Which has precedent (R/S naming)

[MTD52]

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CH2OH or CHO?

I thought you were supposed to go one by one on the elements attached to the chiral carbon, so I thought it was CH2OH. Here's my reasoning:

CH2OH --> C, O, H, H
CHO --> C, O, H, nothing

Since the first three are the same, the CH2OH should be higher because there is a final H as opposed to no element attached. Is that right?

 

[dentista123]

The CHO...has a double bond (aldehyde) So, it technically has 2 bonds to C-O


CHO: C-O, C-O, C-H BETTER ONE!!
CH2O: C-H, C-H, C-O

 

[MTD52]

The CHO...has a double bond (aldehyde) So, it technically has 2 bonds to C-O


CHO: C-O, C-O, C-H BETTER ONE!!
CH2O: C-H, C-H, C-O

Ohhhh. My gut was telling me that CHO had to have precedent, but I couldn't figure out why lol


PS: Do D and L configurations for glyceraldehyde correspond to R and S respectively, for other compounds?

 

[dentista123]

Your Q was, "PS: Do D and L configurations for glyceraldehyde correspond to R and S respectively, for other compounds? "


As far as I know, NO

D and S can dictate + and - rotation of light and that is it.

That is my understanding. R and S gives us (as chemists) an opportunity to distinguish written compounds. D and S and + and - are found through experimentation. Hopefully that is accurate. You might want to check twice on that.

 

[loveoforganic]

D and L stand for dextrorotary and levorotary, respectively. D means it rotates light clockwise; L means it rotates light counterclockwise. There is no way to determine from R or S configuration whether a compound will be D or L.

 

[MTD52]

Your Q was, "PS: Do D and L configurations for glyceraldehyde correspond to R and S respectively, for other compounds? "


As far as I know, NO

D and S can dictate + and - rotation of light and that is it.

That is my understanding. R and S gives us (as chemists) an opportunity to distinguish written compounds. D and S and + and - are found through experimentation. Hopefully that is accurate. You might want to check twice on that.

Well I don't know the answer, so in order to check twice, I need some other opinions 🙂

You're definitely right that D and S dictate the rotation. But it says in the Kaplan book that D and S were earlier terms that came before R and S, so I thought there was a correlation.

 

[MTD52]

D and L stand for dextrorotary and levorotary, respectively. D means it rotates light clockwise; L means it rotates light counterclockwise. There is no way to determine from R or S configuration whether a compound will be D or L.

Good call. I did know that stuff about it, but apparently they're unrelated. Thanks!

 

[loveoforganic]

I think it was Emil Fischer that came up with D and L nomenclature. He arbitrarily assigned D to the sugars that had R stereochemistry in their last position, and turns out he lucked out and was right.

 

[MTD52]

I think it was Emil Fischer that came up with D and L nomenclature. He arbitrarily assigned D to the sugars that had R stereochemistry in their last position, and turns out he lucked out and was right.

Hopefully more than I need to know lol. Thank you