Question

How do you identify stereocenters on a complex molecule?

Answer 1

Perhaps you can analogize off of the answer I will put here. This is a rather comprehensive molecule I got on an exam for identifying stereocenters:

Morphine

`~95%` of the time, stereocenters are in `sp^3` carbons. The stereocenters I identify are:

• Carbon-5, connected to an `1^o` alkoxide group, a tert-butyl group, a proton, and a `2^o` alcohol group. The priorities from high to low are:

  `1^o` alkoxide, `2^o` alcohol, tert-butyl, proton

Since the proton is in the front, and you go counterclockwise to follow these priorities, you get the reverse of S, which is R.

• Carbon-6, connected to a `2^o` alkoxide group, a vinyl or alkenyl group, a proton, and a hydroxyl group. The priorities from high to low are:

  hydroxyl, `2^o` alkoxide, vinyl (counted similar to isopropyl), proton

Since the proton is in the front, and you go clockwise to follow these priorities, you get the reverse of R, which is S.

• Carbon-9, connected to a `2^o` amine group, a proton, a methylene group (`CH_2`), and an isopropyl group. The priorities from high to low are:

  `2^o` amine, isopropyl, methylene, proton

Since the proton is in the back and you go clockwise to follow the priorities, this is R.

• Carbon-13 (the one that branches upwards), connected to a benzene ring, a `2^o` alkoxide group, an isopropyl group, and a `1^o` alkyl group. The priorities from high to low are:

  `2^o` alkoxide, benzene ring (counted similar to tert-butyl), isopropyl, `1^o` alkyl

Since the `1^o` alkyl is upwards and you go clockwise to follow the priorities, this is the reverse of R, which is S.

• Carbon-14, connected to a proton, a tert-butyl group, a vinyl or alkenyl group, and a `2^o` amine group. The priorities from high to low are:

  `2^o` amine, tert-butyl, vinyl (counted similar to isopropyl), proton

Since the proton is in the front and you go counterclockwise to follow the priorities, this is the reverse of S, which is R.