1001 Organic Chemistry Discrepancy

[NigerianBull87]

Hey guys,

I have a quick question regarding two problems in the 1001 Orgo through EK.

For those whom have the book it is regarding problems 137 Pg.16 and 177 Pg. 20.

1) A carbon has four substiuents as follows: CHO, Br, OH, and CH3. What priority does CHO have? The book says 2, but that is false I believe that it is 3, behind the OH and Br right?

2) An allene molecules is mirrored to begin with right. The question asks what is the relationship between a mirrored allene. The book says that they are enantiomers. Now I thought the book definition for an enantiomer was one that mirrored each other alright, but also have different absolute configurations. The allene molecule has no absolute configuration because it is not even chiral, therefore how could it even be a stereoisomer, let alone an enantiomer.

I would really appreciate the help guys. I am doing a book a week through EK along with the 1001, so I will be done with Orgo by tomorrow and the 1001 and am starting on Monday with the 1001.

Take Care.

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[RySerr21]

Hey guys,

I have a quick question regarding two problems in the 1001 Orgo through EK.

For those whom have the book it is regarding problems 137 Pg.16 and 177 Pg. 20.

1) A carbon has four substiuents as follows: CHO, Br, OH, and CH3. What priority does CHO have? The book says 2, but that is false I believe that it is 3, behind the OH and Br right?

seems as though you are correct on this one, unless there is some weird rule i dont know about. probablly pretty likely tho.

2) An allene molecules is mirrored to begin with right. The question asks what is the relationship between a mirrored allene. The book says that they are enantiomers. Now I thought the book definition for an enantiomer was one that mirrored each other alright, but also have different absolute configurations. The allene molecule has no absolute configuration because it is not even chiral, therefore how could it even be a stereoisomer, let alone an enantiomer.

i'm not too sure on this one. can't you talk about stereoisomers among molecules with double bonds that dont have any chiral carbons? for example E and Z forms of molecules are considered stereoisomers. if the mirror image of an E or Z molecule isnt superimposable, then couldnt it be considered an enatiomer?

 

[NigerianBull87]

You Make a very good point, regarding the enantiomer problem. I appreciate it.

 

[unsung]

Hey guys,

I have a quick question regarding two problems in the 1001 Orgo through EK.

For those whom have the book it is regarding problems 137 Pg.16 and 177 Pg. 20.

1) A carbon has four substiuents as follows: CHO, Br, OH, and CH3. What priority does CHO have? The book says 2, but that is false I believe that it is 3, behind the OH and Br right?

2) An allene molecules is mirrored to begin with right. The question asks what is the relationship between a mirrored allene. The book says that they are enantiomers. Now I thought the book definition for an enantiomer was one that mirrored each other alright, but also have different absolute configurations. The allene molecule has no absolute configuration because it is not even chiral, therefore how could it even be a stereoisomer, let alone an enantiomer.

I would really appreciate the help guys. I am doing a book a week through EK along with the 1001, so I will be done with Orgo by tomorrow and the 1001 and am starting on Monday with the 1001.

Take Care.

I think allenes CAN be chiral- rem it's NOT planar, 'cuz of the way the p orbitals are arranged, so 2 of the substit off 1 end C are in 1 plane, and the other 2 of the subsit of the other end C are in another plane that's perpendicular to the 1st plane

First Q.. apparently I circled that problem. I thought it would be B too.

Okay, now I've got a Q... so the whole R/S system, and the D/L system, both designate "absolute configuration", right? Whereas +/- or d/l (small letter) designates "relative configuration"? I'm always getting those confused.

But anyway, I think 137 is a typo... otherwise, it doesn't make sense ??

 

[NigerianBull87]

Well the D/L system to the best of my knowledge has nothing to do with relative configuration. It deals with the OH groups on carbohydrates and other biological molecules. The D is if the OH is on the right and the L is if it is on the left side of the molecule. This can usually be seen on Fischer projections. This is what I believe anyway.

The "d" and "l" pertain to the observed and specific rotation in a polarimeter. If the polarimeter rotates the light clockwise it is (d, +) if it rotates the light counterclockwise then it is (l,-).

Relative configuration relates the different R,S configurations with the removal or rearranging of one substiuent on the chiral carbon.

 

[unsung]

Well the D/L system to the best of my knowledge has nothing to do with relative configuration. It deals with the OH groups on carbohydrates and other biological molecules. The D is if the OH is on the right and the L is if it is on the left side of the molecule. This can usually be seen on Fischer projections. This is what I believe anyway.

The "d" and "l" pertain to the observed and specific rotation in a polarimeter. If the polarimeter rotates the light clockwise it is (d, +) if it rotates the light counterclockwise then it is (l,-).

Relative configuration relates the different R,S configurations with the removal or rearranging of one substiuent on the chiral carbon.

Doesn't R/S refer to absolute configuration? Like in the EK Q about assigning priorities, they phrased it as "what is the priority of CHO in the absolute configuration".

 

[NigerianBull87]

Yes that is the only way to describe absolute configuration.