NAME: SPRING 2015 MIDTERM

page 1 pts NAME: SPRING 2015 MIDTERM hemistry 231 Professor: Dr. Gergens take-home portion (DUE at the beginning of the period, 4/6) Do your best on this take-home portion of your mid-term. I may grade only selected problems and/or the whole exam. Late mid-terms will not be accepted. Answers to this midterm will be made available on 4/6 after 7pm Place your correct response on the scantron provide by your instructor. NLY answers on the scantron and selected problems on this exam will be graded. 1. The are three isotopes: hydrogen-1, hydrogen-2, and hydrogen-3. omplete the following for Element Symbol Atomic Number Mass Number # of Protons # of Neutrons # of Electrons hydrogen-3 an atomic number of 3 and 0 electrons D. a mass number of 3 and 2 neutrons an atomic number of 1 and mass number of 2 E. a mass number of 3 and 0 neutrons. 1 protons and 1 neutron 2. Which of the species below is more basic than sodium amide, NaN 2. 3 Li, methyl lithium D. both b and c sodium alkoxide, RNa E. all of the above. 3 2 Na, sodium acetate 3. preferred side of equilibrium N + Ph - N + Ph 4. most basic anion 2 N 2. D. 5. most stable conformer 3 3 3 3 3 3 3 3 A B 6. the numerical value for the overall G for conformer B going to in question 6? + - 0. 3 7. For every 1.36 kcal/mol change in free energy difference, G, at 25, Keq will vary by a factor of 0 1. 2 D. 10 E. 100 8. most likely to ring "flip" Me Me Me Me Me Me. Me Me D. 9. affords the most 1,3-diaxial interaction in monosubstituted cyclohexane i-pr n-bu n-pr t-bu Et. D. E.

page 2 pts 10. The predicted valence bond theory bond angle in 2 would be less than 90. The actual experimental bond angle in the bond angle in 2 has been experimentally determine to be 104.5. experimentally observed bond angle for 2? 16 8 1s 2 orbital configuration 2s 2 Which valence bond picture is consistent with the 2p 4 16 8 16 8 VBT bondig model. 16 8 For the compound on the right. Pick the best choice for the questions 11-17: 2 1 N 3 3 3 11. The major functional groups in the molecule are 3 amine 1 amine. 3 amine D. 3 amine E. 3 amine ether ketone ester ketone 3 amide 12. ow many non bonding electron pairs are in this molecule? 1 2. 3 D. 4 E. 5 13. What is the degree of unsaturation in this molecule. 2 3. 4 D. 5 E. greater than 5 14. What is the hybridization about the atom identified as 1? p sp. sp 2 D. sp 3 E. sp 4 15. The geometry about the atom identified as 2? tetrahedral trigonal planar. pyramidal D. bent E. linear 16. The bonding molecular orbital(s) the between the = and the atom identified as 3 σ( sp 2 - sp 2 ) 2 σ( sp - sp 2 ) π( p - p). σ( sp 2 - sp 3 ) D. σ( sp - sp 2 ) π( p - p) E. σ( sp - sp) π( p - p) 17. The nitrogen atom is conjugated with the = bond True False. Not enough information

page 3 pts 18. Which is the major resonance contributor? 2 2 2 2. D.. D. E. none are valid 19. In the Newman projection, letters B and E are both equatorial & cis both axial & cis. both axial & trans D. both equatorial & trans E. axial & equatorial & cis 20. The Lewis acid in the reaction below? S 2 (g) + BF 3 (g) ---> S 2 BF 3 (S) BF 3 is the Lewis acid because boron is trigonal planar having an empty p orbital which is capable of accepting an electron pair. BF 3 is the Lewis acid because boron is trigonal pyramidal having an empty p orbital which is capable of accepting an electron pair.. BF 3 is the Lewis acid because boron is trigonal planar having an empty p orbital which is capable of donating an electron pair. D. S 2 is the Lewis acid because sulfur is bent in geometry having an electron pairs capable of electron pair donation. E. S 2 is the Lewis acid because sulfur is linear in geometry having an electron pairs capable of electron pair donation. 21. Which cation forms the fastest under the reaction? 2 1 + l 2. D. can't be determined E. none are valid 22. least stable radical. 3 3 3 2 2 2 A B D. l 23. radical above is allylic vinylic benzylic. tertiary D. secondary E. 24. most stable carbocation. D.

page 4 pts Look at the reaction energy diagram shown here for X(g) + Y(g) XY(g) and use it to answer the following questions 25-31 X + Y XY 25. ow many reactive intermediates are there? 1 2 3 4 5. D. E. 26. ow many transition states are there? 1 2 3 4 5. D. E. 27. Which transition states is faster? 1 2 3 4 5. D. E. 28. The overall reaction is for A going to B is? 29. the numerical value for the overall G for the reaction for A going to B? endothermic exothermic + - 0. K eq >1 K eq <1 K eq =0 K eq <-1 K eq =1 30. the numerical value for the overall Keq for the reaction A going to B in the above?. D. E. 31. S for the reaction is predicted to be + - 0. 32. In the free radical chlorination of methane, the second propagation step in the mechanism is 4 + l ---> 3 + l. l + 3 ---> 3 l l 2 ---> 2 l D. 3 + l 2 ---> 3 l + l 33. least thermodynamically stable double bond 3 3 3 34. least negative heat of hydrogenation, (-) A 3 B 3 3 35. substituent w/ highest ranked priority by ahn-ingold-prelog rules 2 2 3 2 A B D 36. Which is the l l Z stereoisomer l l. D.

M Theory page 5 pts 1) Draw the resulting M's formed from the combination of A's and 2) give the resulting M an appropriate M label + + + - + + + - - Acid-Base onjugates omplete by drawing in the corresponding conjugates and any contributing resonance forms: N acid A conjugate base A B B Stability Mantra b. ircle the letter for the conjugate which is most stable: A B c. Applying your stability mantra learned in class, give a full explanation for your choice in (b) above.

page 6 pts Acid-Base Reactivity a Draw the specified conjugates, A-D. Include formal charge and resonance contributors where appropriate. b. RANK the lettered conjugates starting with the most stable on the left to the least stable ending the right. add a proton + to the carbonyl oxygen A add a proton + to the α-carbon to the carbonyl B N add a proton + to the α-carbon to the nitrogen D add a proton + to the nitrogen Structure, Functional Groups & Abbreviations a. Draw the line-angle structure for the substance on the left 2 2 2 ( 2 ) 3 ( 3 ) 2 b. Identify and give a label to bond positions A & B c. Identify and name the functional groups 1 & 2 1 2 1. 2. Draw the line-angle structure for the abbreviated substances below potassium t-butoxide, tbuk PhiBu

page 7 pts Resonance Structures & Arrow Pushing Within a Substance Draw all possible resonance structures for the following substance. Use curved arrows to show the flow of electrons and all formal charges. 3 N Stability a. Give each substance a logical identifiable label (i.e., benyzlic, onium ion, chloronium ion, primary cation, etc.) b. RANK the lettered substances starting with the most stable on the left to the least stable ending the right. c. Give a brief explanation for your overall ranking in b above. 2 2 3 2 3 3 2 2 2 2 2 2 2 2 2. Acid-Base Reactivity & Arrow Pushing Between Substances For the reactants, complete the reaction for the given arrow push and draw the predicted product formed under the reaction and any contributing resonance forms. 2 + l N N l Which nonbonded pair of electrons is protonated? Draw in the arrow push and complete the reaction. - Which hydrogen is deprotonated by base? Draw in the arrow push and complete the reaction draw the substances formed and any resonance structures

page 8 pts Mechanism a. Name the reaction and state the reaction. b. Give a stepwise mechanism for the following reaction. Your mechanism should show individual steps in the reaction that lead to all the products formed. Use curved arrows and indicate all formal charges. 3 hv + 2 + 3 reaction name/type c. Draw a representative potential energy curve that correctly shows your mechanism. Label important intermediates and transition states in your mechanism and on your potential diagram. energy reaction time d.alculate for the reation using the given bond dissociations energies (kcals/mol) 3 3 hv + 2 + = BDE (kcal/mole) 104 119 46 88 1-98 2-95 3 91 1 92 2 91 3 90 1-69 2-68 3 65 = 146 82 e. Describe in words your the individual steps in your mechanism. Be brief, accurate, precise and to the point.

Give labels, identify, complete and name the reactions. onditions (acidic, basic, neutral, oxidizing, reducing, polar protic, polar aprotic, etc.) page 9 pts 2 l reaction name/type 3 2 Na metal 3 -N 2 l 3 - Na Li l omplete the reactions: reaction name/type reaction name/type 2, 2 l specify stereochemistry 3 RR reaction name/type 1.B 3 TF 2. 2 2, reaction name/type specify stereochemistry

page 10 pts Alkane onformation Analysis a. Draw in ( ) all gauche interactions. 3 3 b. ircle the most stable conformer 3 A 3 3 B 3 3 3 3 c. X the least stable conformer. d. Draw the substance's line-angle structure. draw line-angle structure e. Name the substance: name: f. The substance is a alkyl halide (circle one) Bz allylic 3 2 1 Me vinyl Ph Draw the Newman projection for the substance shown above about the 2-3 bond in the eclipsed, staggered, and skewed conformations. Label all gauche interactions and calculate a torsional strain for each conformation. Plot a graph of the torsional strain observed see above as it rotates about the 2-3 bond. Begin with a conformer being totally eclipsed and a dihedral angle of zero. Place into the box the total torsional strain for each conformer. torsional eclipsing methyl groups > eclipsing methyl-hydrogen > eclipsing hydrogen-hydrogen strain 3.0 kcal 1.3 kcal 1.0 kcal torsional eclipsing methyl bromine > eclipsing bromine-hydrogen > eclipsing hydrogen-hydrogen strain 2.1 kcal 1.1 kcal 1.0 kcal Energy (kcal/mole) 5.5 5.0 2.5 0.0 0 1.1 60 120 180 240 300 360 energy (kcal/mole) 3.0 3 3 3 1.3 totally eclisped 5.4.

page 11 pts ycloalkane onformation analysis omplete this picture for the following equilibrium: a. Draw the chair conformations for the cis-1-hydroxy-4-methylcyclohexane b. Draw Newman Projection sighting down 2-1 and 4-5 for each conformer. c. ircle the most stable conformer. d. alculate G and K eq at 25 value for the energy value. 4 3 5 2 6 1 G =, K eq @ 25 = A B 4 2 4 2 e. Describe mathematically how you would calculated a free energy difference between the two conformers. \ f. alculate the percentage of each conformer present at 25 for your defined equilibrium above? SW YUR WRK FR FULL REDIT. A% & B% Thermodynamics Predict the sign for the given thermodynamic term: + - 0 + S + - 0 + G + - 0 +

Mantras - (write out our mantra exactly as stated in class; be accurate and precise in your response) page 12 pts a) I say "chemistry", give mantra" b) I say "IA", give mantra" c) "electronegativity", give mantra d) Atoms chemically... (complete this mantra exactly as stated in class) e) Explain in detail why magnesium metal's favorite oxidation state as an ion is 2+. f) I say "reaction," give mantra g) I say "stability," give mantra h) I say "resonance," give mantra i) I say "acid," give mantra j) I say, "conjugate base," give mantra k) pi bond (fill in blank)