Zadanie 6b
Wzorowane na: Chemistry HL Paper 2, May 2022, TZ1, pytanie 6(b). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
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Polecenie
Benzene reacts with bromine in the presence of an iron(III) bromide catalyst to form bromobenzene. The reaction is an electrophilic substitution in which the electrophile is Br+.
(i) Draw the structural formula of the carbocation intermediate formed as Br+ attacks a benzene ring.
(ii) Dibromobenzene exists as three isomers. Deduce how many signals appear in the 1H NMR spectrum of 1,3-dibromobenzene and the relative areas of those signals.
Number of signals:
Relative areas:
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) six-membered ring in which one carbon is sp3 and carries both H and Br, with a positive charge delocalized over the other five ring carbons ✔
(ii) number of signals: three / 3 ✔
relative areas: 1 : 2 : 1 ✔
Schemat punktowania
(i) [1]; accept the delocalized «horseshoe» representation or any of the three resonance structures with the + on a ring carbon. A structure that omits the positive charge is not accepted. (ii) [1] for the number of signals and [1] for the ratio; the ratio 1 : 2 : 1 may be given in any order.