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3. (a) The structures of 2-propenal and buta-1,3-diene are given below. Both show absorption peaks in the 170 to 400 nm range of their UV spectra. propenal buta-1,3-diene (i) State how many peaks you would see for each compound and state where you would expect them to occur (to the nearest 10 nm). [5 marks] (i) What are the transitions that give rise to these peaks and assign the transition to the peaks you identified in part (a)? [3 marks] (iii) What difference would you expect to see between the UV-vis spectra of (3E,5E)-octa-1,3,5,7-tetraene and that of buta-1,3-diene assuming the same measurement conditions? Give a brief explanation for your answer. [4 marks] (b) Toluene shows an absorption band at ~ 265 nm in its UV spectrum under the appropriate conditions. Three samples of toluene were subjected to UV- vis analysis: A. Toluene in hexane in a quartz cuvette B. Toluene in hexane in a plastic cuvette; C. Toluene in benzene in a quartz cuvette. Of the three UV spectra obtain only sample A sho peak attributable to toluene (Amax ~ 265 nm); for samples B and C the readings were off the scale. Give an explanation for this observation. [8 marks]

3. (a) The structures of 2-propenal and buta-1,3-diene are given below. Both show absorption peaks in the 170 to 400 nm range of their UV spectra. propenal buta-1,3-diene (i) State how many peaks you would see for each compound and state where you would expect them to occur (to the nearest 10 nm). [5 marks] (i) What are the transitions that give rise to these peaks and assign the transition to the peaks you identified in part (a)? [3 marks] (iii) What difference would you expect to see between the UV-vis spectra of (3E,5E)-octa-1,3,5,7-tetraene and that of buta-1,3-diene assuming the same measurement conditions? Give a brief explanation for your answer. [4 marks] (b) Toluene shows an absorption band at ~ 265 nm in its UV spectrum under the appropriate conditions. Three samples of toluene were subjected to UV- vis analysis: A. Toluene in hexane in a quartz cuvette B. Toluene in hexane in a plastic cuvette; C. Toluene in benzene in a quartz cuvette. Of the three UV spectra obtain only sample A sho peak attributable to toluene (Amax ~ 265 nm); for samples B and C the readings were off the scale. Give an explanation for this observation. [8 marks]

1. The molecular structures of three common monomers that can be polymerised ionically are given below. N 1,3-butadiene acrylonitrile methyl vinyl ether (a) One of these monomers can be polymerised using a cationic initiator (1), one using an anionic initiator (1") and one can be polymerised using either a cationic or anionic initiator (it or 1-). Identify which monomer is polymerised using which initiator (s). [3 marks] (b) Draw the reaction mechanisms (including curly arrows) of the first step in the polymerisation process (initiation) for all three monomers. There is no need to give the structure of the initiators (i.e. I*, I may be used). [6 marks] (c) With reference to the reaction mechanisms and structures you have given in your answer for part (b) justify your reasoning for the answers you gave in part (a). [6 marks] (d) Assuming the molar ratio of initiator to monomer in a polymerisation of acrylonitrile was 1:750 calculate the number weight average of polyacrylonitrile at 70% monomer conversion. Please show your workings. [3 marks] (e) Sketch a plot of molecular weight (MW) versus monomer conversion illustrating the change in MW for polyacrylonitrile (part d) during polymerisation [2 marks]