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Which of the following would be ranked as the highest priority group?

Group of answer choices

-Cl

-CH2CH3

-NH2

-OH

3 answers

To determine the highest priority group among the given options, we can use the Cahn-Ingold-Prelog priority rules, which are commonly used in organic chemistry for assigning priorities in stereochemistry.

Here are the groups and their general features:

  1. Cl (Chlorine): This is a halogen and has a higher atomic number than the carbon, oxygen, and nitrogen in the other groups.
  2. CH2CH3 (Ethyl group): This is a carbon chain, which typically has a lower priority than more electronegative atoms or groups.
  3. NH2 (Amino group): This group has a nitrogen atom, which is less electronegative than oxygen and has a lower atomic number than chlorine.
  4. OH (Hydroxyl group): This group contains an oxygen atom, which is more electronegative than nitrogen and carbon but less than chlorine.

Based on the atomic numbers of the first atoms in each group, the order from highest to lowest priority is:

  1. Cl (Chlorine) - Highest (because of its higher atomic number)
  2. OH (Oxygen) - Next (because oxygen is more electronegative than nitrogen)
  3. NH2 (Nitrogen) - Lower (because nitrogen has a lower atomic number than oxygen)
  4. CH2CH3 (Carbon chain) - Lowest

Therefore, the highest priority group is Cl (Chlorine).

Why did you say before the answer is -OH? So which is it? Cl or OH and why.

I apologize for any confusion in my response. Let me clarify:

To rank these groups using the Cahn-Ingold-Prelog priority rules, we assign priority based on the atomic number of the atoms directly attached to the chiral center. Priority is assigned as follows:

  1. Cl (Chlorine): Atomic number 17
  2. OH (Hydroxyl group): The oxygen has an atomic number of 8
  3. NH2 (Amino group): The nitrogen has an atomic number of 7
  4. CH2CH3 (Ethyl group): The highest atomic number of the carbon would be 6

When comparing these atoms directly:

  • The chlorine atom (Cl) has the highest atomic number among all options, making Cl the highest priority group.
  • The hydroxyl group (OH), while it is a functional group that can often be highly reactive, does not surpass chlorine in priority based on atomic number.

Thus, Cl is the highest priority group, not OH. Thank you for pointing out the inconsistency, and I appreciate your understanding.