Zadanie 6a, Paper 2, specimen 2025, Chemia IB HL
Wzorowane na: Chemistry HL Paper 2, specimen 2025, pytanie 6(a). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
Darmowe konto pozwoli wrócić do niego później.
Zadanie
Wspólne informacje do wiązki zadań
Halogens and halogenoalkanes are widely used as reactants in the laboratory and in industry.
Polecenie
(i) Iodine molecules, I2, undergo homolytic fission when they absorb light. Write an equation for this process, using curly arrows to show the movement of the electrons.
(ii) In the presence of a suitable reagent the I–I bond can instead break heterolytically. Write an equation for the heterolytic fission of I2, again showing the movement of the electrons with curly arrows.
(iii) Three different iodine species appear as products in (a)(i) and (a)(ii). Identify the one that is an electrophile and give a reason for your choice.
(iv) Hydrogen iodide adds to but-1-ene through a carbocation intermediate. Draw the more stable of the two possible carbocations as a full structural formula.
(v) Outline what makes this carbocation more stable than the alternative one that could have formed.
Korepetytor AI
Nie wiesz, jak ruszyć? Korepetytor zna to zadanie i poprowadzi Cię krok po kroku, bez gotowca.
3 rozmowy · bez karty · Zaloguj się
Sprawdź się
Odpowiedz i oceń, jak poszło. Klucz odsłoń dopiero, gdy masz swoją odpowiedź.
Zanim porównasz z kluczem
Jak poszło Ci z tym zadaniem?
Zaloguj się, żeby zapisać ocenę i wrócić do zadania później.
Pokaż rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) I−I → 2 I• «two iodine radicals/atoms, each with one unpaired electron shown» ✔
two single-barbed (fish-hook) curly arrows, one from the middle of the I–I bond to each iodine atom ✔
(ii) I−I → I+ + I− with one full (double-barbed) curly arrow from the I–I bond to one of the iodine atoms AND charges shown on both ions ✔
(iii) I+ because it is electron-deficient and can accept an electron pair «from a nucleophile» to form a new covalent bond ✔
(iv) H₃C–CH₂–C⁺H–CH₃ drawn with every atom and every bond shown, the positive charge on the second carbon «secondary carbocation, CH3CH2CH+CH3» ✔
(v) the positively charged carbon is bonded to two alkyl groups (ethyl and methyl), whose positive inductive effect «electron donation» spreads out / reduces the positive charge «the alternative primary carbocation has only one alkyl group» ✔
Schemat punktowania
(i) [2]: M1 2 I• with the unpaired electrons shown (accept iodine atoms); M2 single-barbed arrows from the bond to each atom. (ii) [1]: full curly arrow AND both charges required. (iii) [1]: I⁺ with the electron-pair-acceptor reason; I⁺ alone scores zero. (iv) [1]: full structural formula of the secondary carbocation CH3CH2CH⁺CH3 with all bonds drawn; a condensed formula does not score. (v) [1]: positive inductive effect (or electron donation) of two alkyl groups.
Komentarz. Homolytic fission gives two identical radicals (one arrow to each atom); heterolytic fission moves the whole pair to one atom. Markovnikov addition of HI to but-1-ene goes through the secondary cation on C2.