Question

Based on your research, respond to the following: What are the differences between alkenes and alkynes? What are the differences between cis- and trans-isomers? How are cistrans isomers used for night vision?

Answer 1

3)when an atom or molecule absorbs a photon, its electrons can move to higher-energy orbitals, and the atom or molecule makes a transition to a higher-energy state. In retinal, absorption of a photon promotes a p electron to a higher-energy orbital (a p-p^* excitation). This excitation "breaks" the p component of the double bond, thus allowing free rotation about the bond between carbon atom 11 and carbon atom 12 in cis-retinolThus, when 11-cis-retinal absorbs a photon in the visible range of the spectrum, free rotation about the bond between carbon atom 11 and carbon atom 12 can occur and the all-trans-retinal can form. This isomerization occurs in a few picoseconds (10^-12 s) or less. Energy from light is crucial for this isomerization process: absorption of a photon leads to isomerization about half the time; in contrast, spontaneous isomerization in the dark occurs only once in 1000 years! The molecule resulting from the isomerization is called all-trans-retinal. In the cis configuration, both of the attached hydrogens are on the same side of the double bond; in the trans configuration, the hydrogens are on opposite sides of the double bond.