Predict the splitting patterns for the signals given by each of the compounds in Problem 3 .

Name: Problem 25, Chapter 14: Organic Chemistry
Uploaded: 2021-06-21T03:59:34-08:00
Duration: 10 min 58 s
Channel: Natalie Johns
Description: Predict the splitting patterns for the signals given by each of the compounds in Problem 3 .

Predict the splitting patterns for the signals given by each...

Key Concepts

Coupling Constants (J values)

Coupling constants are numerical values that measure the interaction strength between coupled nuclei, typically expressed in Hertz. They influence the spacing between peaks in a splitting pattern and can provide insights into the distance and dihedral angles between interacting protons.

Spin-Spin Coupling

Spin-spin coupling is the interaction between magnetic nuclei that causes the splitting of NMR signals into multiple peaks. This phenomenon provides structural information by showing how many neighboring protons are coupling with the nucleus of interest, which is key to interpreting signal patterns.

n+1 Rule

The n+1 rule is a simple guideline used in NMR spectroscopy to predict the number of peaks in a split signal. It states that if a proton has n equivalent neighboring protons, its signal will be split into n+1 peaks. This rule is fundamental for determining the multiplicity of NMR signals in straightforward cases.

Chemical Equivalence

Chemical equivalence describes nuclei that are in the same magnetic environment and thus have identical chemical shifts and do not split each other’s signals. Understanding which protons are chemically equivalent is crucial for correctly applying the n+1 rule and analyzing splitting patterns.

Multiplicity and Signal Patterns

Multiplicity refers to the number and arrangement of peaks observed in an NMR signal due to spin-spin coupling. By predicting and analyzing these patterns, chemists can deduce structural information about molecules, such as the number and arrangement of neighboring protons, making it a vital aspect of NMR spectral interpretation.

Transcript

00:01 This question asks us to look at splitting patterns in nmr spectroscopy.

00:07 So splitting is based on neighboring hydrogens.

00:11 So as the hydrogens see their neighbors, they will split.

00:14 And the rule is typically n plus one.

00:17 So if they see one hydrogen, they will split into two peaks.

00:22 So starting with our first compound, we can first identify how many different types of hydrogens we have.

00:30 Since there is symmetry in the molecule, we know we only have to do one half of the molecule.

00:36 So we have a hydrogen that would be here, and we can draw in the rest of them for clarity on the first one.

00:45 I probably won't take the time to do it on all of them.

00:48 And then we will also have hydrogens.

00:54 And the hydrogens in the same color are chemically equivalent.

00:57 So that's why i drew them all in the same color.

01:00 So they'll show up as the same peak on the spectrum.

01:03 And so then when we're looking at these, our green hydrogens see three other hydrogens as their neighbor.

01:10 So you can think it's about three bonds away.

01:13 So we go from our green hydrogen, one bond, the black bond, the pink bond, and we're at the hydrogens.

01:19 So with three neighbors, n plus one would cause a quadruplets split.

01:25 So they see three plus one.

01:27 So green will be split into four.

01:31 And then our pink one sees two neighbors, so that will be split into three.

01:38 Okay? and because they're chemically equivalent, we can think that the integration of our peaks will be double.

01:46 The what we have here, because it's also, we can think the same thing on this side.

01:52 I'm not going to take the time to draw it in.

01:53 But that's how you can figure that.

01:55 But in this question, we're just focusing on the splitting.

01:58 So we're looking at four and three.

02:01 In this question, we also have symmetry in this molecule, so we only have to do one side.

02:07 And then from this side, we only have one set of hydrogens.

02:10 So we have our hydrogens here.

02:15 And then our hydrogens here, see the other hydrogens right here.

02:22 And so these will split into 2 plus 1, so 3.

02:27 I'm going to go a little bit faster on the rest of these just because i'm not going to take the time to drought the rest of them.

02:33 In this molecule, we have two hydrogens right here, and we have one hydrogen here.

02:41 So the green hydrogen will see 2 plus 1, 3, and the blue hydrogen will see 1 plus 1, 2.

02:50 So these numbers are referring to the number of peaks that the singular peak is going to split into.

02:58 And we can refer to those peaks as doublets, triplets, quartets, etc.

03:03 Okay, and then looking at the rest of these moving forward, we have one, two, one.

03:16 We'll change colors.

03:19 And so the green hydrogen sees one, so it's going to split into two peaks.

03:24 The blue hydrogen sees three, so it's going to split into four peaks.

03:30 Whoops.

03:35 Four peaks in the pink hydrogen sees one, so it's going to split into two peaks.

03:42 And in this one we have symmetry this way in our molecule.

03:51 So we have, and then our green hydrogen sees three, because remember, we have these ones over here too.

04:13 So our green hydrogen is going to see three, so it's going to split into four.

04:19 Our blue hydrogen sees three, so it's going to split into four.

04:24 And our pink hydrogen sees two, and so it's going to split into three.

04:31 Our next one we can think there's three there.

04:40 There would be two here.

04:42 There would be one here.

04:45 And there would be three here...

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