2nd Organic chemistry xperiment.docx

4 cap test tube a to e loosely and place it into a

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4. Cap test tube A to E loosely and place it into a test tube holder. 5. Place the test tube holder into a water-bath and heat at 60°C for 5 minutes. 6. After 5 minutes, quickly add 1cm³ of aqueous silver nitrate solution from test tube E to test tube A to D by using measuring cylinder and start the stopwatch. 7. Cap the test tube A to D loosely and place it into water-bath again. 8. Shake the 4 test tubes once to mix the contents. 9. Observe and record the result into table when cloudy precipitate first appears. Results Reaction Time for observation
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precipitate to appear(minute) A 1-chlorobutane 11 Solution become cloudy and white precipitate is formed B 1-bromobutane 6 Solution become very cloudy and cream precipitate is formed C 1-iodobutane 0.1 Solution become yellowish and yellow precipitate is formed D Chlorobenzene - No reaction Discussion From the experiment, we are added aryl alkane and alkyl alkane with alcohol to substitute the halide group to alcohol by nucleophilic substitution which is S N 2 reaction which both molecules involve in transition state of the rate determining step. This is due to the productive collision occur while the alcohol group hit the carbon on the opposite site of the leaving group. This mechanism show that alkyl halide and alcohol group come together in the transition state of the one step reaction. Therefore, increase idle one of their concentration will make their collision more probable. Thus, the reaction following the second order kinetics and the product of alcohol and halide ion is produced. Based on the result, we know that halogenoalkanes can react with silver nitrate solution (Argentum ion, Ag ) and form precipitate. However, there is no reaction between halogenoarenes (chlorobenzene) and silver nitrate solution. This is due to halogenoalkanes is reactive but the halogenoarenes is not reactive. The carbon-halogen bond in halogenoalkanes is weak but the carbon-halogen bond in halogenoarenes is strong. Weaker bond will be broken easier to form halide ion to react with silver ion(Ag ) to form precipitate. The benzene ring of chlorobenzene is strong enough because of the pie bond overlapping so that the bond will not break easily and the distance between two nuclei is closer compare with others. The extra strength of the chlorobenzene is because of There is an interaction between one of the lone pairs on the chlorine atom and the delocalised ring electrons, and this strengthens the bond. Other than that, the repulsion of the incoming electron also face great repulsion of the chlorobenzene own electron. As an example, if the halogen atom is attached to a benzene ring, the incoming hydroxide ion is going to be faced with the delocalised ring electrons above and below that carbon atom. The negative hydroxide ion will simply be repelled. Thus, the covalent bond of the of the benzene ring. However in order to allowed nucleophilic substitution of alcohol took place, the benzene ring of chlorobenzene must be broken which only able to break upon 200°C and 200 atmospheres.
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