Nomenclature and Isomerism Flashcards
What are optical isomers?
Pairs of molecules (enantiomers) that have the same structural formula and are non-superimposable mirror images of each other. They each have at least one chiral carbon which has four different groups attached to it.
How to distinguish between two optical isomers
Polarised light is passed through two solutions of the same concentration of different isomer. One solution will rotate the plane of polarisation through a particular angle clockwise (+ isomer). The other will rotate it by the same angle anti-clockwise (- isomer). Optical rotation measured using a polarimeter.
What is a racemic mixture?
A 50:50 mixture of two optical isomers. It is not optically active as the effects of the two isomers cancel each other out.
Mechanism for nucleophilic addition with a C=O bond
Uses hydrogen cyanide. Arrow from lone pair on CN- to delta + carbon in C=O and arrow from double bond to the O. Arrow from new lone pair on O- to separate H+. Forms a nitrile with hydroxy group.
Why is a racemic mixture formed in nucleophilic addition with a C=O bond?
The C=O bond is planar so the nucleophile has an equal probability of adding from above or below the molecule. Therefore, an equal number of each isomer is made. Only works with aldehyde or unsymmetrical ketone.
