(CH3) 2 ?

a) a triplet and a doublet b) a doublet and a quartet c) two singlets d) a septet and a doublet

7. Which statement concerning the use of TMS as a reference for NMR chemical shifts is false?

a) The protons in TMS, (CH3)4Si, are all equivalent giving rise to a strong singletb) The protons are highly deshielded by the Si; most H’s in organic molecules are more shielded

and will appear upfield (higher magnetic field strength) compared to those in TMS c) TMS is inert and has a low boiling point allowing it to be readily removed from sample

d) Its NMR signal is arbitrarily set at 0 ppm and other signals related to it by their chemical shift)

8. Alcohols were used as reactants in two experiments being converted to an alkyl chloride and an alkene. Which of these classes of compounds has the highest boiling point per given molecular weight, a factor that came in handy in isolating many of the above products?

a) ROH b) Alkene (cyclohexene) c) RCl d) All 3 have similar boiling points

9. Based on your experience with the kinetic experiment, in which of the following solvents would you expect the reaction of 2-methyl-2-chlorobutane to be the fastest?

a) 45% H2O/55% isopropanol b) 55% H2O/45% isopropanol c) hexane, C6H14 d) pure isopropanol

10. Which one of the following experiments likely does not involve a carbocation intermediate?

a) n-butyl bromide + NaO2CCH3 n-butyl acetate b) + HCl t-pentyl chloridec) cyclohexanol + H3PO4 cyclohexene d) t-pentyl chloride + H2O t-pentanol

11. The purpose of washing your pet ether solution of 2-chlroro-2-methylbutane product from the HCl—2-methyl-2-butanol reaction with NaHCO3 in your separatory funnel was

a) to try to better fill the scheduled 3-hour lab period b) to remove traces of HCl remaining in the organic c) to remove traces of remaining impurities in your compound d) to break up an emulsion that formed in your separatory funnel

12. The relationship between the three structures (A-C) shown below which are possible bromination products of trans-cinnamic acid is:

a) A & B are enantiomers, C is a constitutional isomer of A & Bb) B & C are enantiomers, A is a diastereomer of B & Cc) A & B are enantiomers, C is a diastereomers of A & Bd) All are just different drawings of the same molecule

13) The relative intensity of the three peaks of a NMR triplet will be (results from the statistical arrangements of the 2 neighboring protons acting as bar magnets):

a) 1:3:1 b) 1:1:1 c) 1:2:4 d) 1:2:1

(end of multiple choice, write answers to the following questions directly on exam)

14. (18 pt) NMR Spectroscopy

a) Indicate the multiplicity expected for the signals of H’s a-d in the compounds below:

a c d

ClCH2C=O ClCH2CH2CH2Cl H

b

(b) Sketch out the expected NMR spectrum for the molecule CH3CH2Cl (4 pt):

___________________________________________________________ 5 ‘ 4 ‘ 3 ‘ 2 ‘ 1 ‘ 0

ppm TMS

(c) Provide the information (1-3) for the 1H NMR signals found for each of the following:

O O O CH3CCH2OCHCl2 CH3O-C-C6H4-C-OCH3

1) Number of signals:

2) Relative integration:

3) Chemical shifts (ppm):

15. (4) IR spectroscopy. The spectrum of a compound C4H10O shown below would be most consistent with what type of molecule (encircle)?

Ester Alcohol Ketone Aldehyde Carboxylic Acid

Point at telltale signal in IR spectrum

16. (4 pt) The preparation of 2-methyl-2-chlorobutane from 2-methyl2-butanol and its reaction in water/isopropanol both involve the same intermediate. Draw its structure

____________________________

17. (12 pt) Show the major organic product(s) for the following reactions:

CH3CH2CH2CH2CH2Br + NaCN _________________________

OH H3PO4

CH3CH2C(CH3)2 + H2O _________________________

CH3 H2O CH3CH2-C-CH3 + Cl CH3CHOHCH3 _______________ ______________

(draw 2 of as many as 4 possible products)

18. Short answer questions (15 pts): DO ONLY 3 OUT of 4:

a) Explain why you carried out the SN1 conversion of t-pentanol to t-pentyl chloride in the presence of strong acid (show partial mechanism if you wish).

b) The bromination of trans-cinnamic acid produces two new stereogenic centers, and the possibility of 4 stereoisomers upon addition of bromine, yet only two are formed. Explain why, showing the key intermediate if necessary.

C6H5CH=CHCO2H + Br2 C6H5CHBrCHBrCO2H (1 pair of enantiomers)

c) Explain how you experimentally followed the rate of the 2-methyl-2-chlorobutane reaction in water (what reactant or product did you follow and how?)

H3PO4

d) The dehydration reaction, cyclohexanol == cyclohexene + H2O, is actually an equilibrium process. Explain the experimental procedure (setup) and theory you used to drive the equilibrium to the right (i.e., to produce cyclohexene).

19) (10 pt) Below are the IR and NMR spectra of a compound with formula, C5H10O

a) Draw its structure and assign all NMR signals to hydrogens in the structure.

b) Also label the 3 IR peaks indicated to be consistent with your chosen structure.

(This signal at 9.7 is actually a triplet) (The signal at 2.4 is actually a quartet)

Yield problem: Calculate the % yield if 8 g of cylcohexanol reacted with excess H3PO4 to produce 4.1 g of cyclohexene (C6H10) [atomic weights: C- 12, H- 1, O- 16].