NAME (print): ___________________________________________________

TA:_____________________ Day:_________________ Time:__________

Take a few moments to look over the exam. Answer each question on the exam paper.

Important items are in bold.

The exam is 100 points with 10 optional bonus points. You can earn 110 points on a 100 point

exam.

Do all preliminary drawing or computations on the work sheets at the end of the exam. The

work sheets will not be graded.

The exam is 55 minutes.

STOP writing and hand in your exam when you are asked to do so.

REMEMBER: Neatness is to your advantage.

1. (20 pts) ______

2. (20 pts) ______

3. (20 pts) ______

4. (20 pts) ______

5. (20 pts) ______

6. (10 pts) bonus ______

_______________________________

Total (110 pts)

1. (20 pts) Compound 1 is a cis-1,4-disubstituted cyclohexane.

a) (5 pts) Place the substituents in their appropriate positions in 1a and 1b.

b) (5 pts) Figure 1b is present in 90.9%. Calculate DG^o for this equilibrium. Show

work. DG^o = -1.4 log₁₀K_eq; K_eq = 1b/1a ]

c) (5 pts) What is the DG^o value (kcal/mol) for the acetylene substituent? Show work.

[DG^o = 1.7 kcal/mol for an axial vs. equatorial methyl group].

d) (5 pts) What term best describes the relationship between 1a and 1b?

2. (20 pts) The allyl cation [CH₂=CH-CH₂+] is a resonance stabilized carbocation. Draw a

molecular orbital representation of this species that clearly illustrates the molecular

orbitals and the resonance involved.

3. (20 pts) For the eclipsed and staggered conformations of 2-methylbutane viewed along the

C₂-C₃ sigma bond, draw a Newman projection of the least stable eclipsed and

staggered conformations. Place the appropriate energies in the Newman projections below.

[Use the circles as templates for the Newman projections.] Calculate the energy

(kcal/mol) of each conformation. Place your answer in the appropriate box. Show work.

[H/H, eclipsed, 1.0 kcal/mol; CH₃/H eclipsed, 1.3 kcal/mol; C₂H₅/H, eclipsed, 1.1

kcal/mol; CH₃/CH₃, eclipsed, 3.0 kcal/mol; CH₃/CH₃, gauche, 0.9 kcal/mol; CH₃/C₂H₅,

gauche, 1.0 kcal/mol.]

4) (20 pts; 4 pts. each) Circle the best answer(s) in each of the following problems.

a) The compound(s) with a net dipole moment

b) The incremental heat of combustion (DH^o) for an unstrained methylene group is

-157 kcal/mol. What is the incremental heat of formation (D H_f^o ) of an unstrained

methylene group? [D H_f^o (H₂O) = -68 kcal/mol; D H_f^o (CO₂) = -94 kcal/mol]

 

-162

+162

+157

-89

-5

+5

c) The alkane expected to have the largest heat of combustion.

 

n-pentane

2-methylbutane

n-hexane

2,2-dimethylhexane

2,2-dimethylpropane

d) Compound(s) containing sp² hybridized atoms

 

CH2O

CH2=C=CH2

CH3CN

BCl3

BeH2

e) Compound(s) that are deprotonated by NaOCH₂CH₃ (pK_a (C₂H₅OH) = ~16)

 

CH3CO2H

hexane

NH3

HCN

water

5) (20 pts) The heat of formation (D H_f^o) of n-octane is -49.8 kcal/mol and that of 2,2,3,3-

tetramethyl butane is -56.4 kcal/mol.

a) (15 pts) What is the difference in the heat of combustion of the two isomers? Illustrate

with a diagram.

b) (5 pts) Which isomer liberates more heat upon combustion?

6) (10 pts; 2 pts. each) Match the following luminaries in the history of organic chemistry

with their contributions: Baeyer, Kekule/Couper, Lavoisier, Liebig, Dumas/Laurent, van't

Hoff/LeBel. Enter the name on the line below..

Theory of combustion __________________

Tetrahedral carbon _______________________

Tetravalent carbon _________________________

Substitution theory _________________________

Baeyer strain theory ________________________

Work Sheets

Work Sheets

Work Sheets

Work Sheets