Home / AS & A Level Chemistry 33.2 Esters: Exam Style Questions Paper 4

AS & A Level Chemistry 33.2 Esters: Exam Style Questions Paper 4

Question

(a) The mass spectrum of compound X, C5H10O2, is recorded.

      The peak heights of the M and M+1 peaks are 22.65 and 1.25 respectively.

(i) Use these data to show that there are five carbon atoms present in one molecule of X.

     Show your working.

(ii) The mass spectrum has a peak at m/e = 57.

       Complete the equation to show the fragmentation of X to produce this peak.

       [C5H10O2] + ___________________ + _____________________

(b) State the use of TMS and CDCl3 in NMR spectroscopy.
 
        ● TMS
 
        ● CDCl3
 
(c) The proton NMR spectrum of compound X, C5H10O2, is shown.

(i) By considering both the relative peak areas and their δ values, use the Data Booklet to

     ● deduce the part of the molecule that produces the peak at δ2.2,

                               ● deduce the part of the molecule that produces the peaks at δ1.2 and δ3.5,

     ● deduce the part of the molecule that produces the peak at δ4.0.

(ii) When reacted with aqueous alkaline iodine, X produces a yellow precipitate.

       Use this information and your answers to (c)(i) to suggest a structure for X.

(d) Compound W is an ester with the molecular formula C5H10O2.

       The proton NMR spectrum of W contains only two peaks.

       The relative areas of these two peaks are in the ratio 9:1.

       Suggest a structure for this ester, W.

(e) Compound V is a carboxylic acid which contains a chiral centre. It also has the molecular
       formula C5H10O2.

(i) Explain what is meant by the term chiral centre.

(ii) Suggest a structure for V.

Answer/Explanation

Answer:      (a)(i) no. of carbons = 100 × 1.25 / (22.65 × 1.1) (= 5.02) 

(a)(ii) M1: C2H5O

   M2: C3H5O+ (positive sign required for m / e = 57 fragment)

(b) TMS: Reference
          CDCl3: Solvent

(c)(i) M1: CH3CO

 M2: CH3CH2O

 M3: (CO)CH2O

(c)(ii) CH3COCH2OCH2CH

(d) HCO2C(CH3)

(e)(i) this is a (carbon) atom which has four different atoms or groups attached to it

(e)(ii) CH3CH2CH(CH3)COOH

Question

(a) Ethanedioate ions, C2O42–, are bidentate ligands.

      Explain what is meant by the term ligand.

(b) Cr3+(aq) and C2O42–(aq) ions form the complex ion [Cr(C2O4)2(H2O)2].

       Draw two stereoisomers of this complex ion.

       You may use to represent C2O42–.

(c) The solubility of calcium ethanedioate, CaC2O4, is 6.65 × 10–3 gdm–3 at 298K.

(i) Write an expression for the solubility product, Ksp, of CaC2O4. Include its units.

(ii) Calculate the numerical value of Ksp CaC2O4 at 298K. Give your answer in standard form
       to two significant figures.

Answer/Explanation

Answer:       (a) species that forms dative bond(s) to a (central) metal atom / ion

(b) 

(c)(i) Ksp = [Ca2+][C2O42–] [1]
              units mol2 dm–6 [1]

(c)(ii) [Ca2+] = [C2O42–] = 6.65 × 10–3/128.1 = 5.19 × 10–5 mol dm–3 [1]                                                                                                                                                                                                  Ksp = (5.19 × 10–5)2 = 2.7 × 10–9 mol2 dm–6 [1]

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