Qvault Orgo Question (Z Isomer)

[tbogdan89]

Advertisement - Members don't see this ad

Can someone please explain why the answer is E and not C?

In C the relative position of the two highest priorities (T-Butyl and Br) are on the same side of the db, so I would expect Z? Unless I am overlooked something very obvious 🤔

 

[DAT Destroyer]

Can someone please explain why the answer is E and not C?

In C the relative position of the two highest priorities (T-Butyl and Br) are on the same side of the db, so I would expect Z? Unless I am overlooked something very obvious 🤔

The answer is E.....The Br has priority over Cl......based on atomic number......The t-butyl group is branched....has greater priority than that of the straight chain.

Make sure you are comparing the groups that are attached to the same carbon......

In C....Br has priority over carbons......and Cl has priority over carbons as well.....

Hope this clears it up.

Dr. Jim Romano

 

[PocketRocket]

The answer is E.....The Br has priority over Cl......based on atomic number......The t-butyl group is branched....has greater priority than that of the straight chain.

Make sure you are comparing the groups that are attached to the same carbon......

In C....Br has priority over carbons......and Cl has priority over carbons as well.....

Hope this clears it up.

Dr. Jim Romano

Do the Halogens take priority over the carbons regardless of how long or branched the carbon chain is?

 

[FeralisExtremum]

Do the Halogens take priority over the carbons regardless of how long or branched the carbon chain is?

For determining E/Z (and R/S) priority, use Cahn–Ingold–Prelog priority rules (long story short: compare the two substituent atoms with the highest atomic numbers - higher one gets higher priority. Only if the two highest atomic number substituents are the same should you compare the next highest, and so forth). There are also rules for prioritizing further when the higher priority atom is the same. It's worth brushing up on: http://en.wikipedia.org/wiki/Cahn–Ingold–Prelog_priority_rules

A branched carbon, no matter how many substituents it has, would still be evaluated as lower priority against the higher atomic number halogens. Branching would affect priority if you were comparing two substituent carbons and one was connected to a single C while the other was connected to multiple C's (latter having higher priority).

 

[DAT Destroyer]

Do the Halogens take priority over the carbons regardless of how long or branched the carbon chain is?

Yes...indeed they do .

 

[jefnawe]

Can someone please explain why the answer is E and not C?

In C the relative position of the two highest priorities (T-Butyl and Br) are on the same side of the db, so I would expect Z? Unless I am overlooked something very obvious 🤔

look at the correct answer and compare the C (CH3)3 to the carbon that is one the bottom you will notice that you have C-C Vs. C-H and that's why