How To Draw The Proton NMR Spectrum of an Organic Molecule

The Organic Chemistry Tutor
15 Jan 201912:05
EducationalLearning
32 Likes 10 Comments

TLDRThis educational video script provides a step-by-step guide on drawing proton NMR spectra for organic molecules, using ethyl bromide and an ester as examples. It explains identifying unique hydrogen environments, calculating chemical shifts, applying the n+1 rule for splitting patterns, and considering integration for relative peak heights. The script simplifies complex NMR concepts, making it accessible for learners to visualize and understand molecular structures through their NMR spectra.

Takeaways
  • 🔍 Identify the number of signals in an NMR spectrum by recognizing different types of hydrogen atoms in the molecule.
  • 📊 Organize the information in a table with columns for types of protons, chemical shift, splitting pattern, and integration.
  • 🌀 Chemical shift values can be found in textbooks and are influenced by the proximity to electronegative atoms like bromine or oxygen.
  • 📐 Use the 'n plus one' rule to determine the splitting pattern, where 'n' is the number of adjacent protons on the carbon.
  • 📊 The splitting pattern corresponds to different peak shapes: singlet, doublet, triplet, quartet, etc.
  • 📈 Pascal's triangle can be used to remember the intensity ratios of the splitting patterns.
  • 📊 Integration in the NMR spectrum represents the number of protons and affects the height of the peak.
  • 📝 Signal height in the NMR spectrum correlates with the number of protons; more protons result in a taller peak.
  • 🖌️ When drawing the NMR spectrum, start with the chemical shift scale and plot signals accordingly, considering their types and integration.
  • 🔑 Understanding the NMR spectrum involves knowledge of chemical shifts, splitting patterns, and integration, which are crucial for interpreting the structure of organic molecules.
Q & A

  • What is the main topic of the video?

    -The main topic of the video is how to draw the proton NMR (Nuclear Magnetic Resonance) spectrum of an organic molecule.

  • Why are there only two different types of hydrogen atoms in ethyl bromide despite having five hydrogen atoms?

    -In ethyl bromide, the three hydrogen atoms in the methyl group are equivalent and show up as one signal (signal A), and the two hydrogen atoms in the ethyl group are also equivalent but different from the methyl group, forming another signal (signal B).

  • What is the chemical shift range for a CH2 group attached directly to a bromine atom?

    -The chemical shift for a CH2 group attached directly to a bromine atom is typically between 3 and 4 ppm.

  • What is the chemical shift value chosen for the methyl group in ethyl bromide in the video?

    -The chosen chemical shift value for the methyl group in ethyl bromide is 1.6 ppm.

  • How is the splitting pattern in an NMR spectrum determined?

    -The splitting pattern in an NMR spectrum is determined using the n plus one rule, which considers the number of adjacent protons on the carbon.

  • What does the n plus one rule state for the splitting pattern of proton A in ethyl bromide?

    -For proton A in ethyl bromide, which has two adjacent protons, the n plus one rule indicates a splitting pattern of three (2 + 1), corresponding to a triplet.

  • How can Pascal's triangle be used to remember the intensity ratios of splitting patterns?

    -Pascal's triangle can be used to remember the intensity ratios by looking at the numbers in each row, where the first level corresponds to a singlet, the second level to a doublet with an intensity ratio of one to one, and so on, with the sum of the middle numbers in each row representing the intensity ratio of the corresponding splitting pattern.

  • What does the integration in an NMR spectrum represent?

    -The integration in an NMR spectrum represents the area under the curve, which is proportional to the number of protons contributing to that signal.

  • How does the integration of signal A compare to signal B in ethyl bromide?

    -In ethyl bromide, signal A, which corresponds to three protons, has an integration that is 1.5 times greater than signal B, which corresponds to two protons.

  • What is the significance of the height of the peaks in the NMR spectrum when drawing it?

    -The height of the peaks in the NMR spectrum is significant as it usually represents the number of protons contributing to that signal; a signal with more protons will generally be taller.

Outlines
00:00
🧪 Drawing Proton NMR Spectra for Organic Molecules

This paragraph introduces the process of drawing proton nuclear magnetic resonance (NMR) spectra for organic molecules, using ethyl bromide as an example. It explains the importance of identifying the number of unique signals, which in the case of ethyl bromide are two, corresponding to different types of hydrogen atoms. The paragraph also covers the organization of information in a table, including chemical shift values that can be found in textbooks. It provides an example of assigning chemical shifts to the CH2 and CH3 groups, and explains the use of the 'n plus one' rule to determine splitting patterns, resulting in a triplet for the CH2 group and a quartet for the CH3 group. The paragraph concludes with a discussion on the intensity ratios of these patterns and the use of Pascal's triangle to remember them, as well as the concept of integration, which represents the relative number of protons in each signal.

05:00
📊 Understanding NMR Signal Integration and Peak Height

The second paragraph continues the discussion on drawing NMR spectra, emphasizing that while the exact area under the curve is not crucial, the relative height of the peaks is important, as it corresponds to the number of protons. It then provides a step-by-step guide on how to draw the NMR spectrum for a molecule with a CH3 group next to a carbonyl group, attached to an oxygen and two methyl groups, which forms an ester. The paragraph explains how to determine the number of signals, assign chemical shifts, and use the 'n plus one' rule to find the splitting patterns, resulting in a singlet for the CH3 next to the carbonyl, a septet for the CH group, and a doublet for the methyl groups. The paragraph also discusses the intensity ratios for these patterns and concludes with a brief mention of how to draw the actual NMR spectrum.

10:02
📈 Drawing NMR Spectra with Integration and Peak Heights

The final paragraph focuses on the integration aspect of NMR spectra, which indicates the number of protons corresponding to each signal. It provides a detailed explanation of how to draw the NMR spectrum for the ester molecule, including the placement of the TMS signal, the singlet at 2.3 ppm, the septet at 3.5 ppm, and the doublet at 1.4 ppm. The paragraph explains that the height of the peaks should reflect the number of protons they represent, with the tallest peak corresponding to the signal with the most protons. It concludes by summarizing the process of drawing NMR spectra and thanks the viewer for watching.

Mindmap
Keywords
💡Proton NMR Spectrum
Proton Nuclear Magnetic Resonance (NMR) Spectrum is a technique used to determine the structure of organic compounds by analyzing the magnetic properties of hydrogen atoms within a molecule. In the video, the main theme revolves around how to draw the proton NMR spectrum for an organic molecule, specifically using ethyl bromide and an ester as examples. The process involves identifying signals, chemical shifts, splitting patterns, and integration, which are all crucial for interpreting the spectrum.
💡Ethyl Bromide
Ethyl bromide is an example of an organic compound used in the video to illustrate the process of drawing its proton NMR spectrum. It is a simple molecule with a bromine atom attached to an ethyl group, which contains five hydrogen atoms. The video explains how these hydrogen atoms result in two distinct signals in the NMR spectrum, demonstrating the concept of signal differentiation based on the chemical environment of the hydrogen atoms.
💡Chemical Shift
The chemical shift in NMR spectroscopy refers to the variation in the resonance frequency of a nucleus in a molecule due to its local electronic environment. In the video, the chemical shift is used to differentiate the signals from different types of hydrogen atoms. For instance, the script mentions that a CH2 group attached to a bromine atom has a chemical shift between 3 and 4, while a methyl group near an electron-withdrawing group like bromine will have a slightly different chemical shift.
💡Splitting Pattern
Splitting pattern in NMR spectroscopy is the result of the interaction between neighboring protons, which causes the main signal to split into multiple peaks. The video uses the 'n plus one rule' to predict the splitting pattern for different types of hydrogen atoms in the molecules. For example, the script explains that three adjacent protons will result in a triplet, while four adjacent protons will result in a quartet.
💡N Plus One Rule
The 'n plus one rule' is a simple method used in NMR spectroscopy to predict the number of peaks in a splitting pattern based on the number of neighboring protons (n). The video script uses this rule to determine the splitting patterns for the hydrogen atoms in the example molecules, such as predicting a triplet for a CH2 group with two neighboring protons and a quartet for a methyl group with three neighboring protons.
💡Intensity Ratio
The intensity ratio in NMR spectroscopy refers to the relative heights of the peaks in a splitting pattern. The video script describes the intensity ratios for different splitting patterns, such as a triplet having a ratio of 1:2:1 and a quartet having a ratio of 1:3:3:1. These ratios help in visualizing and interpreting the NMR spectrum.
💡Pascal's Triangle
Pascal's Triangle is used in the video as a mnemonic device to remember the intensity ratios of NMR splitting patterns. The script explains how each level of Pascal's Triangle corresponds to a different splitting pattern, with the numbers at each level representing the relative intensities of the peaks in the pattern.
💡Integration
Integration in NMR spectroscopy represents the relative number of protons contributing to a signal, which is indicated by the area under the curve of the signal. The video script explains how integration is used to determine the relative heights of signals in the NMR spectrum, with a signal from more protons generally being taller, such as a signal from three protons being 1.5 times taller than one from two protons.
💡TMS Signal
TMS, or Tetramethylsilane, is a common reference compound in NMR spectroscopy, with its signal set at 0 ppm on the chemical shift scale. In the video, the script mentions the TMS signal as a starting point for the NMR spectrum, providing a reference for the chemical shifts of other signals in the spectrum.
💡Ester
An ester is a functional group found in organic chemistry, consisting of a carbonyl group attached to an oxygen atom, which is then connected to an alkyl or aryl group. In the video, an ester is used as a second example to demonstrate the drawing of an NMR spectrum, highlighting the unique signals and chemical shifts associated with this functional group.
💡Methyl Group
A methyl group is a chemical group consisting of one carbon atom bonded to three hydrogen atoms (CH3). In the video, the script discusses the chemical shift and splitting patterns of methyl groups in different chemical environments, such as being adjacent to a carbonyl group or an oxygen atom, and how these affect the NMR spectrum.
Highlights

Introduction to drawing the proton NMR spectrum of an organic molecule using ethyl bromide as an example.

Identifying the number of signals in the NMR spectrum by recognizing different types of hydrogen atoms in the molecule.

Ethyl bromide has two signals due to the presence of two distinct types of hydrogen atoms.

Organizing information in a table format to discuss different types of protons and their chemical shifts.

Chemical shift values for CH2 and CH3 groups adjacent to a bromine atom and their typical ranges.

Using the 'n plus one' rule to determine the splitting pattern of proton signals in the NMR spectrum.

Explanation of the triplet splitting pattern for proton A in ethyl bromide.

The quartet splitting pattern for proton B in ethyl bromide as determined by the 'n plus one' rule.

Utilizing Pascal's triangle to remember the intensity ratios of different splitting patterns.

The concept of integration in NMR spectroscopy and its relation to the number of protons.

Drawing the NMR spectrum by considering the height of peaks corresponding to the number of protons.

Demonstration of drawing the NMR spectrum for ethyl bromide with specific chemical shift values and peak heights.

Transition to a second example involving an ester molecule with different chemical environments.

Determination of the number of signals for the ester molecule based on the chemical environment of protons.

Assigning chemical shifts to different types of protons in the ester molecule based on their proximity to functional groups.

Analyzing the splitting patterns for the ester molecule using the 'n plus one' rule for each type of proton.

Explanation of the singlet, septet, and doublet splitting patterns for the ester molecule's protons.

Drawing the NMR spectrum for the ester molecule with appropriate peak heights and splitting patterns.

Final demonstration of how to draw the NMR spectrum for an organic molecule, emphasizing the practical application of the discussed concepts.

Transcripts

Browse More Related Video

More Practice With H-NMR Spectra

30c: Determining molecular structure from H-NMR spectra

NMR Spectroscopy

15.5a The Chemical Shift in C 13 and Proton NMR | Organic Chemistry

Proton NMR - How To Analyze The Peaks Of H-NMR Spectroscopy

15.6a Interpreting NMR Example 1 | Organic Chemistry

Rate This

5.0 / 5 (0 votes)

Thanks for rating:

Related Tags
NMR SpectroscopyOrganic ChemistryEthyl BromideChemical ShiftSplitting PatternIntegrationMethyl GroupCarbonyl GroupEster MoleculeProton SignalsEducational Guide