Question

Which of the following groups has the highest priority using Chan, Ingold, Prelog rules?
(A) -COOH
(B) -CHO
(C) -OH
(D) -OR​

Answer 1

Highest priority using Chan, Ingold and Prelog rules is -OH

Steps for naming:

1. Identification of stereocenters and double bonds
2. Assignment of priorities to the groups attached to each stereocenter or double-bonded atom; and
3. Assignment of R/S and E/Z descriptors.

Highest priority for an atom:

• An electron donating group or electron releasing group is an atom or functional group.
• It donates some of its electron density into a conjugated T system via resonance or inductive electron.
• Withdrawal, Thus making the system more nucleophilic is called exert +M effect .
• -OH is an activating group exert +M effect while -CHO and -COOH are deactivating groups.
• Methyl group is also called to be activating group due to its +I inductive effect but it does not have any participation in conjugation , therefore ,can not be considered to have +M effect

  Highest priority using Chan, Ingold and Prelog rules is -OH

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Answer 2

The group which has the highest priority using Chan, Ingold, and Prelog rules is

The Cahn-Ingold-Prelog sequence rule states,

• If we compare the atomic number (Z) of the atoms, which are directly attached to the stereocenter; the group which has the atom of higher atomic number receives higher priority.