Chiral center is defined as?

• A. A carbon that has four different groups
• B. A carbon that has three identical groups
• C. A carbon that has two identical groups and two different groups
• D. A nitrogen with a lone pair

Answer: (A)

Chirality shows up when a carbon atom is bonded to four different substituents, giving two mirror-image arrangements that cannot be superimposed. This makes that carbon a stereocenter, and the molecule can exist as enantiomers that are non-identical mirror images. If any two substituents are the same, or if there are only three or two different groups, the center isn’t stereogenic because a plane of symmetry appears and the molecule becomes achiral. A nitrogen with a lone pair isn’t treated as a chiral center in the usual sense, since amines rapidly invert, so that arrangement doesn’t give a stable, non-superimposable mirror image. Therefore, the defining situation is a carbon bonded to four different groups.