Zadanie 3c
Wzorowane na: Chemistry HL Paper 2, November 2023, TZ2, pytanie 3(c). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
Darmowe konto pozwoli wrócić do niego później.
Informacja do zadań 3a-3d.
Propanoic acid can be converted into an ester, CH3CH2COOCH3, by heating it with a second reagent in the presence of an acid catalyst.
Polecenie
The conversion of propanoic acid into the ester can be followed by changes in spectra.
(i) Compare the infrared (IR) spectra of propanoic acid and of the ester between 1500 and 3500 cm−1 by stating one feature they share and one feature in which they differ. Use section 20 of the data booklet.
(ii) The 1H NMR spectrum of one of these two compounds shows three peaks. The integration trace gives the relative areas under the peaks as 3 : 2 : 3. Deduce, referring to the integration trace, whether the spectrum is that of propanoic acid or of the ester.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) Similarity:
both show «absorption at» 1700–1750 cm−1 «C=O»
OR
both show «absorption at» 2850–3090 cm−1 «C–H» ✔
Difference:
propanoic acid «has a very broad absorption at» 2500–3000 cm−1 «O–H» which is absent from the ester ✔
(ii) the ester AND the ratio of areas 3 : 2 : 3 «corresponds to 8 hydrogens: CH3, CH2, OCH3»; propanoic acid would give 3 : 2 : 1 ✔
Schemat punktowania
(i) [2]: one mark for a similarity quoted with its wavenumber range or bond, one for the difference. Do not accept the C–O absorption (1050–1410 cm−1), which lies outside the region given, and do not accept 3200–3600 cm−1, which is the O–H of alcohols. (ii) [1]: the deduction must use the ratio of areas, not chemical shifts.