Chemistry 9701 · AS & A Level · Hydrocarbons

Hydrocarbons — practice question

T is one isomer with formula $\text{C}_6\text{H}_{12}$.
(a)[1]

State the name of T.

(b)[1]

Draw the skeletal formula of a structural isomer of T that exhibits cis-trans (geometrical) isomerism.

(c(i))[1]

On the diagram, show the orbitals that represent the pi ($\pi$) bond also present in T.

(c(ii))[1]

State the hybridisation of the two carbon atoms between which the pi ($\pi$) bond forms.

(d(i))[1]

Give the reagent(s) and conditions for reaction 1.

(c)

Every carbon atom in T forms a sigma ($\sigma$) bond to at least one other carbon atom, as shown.

(d)

A reaction scheme beginning with T is shown. Reaction 2 takes place in the presence of a catalyst; knowledge of the mechanism for this reaction is not required.

(d(ii))[2]

State and explain how 2,4-dinitrophenylhydrazine (2,4-DNPH) can be used to detect V as the product of reaction 2.

(d(iii))[2]

The progress of reaction 2 can be followed using infrared spectroscopy. The absorption due to O-H bonds is always present because water is used as the solvent. Identify two absorptions, and the bonds responsible for them, whose appearance changes significantly during the reaction.

(e)

V is involved in a wide range of organic reactions. Some reactions of V are shown.

(e(i))[1]

V and W are colourless and soluble in water. State what you would observe in reaction 3.

(e(ii))[1]

Reaction 3 is a redox reaction. Identify which reactant is reduced in this reaction.

(e(iii))[1]

Construct an equation for reaction 4. Use $[\text{H}]$ in the equation to represent an atom of hydrogen from NaBH$_4$. $\text{C}_6\text{H}_{12}\text{O} + \ldots$

(e(iv))[2]

X is a mixture of two optical isomers. Draw the two optical isomers in the boxes provided.

(e(v))[1]

Both optical isomers of X can be dehydrated to give a single product, Y. Give the reagent(s) and conditions required for reaction 5.

(e(vi))[1]

Y can form an addition polymer Z. Draw one repeat unit of Z.

(e(vii))[1]

Reaction 6 does not occur rapidly at room temperature. Suggest why this is the case.

Worked solution & mark scheme

This 17-mark question has a full step-by-step worked solution and mark scheme. One marking point: (2,3)-dimethylbut-2-ene

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