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Halogenoalkanes

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Introduction

Halogenoalkanes Aim The aim of the plan is to investigate and identify a suitable nucleophilic substitution reaction of a halogenoalkane. Also to plan an experiment that compares how the rate of displacement reaction of the halides differs in respect to the bonds between the carbon and the halogen. What are halogenoalkanes? Halogenoalkanes are compounds that have replaced one or more hydrogen atoms with a halogen atom such as fluorine, chlorine, bromine or iodine in an alkane. Halogenoalkanes are also known as haloalkanes or alkyl halides. These compounds are based on the bond between the carbon and the halogen; so in order to investigate the nucleophilic substitution reaction we need to consider bond strengths, bond lengths, electronegativity of the halogens and the carbon atoms and the boiling points for the bond between carbon and halogen to be broken. This is because the nucleophilic substitution reaction involves in breaking these bond so that it can take place. What is a nucleophilic substitution reaction? The most common type of reaction found in halogenoalkanes is a substitution reaction. ...read more.

Middle

This makes it difficult for us to handle. So in this experiment we only work with chlorine, bromine and iodine. The chemical that is going to provide the nucleophile is ethanol. Hydrolysis of halogenoalkanes During hydrolysis a bond in the halogenoalkanes is broken and also an OH bond in the nucleophile. The OH is the nucleophile that is going to substitute the halogen on the alkane. This results in an alcohol. We are looking at the hydrolysis of 1-chlorobutane, 1-bromobutane and 1-iodobutane. The nucleophilic substitution reaction of these halogenoalkanes require the carbon-halogen bond to be broken. "X" Represents a halide "R" Represents alkanes R-X + OH- --> R-OH + X- The harder it is to break these bonds the slower the rate of reaction is going to be. The tables above aid in distinguishing which carbon-halogen bond will be broken easily amongst chlorobutane, bromobutane and iodobutane. Bond length increases down the group so iodine has the longest bond length. Bond strengths decrease down the group and iodine has the lowest value. ...read more.

Conclusion

Make sure that all the readings are made below the meniscus. Procedure 1. Set-up 3 test tubes and label them A, B and C and heat water in a beaker over the Bunsen burner. 2. In each test tube place 1cm3 of ethanol using the 3cm3 pipette and 1cm3 of silver nitrate. 3. Place all the test tubes into a beaker that has warm water about 40oC. Use the thermometer to determine the temperature of the water. 4. When the contents in the test tube reach the temperature of the water add 3 drops of 1-chlorobutan into test tube A, 1-bromobutane in test tube B and 1-iodobutane in c. 5. Place the test tube stopper on the test tube. Shake the contents of the test tube, place it back in the beaker with the stopper on loosely. Then start the stop clock. Record the time as soon as a precipitate is visible. 6. The same must be done for 1-bromobutane and 1-iodobutane. 7. The experiment must be repeated three times so that the average reading can be taken for it to be more accurate. ...read more.

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