A Data Booklet may be used.
Source: Learners' Alley, Alkenes slides
Source: Learners' Alley, Alkenes slides
Source: Learners' Alley, Alkenes slides
Source: Learners' Alley, Alkenes slides
Source: Learners' Alley, Alkenes slides
Source: Learners' Alley, Alkenes slides
Source: Learners' Alley, Alkenes slides
CommonEthene reacts with bromine to form dibromoethane. Which statement best describes the organic intermediate in this reaction?
Source: SRJC 2009 Prelim P1 Q24, via EJC 2022 JC1 Alkenes Tutorial, Q5
Which of the following statements about the two alkenes CH3CH2CH=CH2 and CH3CH=CHCH3 is correct?
Source: A Level 1990 P1 Q22, via EJC 2022 JC1 Alkenes Tutorial, Q12
Source: EJC 2022 JC1 Alkenes Tutorial, Q1
CommonFor each pair of compounds, describe one simple chemical test which would enable you to distinguish between them. State clearly how each compound behaves in the test and write balanced equations for the reactions involved.
Source: RJC H2 Chemistry Tutorial 12 (Alkenes), Discussion Q3
Source: 2019 CJC J1 Promo P2 Q6(d)
ChallengeSix isomeric hydrocarbons, A to F, have the same molecular formula, C4H8. A and B are geometrical isomers and A has a higher boiling point than B. C reacts with aqueous bromine to yield a product G, which has a chiral centre. D reacts with hydrogen to form a branched-chain alkane, H. E and F are saturated hydrocarbons.
Source: RJC H2 Chemistry Tutorial 12 (Alkenes), Discussion Q5(i), (iii) and (iv)
Only (b). In (a), C1 has two H. In (c), C2 has two CH3.[1]
2-bromobutane, CH3CHBrCH2CH3[1]
H adds to C1 (more H atoms), giving a 2° carbocation[1]
stabilised by two electron-donating alkyl groups which disperse the positive charge more than in the 1° carbocation.[1]
Propanone comes from the =C(CH3)2 end of the alkene, and ethanoic acid comes from the =CHCH3 end.[1]
(CH3)2C=CHCH3, 2-methylbut-2-ene[1]
Restricted rotation about C=C, and each C of C=C has two different groups.[1]
Steam, H3PO4 catalyst, 300 °C, 60 atm.[1]
Electrophilic addition.[1]
CO2 and H2O.[1]
CIt is an electrophile.[1]
It is an electrophile, as the carbon carrying the positive charge is electron deficient.
BNeither reacts with bromine to give 1,4-dibromobutane.[1]
The electrophilic addition of bromine to an alkene occurs across adjacent carbon atoms. CH3CH2CH=CH2 gives CH3CH2CHBrCH2Br (1,2-dibromobutane), while CH3CH=CHCH3 gives CH3CHBrCHBrCH3 (2,3-dibromobutane).
A C=C double bond consists of a sigma (σ) bond and a pi (π) bond. The π bond is a region of high electron density and is susceptible to attack by electrophiles (electron deficient species).[1]
Many reactions involve breaking the weak π bond while the σ bond remains intact. Alkanes are less reactive, as they contain the stronger σ bonds only.[1]
Reagent: Br2 in CCl4. Condition: dark, room temperature. Bubble a sample of each gas through Br2 dissolved in CCl4.[1]
When ethene is bubbled through, orange Br2 is decolourised: CH2=CH2 + Br2 → CH2BrCH2Br. Orange Br2 does not decolourise when ethane is bubbled through it.[1]
Reagent: KMnO4(aq), H2SO4(aq). Condition: heat. Bubble a sample of each gas into a mixture of several drops of KMnO4(aq) in excess sulfuric acid, and heat.[1]
With but-1-ene, the purple KMnO4 is decolourised and a colourless gas (CO2), which forms a white precipitate when bubbled through Ca(OH)2(aq), is evolved. CH3CH2CH=CH2 + 5[O] → CH3CH2COOH + CO2 + H2O, CO2 + Ca(OH)2 → CaCO3 + H2O[1]
With but-2-ene, the purple KMnO4 is decolourised, but no gas is evolved. CH3CH=CHCH3 + 4[O] → 2CH3COOH[1]
Mechanism: electrophilic addition
[3]
A: cis-but-2-ene B: trans-but-2-ene [1]
C: but-1-ene, CH2=CHCH2CH3 D: 2-methylpropene, (CH3)2C=CH2[1]
E: cyclobutane F: methylcyclopropane [1]
A is polar (non-zero net dipole moment), while B is non-polar (zero net dipole moment).[1]
The intermolecular forces between molecules of cis-but-2-ene (permanent dipole–permanent dipole and instantaneous dipole–induced dipole interactions) are stronger than those between molecules of trans-but-2-ene (only instantaneous dipole–induced dipole interactions). Since boiling involves overcoming the intermolecular forces, cis-but-2-ene has a higher boiling point than trans-but-2-ene.[1]
A: CH3COO−Na+ B: CH3COO−Na+[1]
C: CH3CH2COO−Na+ + Na2CO3 D: CH3COCH3 + Na2CO3[1]