Which member in each of the following sets ranks higher? (a) -H or -Br (b) - Cl or -B r (c) -CH3

Which member in each of the following sets ranks higher? (a)...

Which member in each of the following sets ranks higher? (a) $-\mathrm{H}$ or $-\mathrm{Br}$ (b) - Cl or $-B r$ (c) $-\mathrm{CH}_{3}$ or $-\mathrm{CH}_{2} \mathrm{CH}_{3}$ (d) $-\mathrm{NH}_{2}$ or $-\mathrm{OH}$ (e) $-\mathrm{CH}_{2} \mathrm{OH}$ or $-\mathrm{CH}_{3}$ (f) $-\mathrm{CH}_{2} \mathrm{OH}$ or $-\mathrm{CH}=\mathrm{O}$

Which member in each of the following sets ranks higher?
(a) $-\mathrm{H}$ or $-\mathrm{Br}$
(b) - Cl or $-B r$
(c) $-\mathrm{CH}_{3}$ or $-\mathrm{CH}_{2} \mathrm{CH}_{3}$
(d) $-\mathrm{NH}_{2}$ or $-\mathrm{OH}$
(e) $-\mathrm{CH}_{2} \mathrm{OH}$ or $-\mathrm{CH}_{3}$
(f) $-\mathrm{CH}_{2} \mathrm{OH}$ or $-\mathrm{CH}=\mathrm{O}$

Key Concepts

Substituent Branching and Tie-Breaking

When the directly attached atoms are identical between two substituents, the priority is determined by examining the next set of atoms along the chain. The substituent whose next attached atom has a higher atomic number, or a more closely connected set of atoms, will be ranked higher. This is essential in differentiating between substituents of similar primary atoms but different branching.

Multiple Bond Equivalence

In cases where substituents contain double or triple bonds, these bonds are conceptually converted into equivalent sets of single bonds for the purpose of comparison. This treatment ensures consistency in applying the CIP rules across a wide range of functional groups and bonding scenarios.

Cahn-Ingold-Prelog (CIP) Priority Rules

This set of rules is used in stereochemistry to assign priorities to substituents attached to a stereocenter. The rules establish an order by comparing the atomic numbers of the atoms directly attached to the chiral center and, if those are identical, by moving outward along the substituent's chain until a point of difference is found.

Atomic Number Consideration

One of the fundamental aspects of the CIP rules is that atoms with higher atomic numbers are given higher priority when attached directly to the chiral center. This means that, in a comparison, an atom like bromine (with a higher atomic number) will outrank hydrogen, regardless of other factors.

Transcript

00:01 So we want to determine which of these sets of atoms would rank higher.

00:09 So remember, one of the things we are going to want to look for is which has the higher atomic number to start.

00:17 So between hydrogen and bromine, well, hydrogen is one.

00:21 Let me actually scoot this down a little bit.

00:23 So i can actually write above.

00:25 So hydrogen is one.

00:29 And bromine is 35.

00:33 So obviously 35 is going to be larger than just one.

00:38 So that means bromine is going to be the higher between those two.

00:42 Now, when we compare bromine and chlorine, so we already said bromine is 35.

00:48 Chlorine is 17, so bromine has a higher atomic number.

00:52 So again, bromine is going to be the higher of the two groups.

00:56 Now, we're going to compare this methyl versus this.

00:59 Ethyl here.

01:01 So notice that if we actually draw this out first, so we have this carbon here.

01:07 So i'll just have an r group that's attached to, and then we have these hydrogens.

01:12 And then over here, we're going to have the r group, a carbon, another carbon.

01:17 So then we have two hydrogens, two hydrogens, and then a carbon with three hydrogens attached.

01:24 So how i like to kind of think about this is, so we have the carbons for each.

01:28 So both of those are the same.

01:29 Then we start comparing what groups are attached to both of these carbons.

01:34 Well, they have two of the same, so those hydrogens kind of knock each other out.

01:38 And then for the last group, here we have a carbon attached, and then we have a hydrogen.

01:43 Well, again, hydrogen has a priority of one, and carbon, or atomic number, i should say, and carbon has an atomic number of eight.

01:54 So that means this ethyl group is going to have the higher priority.

01:58 And it's important for later down the line that you compare them like this.

02:03 Because even if we had something with a lot higher priority down the line, you still have to go step by step like what we're doing here.

02:14 So i figured i'd just bring that up...

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