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 displayed by transition element complexes.

(b)[1]

The complexes $[\text{Pt}(\text{NH}_3)_2\text{Cl}_2]$ and $[\text{Pt}(en)_2]^{2+}$ share the same geometry around the metal ion. $[\text{Pt}(\text{NH}_3)_2\text{Cl}_2]$ can form two stereoisomers, while $[\text{Pt}(en)_2]^{2+}$ has only one possible arrangement. State the geometry around the metal ion.

(c)[3]

The complex $[\text{Cr}(en)_3]^{2+}$ has two stereoisomers, whereas the complex $[\text{Cr}(\text{OCH}_2\text{CH}_2\text{NH}_2)_3]^{3-}$ has four stereoisomers. Complete the three-dimensional diagrams in Fig. 2.1 so that the four stereoisomers of $[\text{Cr}(\text{OCH}_2\text{CH}_2\text{NH}_2)_3]^{3-}$ are shown. Show the ligand $-\text{OCH}_2\text{CH}_2\text{NH}_2$ using the O-N linkage provided.

(d(i))[3]

Suggest the mechanism for step 1 in the reaction of oxirane with ammonia shown in Fig. 2.3. Include every relevant curly arrow, lone pair of electrons, charge and partial charge. 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 formation of by-product E can be minimised.

(d(iii))[2]

Compound F, $\text{C}_4\text{H}_9\text{NO}$, is obtained from by-product E, $\text{C}_4\text{H}_{11}\text{NO}_2$, when it reacts with concentrated $\text{H}_2\text{SO}_4$. Compound F is a saturated, basic organic compound. Suggest a structure for compound F. State the type of reaction that E undergoes 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: Optical isomerism AND geometrical (cis-trans) isomerism

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