A Data Booklet may be used.
CommonCompound S, upon reaction with hot acidified potassium manganate(VII), yields CH3COCH3, CH3COCH2CH2CO2H and HO2CCH2CO2H. A possible structure of S is
Source: SAJC 2007 Prelim P1 Q21, via EJC 2022 JC1 Alkenes Tutorial, Q8
Muscalure, a fly sex pheromone, has the structure CH3(CH2)7CH=CH(CH2)12CH3. Which of the following statements about Muscalure is incorrect?
Source: RJC 2007 Prelim P1 Q22, via EJC 2022 JC1 Alkenes Tutorial, Q13
Propan-1-ol, CH3CH2CH2OH, is dehydrated by passing its vapour over hot aluminium oxide to give a hydrocarbon. What is the product obtained when the hydrocarbon reacts with bromine?
Source: A Level 1996 P3 Q21 (modified), via RJC H2 Chemistry Tutorial 12 (Alkenes), Self-check Q3
An alkane B is a component of petrol. When treated with bromine in the presence of uv light, it produces a mixture of brominated compounds, including C, C6H12Br2. Dehydrobromination of C produces D, C6H10. When D is oxidised by hot acidified KMnO4, three compounds, CO2, CH3CO2H and CH3COCO2H, are formed in equimolar amounts.
Source: EJC 2022 JC1 Alkenes Tutorial, Q4
CommonHex-3-ene occurs in two isomeric forms but cyclohexene occurs only in one form.
Source: A Level 2000 P1 Q6, via RJC H2 Chemistry Tutorial 12 (Alkenes), Discussion Q4(a), (c) and (d) (adapted)
ChallengeSuggest suitable reagents and conditions to carry out the conversions given below. Give the equation for each step.
Source: RJC H2 Chemistry Tutorial 12 (Alkenes), Discussion Q2
B(CH3)2C=CHCH2CH2C(CH3)=CHCH2CH2OH[1]
Note: 1° alcohols can be oxidised to carboxylic acids using hot acidified potassium manganate(VII). Products of oxidation:
CIt gives a diol with cold, alkaline potassium dichromate(VI).[1]
Incorrect: only potassium manganate(VII), not potassium dichromate(VI), can oxidise alkenes.
D1,2-dibromopropane[1]
D: CH3CH=C(CH3)CH=CH2 or CH3CH=CHC(CH3)=CH2[1]
B: CH3CH2CH(CH3)CH2CH3 or CH3CH(CH3)CH2CH2CH3[1]
Any 2 of: CH3CHBrCH(CH3)CHBrCH3, CH3CH2CBr(CH3)CH2CH2Br, CH3CHBrCH(CH3)CH2CH2Br, CH3CH2CBr(CH3)CHBrCH3[2]
Condition for cis-trans isomerism to exist: the carbon atoms that are part of the C=C must each have two different groups or atoms bonded to them. Number of stereoisomers = 21 = 2[1]
[2]
In cyclohexene, only the cis isomer exists (with the alkyl groups on the same side of C=C). There is no trans isomer due to ring strain. The trans isomer could only be formed by breaking the carbon–carbon single bond in cyclohexene.[1]
The sp2 hybrid orbitals of each carbon atom of the C=C bond lie in a trigonal plane, while the sp3 hybrid orbitals of the adjacent carbon atom are arranged tetrahedrally. In the "trans" form, the sp3 hybrid orbital of one of the adjacent carbon atoms would not be able to overlap head-on effectively with the sp2 hybrid orbital of the doubly bonded carbon atom to form a C–C σ bond. or The trans isomer of cyclohexene, if formed, would experience considerable strain in the ring and would be (energetically) unstable.[1]
As such, the trans isomer of cyclohexene does not exist, and cyclohexene cannot exhibit geometrical isomerism.[1]
Regardless of whether cis-hex-3-ene or trans-hex-3-ene reacts with hydrogen bromide, the same carbocation intermediate, CH3CH2CH2C+HCH2CH3, is formed.[1]
As the positively charged carbon atom is sp2 hybridised, it is equally probable for the bromide ion to attack from above or below the trigonal plane containing the positively charged carbon atom. This leads to the formation of a pair of enantiomers in a 1 : 1 ratio.[1]
CH3CH=CH2 → CH3CH(OSO3H)CH3 (cold, concentrated H2SO4)[1]
CH3CH(OSO3H)CH3 → CH3CH(OH)CH3 + H2SO4 (H2O, warm)[1]
CH3CHClCH3 → CH3CH=CH2 + NaCl + H2O (NaOH, ethanol, heat)[1]
CH3CH=CH2 → CH3CHBrCH2Br (Br2/CCl4, dark)[1]
CH3CH2CH2CH2OH → CH3CH2CH=CH2 (excess concentrated H2SO4, 170 °C)[1]
CH3CH2CH=CH2 → CH3CH2CH(OSO3H)CH3 (concentrated H2SO4, cold), then CH3CH2CH(OSO3H)CH3 → CH3CH2CH(OH)CH3 + H2SO4 (H2O, warm)[1]