(a) Write the structural formula of: (i) 2, 2, 4 - trimethylpentane, (ii) ethylmethanoate, (iii) trans 2, 3 - dimethylbut - 2-ene. (b) Write the structure o...
Question 1 Report
(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.
Answer Details
(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.
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