RMN - Integração e desdobramento de sinal

KiFacil

12 Aug 202106:49

Summary

TLDRThis video continues the study of nuclear magnetic resonance (NMR), focusing on signal integration and splitting. The video explains how NMR spectra can distinguish different types of protons in a molecule and how the area under each peak relates to the number of protons. Using benzyl acetate as an example, the process of normalizing and interpreting signal data is demonstrated. The concept of spin-spin coupling and the n+1 rule are also introduced, showing how adjacent protons affect signal splitting. The video aims to deepen the understanding of NMR spectroscopy, preparing viewers for the next topic: coupling constants.

Takeaways

😀 The video continues the study of nuclear magnetic resonance (NMR) with a focus on integration and signal splitting.
📊 NMR spectra can distinguish different types of protons in a molecule, showing how many different hydrogen types are present.
🔬 The position of each NMR signal indicates how shielded or deshielded a hydrogen nucleus is, based on factors like resonance effects and proximity to electron-withdrawing groups.
🔢 The area under each peak in the NMR spectrum is proportional to the number of hydrogens generating that peak, which can be quantified using data analysis software.
🧮 In the case of benzyl acetate, the integrated values of the signals are normalized and rounded to represent the number of protons in each group, resulting in 5 protons for group C, 2 for group B, and 3 for group A.
📈 Signal splitting in NMR is caused by spin-spin coupling, where adjacent protons influence each other's magnetic environment, resulting in the splitting of peaks.
📐 The rule of 'n + 1' is used to predict the number of peaks in a signal, where n is the number of equivalent protons adjacent to a given proton, and the multiplicity reflects the number of peaks.
🧪 Spin-spin coupling effects are typically observed between protons separated by no more than three sigma bonds.
🛠 In specific examples, the hydrogen atoms in a molecule like 1,2-dichloroethane form a triplet and doublet due to the n + 1 rule, demonstrating the splitting pattern.
📚 The next video will cover the concept of coupling constants and provide more practice problems involving NMR spectroscopy.

Q & A

What is the purpose of the video?
-The video continues the discussion on nuclear magnetic resonance (NMR) spectroscopy, focusing on the concepts of signal integration and signal splitting (multiplicity).
What was covered in the previous video?
-The previous video explained the concepts of proton shielding and chemical shift in NMR spectroscopy.
What information can NMR spectra provide about a molecule?
-NMR spectra can distinguish different types of protons in a molecule, indicate their chemical environments, and show the number of protons through signal integration. It also provides insight into the splitting of signals caused by neighboring protons.
How does the integration of NMR signals help in understanding the structure of a molecule?
-The area under each NMR peak is proportional to the number of protons responsible for that peak. By normalizing the integration values, the exact number of protons in each environment can be determined.
What are the integration values for benzyl acetate in the video, and how are they normalized?
-The integration values for benzyl acetate are 57.19, 23.1, and 35.4. These values are normalized by dividing by the smallest value (23.1), resulting in 2.5 for group C, 1 for group B, and 1.5 for group A. These values are then multiplied by two to give the final proton counts of 5, 2, and 3 for groups C, B, and A, respectively.
What does signal splitting in NMR represent?
-Signal splitting (or multiplicity) in NMR occurs due to interactions between a proton and adjacent protons through spin-spin coupling, revealing the number of protons on neighboring atoms.
What is the n+1 rule in NMR spectroscopy?
-The n+1 rule states that a proton with 'n' equivalent neighboring protons will split into n+1 peaks. For example, a proton adjacent to two equivalent protons will produce a triplet (2+1=3).
How is signal splitting observed in the 1,2-dichloroethane molecule?
-In 1,2-dichloroethane, the proton A generates a triplet due to interaction with the two equivalent protons B (n=2, so n+1=3), and the protons B generate a doublet due to the single proton A (n=1, so n+1=2).
Why are there five peaks observed in the high-resolution NMR spectrum of dichloromethane?
-In the high-resolution NMR spectrum of dichloromethane, five peaks are observed due to the splitting of signals caused by the spin-spin coupling between protons. The proton A is split into a triplet (n=2, n+1=3), and the protons B are split into a doublet (n=1, n+1=2), resulting in multiple peaks.
What happens in the NMR spectrum of tert-butyl methyl ether regarding signal splitting?
-In tert-butyl methyl ether, no signal splitting is observed because the protons in group A are separated from the protons in group B by more than three sigma bonds, which prevents coupling and results in singlets.

Outlines

00:00

📚 Introduction to NMR and Video Series Overview

The video begins by welcoming viewers to a continuation of the Nuclear Magnetic Resonance (NMR) study series. It encourages viewers to like, subscribe, and follow the channel for updates. The video transitions into a brief recap of previous topics, such as proton shielding and chemical shift. The focus of this segment will be on signal integration and splitting, demonstrated using the benzyl acetate molecule. It highlights that the NMR spectrum helps distinguish between different proton environments and shows how many different types of hydrogen atoms are present in the molecule.

05:02

🧪 Analyzing Proton Groups and Signal Integration

This section delves deeper into the NMR spectrum of benzyl acetate, explaining how signals correspond to different proton groups (labeled A, B, C, D, E) in the molecule. The position of each signal reveals how shielded or deshielded the hydrogen nucleus is due to factors like resonance and proximity to electron-withdrawing groups. It further explains that the area under each peak is proportional to the number of hydrogens responsible for that signal, introducing the concept of signal integration. Normalization and multiplication processes help to calculate the actual number of protons for each group, confirming the presence of 10 protons in the molecule.

🔬 Understanding Signal Splitting (Spin-Spin Coupling)

The video introduces the concept of signal splitting, which results from the spin-spin coupling effect caused by the magnetic fields of neighboring protons. This effect is transferred via bonds and is typically seen when protons are separated by three bonds or fewer. The N+1 rule is used to predict the splitting pattern, where 'N' is the number of equivalent protons on adjacent carbons. This segment explains how the hydrogen atom in one environment interacts with neighboring hydrogens, leading to the formation of multiplets such as doublets, triplets, and so on.

🧩 Applying the N+1 Rule to Molecules

Using the benzyl acetate molecule as an example, this section applies the N+1 rule. For the protons in group A (with two neighboring protons), the signal splits into three peaks (triplet). For the protons in group B (with one neighboring proton), the signal splits into two peaks (doublet). The explanation extends to more complex molecules like 2-nitropropane and tert-butyl methyl ether, showing different splitting patterns based on proton interactions and distances. The section wraps up with a preview of upcoming topics, including coupling constants and practical applications of NMR.

Mindmap

Keywords

💡Nuclear Magnetic Resonance (NMR)

NMR is a powerful analytical technique used to determine the structure of molecules based on the magnetic properties of atomic nuclei, particularly hydrogen protons. In the video, NMR is discussed as a way to distinguish between different types of protons in a molecule, such as in the example of benzyl acetate.

💡Chemical Shift

Chemical shift refers to the resonant frequency of a nucleus relative to a standard in an NMR experiment. It is influenced by the electron density around the nucleus and provides information about the chemical environment of a proton. The video explains how the position of a signal in the spectrum indicates whether a hydrogen nucleus is shielded or deshielded.

💡Signal Splitting

Signal splitting, also known as spin-spin coupling, occurs when the magnetic fields of nearby protons influence each other, causing the signal to divide into multiple peaks. The video demonstrates this concept with examples like triplets and doublets, explaining how the number of neighboring protons affects the splitting pattern using the n+1 rule.

💡Integration

Integration in NMR measures the area under each signal in a spectrum, which is proportional to the number of protons contributing to that signal. The video shows how integration helps to determine how many protons of each type are present in a molecule, such as in the analysis of benzyl acetate.

💡Multiplicity

Multiplicity refers to the number of peaks into which an NMR signal is split. It is related to the number of neighboring protons (n) by the formula n+1. The video explains how this concept helps in interpreting the structure of a compound, with examples like singlets, doublets, and triplets.

💡Benzyl Acetate

Benzyl acetate is a chemical compound used as an example in the video to explain NMR concepts. The different proton environments in this molecule are analyzed to show how NMR spectra distinguish between different types of hydrogen atoms, based on chemical shifts, integration, and signal splitting.

💡Shielding and Deshielding

Shielding occurs when electrons around a proton protect it from the external magnetic field, causing a shift upfield, while deshielding happens when the proton is exposed to the magnetic field due to reduced electron density, causing a shift downfield. The video discusses how these effects are observed in NMR spectra.

💡Acetate

Acetate refers to a specific group (-COOCH3) present in the benzyl acetate molecule discussed in the video. The NMR spectrum of benzyl acetate shows how the protons in the acetate group have different chemical environments compared to other parts of the molecule.

💡Spin-Spin Coupling

Spin-spin coupling is the interaction between the magnetic fields of neighboring protons, which results in signal splitting in NMR spectra. The video explains how this phenomenon is responsible for the formation of multiplets, such as doublets and triplets, based on the proximity of protons to each other.

💡Proton Equivalence

Proton equivalence refers to protons in a molecule that experience the same chemical environment and thus produce the same signal in an NMR spectrum. The video discusses how different groups of protons, such as in benzyl acetate, can be classified into equivalent groups, simplifying the interpretation of the spectrum.

Highlights

Introduction to the video topic: Continuation of studies on nuclear magnetic resonance (NMR).

Explanation of the concepts of proton shielding and chemical shift covered in the previous video.

Introduction of new topics: signal integration and signal splitting in NMR.

Analysis of benzyl acetate molecule using NMR to distinguish different types of protons.

Explanation of how the number of signals in the NMR spectrum indicates different types of hydrogen atoms present in the molecule.

Detailed analysis of the benzyl acetate NMR spectrum, focusing on equivalent groups and their chemical environments.

Description of how the area under each peak is proportional to the number of hydrogens generating that peak.

Introduction of the concept of normalization of integrated values in NMR analysis.

Steps to normalize the values and interpret the results for the benzyl acetate molecule.

Explanation of signal intensity and how it relates to the number of hydrogens of the same type in the molecule.

Introduction to the phenomenon of signal splitting in NMR, caused by spin-spin coupling.

Explanation of the n+1 rule used to predict the splitting pattern in NMR spectra.

Application of the n+1 rule to analyze the spectrum of 1,2-dichloroethane and other molecules.

Interpretation of the NMR spectrum of 2-nitropropane and explanation of the resulting doublet and septet patterns.

Discussion of when signal splitting is not observed, using tert-butyl methyl ether as an example, due to the separation of protons by more than three sigma bonds.