Destroyer OC question

[Emmie]

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destroyer 2008 version OC #89

said if a D-sugar, put CH2OH group at C-6 above the plane of the ring. So does that imply a L-sugar when C-6 points down?

How do I know whether the ring will open or not?

As for the Fischer projection structure on the left, Kaplan said if the OH group attached to the right side of the last chiral carbon, then it's a D-sugar. What if we flip the structure left to right, then the OH group will be on the right side. Is the carbon in CHO group always counts as #1?

I've never taken Biochem (take it in the fall 09), so these questions are challenging for me! Thanks.




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destroyer 2008 version OC #59 SOLVED by UCB05, thanks!

Why allene is optically active? I thought all optically active structures must have 4 things attach to the central carbon, which mean they are all single bonds. 😕 SOS!

 

[UCB05]

destroyer 2008 version OC #59

Why allene is optically active? I thought all optically active structures must have 4 things attach to the central carbon, which mean they are all single bonds. 😕 SOS!

RR'-C=C=C-R''R'''

The first pi bond is rotated 90 degrees from the second, and they're stiff bonds with no rotation. That makes the R substituents sit 90 degrees rotated from the other set, too. If R and R' are on the page, R'' and R''' stick in and out of the page. The C=C=C makes the same general bond shape as if the group were one chiral C

 

[Emmie]

Can this RR'-C=C-R''R''' be optically active as well?

 

[Emmie]

see first post

 

[Emmie]

nobody😕

 

[UCB05]

Can this RR'-C=C-R''R''' be optically active as well?

Don't think so. It's planar.

*Edit*

For the sugar question, I've never seen the CH2OH group drawn pointing down =/ L/D is determined by the orientation of the chiral carbon furthest from the carbonyl group. Numbering begins at the end closest to the carbonyl group. Aldohexoses begin with the carbonyl carbon as 1. Ketohexoses will have the carbonyl carbon numbered something different.

Ring opening and closing is in equilibrium in solution. Assume it happens always.

If you flip an entire structure, you'll have a different molecule. Not only will it be L, it will also be named something else 🙂