Zadanie 8d, Paper 2, maj 2025, TZ1, Chemia IB HL
Wzorowane na: Chemistry HL Paper 2, May 2025, TZ1, pytanie 8(d). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
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Zadanie
Wspólne informacje do wiązki zadań
Many everyday materials, flavourings and fuels are organic compounds.
Polecenie
When 1-bromopropane is warmed with aqueous sodium hydroxide, NaOH(aq), propan-1-ol is formed.
(i) State the name given to this reaction's mechanism.
(ii) Draw the structure of the transition state that occurs during this mechanism.
(iii) Deduce the rate equation consistent with this reaction's mechanism.
(iv) Predict the quantitative effect on the reaction rate of halving the concentration of NaOH(aq) while all other conditions are kept the same, and give a reason for your answer.
(v) Outline how the rate of this reaction compares with the rate at which 1-iodopropane reacts with sodium hydroxide under the same conditions.
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Pokaż rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) «bimolecular» nucleophilic substitution / SN2 ✔
(ii) [HO···C(H)(H)(CH2CH3)···Br]−: the carbon drawn with its two H atoms and the CH2CH3 group, partial «dotted» bonds from O to C and from C to Br, the whole species in square brackets with a negative charge ✔
(iii) «rate =» k[CH3CH2CH2Br][OH−] ✔
(iv) rate is halved AND the reaction is first order with respect to OH− / rate is proportional to [OH−] ✔
(v) 1-iodopropane reacts faster «than 1-bromopropane» AND the C-I bond is weaker / longer than the C-Br bond / iodide is a better leaving group ✔
Schemat punktowania
(i) [1]; accept SN2 but not SN1. (ii) [1]; the charge, the square brackets and both partial bonds are required; accept δ- on O and Br; accept any angle for the partial bonds. (iii) [1]; accept [NaOH] for [OH-]. (iv) [1] for the halved rate with the order or the proportionality; ECF «rate unchanged, zero order with respect to OH-» if SN1 was named in (i). (v) [1] for the faster iodo compound together with a bond-strength or leaving-group reason.