2,3-dimethylpent-2-ene, $$$\left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}=\mathrm{C}\left(\mathrm{CH}_{3}\right) \mathrm{CH}_{2} \mathrm{CH}_{3}$$$, is treated with cold, dilute $$$\mathrm{KMnO}_{4}$$$. The product of this reaction is treated with an excess of concentrated $$$\mathrm{H}_{2} \mathrm{SO}_{4}$$$ at $$$180^{\circ} \mathrm{C}$$$, giving a mixture of isomeric hydrocarbons with molecular formula $$$\mathrm{C}_{7} \mathrm{H}_{12}$$$. What is the name of one of the isomeric hydrocarbons?

2,3-dimethylpenta-1,2-diene

cis-2,3-dimethylpenta-1,3-diene

2,3-dimethylpenta-1,4-diene

3,4-dimethylpenta-1,3-diene

Chemistry

IGCSE&ALevel

CAIE

Exam No：9701_w17_qp_12 Year：2017 Question No：24

Answer:

Knowledge points:

14.1.1.1 addition of hydrogen to an alkene in a hydrogenation reaction, H2(g) and Pt/Ni catalyst and heat

14.1.1.2 cracking of a longer chain alkane, heat with

14.1.2.1 the complete and incomplete combustion of alkanes

14.1.2.2 the free-radical substitution of alkanes by in the presence of ultraviolet light, as exemplified by the reactions of ethane

14.1.3 describe the mechanism of free-radical substitution with reference to the initiation, propagation and termination steps

14.1.4 suggest how cracking can be used to obtain more useful alkanes and alkenes of lower from heavier crude oil fractions

14.1.5 understand the general unreactivity of alkanes, including towards polar reagents in terms of the strength of the C–H bonds and their relative lack of polarity

14.1.6 recognise the environmental consequences of carbon monoxide, oxides of nitrogen and unburnt hydrocarbons arising

14.2.1.1 elimination of HX from a halogenoalkane by ethanolic NaOH and heat

14.2.1.2 dehydration of an alcohol, by using a heated catalyst

14.2.1.3 cracking of a longer chain alkane

14.2.2.1.1 hydrogen in a hydrogenation reaction, and Pt/Ni catalyst and heat

14.2.2.1.2 steam, catalyst

14.2.2.1.3 a hydrogen halide, HX(g) at room temperature

14.2.2.1.4 a halogen,

14.2.2.2 the oxidation by cold dilute acidified to form the diol

14.2.2.3 the oxidation by hot concentrated acidified leading to the rupture of the carbon–carbon double bond and the identities of the subsequent products to determine the position of alkene linkages in larger molecules

14.2.2.4 addition polymerisation exemplified by the reactions of ethene and propene

14.2.3 describe the use of aqueous bromine to show the presence of a C=C bond

14.2.4 describe the mechanism of electrophilic addition in alkenes, using bromine / ethene and hydrogen bromide / propene as examples

14.2.5 describe and explain the inductive effects of alkyl groups on the stability of primary, secondary and tertiary cations formed during electrophilic addition (this should be used to explain Markovnikov addition)

Answer:

Knowledge points:

Solution:

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