Chemistry 9701 · AS & A Level · Chemistry of transition elements

Chemistry of transition elements — practice question

(a)[1]

Some transition element complexes are capable of stereoisomerism. State two kinds of stereoisomerism shown by transition element complexes.

(b)[1]

The complexes $[\text{Pt}(\text{NH}_3)_2\text{Cl}_2]$ and $[\text{Pt}(\text{en})_2]^{2+}$ have an identical geometry (shape) around the metal ion. $[\text{Pt}(\text{NH}_3)_2\text{Cl}_2]$ appears as two stereoisomers whereas $[\text{Pt}(\text{en})_2]^{2+}$ has only one possible arrangement. State the geometry around the metal ion.

(c)[3]

The complex $[\text{Cr}(\text{en})_3]^{2+}$ has two stereoisomers whereas $[\text{Cr}(\text{OCH}_2\text{CH}_2\text{NH}_2)_3]^{3+}$ has four stereoisomers. Complete the three-dimensional diagrams in Fig. 2.1 so that they display the four stereoisomers of $[\text{Cr}(\text{OCH}_2\text{CH}_2\text{NH}_2)_3]^{3+}$. Show the ligand $-\text{OCH}_2\text{CH}_2\text{NH}_2$ exactly as given.

(d(i))[3]

Suggest the mechanism for step 1 of the reaction of oxirane with ammonia in Fig. 2.3. Show all relevant curly arrows, lone pairs of electrons, charges and partial charges. Draw the structure of the organic intermediate.

(d(ii))[1]

A small quantity of by-product E, shown in Fig. 2.4, is formed in the reaction shown in Fig. 2.2. Suggest how the production of by-product E can be reduced.

(d(iii))[2]

Compound F, $\text{C}_4\text{H}_9\text{NO}$, may be made from the reaction of by-product E, $\text{C}_4\text{H}_{11}\text{NO}_2$, with concentrated $\text{H}_2\SO_4$. Compound F is a saturated, basic organic compound. Suggest a structure for compound F. State the type of reaction undergone by E to form F.

Worked solution & mark scheme

This 11-mark question has a full step-by-step worked solution and mark scheme. One marking point: geometrical / cis-trans together with optical isomerism

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