Zadanie 4d, Paper 2, maj 2025, TZ3, Chemia IB SL
Wzorowane na: Chemistry SL Paper 2, May 2025, TZ3, pytanie 4(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
Halogenoalkanes are widely used as intermediates in organic synthesis. Compound Y has the condensed structural formula CH3CHClCH(CH3)2.
Polecenie
Compound Y undergoes nucleophilic substitution with a hydroxide nucleophile.
(i) Describe the movement of electron pairs during the reaction using curly arrows.
(ii) Contrast homolytic and heterolytic fission of the C–Cl bond in compound Y.
(iii) Explain, using collision theory, how an increase in temperature increases the rate of this reaction.
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Pokaż rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) curly arrow from the lone pair / negative charge on the O of HO− to the carbon atom bonded to Cl ✔
curly arrow from the C–Cl bond to the Cl atom ✔
(ii) Homolytic fission: each atom keeps one of the bonding electrons / «neutral» radicals are formed ✔
Heterolytic fission: both bonding electrons go to one atom «Cl» / ions are formed ✔
(iii) at a higher temperature the particles move faster and have a greater average kinetic energy ✔
collisions between reacting particles happen more often per unit time ✔
a greater fraction of the colliding particles possesses energy equal to or above the activation energy, so proportionally more collisions are successful ✔
Schemat punktowania
(i) [1] each: nucleophilic attack arrow from HO-, arrow for the C–Cl bond breaking. Ignore bond connectivity and small errors in the carbon skeleton; do not require HO and Cl at 180°. (ii) [1] each; award [1 max] if the two descriptions are reversed. (iii) [1] each, max [3]; the collision-frequency point needs a reference to time or number of collisions, the energy point must refer to the activation energy.
Komentarz. Two curly arrows are enough for the marks asked here; a transition state and a named product are not required at this level.