Multiplicity of peak in 1H-NMR spectroscopy

Multiplicity of peak in 1H-NMR spectrum is splitting of one peak in to two or many peaks.

Hi Friends, in this article we will learn about splitting and multiplicity of peak in 1H-NMR. In previous article we have seen that how we can find coupling constant or J-value of the peak in ¹H-NMR spectrum.[Link]

We have discussed various applications of spectroscopy in chemistry, medicine and environmental science in another article. Please check out for more details. [Link]

Let’s understand both the terminologies;

Introduction

What is splitting of peak?

If a peak appears as single line, then it is known as “singlet”. There are certain situations where singlet peak divided into two or many lines, this phenomenon is known as splitting of the peak.

What is multiplicity of peak?

The number of lines formed due to splitting is known as multiplicity.

Some of the splitting patterns are given below;

Table :1 Splitting and multiplicity in Proton NMR

How to calculate multiplicity of the peak?

We can predict multiplicity of peak which is formed by splitting of that peak by using following formula;

Multiplicity of peak = No. of H on adjacent Carbon + 1

Let’s understand this with some examples

Ethyl acetate

Ethyl acetate is an ester compound which has formula as shown below.

It has three types of proton groups;

CH3 (red colour)

CH3 (blue colour)

And CH2

So the 1H-NMR spectrum shows three different peaks.

Now we will see multiplicity for each peak.

CH3 (red colour) does not have H on adjacent carbon, so according to formula;

Multiplicity of peak = No. of H on adjacent Carbon + 1

Multiplicity of peak = 0 + 1

Multiplicity of peak = 1 (one line)

That mean peak for CH3 (red) appears as “singlet”.

In similar way multiplicity of CH3 (blue) can be calculated. It has adjacent CH2.

Therefore,

Multiplicity of peak = No. of H on adjacent Carbon + 1

Multiplicity of peak = 2 + 1

Multiplicity of peak = 3 (three lines)

That mean peak for CH3 (blue) appears as “triplet”.

what about CH2 peak?

CH2 group has adjacent CH3

Hence according to above formula;

Multiplicity of peak = No. of H on adjacent Carbon + 1

Multiplicity of peak = 3 + 1

Multiplicity of peak = 4 (four lines)

Therefore, we can predict that CH2 peak appears as “Quartet”.

Let’s see another example;

Propane

Propane molecule consist of two types of protons, that is two CH3 and one CH2.

What will be multiplicity of CH3 peak? It has 3 H on adjacent carbon.

So, according to formula,

Multiplicity of peak = No. of H on adjacent Carbon + 1

Multiplicity of peak = 2 + 1

Multiplicity of peak = 3 (three lines)

So, it is clear that CH3 peak appears as “triplet”

Now we will see multiplicity of CH2 peak, here it has 6 H on adjacent carbon.

Therefore,

Multiplicity of peak = No. of H on adjacent Carbon + 1

Multiplicity of peak = 6 + 1

Multiplicity of peak = 7 (seven lines)

This type of multiplicity is known as “septet”.

1-bromobutane

1-bromobutane molecule has four types of protons groups.

That means 1H-NMR shows four different peaks.

Possible multiplicity of each peak is described in table,

Table 2: Multiplicity of protons in 1-bromobutane

Friends, I hope that from above examples we learned how to find multiplicity of the peak in ¹H-NMR.

We can also find out distance between two lines of the peak. It is known as coupling constant or J value. This we have discussed in previous article. I would suggest that after understanding multiplicity, please check coupling constant calculations.

If you feel this information helpful, then please do write in the comment section below.

That’s all for this topic. See you in the next blog.