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Which of the following groups has the highest priority according to Cahn-Ingold-prelog sequence rules?
A.$C{H_3}$
B.$C{H_2}Cl$
C.$C{H_2}OH$
D.CHO

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Last updated date: 16th Jun 2024
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Answer
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Hint: The Cahn-Ingold-prelog sequence rule says that the atom or the atoms present in the group having the highest atomic number which is directly adjoined with the central carbon atom is considered as the highest priority group.

Complete step by step answer:
The Cahn-Ingold-prelog sequence rule was named after the organic chemists Robert Sidney Cahn, Christopher Kelk Ingold and Vladimir Prelog. The Cahn-Ingold-prelog sequence table is also named as CIP priority rule. In organic chemistry, it is the standard way to determine the name of the stereoisomers of the molecules.
In $C{H_3}$, the carbon atom is attached with three hydrogen atoms. The atomic number of hydrogen is one and the total atomic number will be 3.
In $C{H_2}Cl$, the carbon atom is attached to one chlorine atom and two hydrogen atoms 17 and the atomic number of hydrogen is 1. Therefore, the total atomic number will be 19.
In $C{H_2}OH$, The carbon atom is attached to three hydrogen atoms and one oxygen atom. The atomic number of oxygen is 8 and the atomic number of hydrogen is 1. The total atomic number will be 11.
In CHO, the carbon atom is attached with one oxygen by a double bond and with a hydrogen atom by a single bond. The atomic number of oxygen is 8 and the atomic number of hydrogen is 1. The total atomic number will be 9.
According to the sequence rule, the highest priority will be given to $C{H_2}Cl$ and the lowest priority will be given to $C{H_3}$.

So, the priority order will be. $C{H_2}Cl > CHO > C{H_2}OH > C{H_3}$

Note: During the calculation of the atomic number, the atoms or groups with similar atomic numbers are then prioritized according to their bonding. Groups having double or triple bonds have higher priority than groups with single bonds.