How many ^13C NMR signals does each compound exhibit? |...

Name: Problem 50, Chapter 14: Organic Chemistry
Uploaded: 2019-05-20T01:59:12-08:00
Duration: 8 min 16 s
Channel: Nima Gharibi
Description: How many ^13C NMR signals does each compound exhibit?

Key Concepts

Unique Carbon Environments

The number of signals observed in a 13C NMR spectrum depends on the number of distinct carbon environments in the molecule. Carbon atoms that share an identical surrounding, or are chemically equivalent, will produce the same signal, thus reducing the total count of distinguishable peaks.

Molecular Symmetry

Molecular symmetry plays a key role in determining the number of unique carbon environments. In molecules with a high degree of symmetry, several carbon atoms may be equivalent, leading to fewer NMR signals. Understanding symmetry helps in predicting and interpreting the NMR spectrum effectively.

13C NMR Spectroscopy

13C NMR spectroscopy is an analytical technique that reveals information about the carbon atoms in a compound by detecting their magnetic properties. It produces a spectrum in which each signal corresponds to a unique carbon environment within the molecule, making it a fundamental method for confirming molecular structure in organic chemistry.

Transcript

00:01 Hello everyone, today we're doing chapter 14, problem 50, and this question asks us to determine how many carbon nmr signals does each of these following compounds show? so like before, we know how to do this.

00:13 We know how that each peak or each signal in hnmr or carbon nmr is from a chemically distinct carbon that exists in its unique chemical microenvironment.

00:24 So we know that something like this has one carbon here that's bound to hydrogen, bound to three carbons.

00:36 And then we have three carbons here.

00:40 Each of these three carbons is bound to three hydrogens and one carbon.

00:43 So because these three carbons, these three methyl groups here are bound to the same constituents, we can say that these are going to be the same type of carbons.

00:52 Then we have this carbon down here, that's a central carbon that's bound to, hydrogen and three carbon.

00:59 So we're going to have two types of carbon signals in this molecule.

01:05 So what about this molecule here? well, we see that we have a carbon here that's bound to three hydrogens and one carbon.

01:19 We have the central carbon that's bound to four carbons.

01:22 These two methyl carbons are bound to three hydrogens and one central carbon here.

01:29 We have been in ch2 here, ch2 here, and a ch3 here.

01:35 So right off the bat, we know that these two carbons are the same.

01:43 They're bound to three hydrogens and they're bound to the same central carbon atom down here.

01:49 So we have one type there.

01:53 And then we know that this terminal carbon here is bound to three hydrogens and one carbon.

02:03 This one carbon is bound to those two methyl groups.

02:07 Is bound to another r group.

02:09 So we're another tip of carbon here.

02:12 Obviously the central carbon here is very unique because the only carbon that's bound to four non -hydrogen substitutes.

02:19 So actually do that a different color.

02:22 We have this one here.

02:35 But in essence, what we can actually determine is that this blue carbon being bound to three protons and this central carbon here, well, like, what's the difference between this blue one and this green one? so there's actually no difference between them.

02:54 So these green carbons are actually these three carbons here, because each of these three carbons are bound to three protons and the central carbon atom in the middle.

03:05 So these three carbons are all one type.

03:08 Then we have the central carbon that's one type.

03:11 Then we have each of these ch2s that are one type, because this ch2 is adjacent to a carbon that's bound to four non -carbon substituents, while the ch2 is bound to a terminal methyl.

03:20 So then we have one type, these green, these three carbons that are these green carbons, one, two, three, four, five.

03:32 So we have five chemically distinct carbon signals here.

03:38 What about for this example here? so i always like to draw it out if it's given in this sort of formula form, just so i could very easily distinguish everything.

03:50 And here we see that we have this terminal carbon here that's adjacent to an oxygen.

03:54 So we have one carbon type here.

03:55 We have the central carbon that's bound to two carbons, one oxygen, one hydrogen.

04:01 So we have a second type of carbon here...

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