REVIEW PROBLEM SET CH F. (b) Both cis and trans dibromides are obtained in the following reaction. Explain.

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1 REVIEW PRBLEM SET CH F [1] Provide brief answers to the following questions. (a) Write Newman projections for the chiral and meso forms of the following molecule looking down the bond connecting the two stereogenic centers. Explain why the hydroxy groups prefer to be gauche to each other in the chiral form but not in the meso form. H H (H 3 C) 3 CCH CHC(CH 3 ) 3 (b) Both cis and trans dibromides are obtained in the following reaction. Explain. Br 2 mixture of cis and trans dibromides! (c) When optically active 1-bromo-3-ethylcyclopentane was treated with potassium tertbutoxide in tert-butanol, two isomeric products were obtained. Propose structures for these products and predict whether they will be optically active or not. (d) How would you tell the following three isomers apart by 13 C NMR spectroscopy? (e) Reaction of CH 3 BH 2 with 1,4-pentadiene affords a compound containing a ring (formula C 6 H 13 B). Identify this compound and show how it might be formed. (f) (4 pts) Which of the following molecules is least likely to show a band for the stretching of the C=C group in its IR spectrum? [2] Chlorine adds across the double bond of cyclopropene to give two products, A and B. Cl 2 A and B (each C 3 H 4 Cl 2 ) (a) What are the structures of A and B and how are the two related to each other? (b) Draw another stereoisomer of A (or B) that is not formed in this reaction. Let's call this C. (c) Carefully write a mechanism for this reaction to show why only A and B are formed but not C. (d) Which do you think is least stable, A, B, or C? Give two reasons for your answer.

2 [3] Addition of HCl to 1-methylcyclohexene produces a single product X. HCl X (a) What is X and how is it formed? (b) Would the reaction be endothermic or exothermic? By how much? (Use table on page 277 in your text.) (c) Carefully draw, and label, an energy diagram to describe this reaction. (d) Give the structure of another alkene which will also lead to X as the sole product upon addition of HCl. (e) The following reaction, however, might be expected to produce two products, Y and Z. What are they, and how might they be formed? (Hint: Y and Z can each exist as a pair of enantiomers.) F 3 C HCl Y + Z [4] Match the IR spectrum below with one of the four given compounds and clearly justify your choice. You may consult the IR table handed out in class. CN H H H Reasoning:

3 [5] Indicate which one of the following compounds gives the mass spectrum shown below. Clearly justify your choice and specifically explain how the species responsible for m/z signals at 86, 71, 58, and 43 in the spectrum are formed. H H [6] (a) Show how you might selectively synthesize cis-1-bromo-2-methylcyclohexane from 1- methylcyclohexene. Clearly explain why the preparation of this compound by the addition of HBr to 3-methylcyclohexene is not efficient. (b) Suggest efficient synthetic routes to the following compounds starting from isobutene. You need not show mechanisms. CH 3 Cl D [7] Complete the equation shown below and answer the questions that follow. HBr H Br (a) What is the configuration at the stereogenic center of the substrate? (b) Draw the most stable conformation of each of the products formed in the reaction. (c) Examine each product and tell whether it is chiral or achiral. (d) How are the products related to one another?

4 [8] A molecule of the formula C 5 H 10 gives the 1 H and 13 C NMR spectrum shown below. What is the structure of this molecule? [9] Propose reasonable mechanisms for the following reactions. (a) Br 2 Br H

5 Br (b) HBr Br + (c) H H 3 + /H 2 H (d) H 3 + /H 2 H [10] Try the crossword puzzle on the next page. Clues are on the last page.

6 CH241F17 puzzle Teacher: Das Thama oor PDFCRWD.CM

7 Across Alcohols tend to lose this in a mass spectrometer This has two adjacent double bonds Preferred cyclohexane conforma on Number of signals in the carbon NMR of 2,3- dimethyl-2-butene Elimina on that leads to more stable alkene This instrument separates the compounds in your sample and determines their masses These compounds travel slowly down a silica gel column Technique of separa ng compounds When a bond it absorbed energy p cal rota on of a racemic mixture Can be used to tell between E and Z isomers by NMR All in a row Like dissolves Favorable orienta on for E2 Hydrobora on involves this type of addi on Vibra ons that don't change this are not visible in the IR Boron reagent rganomagnesium reagent Stereochemical outcome of an SN2 reac on The strongest hydrohalic acid (also double as a gree ng) Groups with priori es 1,2, and 3 go this way in an R stereocenter. A pro c solvent You cannot put this double bond in a small ring Natural source of photons This projec on helps visualize eclipsed and staggered conforma ons rganometallic reagents are sensi ve to this An alkoxide is a good Accepts electrons The ra o of protons causing signals in the NMR can obtained from these. This involves spo ng a plate These stereoisomers are not mirror images of each other Down E1 and SN1 have this in common ne might give this and a leg to do well in the chem final This could be a degree of unsatura on An aldehyde group What you turn in before lab. This has four different groups on it A ter ary ca on is stable than a secondary ca on Generic alcohol Larger groups avoid this posi on on a cyclohexane An ether Scale of NMR spectra These are in the same group Another name for a posi vely charged H. Two neighbors might give this Product of alkene reac on with peracid Has symmetry despite having stereocenters An sp carbon This has two common isotopes in a 3:1 ra o When two iden cal groups are on the same side Does not mix with water This group shows a band around 1700 cm-1 A good leaving group and nucleophile Molecular are formed when the sample is bombarded by high energy electrons. SN1 and E1 reac ons are molecular Some Chem problems are The transi on state of this reac on resembles product Allyl ca ons are stabilized by this. The rate of an SN1 reac on depends on this Not superimposable on its mirror image This aspect of a reac on is determined by the ac va on barrier This triangle helps analyze NMR spli This bond is usually sigma. A compound of the type RCR Good place to do Chem research NMR reference compound ng pa erns. PDFCRWD.CM