@jcmc2002 do you have the page number handy?
This Extra field is a mess.
- Kaplan refers to R/S as absolute (using Cahn-Ingold-Prelog), page 54 O. Chem.
- Kaplan refers to relative as being “compared to another chiral molecule”, in many/most cases glyceraldehyde, page 54 O. Chem.
- UWorld textbooks refer to absolute configuration (R/S) as using Cahn-Ingold-Prelog, page 96 O. Chem.
- UWorld textooks refer to L/D as relative (again glyceraldehyde), page 107 O. Chem.
So far so good; all in agreement.
JackWestin does indeed say that L/D is absolute, though I trust that source less: https://jackwestin.com/resources/mcat-content/carbohydrates/absolute-configuration
I don’t care to track down KA atm though might be helpful. The rest of the sources listed here simply aren’t MCAT-specific and, while I don’t doubt that the real world may have some variance in how the terminology is employed, my instinct is that the AAMC is not going to leave this one up in the air.
Thoughts?
Pretty strange. I don’t think this video is well done and its hard to tell but it seems like KA is suggesting that D/L is absolute configuration here:
But in this video:
- 1:15 in space, so when I’m assigning absolute configuration,
- 1:18 look at the fact that it’s going one, two, three,
- 1:21 it’s going around this way, it’s going around clockwise,
- 1:23 therefore this is the R enantiomer of lactic acid.
I could be convinced there’s some weird voodoo somewhere, but L/D is…pretty famously relative to glyceraldehyde unless I’m having a Grand-mal
Same. I’ve only ever heard of R/S being absolute and L/D being relative in school.
Unless someone can verifiably prove otherwise, I’ll eat my hat on the fact that L/D is relative to glyceraldehyde. Unless there’s some weird vernacular I don’t know about, which if so then fine.
But until a primary MCAT source says so, it feels disingenuous to leave all this weird tertiary resource up conflating the two and causing a bunch of weird confusion.
This particular suggestion isn’t getting approved without a source citation, but Im of more than half a mind to clean up all that nonsense in the Extra field. I don’t even want to go through and find who made that edit, or approved it.
Yeah I really don’t know what to make of that first Khan academy video. The title has absolute configuration in it but he never actually says “absolute configuration” in the video but does spend the whole video talking about D/L. Definitely no reason to include all those random non mcat sources though.
a few people seem to have noticed this as well:
https://www.reddit.com/r/Mcat/comments/1g8ea6f/absolute_and_relative_configuration_what_am_i/
This is why we look askance at KA outside of P/S; stuff like this is just too loose-y goose-y
i’ll jump on it tomorrow. Boo hisssss