when placing largest group equitorial

[super112]

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Am I supposed to use R and S stereocenter configuration rules to find the biggest group or am I just counting atoms?
Thanks

 

[BYU4you]

It's usually pretty obvious, use the periodic rules.

Methyl group is bigger than something like F and something bulky like isopropyl is bigger than methyl.

 

[super112]

What if it's iodine vs methyl or ethyl group? I'm hoping they won't ask something like that but idk what to answer in case they do ask

 

[DAT Destroyer]

Am I supposed to use R and S stereocenter configuration rules to find the biggest group or am I just counting atoms?
Thanks

R ans S is not based on size....priority is based on ATOMIC number,,,,,,For example,,,,,,Fluorine has a greater priority than Carbon...since it has a greater atomic number.

Dr. Romano

 

[super112]

Oh wow haha silly mistake. So between iodine and and a methyl (or ethyl) group, is there anyway to know which is largest so we can place it equatorial? Do we compare the first atom of each group or just count total atoms per group?

 

[BYU4you]

You go of of A values

I would say a general rule of thumb is what has the most atoms.

iodide is bigger than carbon on methyl however the Hs stick out so methyl is bigger.

 

[DAT Destroyer]

Oh wow haha silly mistake. So between iodine and and a methyl (or ethyl) group, is there anyway to know which is largest so we can place it equatorial? Do we compare the first atom of each group or just count total atoms per group?

Think of the methyl group as 4 atoms,,,,,this will beat any of the halogens,,,,,thus place methyl equatorial if you need to choose.

Dr. Romano