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reaction of halogenoalkanes

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Introduction

Rates of reaction of halogenoalkanes Introduction In my experiment I will be comparing how the rate of displacement of the halide ion in a nucleophilic substitution reaction varies with respect to the C-X bond(where X is a halogen- either Cl, Br, or I). Firstly, I will show how nucleophilic substitution works with the equation below: C2H5Br + H2O � C2H5OH + HBr Bromoethane water ethanol hydrogen bromide In the above equation the OH� from the water acts as a nucleophile. Nucleophiles have a spare pair of electrons and so are attracted to the positive carbon atom in the bromoethane: H H ? ? H-C-C-Br OH� (you can also see that the bromoethane is a primary ? ? structure as it has two hydrogen atoms bonded to the H H main carbon atom) This nucleophile forms an intermediate and so the carbon has 5 bonds (10 electrons) in its outermost shell. H H OH ? ...read more.

Middle

However if the polarity of the bonds is considered, the halogens are more electronegative than carbon so the polarity will be C - X� (where X is a halogen). These bonds are attacked by nucleophiles (as in introduction) at the carbon atom. As you go down the group of halogens, their electro negativity decreases (essential as chemistry for OCR). This makes the polarity of the bonds decrease as you go down the group because the difference in charge between the C and X decreases. However, this would predict that Chlorine is the most reactive as it is the most polar, but I predict that iodine is the most reactive because of bond enthalpy, that iodo-compounds have the weakest bonds (essential AS chem. OCR pg 115) Apparatus * Three test tubes and test tube rack * Ethanol (as a solvent) * Water (to provide OH ion) * Measuring cylinder * Safety goggles * Chloroethane, bromoethane and iodoethane( these are primary substrates and good for substitution reactions, if I was to do an elimination I would use tertiary structures) ...read more.

Conclusion

(essential as chemistry for OCR section 6.2.4) * 1cm� of 0.05 mol dm� silver nitrate solution is added to each of the test tubes, a bung put on each and the tubes are shaken and the time taken for the precipitate to form can be recorded using a stop watch. * When the precipitate forms, stop timing. * The precipitate that forms first will have the fastest reaction because, firstly the halogenoalkane reacts with the nucleophile to leave an alcohol (in this case, ethanol) and the halide ions, which will then form precipitates with the aqueous silver nitrate. Precautions Safety glasses must be worn to prevent any mixtures from entering the eye. Care must be taken using ethanol as it is flammable so no naked flames. (Although, the experiment doesn't require heat). Stools and bags must be under desks to prevent tripping up whilst carrying chemicals and hair tied back as to prevent it obstructing sight and getting in chemicals. A lab coat is also essential to prevent spillages onto clothing. ?? ?? ?? ?? Holly Wilkinson 08/05/08 1 ...read more.

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