CF3

A

B

1. base      2.   CH3

CH3

OH     CH3

NH

                 OH

AD-mixβ     contains     the     following     components:     (DHQD)2PHAL, K2 [OsO2(OH)4], and K3Fe(CN)6 . Identify the specific role of each of these

components in the AD reaction.                                                                      [3]

Draw the mnemonic that can be used to rationalise the outcome of a Sharpless

AD reaction and use it to predict the stereochemistry of product B.          [4]

Draw simple reaction profiles for the production of B and its enantiomer (ent)-B from starting material A and use these to explain why this reaction is enantioselective.                                                                                         [4]

Draw a diastereomer of B and suggest how you could separate it from B.

[2]

     Propose a mechanism for the two-step conversion of B into aminodiol C.

[3]

2.      Answer all parts

(a)     This question is about radical chain reactions.

(i)     Draw  the  mechanism  of  the  following  reaction,  indicating  clearly  the initiation and propagation steps.                                                                   [4]

NC

                 AIBN

CN

(ii)     An unwanted reduced side product is formed in the above reaction. Provide

the structure of this side product and explain the mechanism of its formation.

[2]

(iii)   What reagent could be used instead ofBu3 SnH, to make the reaction residues

less toxic and easier to remove?                                                                         [1]

(b)    This question is about C-H insertion reactions of carbenes.

X

R2C:  +     H      

Z Y

singlet carbene

X

R2C    +    H      

Z

triplet carbene

A

A

+    B

      What are the expected products A and B in the above examples?                [2] Provide full mechanisms for these C-H insertion reactions indicating any

further   intermediates   or  transition   states.  Explain  the  relation  between

products A and B and why they are formed in the case of triplet carbenes. [3]

   Which mechanism is followed by dichlorocarbene (Cl2C:).   Explain your answer.                                                                                                          [2]

 Question 2 continues overleaf

Question 2 continued

     This question is about radical polymerization.

radical

polymerization

O

vinyl propionate

Draw the structure of the polymer C that is formed when a radical initiator is

added to a mixture of vinyl propionate and methyl acrylate.                          [3]

Draw  the  mechanism  and  explain  the  selectivity  of this  polymerization

reaction based on the substituents adjacent to the formed radicals.               [3]

3.      Answer all parts.

(a)     Provide the structures of A-C in the reactions below (mechanisms are not required). [3]

(b)    Provide detailed mechanisms for the following synthesis                                    [4]

(c)     Shown below is a two-step synthesis of amine F from alcohol D.

(i)     Provide a mechanism for step 1 and explain the stereoselectivity.              [5]

(ii)     Explain why ammonia (NH3) cannot be used as the pronucleophile in step 1,

to  directly  access  amine  F,  whereas  sulfonamide  E  can  be  used  as  the pronucleophile.                                                                                                 [3]

(iii)   Provide  a mechanism  for  step  2  and  explain the  importance  of the nitro

substituent (–NO2) on the aromatic ring.                                                          [5]

4.      Answer all parts.

(a)     Show that the  {C-H} fragment and the anionic  {Ph3P→Pt}−  fragment present in

compounds A and B, respectively, are isolobal.

Me

H     C 

Me

Me

Me

Ph3P    Pt    Me

Me

A                                  B                                                                              [3]

(b)     Explain the chemical origin of the differences in the magnitudes of the first and

fourth ionization energies (I.E.) for antimony (Sb) compared with bismuth (Bi). Fourth I.E. refers to the oxidation of M(g)3+ to M(g)4+ (M = Sb or Bi).

Fourth I.E. (kJ mol− 1):                 Sb = 4260 ;                 Bi = 4370.                     [4]

(c)     Provide a simplified molecular orbital diagram for the bridging Si-H-Si unit of cation C and use it to describe the bonding in the Si-H-Si unit.

Me     H     Me

Me                    Me

C

[3]

(d)    Which  dianion,  [O2]2−   or  [S2]2− ,  has  the  greater bond  strength?  Provide  your reasoning.                                                                                                              [3]

(e)     Explain using molecular orbital theory why the H-Sb-H bond angle in SbH3 (91.5°)

is smaller than the H-P-H bond angle in PH3  (93.4°).                                               [4]

(f)      Explain why perbromate, [BrO4]− , is significantly more oxidising than perchlorate,

[ClO4]− , in contrast to the general trend in Group 17 compounds.

[3]

5.      Answer all parts.

(a)     Which complex from each of the following pairs would you expect to be more

(i)        [Co(dmpe)2]+ or [Ir(dmpe)2]+  (dmpe = (CH3)2PCH2CH2P(CH3)2)           [2]

(ii)       RhCl(PPh3)3 or RhCl(CO)(PPh3)2                                                                                                   [2]

(iii)      Cp*Ru(PiPr3) or Cp*Ru(PPh3)                                                                   [2]

(b)     For  each  combination  of reactants below, predict the products  of the reaction,

classify  it  as  an  oxidative  addition  or  reductive  elimination,  and  indicate  the oxidation state change for the metal.

(i)        CpRh(CO)2 + PhCF2I                                                                             [2] (ii)       Cp*2W(CH3)H                                                                                        [2] (iii)      CpRe(CO)3 + I2                                                                                                                                          [2]

(c)     When a red solution of the chromium carbyne complex A is treated with tetra-n- butyl ammonium fluoride, a colour change to yellow occurs. The colour change is accompanied in the 13C{1H} NMR spectrum by the loss of a signal at δ 282.2 (s) and the appearance of a new signal at δ 245.7 (d, J = 393.1 Hz).

(i)         Suggest a suitable solvent, justifying your choice, for the reaction of A

with [nBu4N]F                                                                                                    [2]

(ii)       Assign the provided NMR data and identify the product B and the by-

product C.                                                                                                           [3]

(iii)      Suggest a suitable reagent and provide a mechanism for the preparation of

A from its precursor, (OC)5Cr=C(OEt)NEt2 .                                                 [3]

6.      Answer all parts.

(a)

(i)      Explain why polymers prepared from the chain-growth polymerisation of monomers, which contain a double-bond, have a ceiling temperature (Tc). [1]

(ii)     Calculate the Tc of a polymer, given that it has an enthalpy of polymerisation

∆Ηp  = − 130 kJ mol− 1  and an entropy of polymerisation ∆Sp  = − 109 J mol−1 K−1 .                                                                                                                    [1]

(iii)   Why is the Tc of poly(2-methylpropene) lower than that of poly(propene)? [1]

(b)     Suggest how chain-branching can be introduced into polymers produced by (i) step-

growth and (ii) chain-growth polymerisation.                                                            [2]

(c)     Suggest a monomer and suitable initiator for making polymers A-C and explain the mechanism of initiation.

[6]

(a)     Consider the following polymerisation.

(i)     Draw the structure of F and name any by-products.                                     [2]

(ii)     If 100 g of D were to be polymerised, how much Monomer E would be

required to obtain the maximum DP?                                                                [1]

(iii)   For the polymerisation reaction in (d)(ii), if a 97% monomer conversion were

achieved, predict the average molecular mass (Mn) of the resulting F.         [1]

(iv)      For a polymerisation using 100 g of  D and 100 g of E, what would be the

average Mn   of the resulting F assuming a  100% monomer conversion? .  [1]