CHM 215 Eksamen / Examination

Transcription

1 CHM 215 Eksamen / Examination Fakulteit Natuur- & Landbouwetenskappe Departement Chemie 09/06/2009 Tyd / Time: 150 min Punte / Marks: 100 (+2) INTERNE EKSAMINATRE / INTERNAL EXAMINERS: EKSTERNE EKSAMINATRE / EXTERNAL EXAMINERS: Dr S Bauermeister Dr M Rademeyer Dr L van der Merwe Dr M Potgieter Prof P H van Rooyen Finale Punt: / Final Mark: Voorletters & Van: / Initials & Surname: Studentenommer: / Student Number: Handtekening: / Signature: Kontaktelefoonnommer: / Contact telephone number: Beantwoord beide Afdelings direk op die vraestel. Indien die antwoord nie in die gegewe spasie verskaf word nie, moet die nuwe posisie duidelik aangetoon word. Answer both Sections directly on the question paper. If the answer is not given in the space provided, please clearly indicate location. AFDELING 1: RGANIESE CHEMIE / SECTIN 1: RGANIC CHEMISTRY [75 (+2)] Vraag 1 / Question 1 (6 punte / marks) 1.1 Benaam die volgende verbindings soos gespesifiseer: Name the following compounds as specified: a) n Volledige IUPAC sistematiese naam: (3) A complete IUPAC systematic name: (3) CH Page 1 of 10

2 b) n Algemene (triviale) naam: (1) / A common (trivial) name: (1) 1.2 Teken n lynstruktuur van n δ-laktoon: (2) Draw a line structure of a δ-lactone: (2) Vraag 2 / Question 2 (11 punte / marks) 2.1 Verduidelik die volgende waarnemings deur van reaksies, meganismes en kort beskrywings gebruik te maak: Waarneming 1: Wanneer t-butielbromied met natriummetoksied (Na + - CH 3 ) in metanol behandel word, verander die tempo van t-butielmetieleter ((CH 3 ) 3 CCH 3 ) vorming nie noemenswaardig soos die konsentrasie van die natriummetoksied verhoog word nie. Waarneming 2: Verhoging in die natriummetoksiedkonsentrasie veroorsaak egter wel n merkbare verhoogde tempo waarteen die t-butielbromiedsubstraat se konsentrasie afneem en uit die mengsel verdwyn. [Wenk: Kompeterende reaksies vind plaas.] (6) Write reactions, mechanisms and brief descriptions to explain the following observations: bservation 1: When t-butyl bromide is treated with sodium methoxide (Na + - CH 3 ) in methanol, the rate of t-butyl methyl ether ((CH 3 ) 3 CCH 3 ) formation does not change appreciably as the concentration of sodium methoxide is increased. bservation 2: However, increasing the concentration of the sodium methoxide causes a marked increase in the rate at which the concentration of the t-butyl bromide substrate decreases and disappears from the mixture. [Hint: Competing reactions occur.] (6) Page 2 of 10

3 2.2 Maak gebruik van strukture, eenvoudige skematiese voorstellings en kort beskrywings om die volgende tendense te verduidelik: (5) Make use of structures, simple schematic representations and brief descriptions to explain the following trends: (5) I >> F In etanol In ethanol Nukleofilisiteit in S N 2 reaksies Nucleophilicity in S N 2 reactions I << F In dimetielsulfoksied (DMS) In dimethyl sulfoxide (DMS) Page 3 of 10

4 Vraag 3 / Question 3 (12 punte / marks) 3.1 Rangskik die volgende verbindings in volgorde van toenemende suursterkte. Verduidelik jou antwoord deur onder andere van strukture gebruik te maak. (6) Arrange the following compounds in order of increasing acidity. Use structures, among others, to explain your answer. (6) CF 3 CH; CH 4 ; CH 3 CH; CH 3 CH 2 H A B C D rde van toenemende suursterkte: / rder of increasing acidity: Verduideliking: / Explanation: Page 4 of 10

5 3.2 a) Hoe sal jy 1,3,5,7-siklononatetraeen omskakel na n aromatiese verbinding? Skryf n reaksievergelyking vir die omskakeling. (2) How would you convert 1,3,5,7-cyclononatetraene to an aromatic substance? Write a reaction equation for the conversion. (2) 1,3,5,7-siklononatetraeen 1,3,5,7-cyclononatetraene b) Analiseer die produk wat in bostaande reaksie gevorm sal word en verduidelik volledig waarom jy dit as aromaties beskou. (4) Analyse the product formed in the above reaction and explain why you would consider it to be aromatic. (4) Vraag 4 / Question 4 (25 punte / marks) 4.1 Anisool (metoksibenseen of fenielmetieleter) (C 6 H 5 CH 3 ) is meer reaktief as benseen ten opsigte van elektrofiele aromatiese substitusie. Gebruik lynstrukture, meganismes, resonans- en induktiewe effekte met kort beskrywings om beide die reaktiwiteit van anisool asook die substitusiepatroon van die produkte vir die chlorinering van anisool te verduidelik. (10) Anisole (methoxybenzene or methyl phenyl ether) (C 6 H 5 CH 3 ) is more reactive than benzene with regard to electrophilic aromatic substitution. Use line structures, mechanisms, resonance and inductive effects with a short description to explain the reactivity of anisole as well as the substitution pattern of the products for the chlorination of anisole. (10) Page 5 of 10

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7 4.2 Teken n lynstruktuur van n xileen konstitusionele isomeer wat na brominering slegs een monogebromineerde derivaat lewer. (2) Draw a line structure of a xylene constitutional isomer that gives only one monobromo derivative upon bromination. (2) 4.3 Die volgende reaksie sal nie verloop soos aangedui nie. Verduidelik waarom nie en toon aan hoedat die sintese gewysig moet word om die vereiste produk (vanaf n mono-gesubstitueerde benseen) te verkry (4). The following reaction will not proceed as indicated. Explain why not and show how the synthesis must be modified to obtain the desired product (from a monosubstituted benzene). (4) H 1. 2 MgCl eter / ether H 2 HMgBr 2. H a) Stel n multi-stap sintese voor vir verbinding E met anilien (C 6 H 5 NH 2 ) en etanol as enigste organiese uitgangstowwe. Neem aan dat oplosmiddels en enige ander anorganiese reagense beskikbaar is. Toon alle stappe volledig met reagense en organiese produkte. Geen meganisme of stereochemie word vereis nie. (7) Propose a multi-step synthesis for compound E starting from aniline (C 6 H 5 NH 2 ) and ethanol as the only organic starting materials. Assume that solvents and any other inorganic reagents are available. Show all steps complete with reagents and organic products. No mechanism or stereochemistry is required. (7) NH 2 H 3 S E Page 7 of 10

8 b) Benaam verbinding E in vraag 4.4 a). (2) Name compound E in question 4.4 a). (2) Vraag 5 / Question 5 (23 punte / marks) 5.1 a) Rangskik die volgende verbindings in toenemende stabiliteitsorde: (2) Rank the following compounds in increasing order of stability: (2) H 2 N Cl F G H I b) Gebruik onder andere, strukture om jou keuse in a) te verduidelik. (4) Use among others, structures to explain your choice in a). (4) Page 8 of 10

9 5.2 Die meganisme van verseping van esters volg die patroon van alle asielsubstitusiereaksies. Skryf n stapsgewyse meganisme vir die verseping van verbinding F (in vraag 5.1 a)) met 18 -gemerkte hidroksiedanioon, H 18 in H 18 2 om te bepaal watter produk(te) met die isotoop gemerk sal wees wanneer die reaksie voltooi is. Gebruik lynstrukture en geboë pyle om elektron beweging aan te dui. (6) The mechanism for the saponification of esters follows the pattern of all acyl substitution reactions. Write a stepwise mechanism for the saponification of compound F (in question 5.1 a)) with 18-labelled hydroxide anion, H 18 in H 18 2 to determine which product(s) will be isotopically labelled after completion of the reaction. Use line structures and curved arrows to show movement of electrons. (6) 5.3 Stel n sintese voor vir verbinding J vanuit 2-metielpropanoësuur. Meer as een stap is betrokke. Neem aan dat oplosmiddels en enige ander reagense beskikbaar is. Toon alle stappe volledig met reagense en organiese produkte. Geen meganisme of stereochemie word vereis nie. (6) Propose a synthesis for compound J starting from 2-methylpropanoic acid. More than one step is involved. Assume that solvents and any other reagents are available. Show all steps complete with reagents and organic products. No mechanism or stereochemistry is required. (6) N J Page 9 of 10

10 5.4 Verskaf die ontbrekende reagense en lynstrukture van die produkte (K - N) in die volgende reaksies. Een alfabetiese letter mag meer as een reagens/produk verteenwoordig. Geen meganisme of stereochemie word vereis nie. (5) Provide the missing reagents and line structures of the products (K - N) for the following reactions. ne alphabetical letter may represent more than one reagent/product. No mechanism or stereochemistry is required. (5) K L Br 1. Mg M In 2. C 2 3. H 3 N K = L = M = N = Punte Afdeling 1 / Marks Section 1 Page 10 of 10