Unit F335 - Chemistry by design - Specimen.PDF, 434KB - OCR

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16 5 The rod cells in the retina at the back of the eye contain an alcohol called retinol which is responsible for their sensitivity to light. Retinol is oxidised by an enzyme-catalysed reaction to the aldehyde retinal. retinal (a) (i) Deduce the molecular formula of retinal from its skeletal formula above. ......................................................................................................................................... [1] (ii) Suggest the structure of the alcohol retinol by completing the skeletal formula below. retinol (incomplete) (iii) Name a functional group which is present in both retinol and retinal. ......................................................................................................................................... [1] (b) (i) What reagents and conditions could be used to convert an alcohol to an aldehyde in a laboratory? ............................................................................................................................................. ............................................................................................................................................. ........................................................................................................................................ [3] (ii) How many moles of hydrogen molecules would you expect to react with one mole of retinol? ......................................................................................................................................... [1] O [2]
17 (c) When light shines on the rod cells, an enzyme-catalysed reaction occurs. This changes the arrangement around the double bond from trans to cis, as indicated in the structure below. (i) Suggest the structure of cis-retinal by completing the skeletal formula below. trans cis O retinal cis-retinal (incomplete) (ii) Why are the cis and trans isomers of a compound not identical? ............................................................................................................................................. ........................................................................................................................................ [1] [2] [Turn over
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Unit F335 - Chemistry by design - Specimen.PDF, 434KB - OCR

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