By examining the structures of the reactant and product, how might you recognize
ID: 917637 • Letter: B
Question
By examining the structures of the reactant and product, how might you recognize that the reaction is likely to be endothermic? Explain clearly. Calculate the number of mmol present in the starting material: 100 mg of 2,3-dibromo-3-phenylpropanoic acid (307.97g/mol). Calculate the mass (in mg) of 3.3 equivalents of KOH, relative to the amount (in mmol) of 2,3-dibromo-3-phcnylpropanoic acid. Do you have enough KOH for the reaction to reach completion? Calculate theoretical yield for the reaction: the mass of the product (in mg) you would expect if you were to obtain 100% yield for this reaction, (phenylpropynoic acid: 146.14 g/mol)Explanation / Answer
a) The reaction can be recognised as an endothermic reaction as the number of sigma bonds broken in the reactant are four and the number of pi bonds formed instead in the product are only two.
b)number of moles = given weight / molar mass= 100x 10-3 g/307.97g/mol = 0.0003247 mol
= 0.3247 mmol
c) We need 3.3 equivalents of KOH for complete reaction. Thus for 0.3247 mmol of reactant we need 3.3 x 0.3247 mmol of KOH = 1.07 mmol of KOH
weight of KOH = 60 mg [1.07 x 56]
d) Assuming 100% yield 0.3247 mmol of reactant gives 0.3247 mmol of product. Thus weight of product =
=0.3247 x146.4mg/mmol = 47.53 mg
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