A-LevelChemistryIntroduction to organic chemistry9701/22 · May/June 2021 · Q412 Marks

The table shows the structural formulae of four compounds, A, B, C and D, with molecular formula C4H8. structural formula | name A CH3CH2CH=CH2 | B [Figure of cis-but-2-ene] | C [Figure of trans-but-2-ene] | D CH2=C(CH3)2 |

(a)(i)Complete the table by giving the systematic name of A, B, C and D. [Table with structural formulas and blank name column][4]
(a)(ii)Explain what is meant by stereoisomerism.[1]
(b)(i)W is an alkene with formula C4H8. It reacts with HBr to form two possible carbocations, CH3C+(H)(CH2CH3) and H2C+CH2CH2CH3. Identify W as compound A, B, C or D.[1]
(b)(ii)Draw the skeletal formula of the major organic product formed when HBr reacts with W. Explain why this is the major organic product.[3]
(c)A sample of propan-1-ol reacts with concentrated sulfuric acid to form propene. Identify the role of concentrated sulfuric acid in this reaction.[1]
(d)(i)Alcohol Y reacts completely when warmed with acidified Cr2O72- to form Z. Z is distilled from the reaction mixture as soon as it is made. Tollens' reagent is added to a sample of Z and warmed. A silver mirror forms. Name the type of reaction that occurs when Y reacts to form Z.[1]
(d)(ii)Identify with a tick (✓) the functional group(s) present in Z. [Table with functional groups and blank 'present in Z' column] functional group | present in Z aldehyde | ketone | carboxylic acid |[1]

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Mark scheme

Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.

[1] M1 correct identification of but-1-ene (for A)
[1] M2 correct identification of but-2-ene for B and C
[1] M3 identification of cis / trans (Z / E) for B and C (in correct order)
[1] M4 correct name of D
[1] (molecules with the) same structural formula (and same molecular formula) with different arrangement of atoms / groups in space
[1] A
[1] M1 [skeletal formula only] (of 2-bromobutane)
[1] M2 explanation in terms of increased/greater stability of intermediate / carbocation intermediate / (secondary) carbocation / CH3C+ (H)(CH2CH3) is (more) stable
[1] M3 reason for increased stability of intermediate in terms of greater number of alkyl groups showing largest inductive (electron releasing) effect greater (positive) inductive effect due to two alkyl groups OR greater electron donation of two alkyl groups
[1] dehydrating agent / cause dehydration
[1] oxidation
[1] [tick for aldehyde]

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