Which among following compounds contains phantom atom?

Which among following compounds contains phantom atom?
  1. $\mathrm{CH}_{3} \mathrm{COOH}$
  2. $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Cl}$
  3. $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{2}$
  4. $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}$

Solution

New rule: Expand out multiple bonds with "Phantom atoms" In order to properly compare, we "expand out" all multiple bonds and treat them as single bonds attached to "phantom atoms" (in blue). Phantom Atoms is a pseudoconcept which is only introduced when double and triple bonds are present in compound.

Note that the process of assigning "phantom atoms" to the nitrogen involves looking "backwards" towards the chiral center. This is the only case we ever do this!

Asked in: MHT CET 2020 (14 Oct Shift 1)

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