Stereocenter question

[globy321]

The question attached in pdf file asks to find the the molecule with S stereocenter. I don't understand why the answer is B.
To my understanding, deutrium (D) has the same atomic number as hydrogen (1) and therefore doesn't have a chiral center so the S and R stereochemistry cannot be determined for this molecule. Why is the answer B?

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[Balantidiumcoli]

You're looking for atomic mass which includes neutrons. That makes it possible for one isotope to take precedence over another when assessing chirlaity in a carbon atom. H = 1 AMU, D = 2 AMU. Since deuterium is heavier, it takes priority over the hydrogen bonds.

 

[SKaminski]

Also, i'd recommend at least being familiar with the concept of prochirality.

 

[globy321]

You're looking for atomic mass which includes neutrons. That makes it possible for one isotope to take precedence over another when assessing chirlaity in a carbon atom. H = 1 AMU, D = 2 AMU. Since deuterium is heavier, it takes priority over the hydrogen bonds.

I thought you assign priority based on atomic number when determining whether a chiral center is a S or R stereocenter.
Do you assign priority based on atomic mass also when determining E or Z configuration?

 

[Balantidiumcoli]

I thought you assign priority based on atomic number when determining whether a chiral center is a S or R stereocenter.
Do you assign priority based on atomic mass also when determining E or Z configuration?

Yep. Isotopes don't come up very often in O-chem which is what this question kind of sneaky but you're looking for atomic mass, not atomic number.