Stoichiometry and Jigsaw Problems
A student preparing butyl bromide, C4H9Br,  reacts 75.0 g of potassium bromide with 0.500 moles of butyl alcohol, C4H9OH, in the presence of excess H2SO4.

a) What is the theoretical yield of this reaction.

b) What is the actual yield if they isolate 55.0 g of pure C4H9Br? The equation for the reaction is:

     C4H9OH + KBr + H2SO4 -----> C4H9Br + KHSO4 + H2O


2. Bromotoluene (CH3C6H4Br) may be prepared by reacting toluene diazonium sulphate (CH3C6H4N2HSO4) with a mixture of copper(I) bromide and hydrobromic acid. The equation for the reaction is:

CH3H4N2HSO4 + Cu2Br2 + HBr ------>CH3C6H4Br + N2 + Cu2Br2 + H2SO4

How many grams of bromotoluene are formed by reacting 0.400 moles of toluene diazonium sulphate if the yield is 51.5%?


3.  The nitrogen in an amine maybe converted to NH3 which may then be converted into nitrogen gas by the reaction:

2 NH3 + 3 OBr- ----> N2 + 3 H2O + 3 Br-

If a 0.600 g sample of an amine yields 25.0 mL of N2 at STP, what is the percentage of nitrogen in the amine?


4. The structure of substance A, with the formula C5H6O2, has been determined as follows:

a) A gives a yellow precipitate with 2,4-dinitrophenyl-hydrazine but does not react with Tollen's reagent (an aqueous solution of the ion [Ag(NH3)2]+). The infra-red spectrum of A shows a strong absorption around 1700 cm-1 and a strong, broad band around 3300 cm-1. No absorptions were observed between 2700-2900 cm-1. Write the reaction of the active functional group of A with 2,4,-dinitrophenylhydrazine.

b) A reacts with chromic oxide, CrO3, in acid followed by 1 mole of H2 and a platinum catalyst to give B whose formula is C5H6O. The infra-red spectrum of B does not show any absorption around 3300 cm-1, but new bands at 2850 and 2725 cm-1 are now present. B reacts with Tollen's reagent to give a silver mirror. Write the reaction of the active functional group of B with the Tollen's reagent.

c) An excess of H2 over a nickle catalyst is added to a solution of A. Upon workup, the compound C (C6H12O2) is isolated. The infra-red spectrum of C does not show any absorption around 1700 cm-1. There is also a halogenation of C to D

i) Write the reactions of the active functional groups of A with H2/Ni.

ii) What is the gas which was evolved during the reaction?

d) The ozonolysis of D, followed by a mild reductive workup of the reaction mixture, gives a mixture of three compound E, F, and G in equal molar amounts. The three compounds are then separated and it is found that:

i) E is identical to the product of the reaction between 2-propanol and an acidic aqueous solution of chromic acid, CrO3.

ii) An aqueous solution of F gives methanol upon reaction with NaBH4.

iii) The oxidation of G yields ethanedioic acid.

Using the information given, deduce the structures of compounds A to G.


5. A hydrocarbon with the empirical formula C11H20 takes up two moles of hydrogen during catalytic hydrogenation and yields the following products in the course of oxidation with ozone and the cleavage reaction (ozonolysis); plus further oxidation yields:

       2-butanone (A), propanoic acid (B) and butandioic acid or amber acid (C)
 


a. Write down the constitutional formulas of the products A-C.

b. From which hydrocarbon (constitutional formula, systematic name) are these products formed?

c. Name the compounds formed by complete hydrogenation (a) and addition of bromine (b) respectively.

d. How many asymmetric carbon atoms does the bromine compound contain?


6. An oxygen compound, substance A has the empirical formula C5H12O. When mixed with a CrO3 solution A yields the oxidation product C5H10O (A1) which reacts with phenylhydrazine (A2) but does not reduce Fehling solution. Moreover A can be dehydrated to a hydrocarbon C5H10 (A3) by H2SO4. The oxidation (ozonolysis) of this hydrocarbon gives acetone (2-propanone, A4) and acetic acid (ethanoic acid, A5).

1. Which classes of compounds do the substances A1 to A5 belong to?

2. Which substances are dealt with? Write down the constitutional formula and the IUPAC names of A.
7. Compound A has the empirical formula C6H10. Infra red spectral vibrations of 2260-2100 are very strong in this molecule. Hydrogenation of this molecule with exactly 2 moles of hydrogen gas yields compound B which has the empirical formula C6H14.

Compound A undergoes ozonolysis to give only 1 product called compound C. It gives a strong i.r. spectrum vibration at 3300-2500 and 1725-1700. It also gave i.r. spectrum vibrations at 3750-3200 and 1700-1680. Blue litmus paper turns red in compound C.

Compound C reacts with ethanol in concentrated H2SO4 to give compound D.

Compound D has a fruity smell and gives strong i.r. spectral vibrations at 1200-1150. The empirical formula of D is C5H10O2.

Draw all the formula for compound A thru D.
8. An optically active mole, M, C10H20O, on treatment with ozone followed by Zn and water yielded two products. A, C4H8O, and P, C6H13O2.

Compound A  upon catalytic hydrogenation gave an alcohol B as product. When B was heated with conc sulphuric acid, two isomeric compounds, C and D of formula C4H8 were formed. Both C and D on treatment with ozone followed by Zn and water gave CH3CHO as the only product.

Compound P,which was optically active, reacted with cold KMnO4 P, C6H13O2.  When heated with concentrationed acid P gave R, C6H10O, which on treatment with ozone followed by zinc and water gave S, C4H6O2 and T, C2H4O. Instrumental analysis of S indicated that it contained two CH3 groups.

a) How many sites of unsaturation are present in M, and what functional groups might it contain?

b) Suggest structural formulas for compounds A-D consistent with the above fats, showing your reasoning briefly but clearly.

c) Suggest structural formulas for compounds P- T, again clearly showing your reasoning.

d) Give the possible structure for M.
9.  An organic compound A has the empirical percentages, 83.60% C and 16.40% H, reacts with metallic sodium. It is not oxidised under normal conditions but it forms the monochloro compound B when treated with concentrated hydrochloric acid. The vapour density of B is 3.770 time greater than that of oxygen. B gives the compound C when reacted with an alcoholic solution of sodium hydroxide. When C is treated with ozone followed by hydrogen in the presence of a catalyst, D is the only product formed. Give the structural formulae of compounds A-D.