(a) Write the structural formula of:
(i) 2, 2, 4 - trimethylpentane, (ii) ethylmethanoate, (iii) trans 2, 3 - dimethylbut - 2-ene.
(b) Write the structure of the straight-chain compound that is isomeric with 2,2,4 - trimethylpentane.
(c) Write chemical equations to illustrate the oxidation of: (i) a secondary alkanol (ii) a dihydric alkanol.
(d) When-Crushed cassava was warmed with dilute hydrochloric acid, a sweet-tasting compound, D was obtained. When compcund D was treated with the enzyme, zymase and the mixture distilled a clear and colourleCsliduid, E was obtained. When liquid E was warmed with eth anoic acid i n the presence of a few drops of concentrated tetraoxosulphate (V1) acid, a compound F, with fruity smell was obtained
. (i)To what class of compounds does D belong?
(ii) Name E and F
(iii) Write the fun-ctional group in F
(iv) Write the equation for the reaction between E and ethanoic acid in the presence of concentrated tetraoxosulphate (VI) acid.
(v) Name the type of reaction that takes place between E and ethanoic acid.
(e) Arrange the followingcompounds in their correct order of increasing boiling points: CH\(_3\)CH\(_2\)CH\(_2\)OH, CH\(_3\)CH\(_2\)CH\(_2\)CH\(_2\)CH\(_2\)CH\(_3\) and CH\(_2\)CH\(_2\)CH\(_2\)CH\(_3\); Explain the order.
(a) Structural formulae
- (i) 2,2,4-trimethylpentane: (CH3)3C-CH2-CH(CH3)-CH3
- (ii) Ethyl methanoate: HCOOCH2CH3
- (iii) 2,3-dimethylbut-2-ene: (CH3)2C=C(CH3)2
(b) Straight-chain isomer of 2,2,4-trimethylpentane
The molecular formula is C8H18, so the straight-chain isomer is octane: CH3CH2CH2CH2CH2CH2CH2CH3
(c) Oxidation equations
- (i) Secondary alkanol (gives a ketone), using propan-2-ol:
CH3CH(OH)CH3 + [O] → CH3COCH3 + H2O - (ii) Dihydric alkanol, using ethane-1,2-diol:
HOCH2CH2OH + 4[O] → HOOC-COOH + 2H2O
(d) Cassava sequence
- (i) Compound D belongs to the carbohydrates (a sugar/monosaccharide, glucose).
- (ii) E is ethanol; F is ethyl ethanoate.
- (iii) The functional group in F is the ester (alkanoate) group, -COO-.
- (iv) C2H5OH + CH3COOH → CH3COOC2H5 + H2O
- (v) The reaction is esterification (a condensation reaction).
(e) Order of increasing boiling point
The compounds are butane (CH3CH2CH2CH3), hexane (CH3CH2CH2CH2CH2CH3) and propan-1-ol (CH3CH2CH2OH).
Increasing order: butane < hexane < propan-1-ol
Explanation: butane and hexane are non-polar alkanes held together only by weak van der Waals forces; hexane has a larger molecule with more electrons than butane, so its van der Waals forces are stronger and its boiling point higher. Propan-1-ol contains the -OH group and its molecules are held together by strong hydrogen bonds, which require the most energy to break, so it has the highest boiling point despite its smaller size.
(a) Structural formulae
- (i) 2,2,4-trimethylpentane: (CH3)3C-CH2-CH(CH3)-CH3
- (ii) Ethyl methanoate: HCOOCH2CH3
- (iii) 2,3-dimethylbut-2-ene: (CH3)2C=C(CH3)2
(b) Straight-chain isomer of 2,2,4-trimethylpentane
The molecular formula is C8H18, so the straight-chain isomer is octane: CH3CH2CH2CH2CH2CH2CH2CH3
(c) Oxidation equations
- (i) Secondary alkanol (gives a ketone), using propan-2-ol:
CH3CH(OH)CH3 + [O] → CH3COCH3 + H2O - (ii) Dihydric alkanol, using ethane-1,2-diol:
HOCH2CH2OH + 4[O] → HOOC-COOH + 2H2O
(d) Cassava sequence
- (i) Compound D belongs to the carbohydrates (a sugar/monosaccharide, glucose).
- (ii) E is ethanol; F is ethyl ethanoate.
- (iii) The functional group in F is the ester (alkanoate) group, -COO-.
- (iv) C2H5OH + CH3COOH → CH3COOC2H5 + H2O
- (v) The reaction is esterification (a condensation reaction).
(e) Order of increasing boiling point
The compounds are butane (CH3CH2CH2CH3), hexane (CH3CH2CH2CH2CH2CH3) and propan-1-ol (CH3CH2CH2OH).
Increasing order: butane < hexane < propan-1-ol
Explanation: butane and hexane are non-polar alkanes held together only by weak van der Waals forces; hexane has a larger molecule with more electrons than butane, so its van der Waals forces are stronger and its boiling point higher. Propan-1-ol contains the -OH group and its molecules are held together by strong hydrogen bonds, which require the most energy to break, so it has the highest boiling point despite its smaller size.
