Chemistry Report 4 - College Chemistry(250-06 Laboratory...

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College Chemistry (250-06) Tonny, Chan Kar Yu Laboratory Report Group: B1, Student ID: 10297729 Name: Tonny, Chan Kar Yu, Student ID: 10297729 Date of Experiment: 19 th February 2005, Group: B1 Title: Stereochemistry of Butenedioic acid Objective: To study the interconversion of two geometric isomers, maleic acid (cis isomer) to fumaric acid (trans isomers), the differences in physical properties between this pair of cis-trans isomers and determine the stereochemistry of addition of bromine to butenedioic acid. Chemicals and Apparatus: 2 grams of maleic acid, 10 cm 3 of concentrated hydrochloric acid, 10 cm 3 of bromine water 1 , one 50 cm 3 beaker, one 100 cm 3 beaker, one 250 cm 3 beaker, one 10 cm 3 measuring cylinder, one piece of spatula, one piece of water glass, one glass rod, a few pieces of filter paper, a set of Buchner funnel, a filter flask with side tube, three glass capillary tubes, a set of melting point apparatus, one long hollow glass tubing, one electronic balance, one heater and the oven Background: Stereochemistry is always encountered throughout organic chemistry. And stereochemistry isomerism can be divided into two classes, geometrical isomerism and optical isomerism. Although these categories are not mutually exclusive, it is not uncommon to find compounds that exhibit only one or the other of the two types. Most geometrical isomers result from cyclic systems or restricted rotation about double bonds. The preparation of fumaric acid by isomerization of maleic acid and addition of molecular bromine to fumaric acid was illustrated in the experiment. Geometric isomers can be interconverted if the double bond is temporarily converted to a single bond, about which rotation is relatively free. For example, an electrophile adds to the double bond, rotation becomes possible. Loss of the electrophile then regenerates the double bond. If rotation occurred in the intermediate, the result is the other isomer. The result of this kind of transformation is an equilibrium mixture of the cis and trans isomers. Frequently, the trans isomer is more stable, so the equilibrium mixture would contain more of the trans isomer. The greater the difference is in the stability of the isomers, the greater the concentration of the trans isomer will be at equilibrium. 1 The stock solution of bromine water was prepared by dissolving 232.5 g of Br 2 and 187.5 g KBr in water and diluting to about 750 ml. - 1 -
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College Chemistry (250-06) Tonny, Chan Kar Yu Laboratory Report Group: B1, Student ID: 10297729 Maleic acid and fumaric acid are geometric isomers of butenedioic acid. Each of these isomers has its own distinctive properties such as melting point, solubility, density and stability. In part A of the experiment, Maleic acid could be converted to the more stable fumaric acid when heated with hydrochloric acid as Fumaric acid is less soluble in water than maleic acid. The hydrochloric acid served as an acid-catalyst of the reation. Thus, the π bond was broken. Rotation about the sigma bond occurred readily. Loss of a proton could be lead to the formation of either the cis or the trans
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