Zadanie 5b
Wzorowane na: Chemistry HL Paper 2, May 2022, TZ1, pytanie 5(b). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
Darmowe konto pozwoli wrócić do niego później.
Informacja do zadań 5a-5c.
Organomagnesium compounds react with carbonyl compounds. In one overall reaction, Compound A reacts with methylmagnesium iodide, CH3MgI, and then with water:
Compound A + CH3MgI + H2O → Compound B + Mg(OH)I
Polecenie
Compound B can also be made by the hydration of an alkene. The same reaction also gives a smaller amount of the isomer 3-methylbutan-2-ol, (CH3)2CHCH(OH)CH3.
(i) Draw the structural formula of the alkene that is needed.
(ii) Explain why the reaction produces more of Compound B than of (CH3)2CHCH(OH)CH3.
(iii) Deduce the structural formula of the repeating unit in the addition polymer that this alkene would form.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) (CH3)2C=CHCH3 / 2-methylbut-2-ene ✔
(ii) the carbocation that leads to Compound B, (CH3)2C+CH2CH3 «tertiary», is more stable than the carbocation that leads to the other alcohol, (CH3)2CHCH+CH3 «secondary» ✔
«because the positive charge is» stabilised by more alkyl groups / more electron-donating alkyl groups / a stronger «+I» inductive effect ✔
(iii) −C(CH3)2−CH(CH3)− «the two carbon atoms of the former double bond, with a continuation bond at each end» ✔
Schemat punktowania
(i) [1]; the double bond must be between C2 and C3. (ii) M1: relative stability of the two carbocations; M2: reason for the greater stability. Quoting Markovnikov's rule without an explanation earns nothing. (iii) [1]; missing brackets or the subscript n are ignored, but the bonds extending from both carbon atoms must be drawn.