PRACTICAL IB: ALKENES BROMINATION OF STILBENE INTRODUCTION Alkenes are compounds which contain at least one-carbon-carbo
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- Practical Ib Alkenes Bromination Of Stilbene Introduction Alkenes Are Compounds Which Contain At Least One Carbon Carbo 1 (68.5 KiB) Viewed 43 times
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PRACTICAL IB: ALKENES BROMINATION OF STILBENE INTRODUCTION Alkenes are compounds which contain at least one-carbon-carbon double bond(C=C). One of these bonds is a - bond and the other is a A-bond. Each sigma and pi bond contains two electrons and therefore there are four electrons located between the two carbon atoms of a C=C bond. The C=C bond is thus an electron-rich functional group, and so may be reacted with electrophiles (which are molecules or ions which can accept electrons). Because the electrophiles add to the alkene molecule and non-atoms or groups leave, the overall reaction is known as an electrophilic addition reaction. In these reactions the n-bond of the alkene is broken and two g-bonds (one on each carbon of the original C=C bond) are formed. Note that the C=C bonds in a benzene ring are not as reactive as the alkene C=C bond, and benzene rings do not undergo electrophilic reactions.
Procedure Weigh out 1.0g of stilbene (trans-1,2-diphenylethene) into a 100ml Erlenmeyer flask, add 20ml of ethanoic (acetic) acid and warm gently on the steam bath until dissolved. Then, WORKING IN THE FUME HOODS, add slowly with constant swirling, 2ml of a 20% v/v solution of bromine in acetic acid. Allow the flask to stand for 10 minutes to ensure the reaction goes to completion. Briefly cool the flask in an ice bath, then filter off the product under suction in a Buchner funnel. Wash the crystals with no more than 50ml distilled water, then continue to suck air through the crystals for a few minutes to dry them. When the crystals are dry, weigh them and record the mass obtained. Solvents available for recrystallization are toluene, methanol and acetone. Determine which solvents is most suitable (see recrystallization techniques), and then recrystallize 1.0g of crude product using a minimum of hot solvent. Filter off the recrystallized material and suck dry as before. DO NOT wash the recrystallized product with water. Record the mass of recrystallised product obtained, and determine its melting point. Hand in both your crude and recrystallized product for marking