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CHEM 281 Tutorial Problem Set No. 4 ANSWERS 1. [From p. 132 in text] The ability to see depends in part on a Z-E interconversion taking place in our eyes. A protein called opsin binds to Z-retinal in the rod cells of the retina to form rhodopsin. When rhodopsin absorbs light, one of the double bonds in this molecule isomerises from Z to E, triggering a nerve impulse that is crucial to our vision. The E-retinal is then released from opsin and isomerises back to Z-retinal, and another cycle begins. Typically, to trigger this nerve impulse, a group of about 500 rod cells must register 5 to 7 rhodopsin isomerizations within a few 10ths of a second. 2. a) (1R,3R)-3-(1,1-dimethylethyl)-1-cyclohexanol b) (1S,2S)-2-(1-methylethyl)-1-(2-methylpropyl)-cyclohexane
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Unformatted text preview: c) (1R,2S)-1-(1,1-dimethylethyl)-2-methylcyclohexane d) (1R,2R)-1-(1,1-dimethylethyl)-2,4,4-trimethylcyclohexane 3. a) (2E)-4,4-dimethyl-3-(2-methylpropyl)-2-octene b) (2R,4E,6R)-4,5,6-trimethyl-4-octen-2-ol c) (3S)-1,3-dimethylcyclohexene [note: assume that carbon 1 is alkene AND you do not need to mention E or Z as cyclohexene can only be Z – an E alkene in a 6-membered ring is impossible. d) (1R)-4-methyl-3-cyclohexen-1-ol 4. 5. a) 3-penten-2-one O O O O OH b) (3Z)-3-methyl-1,3-pentadiene c) d) e) all three would be relatively high in energy (less stable) since they require the delocalized electrons in pi system be localized (recall the significant delocalization energy discussed in class) more stable cation same molecule! O O...
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