Review1

WeeklyReviewLecture

ChemS20ab2011

Welcometothefirstweeklyreviewlecture.Thishandoutissplitintotwoparts.First,theresalistofstuffyou needtobeabletodofortheexam.Followingthatarethereviewslides.Wemightnotbeabletogetthrough alltheproblems,butwelldoourbest.Letsseehowmuchgroundwecancover... Fundamentals/Alkanes 1) DrawLewisstructures. 2) Drawandevaluateresonancestructures. 3) Identifythehybridizationandgeometryofallatomsinamolecule. 4) ConvertbetweenLewisstructuresandskeletalstructures. 5) Namealkanesandalkenes,includingtheE/Zconvention. 6) DrawNewmanprojectionsandcomparestabilityofconformations. 7) Identifythefunctionalgroupsonp.14ofthepurplebook. 8) DrawacompleteMOdiagramforagivenmolecule. 9) IdentifytheHOMOandLUMOofagivenmolecule. 10) UsetheHOMOandLUMOtopredictthesinglestepreactionbetweentwomolecules. 11) Drawcurvedarrowstogofromreactantstoproductsinasinglereactionstep. 12) Drawtheproductsthatwouldresultfromagivensetofcurvedarrows. 13) Explaintherelativeacidityofprotonsusing:electronegativity,hybridization,resonance,andcharge. 14) KnowthepKavaluesfortheacidsonp.20ofthepurplebook. 15) FindtheKeqofanacid/basereactionusingpKavalues. Alkenes 1) Explainthedifferencesinstabilityamongcarbocations. 2) Predictalkylshiftsofcarbocationsthatcanbecomemorestable a. Primarysecondaryorsecondarytertiary b. Relievingringstrainof3or4memberedring 3) Drawthemechanismthatresultsinagivenproduct.Thismaybeaproductyoucouldnothave predicted,butyoushoulduseyourknowledgeofmechanismstofigureitout. 4) Knowall4piecesofthereactionchartforthefollowingreactions.Thatmeansbeingabletopredict thestartingmaterials,products,orreagents.Youneedtoknowthemechanismsforallreactions EXCEPTthosemarkedwithan*. a. Alkene+HClorHBr b. Alkene+H2O,H+ c. Alkene+ROH,H+ d. Alkene+X2 e. Alkene+X2+H2O f. Alkene+X2+ROH g. *Alkene+H2,Pd/C h. Alkene+HBr,peroxides i. Hydroboration/oxidationofanalkene*(noneedtoknowmech.forH2O2step) j. Oxymercuration/reductionofanalkene*(noneedtoknowmech.forNaBH4step) k. Alkoxymercuration/reductionofanalkene*(noneedtoknowmech.forNaBH4step) l. *OzonolysisofalkenewithMe2Sworkup m. *OzonolysisofalkenewithH2O2workup

Chemistry S-20ab S 20abReview Lecture, Exam 1Brandon Conley Harvard Summer School July 1, 2011

For each of the molecules shown below: Draw a complete Lewis structure, showing all atoms, lone pairs, and nonzero formal charges. Draw the one most significant alternate resonance structure. Be sure to show, using curved arrows, how you can arrive at the new structure from the old one. Identify each newly drawn resonance structure as less stable, equally stable, or more stable than the original structure structure. NNO OCN-

Functional GroupsWhat are functional groups, and why should you bother learning about them???

Identify the functional groups in the molecule below, and give hybridizations for the circled atoms.

The Joy of NomenclatureQ: What is the systematic name for this deadly little molecule?

N H H N O

H H O

NomenclatureProvide the correct systematic name for the following molecule.

NomenclatureDraw the structure of (Z)-6-tert-butyl-4-isopropyl-3-methyl-3-nonene.

Conformational AnalysisSingle bonds are not fixed axes, nor are molecules static entities (well, at least above absolute zero 0 K) zero, K).

What do we mean when we talk about rotational barriers and energy values?

Consider the conformations of the molecule 1,2-dichloroethane obtained by rotation about the CC bond:

a) This molecule is expected to have a single lowest-energy conformation. Using a Newman projection, show this conformation; be sure to view the molecule along the CC bond.

b) This molecule is also expected to have a single highest-energy conformation. Using a Newman projection, show this conformation.

c) Using the table of interaction energies given below, calculate the energy difference between the highestand lowest-energy conformers of this molecule.

Interaction

Energy (kcal/mol) 2.8 1.4 1.0 1.0

Eclipsed Cl / Cl Eclipsed Cl/ H Eclipsed H / H Gauche Cl / Cl

For each of the molecules shown below: Provide a complete molecular orbital energy diagram showing the energies of all valence orbitals in the molecule. Identify the frontier molecular orbitals (HOMO and LUMO) of each molecule. Using curved arrows, show the result of the most likely interaction between these two molecules, and draw the product that would result from this single step.H3C O Molecule A

H3C C N Molecule B

For the molecule shown, consider the following: The functional group(s) present and the hybridization of all non-hydrogen atoms. The best resonance structure for the molecule. The HOMO and LUMO of the molecule. A curved-arrow mechanism showing the molecule reacting with a nucleophile (CN-). A curved-arrow mechanism showing the molecule reacting with an electrophile (H+).

For the molecule shown, consider the following: The functional group(s) present and the hybridization of all non-hydrogen atoms. The best resonance structure for the molecule. The HOMO and LUMO of the molecule. A curved-arrow mechanism showing the molecule reacting with a nucleophile (CN-). A curved-arrow mechanism showing the molecule reacting with an electrophile (H+).

Each of the following shows a single step in a reaction mechanism. Draw the product(s) that would result from the indicated curved arrow steps, and then identify the relevant Frontier Molecular Orbitals (FMOs) involved in each each.

Br O H

Each of the following shows one step in a reaction mechanism. Show the curved arrows required to get from the reactants to the products.

H3C HO OH HO

H3C OH

Solving Acid-Base Problems Acid BaseYou must keep in mind the following factors that affect acid-base properties. Unfortunately, Unfortunately like many topics in organic chemistry there is no easy algorithm chemistry, to follow every time. Approach problems holistically and you will get the correct Answer with less frustration. pKa values (k K l (know th ones M li the Melissa went over b heart!) t by h t!) hybridization effects (more s-character atoms can stabilize charge better) polarizability (bigger atoms lose protons as acids more easily, and vice versa) inductive/field effects (delocalization of charge through sigma framework) resonance (delocalization of charge through pi systems most important!!!)

Identify the more acidic proton in each of the molecules shown below. Justify your choice.

The following compound, called a sulfonamide, undergoes an acid-base reaction as shown below. Draw the structures of the conjugate acid and base for the reaction, and calculate the value of the equilibrium constant for the acid-base reaction.

Provide a complete curved-arrow mechanism for the following transformation. Use the curved-arrow formalism for each step. Be sure to indicate formal charges for any p , y intermediates. For each step in the mechanism, identify the FMOs involved.EtOH H+ cat. EtO

In the previous reaction, the following products A and B are not formed. Provide a brief explanation to account for this observation.EtOH H+ cat. EtO

NOT formed:A

OEt

or B

OEt

The alkene shown below can react to form four different products bearing a hydroxyl group under different conditions. For each reaction, predict the product and draw a curved-arrow mechanism that explains its formation.H2O cat. H2SO4

The alkene shown below can react to form four different products bearing a hydroxyl group under different conditions. For each reaction, predict the product and draw a curved-arrow mechanism that explains its formation.

The alkene shown below can react to form four different products bearing a hydroxyl group under different conditions. For each reaction, predict the product and draw a curved-arrow mechanism that explains its formation.

The alkene shown below can react to form four different products bearing a hydroxyl group under different conditions. For each reaction, predict the product and draw a curved-arrow mechanism that explains its formation.

Synthesis!Provide a complete synthesis of each of the following molecules starting from any hydrocarbons of 4 or fewer carbons. You may use any inorganic reagents you wish.

O

Desired Product

Synthesis!Provide a complete synthesis of each of the following molecules starting from any hydrocarbons of 4 or fewer carbons. You may use any inorganic reagents you wish.

Synthesis!Provide a complete synthesis of each of the following molecules starting from any hydrocarbons of 4 or fewer carbons. You may use any inorganic reagents you wish.

Br O Desired Product

Alkenes are known to react with thiols by a free-radical mechanism in the presence of peroxides. Propose a mechanism for the following reaction, showing all the pertinent steps involved.

Explain why the other isomer, shown below, is NOT formed in this reaction.