Cahn-Ingold-Prelog selection rules

A polarimeter measures the angle that an enantiomer can rotate plane polarized light. Observed rotation (a) is the value recorded directly from a polarimeter. Specific rotation ([a]) is the standardized value for optical rotation, where [a] = a/l c. The absolute configuration (R or S) of an enantiomer is determined by applying the Cahn-Ingold-Prelog selection rules and the steering wheel model. 

The preceding discussion presented rules required to determine absolute configuration, in narrative form. Three chemists developed these rules, called the Cahn-Ingold-Prelog selection rules. The rules have been formalized and expanded by lUPAC, and they formally constitute the lUPAC rules for determining stereochemistry. The following is a summary ... 

Using the Cahn-Ingold-Prelog selection rules is perhaps a better way to compare the two red carbon atoms. The top carbon atom in 57A is and the bottom red carbon is also so there is no point of difference. Going... 

In the previous examples, the base name is derived from a saturated, or alkane, backbone. Therefore, a heptane chain in a ketone becomes heptanone and a tetradecane chain would be tetradecanone. It is also possible to have a heptene or a heptyne backbone, as in 10 and 11. This raises a problem Which group has the higher priority the C=0 unit or the C=C unit or the C=C unit Using the Cahn-Ingold-Prelog selection rules (Chapter 9, Section 9.3.1), the C=0 unit is the higher priority, and this means that both 10 and 11 will be named as ketones (suffix is one ). A C=0 unit is higher in priority than a C=C unit, so a molecule is named as an en-one when an alkene and a ketone unit are in the same molecule. 

Determining the relative priority a to d) is accomplished by a series of rules, the so-called Cahn-Ingold-Prelog (or CIP) selection rules.1644,15... 

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