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Chirality
AQA A-level chemistry optical isomerism year 13
| Term | Definition |
|---|---|
| Optical isomer | a type of stereoisomerismwhere molecules have the same molecular formulabut a different spatial arrangementof atoms in space. Optical isomers are 2 molecules which are mirror images of each other but not superimposable |
| How optical isomers form | When there are 4 DIFFERENT substituents attached to the same carbon |
| Why they’re called optical isomers | Due to the way they rotate polarised light |
| S isomer | Also known as a (+) isomer and will rotate light clockwise |
| R isomer | Also known as a (-) isomer and will rotate light anticlockwise |
| Optically active | Molecules that have the potential to form optical isomers |
| Polarimeter | Device used to measure optical rotation |
| Polarised light | Wave vibrations are perpendicular to the direction of the wave. Normal light vibrates in all directs but plane-polarised light vibrates only in 1 direction but can be rotated by optical isomers |
| Enantiomer | Pairs of compounds with exactly the same connectivity but opposite three-dimensional shapes |
| Racemate | A mixture of equal amounts of enantiomers (doesn’t rotate polarised light) |
| Chiral | A carbon (or other) atom with four different groups bonded around it so there is no line of symmetry to the molecule |
| Differing properties of enantiomers | Enantiomers have almost the exact same properties (except for how they affect polarised light) and the main differences lie in how they interact with other chiral molecules |
| Side effects of optically active pharmaceuticals | Side effects occur when the drug acts on receptors other than the targeted receptor or inhibits vital biochemicals. This is because receptors are chiral and will only interact properly with one enantiomer so drugs generally need to be pure enantiomers |
| Options for optical drugs: 1 | Separate the enantiomers, but this can be difficult since they are extremely similar and expensive too |
| Options for optical drugs: 2 | Sell the drug as a mixture, but this is wasteful since only half is active |
| Options for optical drugs: 3 | Design an alternative synthesis that only make the required isomer |
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