Stereochemistry question

[virtualmaster999]

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Hi all!

Just wanted to double check on this:

So allenes and biphenyls can be chiral under certain conditions (having different groups).

Now, do BOTH groups on BOTH sides needs to be different?
-Like for an allene, does there need to be two diff substituents on 1 carbon, and ALSO two different substituents on the other carbon (same for diphenyls in the ortho position)

Could someone clarify this for me?

Thanks in advance! Always appreciate everyone's help 🙂

 

[Incis0r]

Yes- each carbon must have two groups that are different from each other. If at least one carbon atom has two groups that are the same, then it is achiral because you can easily create a plane of symmetry.

 

[DAT Destroyer]

Hi all!

Just wanted to double check on this:

So allenes and biphenyls can be chiral under certain conditions (having different groups).

Now, do BOTH groups on BOTH sides needs to be different?
-Like for an allene, does there need to be two diff substituents on 1 carbon, and ALSO two different substituents on the other carbon (same for diphenyls in the ortho position)

Could someone clarify this for me?

Thanks in advance! Always appreciate everyone's help 🙂

Let us consider an allene......The upper left and lower left groups MUST be different.......ALSO.....the upper right and lower right groups MUST be different. That is it. It is fine if the same groups are on opposite sides. Let us do one together......draw 3 carbons and place the double bonds between them.....OK.....upper right put a bromine....lower right put a methyl. Now lets do the upper left.....put in a bromine.....now lower left.....put in a methyl.

Congrats!!!! You have created your very first chiral allene !!!!! In Advanced Organic Chemistry there is actually a technique to confirm R/S...but you need not worry about it.

Hope this Helps !

Happy July 4th to you and all my SDN friends.

Dr. Jim Romano

 

[virtualmaster999]

Let us consider an allene......The upper left and lower left groups MUST be different.......ALSO.....the upper right and lower right groups MUST be different. That is it. It is fine if the same groups are on opposite sides. Let us do one together......draw 3 carbons and place the double bonds between them.....OK.....upper right put a bromine....lower right put a methyl. Now lets do the upper left.....put in a bromine.....now lower left.....put in a methyl.

Congrats!!!! You have created your very first chiral allene !!!!! In Advanced Organic Chemistry there is actually a technique to confirm R/S...but you need not worry about it.

Hope this Helps !

Happy July 4th to you and all my SDN friends.

Dr. Jim Romano

Thanks Dr. Romano, greatly appreciated! Happy 4th of July as well!