(l)-epinephrine and plane polarized light

[sexycani]

question 159 from EK 1001 Orgo

What direction does (l)-epinephrine rotate plane polarized light?

A. Clockwise
B. Counterclockwise
C. It cannot be determined without measurement
D. It does not rotate light

i put C but the correct answer is B. Why?!?!?

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[PiBond]

question 159 from EK 1001 Orgo

What direction does (l)-epinephrine rotate plane polarized light?

A. Clockwise
B. Counterclockwise
C. It cannot be determined without measurement
D. It does not rotate light

i put C but the correct answer is B. Why?!?!?

(l) = levorotary...just means counterclockwise rotation

 

[Danlee07]

By the fact that you put C, I'm pretty sure you don't really get the concept. Chiral molecules rotate polarized light. Epinephrine is chiral. So it has to be A or B. It says (I-) instead of (d) so it's meaning levorotatory. Levorotatory compounds affect polarized light counter-clockwise.[FONT=Times New Roman,Times] .

 

[PiBond]

By the fact that you put C, I'm pretty sure you don't really get the concept. Chiral molecules rotate polarized light. Epinephrine is chiral. So it has to be A or B. It says (I-) instead of (d) so it's meaning levorotatory. Levorotatory compounds affect polarized light counter-clockwise.[FONT=Times New Roman,Times] .

Not necessarily. If we're given the absolute configuration (R) or (S) or D/L then we can't determine the specific rotation of the compound unless we use our laboratory polarimeter. Therefore, the correct answer would be "cannot be determined". My guess is that the OP didn't realize that there's a difference between capital D/L and lower case d/l. The lower case d/l tells us the direction of specific rotation while the upper case D/L does not.

 

[Rabolisk]

By the fact that you put C, I'm pretty sure you don't really get the concept. Chiral molecules rotate polarized light. Epinephrine is chiral. So it has to be A or B. It says (I-) instead of (d) so it's meaning levorotatory. Levorotatory compounds affect polarized light counter-clockwise.

I wouldn't jump to such conclusions.

 

[TheRealAngeleno]

Not necessarily. If we're given the absolute configuration (R) or (S) or D/L then we can't determine the specific rotation of the compound unless we use our laboratory polarimeter. Therefore, the correct answer would be "cannot be determined". My guess is that the OP didn't realize that there's a difference between capital D/L and lower case d/l. The lower case d/l tells us the direction of specific rotation while the upper case D/L does not.

Didn't know that. Thanks for the information.

 

[sexycani]

Thanks, PiBond. I did not indeed know the difference in uppercase and lower case D/L.
Okay, thanks everyone.

 

[Danlee07]

Not necessarily. If we're given the absolute configuration (R) or (S) or D/L then we can't determine the specific rotation of the compound unless we use our laboratory polarimeter. Therefore, the correct answer would be "cannot be determined". My guess is that the OP didn't realize that there's a difference between capital D/L and lower case d/l. The lower case d/l tells us the direction of specific rotation while the upper case D/L does not.

I wasn't jumping to any conclusions. Yeah, R/S D/L is stereo independent of polarized light, but what are you talking about? aren't you just agreeing with me? The question stated lower case l so that means it's talking about lowercase d/l = sense of light rotation, so it's supposed to be a straightforward question. I meant to say it stated l instead of L* in previous post.

 

[Rabolisk]

By the fact that you put C, I'm pretty sure you don't really get the concept. Chiral molecules rotate polarized light. Epinephrine is chiral. So it has to be A or B. It says (I-) instead of (d) so it's meaning levorotatory. Levorotatory compounds affect polarized light counter-clockwise.

The first part is where you sort of jumped to conclusion, IMHO. Most importantly, your (correct) observation that epinephrine is chiral doesn't necessarily mean that the answer has to be A or B, or necessarily show that sexycani doesn't understand the broad concept of chirality. The concept that he missed was that (l-) means levorotatory. To be sure, it's possible that he has absolutely no understanding of chirality at all, but that would be an assumption.