Question

i am unable to find proper resources to learn CIP rule at a high school level withut delving deeper into terms i cant understand and hence the basic confusion.if i am correct one has to first compare the atomic wieght of groups down the chain until a tie is broken so in −CHO and −CH₂OH, first we see that both compound have C attached then −CHO has =O while −CH₂OH has −O. However , acc to CIP rule i only need to chech the mass number and not the double bond until i need to break a tie.so both compounds are attached to O. then −CHO is attached to nothing while −CH₂OH is attached to H, hence as they are of dissimilar lengths −CH₂OH should have the higher priority. what is wrong with my approach

Answer 1

Using the CIP rule, −CHO has higher priority than −CH₂OH because the double bond in −CHO is treated as if the carbon is connected to two oxygens, which takes precedence over the single bonds in −CH₂OH.

Step-by-step explanation:

When using the Cahn-Ingold-Prelog (CIP) sequence rules to assign priority among substituents, the initial comparison is based on the atomic number (Z) of the atoms directly attached to the chiral center. In the case of −CHO versus −CH₂OH, you correctly noticed that both have carbon (C) atoms attached to the chiral center.

However, the next step in the CIP rule involves treating atoms involved in double or triple bonds as if they are bonded to equivalent atoms the number of times they are bonded to the central atom.

For −CHO (formyl group), the oxygen (O) is double bonded to the carbon so it is as though this carbon is connected to two oxygens, which gives it a higher priority over −CH₂OH (hydroxymethyl group), where the carbon is singly bonded to an oxygen and hydrogen (H). The double bond to oxygen in −CHO means it has higher priority than −CH₂OH according to CIP rules.