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c Chemistry 2440 Fall (Loader) Version 1 Test # 2 [50 Marks Total] Name: _____________________ October, 22nd 2004 MUN #: ______________________ 50 minutes Do not remove this cover sheet from your paper! DO NOT OPEN THIS PAPER UNTIL YOU ARE TOLD THAT YOU MAY DO SO. Marks QUESTIONS VALUE 1 18 2 16 3 16 Total 50 -1- MARKS CHEMISTRY 2440 [MARKS] 1. (a) Give the correct IUPAC name for each of the following compounds. CH3 (i) CH H2C C CH3 O CH H2C 3,6-dimethyloctan-4-one CH3 CH3 CH3 O (ii) CH2 H H3C 2-methyl-4-oxopentanal O [10] (iii) (CH3CH2)2CHCH2CH(CH3)COOCH2CH2CH3 propyl 4-ethyl-2-methylhexanoate O (iv) Cl 3-chlorobenzaldehyde C H O (v) OH HO O 4-methylheptanedioic acid CH3 (b) The compound 4-hydroxypentanal can form a hemiacetal. Draw the structure for 4-hydroxypentanal and the intramolecular hemiacetal. H H3C O OH 4-hydroxypentanal H3C H O OH 5-methyltetrahydrofuran-2-ol [3] [5] (c) Explain how you could use a chemical test to distinguish between two test tubes, one containing aqueous propanone, and the other propanal. (Make sure that you show how the test works and give chemical reactions as needed). Propanone (acetone) is CH3COCH3 and propanal is CH3CH2CHO. The aldehyde can be easily oxidized further to the caboxylic acid while propanone is not easily oxidized. The Tollens’ Test for aldehydes makes use of this difference in properties. (Tollens’ reagent is made by adding sodium hydroxide to silver nitrate solution to give a precipitate of silver hydroxide and then redissolving the silver hydroxide in ammonia solution giving a basic solution of Ag(NH3)2OH containing silver(I).) Tollens’ reagent is an oxidizing agent which itself becomes reduced to give metallic silver (formed as a silver mirror on the sides of the test-tube) when it reacts with the aldehyde but does not react with the ketone. The reaction is CH3CH2CHO + Ag+ NH 3 , H 2 O, OH − → CH3CH2COOH + Ag (formed as a silver mirror) In this case the carboxylic acid would be formed as the sodium salt. -2- CHEMISTRY 2440 2. (a) Use the information provided to draw the structure of the described compound. OH (i) Ferulic acid (common name) is widely distributed in plants and is used a food preservative. The HO name given to ferulic acid in the reference book is 3-(4-hydroxy-3-methoxyphenyl)-2-propenoic acid. O O [8] (ii) (iii) Ethyl amyl ketone (common name) is an important organic solvent that is narcotic in high concentrations. The name given to ethyl amyl ketone in the reference book is 5-methyl-3-heptanone. CH3 O CH3 CH3 CH3 Ethchlorvynol (common name) is a sedative and hypnotic that can be addictive. The name given to ethchlorvynol in HC the reference book is 1-chloro-3-ethylpent-1-en-4-yn-3-ol. OH Cl CH3 (iv) Propyl gallate (common name) is used as an antioxidant for foods, fats, oils, ethers, etc. The name given to propyl gallate in the reference book is propyl 3,4,5-trihydroxybenzoate. O O CH3 HO OH OH (b) Elenolide (common name) is extracted from the fruits, bark and leaves of the olive tree (Olea europaea). O H3C alkene a (ii) CH3 d e [4] c O O (i) aldehyde O lactone [4] b H O ester alkene On the diagram above circle and name the functional groups in the molecule Write a paragraph describing two different chemical properties or reactions that you would expect of elenolide Since the compound is and aldehyde it should be easily oxidized using a dilute solution of potassium dichromate in sulfuric acid. The orange colour of the dichromate ion will be replaced by the green colour of the chromium-3 ion. The aldehyde group will be oxidized to the carboxylic acid group. Similarly, it would give a silver mirror with Tollens test. Since the compound is an alkene it should decolourize a yellow solution of bromine in carbon tetrachloride to give a colourless solution of the dibromo compound. The bromine adds across a double bond to give a dibromo compound. -3- CHEMISTRY 2440 3. (a) Fill in the blanks in the following reactions with the structure(s) of the missing reactant(s) and/or product(s). Where indicated, give the reaction conditions. CH3 (i) CH3 O H3C CH2 CH C CH3 + CH2 O CH H3C NaOH(aq) - H3C CH2 + O Na CH2 CH CH2 C + O OH CH H3C CH2 CH3 (ii) + + HBr OH [10 ] H2O Br (iii) H2SO4/140 oC 2 CH 3 CH 2 CH 2 OH CH3CH2CH2OCH2CH2CH3 (reaction conditions) (an alcohol) (iv) CH3CH2CH2CHO + Ni catalyst H2 CH2CH2CH2OH (v) CH2 H2C [3] CH2 C CH (b) CH3 OH o H2SO4/180 C CH2 H2C K2Cr2O7/H+(aq) CH3 CH CH2 C O Explain why aldehydes and CH3 ketones have lower boiling points than the alcohols of similar structure and molar mass. Aldehydes, ketones and alcohols such as propanal, CH3CH2CHO; propanone, CH3COCH3, and 1-propanol, CH3CH2CH2OH are all liquids at room temperature. When a liquid boils the intermolecular forces that hold the molecules in the liquid phase must be overcome to allow the molecules to enter the vapour phase. The stronger the intermolecular forces (for similar molecules) the higher the boiling point. All three of the examples given above are polar molecules so the intermolecular forces are London dispersion forces and dipole-dipole interactions. However, the alcohol is also able to hydrogen bond to other alcohol molecules due to the presence of the -OH group and this is an additional strong intermolecular force that must be overcome when the liquid boils. This leads to the alcohol having a higher boiling point than the similar mass aldehyde and ketone. (c) solution, two layers form, as the ethyl benzoate insoluble in the aqueous sodium hydroxide. If the mixture of ethyl benzoate and aqueous sodium hydroxide is allowed to stand for an hour or so a homogeneous solution forms. Has the ethyl benzoate dissolved? Explain. The ethyl benzoate has not dissolved but has reacted with the sodium hydroxide to give water soluble products. The ethyl benzoate is slowly saponified by the base to give sodium benzoate and ethanol, both of which are water soluble and thus form a homogeneous solution. The reaction is: O O C O CH2 C CH3 + - + O Na NaOH(aq) [3] -4- + OH CH3CH2