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CHEM120 - ORGANIC CHEMISTRY WORKSHEET 1 Some of the objectives To understand and know the hybridization concept Be able to distinguish different geometries, including basic bond lengths and angles within organic structures Name organic molecules Be able to identify different functional groups and name them. Know how to draw organic structures given the name or vice-versa, i.e. given the structure you should be able to name the compound Be able to use line notation and the condensed form to draw your structures as well as being able to draw the complete structure with all the atoms shown. You should be able to draw and name different kind of alcohols or amines, i.e. primary (1˚), secondary (2˚), tertiary (3˚) and quaternary (in the case of amines). Problems 1. Answer the following questions with respect to compounds (A) and (B): 5 CH(CH3)2 (A) CH3C 1 2 CCH CHCH2 4 (B) 6 CHCH2CHCH2COOC(CH3)3 2 O 3 OCHCH3 CH3CH(OH)CH 2CCH 3 1 CH2 CH2CH3 (a) Draw the bond-line notation for the two compounds. (b) Identify the following substituents on structure 1(A): (i) an isopropyl group 1 Dr. V.O. Nyamori (First Year Chemistry Co-ordinator) (ii) a tert-butyl group (iii) a sec butyl group (c) Identify all the functional groups in compounds (A) and (B). (d) Identify the hybridization of the numbered atoms in structures (A) and (B). 2. Name the compounds (a) to (d) below according to the IUPAC rules. (a) CH3CH2CH(CH3)CH2CH(CH2CH3)CH3 (b) (c) (d) 3. Write (i) structural formulae and (ii) draw the bond line notation for the following compounds: (a) 2,2,4-trimethylhexane (b) 3-ethyl-2,4,5-trimethyloctane (c) 2-bromo-2,4,6-trimethyloctane 4. (a) Explain why 2-sec-butyloctane is an incorrect IUPAC name. (b) (i) Write a correct IUPAC name and (ii) draw the bond-line notation for the intended compound. (c) Identify a primary (1˚), secondary (2˚), tertiary (3˚) and a quaternary (4˚) carbon atom in CH3C(CH3)2CH2CH(CH3)CH3. 2 Dr. V.O. Nyamori (First Year Chemistry Co-ordinator) CHEM 120: ORGANIC CHEMISTRY: WORKSHEET 2 Some of the objectives Be able to identify and name different isomers by using acceptable organic nomenclature rules, i.e. for constitutional, geometric and optical isomers. Be able to draw by using a perspective formula, Newman projections and Fischer projections. Problems 1. Name the following compounds by using the IUPAC system. If any alcohols are present, indicate whether they are primary, secondary or tertiary. 2. Draw structures for: (a) 4-isopropyldecane (b) 2,2-dichloropropane 3 Dr. V.O. Nyamori (First Year Chemistry Co-ordinator) (c) 3-heptyne (d) 5,5-dimethylnonane (e) 2-butanol (f) 2-methyl-2-propanol (g) 3-methylpentanal (h) 3-hydroxy-2-hexanone (i) octanoic acid (j) 4-bromo-5 hydroxynonanoic acid 3. There are four structural isomers with the molecular formula C4H9Br. Draw structures for the four isomers. One of these can exist as a pair of optical isomers which one is this? 4. The substance 2-butanol displays optical isomerism. carbon with a ‘*’. Indicate the chiral Draw three dimensional representations of the two enantiomers and label the isomers clearly. 5. Draw structures for the cis- and trans-isomers of 1-chloro-1-propene. 6. Determine the configuration of each of the following alkenes: 7. Draw the structure of trans- 1,3- dichlorocyclobutane. 4 Dr. V.O. Nyamori (First Year Chemistry Co-ordinator) 8. Explain why the cyclohexane boat conformation is much less stable than the chair conformation. 9. Find the stereogenic center (chiral centre) in i) CH3CH2CHICH2CH3 ii) BrFCHCH3 iii) 3-methylcyclohexene iv) 2,3-dibromobutane 10. (a) Which of the following compounds is chiral? i) 1-bromo-1-phenylethane ii) 1-bromo-2-phenylethane (b) Draw three-dimensional structures (perspective formulae) for the two enantiomers of the chiral compound in problem 10(a). 11. The figure below shows Fischer projection structures of 2,3-dichlorobutane. Classify the following molecules of as either enantiomers, chiral, achiral or meso forms. Locate the planes of symmetry, if any, and assign the corresponding configurations (R) or (S). CH3 CH 3 Cl H Cl H CH3 CH3 CH3 Cl H H Cl Cl H H Cl H Cl Cl H CH 3 5 CH3 CH3 Dr. V.O. Nyamori (First Year Chemistry Co-ordinator) CHEM 120: ORGANIC CHEMISTRY: WORKSHEET 3 Some of the objectives Know what homolytic and heterolytic fission is and when each would occur. Know the significance of a full arrowhead and half an arrowhead and when to use each. You must know what a carbocation is. Be able to use arrows to show bond cleavage in a molecule. Know how radicals react to form bonds. Know how cations and anions react to form bonds. Know what nucleophiles and electrophiles are and be able to give examples of each. Be able to identify nucleophiles and electrophiles in a reaction. You must know how the carbonyl group reacts with nucleophiles and be able to write a mechanism for this reaction. Problems 1. Write reactions to show bond cleavage in each case: CH 3 OH CH3 F HO OH Cl Cl H 2. How many electrons are around carbon in each of the following species: CH3 CH3 CH3 6 CH4 Dr. V.O. Nyamori (First Year Chemistry Co-ordinator) 3. Identify the electrophile and nucleophile in the following reaction: BCl3 + NH3 → Cl3BNH2 4. Identify each of the following species as an electrophile or a nucleophile: I-, H+, BF3, OH-, CH3+, CH3-, H2O 5. Write down the mechanism for the following reaction and identify the product that forms: O 1. CN- C H3C CH3 2. H+ 7 Dr. V.O. Nyamori (First Year Chemistry Co-ordinator) CHEM 120: ORGANIC CHEMISTRY: WORKSHEET 4 Some of the objectives Be able to write a mechanism for the halogenation of alkanes. Be able to explain this free radical mechanism and be able to identify the initiation, propagation and termination steps. Be able to explain why a radical is a highly reactive species. Be able to explain the order of stability for 1°, 2° and 3° radicals. Be able to explain how different groups stabilise or destabilise the radical. Be able to write a mechanism for the hydrohalogenation of an alkene. Be able to predict and explain why, which of two possible products will be formed in the greatest yield. Be able to explain why and know under what circumstances, enantiomers will form in electrophilic addition reactions. Know what substrates and reagents are involved in an ozonolysis reaction. Be able to predict the products of an ozonolysis reaction. You must know the conditions under which ozonolysis reactions occur. Problems 1. Write down the mechanism for the formation of CH3CH2Br from the reaction of Br2, CH3CH3 and light (hv). Identify the initiation, propogation and termination steps and briefly explain what occurs at each step. 2. What order of stability would you predict for a) 1°, 2° and 3° carbocations; b) 1°, 2° and 3° carbanions. Explain your answer in each case. 3. Label each of the following carbocations as 1°, 2°, 3° or methyl carbocation and then arrange them in order of increasing stability (least stable to most stable). CH3+; CH3CH2+; (CH3)3C+; 8 (CH3)2CH+ Dr. V.O. Nyamori (First Year Chemistry Co-ordinator) 4. Label each of the carbon radicals as 1°, 2°, 3° and then arrange them in order of increasing stability (least stable to most stable). (CH3)3C CH3CH2 (CH3)2CH 5. Which of the following carbocations is the more stable, ClCH2CH2+ or CH3CH2+. Explain your answer. 6. Write down the mechanism for the following reaction and predict which of the two possible products will be formed in the greatest yield. Write down the structures of the two possible products and explain your answer. CH3 CH CH2 + HBr 7. For each of the following reactions listed below, (a) write down the mechanisms, (b) write down the major and minor products in each case, and (c) indicate which of the products in (b) above would be enantiomers. H3C C C H3C H3C C C H H3C C C H3CH2C H HBr CH3 H HBr CH3 CH3 HBr CH3 8. The following alkene is first treated with a) O3 at -78° C followed by Zn and H2O and then with b) O3 at -78° C followed by H2O2. H3C H C C CH2CH3 H Write down the products that would form in each case. 9 Dr. V.O. Nyamori (First Year Chemistry Co-ordinator) 9. Write down the reagents and reaction conditions for the following reactions: H H C C CH3 H CH2CH3 H H 3C C H 3C C H H3C CH2CH3 H 3C C O H3C + H3CH2C C O HO + H3CH2C C O C O 10. Write down the structure of the missing substrate in the following reactions: 1. O3, -78oC H3C 1. O3, -78oC 2. H2O2 C O H 2. Zn, H2O H3C + H3CH2C H3C HO 10 HO C O + H3CH2C C O C O Dr. V.O. Nyamori (First Year Chemistry Co-ordinator) CHEM 120: ORGANIC CHEMISTRY: WORKSHEET 5 Some of the objectives Be able to recognise when an oxidation or a reduction occurred by looking at the substrates and the products of the reaction. You must know the oxidising and reducing agents described in the module and what substrates they will oxidise or reduce as well as what products will be formed in each case. Problems 1. For each of the following reactions, suggest suitable reagents that could be used. Indicate whether the reaction is an oxidation or a reduction reaction. CH3CH2CH2OH CH3CH2C CH3CH2CHOH CH3CH2C H3C H3 C CHCH2OH CH3CH2C OH O CH3 H3 C O H3 C O C CH3 O CHC H CH3CH2CH2OH OH OH H2 C CH3CHCH3 CHCH3 11 Dr. V.O. Nyamori (First Year Chemistry Co-ordinator) 2. Write down the products for the following reactions. LiAlH4 CH3CH2C O H CrO3/H+ H2/Pd H2O/H+ CH3CH CHCH3 Br2 HCl H2/Lindlar's catalyst H3C C H2/Pd C CH3 12 Dr. V.O. Nyamori (First Year Chemistry Co-ordinator) CHEM 120: ORGANIC CHEMISTRY: WORKSHEET 6 Some of the objectives You must know what general elimination reactions and what SN1 and SN2 reactions stand for. How many molecules are involved in the ratedetermining step of each of these SN1 and SN2 reactions. You must know the mechanisms for SN1 and SN2 reactions. You must know on what substrates each of these reactions can occur and what mechanism a strong or a weak base would favour. Be able to explain why SN1 mechanisms cannot occur for primary alkyl halides but can occur for secondary and tertiary alkyl halides. Know how (a) the carbocation and (b) an electronegative atom affect the acidity of the alpha hydrogen and what the consequences of this are. Be able to identify the nucleophile, the electrophilic centre and the leaving group in a substitution reaction. Be able to determine which of two groups is the better base and be able to predict whether a substitution reaction will occur or not. If a reaction can occur, you must be able to predict the product. For nucleophilic substitution reactions, you must be able to predict when inversion of configuration takes place and when retention of configuration takes place. Problems 1. Write down the following elimination reactions and predict the product in each case. CH3CH2CH2Br NaOCH2CH3 H 2O CH3CHCH3 Br 13 Dr. V.O. Nyamori (First Year Chemistry Co-ordinator) NaOCH2CH3 CH3CH2CHCH2CH3 Br Br H2O CH3CH2C(CH3)2 H2O CH3CH2CH2Br 2. Write down SN2 mechanisms for the following reactions: CH3Cl NaOH + CH3CH2Cl + NaNH2 3. Draw the transition state for the reactions in 2 above. 4. How many reactants are involved in the formation of the reaction intermediate in (a) an SN1 type reaction; (b) an SN2 type reaction? 5. Which of the following reactants will be able to undergo SN1 type reactions? Give reasons for your answer. (a) CH3CH2Cl (b) CH3CH(CH3)Cl (c) CH3C(CH3)2Cl (d) (CH3)3CCH2Cl 6. Write down the products of the following substitution reactions. 14 Dr. V.O. Nyamori (First Year Chemistry Co-ordinator) NaBr NaOCH3 CH3OH + CH 3CH2Br + CH3CH2NH2 + CH3CHCl CH3 7. Indicate which of the products in 6 above would occur with retention of configuration. Explain why. 15 Dr. V.O. Nyamori (First Year Chemistry Co-ordinator) CHEM 120: ORGANIC CHEMISTRY: WORKSHEET 7 Some of the objectives You must know why carboxylic acids, alcohols and terminal alkynes are weak acids and the consequences this has in organic reactions. Be able to predict when a strong base is required to remove the hydrogen of a weak acid. Be able to explain why alcohols and amines are bases in organic chemistry and what consequences this has for organic reactions. You must know why protonating the oxygen in alcohols leads to substitution reactions whereas protonating the nitrogen in amines does not. Problems 1. In which of the two molecules below would a strong base be needed to remove the proton. Explain your answer. OH (CH3)3C OH pKa = 18 pKa = 10 2. Add reagents to carry out the following reaction: CH3CH2Br CH3C CCH2CH3 3. How could the following molecule be synthesised from the given substrate? Write down reactions to show your answer. HC H3C CH CHC CCH2CH3 H3C 16 Dr. V.O. Nyamori (First Year Chemistry Co-ordinator) 4. Verify that trifluoracetic acid (pKa 0.2) is a stronger acid than HF (pKa 3.2). O F3CC OH trifluoracetic acid 5. Which of the following molecules would be a better nucleophile, CH3NH2 (pKa of CH3NH3+ is 10.7) or CH3OH (pKa of CH3OH2+ is -2.5)? 6. Would ethanol react with sodium ethoxide under neutral conditions? If not, explain why, and suggest what can be done to make the reaction work. 17 Dr. V.O. Nyamori (First Year Chemistry Co-ordinator)