A-LevelChemistryIntroduction to organic chemistry9701/23 · May/June 2018 · Q210 Marks

One reason for the wide variety of organic compounds is isomerism, either structural isomerism or stereoisomerism.

(a)(i)Explain the meaning of the term structural isomerism.[2]
(a)(ii)Explain the meaning of the term stereoisomerism.[2]
(b)(i)Pent-1-ene, CH2=CH(CH2)2CH3, does not show stereoisomerism. Give two reasons why pent-1-ene does not show stereoisomerism.[2]
(b)(ii)A structural isomer of pent-1-ene is used as the monomer to form a polymer. The repeat unit of this polymer is shown. [Figure with repeat unit] Draw the displayed formula of the monomer used to make this polymer. Give the name of the monomer.[2]
(b)(iii)A different structural isomer of pent-1-ene shows geometrical isomerism. Draw the structure of one of the two geometrical isomers with the formula C5H10. Give the full name of this isomer.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.

[1] (molecules / isomers with) the same molecular formula / same number of atoms of each element
[1] different structural formulae / different structures
[1] (Molecules / isomers) with the same (molecular and) structural formula
[1] different arrangement of atoms in space / different spatial arrangement of atoms.
[1] two Hs on one of the C=C carbons / terminal C / C-1
[1] no chiral C / no C with 4 different groups / atoms / chains attached has a super(im)posable mirror image
[1] H-C(H)=C(CH3)-CH2CH3 (structure for 2-methylbut-1-ene)
[1] 2-methylbut-1-ene
[1] structure (of cis or trans pent-2-ene)
[1] trans-pent-2-ene or cis-pent-2-ene OR E- or Z-

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