/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 16 Explain whether it is possible t... [FREE SOLUTION] | 91影视

91影视

Log out

Learning Materials

Features

Discover

Chapter 15: Problem 16

Explain whether it is possible to distinguish between the following pairs of isomers based only on the coupling patterns in the \(^{31} \mathrm{P}\) NMR spectra: (a) cisand trans\(-\left[\mathrm{PF}_{4}(\mathrm{CN})_{2}\right]^{-},\) and (b) \(m e r-\) and \(f a c-\) \(\left[\mathrm{PF}_{3}(\mathrm{CN})_{3}\right]^{-}\)

Short Answer

Expert verified
Both pairs of isomers can be distinguished by their ^{31} ext{P} ight]^{-} ight]}- ight} NMR coupling patterns.

Step by step solution

01

Understanding Isomers in NMR

First, we need to understand how isomers can be distinguished using NMR. Isomers are compounds with the same formula but different structural arrangements. In NMR, isomers can show different spectral patterns due to differences in the spatial arrangement of atoms, affecting how nuclei interact with each other, termed as coupling.
02

Analyzing cis and trans Isomers

In the NMR spectra, cis and trans- ext{pf}_{4}( ext{cn})_{2} ight]^{-} ight]}- ight} isomers can exhibit different peak splitting patterns due to the arrangement of the ligands surrounding the central atom. In trans isomers, ligands are opposite each other, often resulting in simpler coupling patterns. Whereas cis isomers have ligands adjacent, resulting in more complex coupling due to proximity, leading to different J-coupling values.
03

Analyzing fac and mer Isomers

For mer and fac- ext{pf}_{3}( ext{cn})_{3} ight]^{-} ight]}- ight} isomers, their different geometry causes differences in the NMR spectra. The facial (fac) isomer has symmetry leading to potentially indistinguishable P environments, possibly revealing a simpler coupling pattern. The meridional (mer) isomer lacks this symmetry, likely showing different coupling in the NMR due to the different relative positions of the ligands.
04

Conclusion on Distinguishability

Based on the differences in spatial arrangement, both sets of isomers (cis-trans and mer-fac) should exhibit noticeably different coupling patterns in ^{31} ext{P} ight]^{-} ight]}- ight} NMR spectra. Thus, it is possible to distinguish between these isomers using their NMR spectral data.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with 91影视!

Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Isomer Distinction in NMR
NMR, or Nuclear Magnetic Resonance, is a powerful technique that helps chemists distinguish between different isomers of a compound. Isomers are molecules that have the same molecular formula but differ in their structure or arrangement of atoms. The distinct spatial arrangements lead to variations in how nuclei within the molecules interact with each other. In the context of NMR spectroscopy, these interactions are observed as different coupling patterns, which are unique to each isomer.
  • Coupling Interactions: These occur when nuclei in nearby atoms influence each other's magnetic environment, leading to splitting of peaks in the NMR spectrum.
  • J-Coupling: The magnitude of splitting is quantified by J-coupling constants. These values can differ significantly between isomers due to their unique geometries.
By analyzing the coupling patterns and J-coupling constants in the NMR spectra, chemists can effectively distinguish between different isomers.
Cis-Trans Isomerism
Cis-trans isomerism is a type of geometrical isomerism where ligands are positioned differently around a central core. In cis isomers, similar or identical ligands are positioned on the same side, while in trans isomers, they are on opposite sides. This spatial arrangement greatly affects their NMR spectra.For example, in the molecule \( ext{cis-trans-PF}_4( ext{CN})_2^{-}\), the arrangement of the ligands changes the electromagnetic environment of the phosphorus atoms.
  • Cis Isomers: They tend to have complex NMR spectra due to closer interaction of the ligands. This results in more split peaks due to more pronounced J-coupling values.
  • Trans Isomers: These usually display simpler NMR spectra because the ligands are further apart, leading to less interaction or coupling, often simplifying the splitting patterns in the spectra.
Fac-Mer Isomerism
Facial (fac) and meridional (mer) isomerism occurs in octahedral complexes where three identical ligands are arranged in distinct geometrical positions. In fac isomers, the three identical ligands form one face of the octahedron, while in mer isomers, the ligands form a "T"-shape.In the molecule \([ ext{PF}_3( ext{CN})_3]^{-}\), these differing ligand arrangements lead to distinct NMR spectra.
  • Fac Isomers: They have a symmetrical arrangement making some environments indistinguishable in the NMR, resulting in simpler and often fewer peaks.
  • Mer Isomers: Due to asymmetry, each ligand environment is distinct, leading to more complex splitting and more NMR peaks.
Fac and mer isomers show marked differences in their NMR spectra, making them distinguishable.
Phosphorus-31 NMR
Phosphorus-31 NMR (\(^{31} ext{P}\) NMR) is a valuable tool in characterizing phosphorus-containing compounds, which are common in coordination chemistry. This type of NMR focuses on the phosphorus-31 isotope, which is NMR active because it has a nuclear spin.Several attributes make \(^{31} ext{P}\) NMR particularly useful:
  • Natural Abundance: \(^{31} ext{P}\) has a high natural abundance and a relatively simple spectra due to its single isotope.
  • Coupling: The interaction between phosphorus and adjacent nuclei (like hydrogen or nitrogen) leads to characteristic splitting patterns in the NMR spectra, particularly valuable for distinguishing isomers.
For phosphorus-containing isomers, differences in splitting patterns, chemical shifts, and coupling constants can be critical for correct identification.
Coupling Patterns in NMR Spectra
Coupling patterns in NMR spectra reflect the interactions between magnetic nuclei within a molecule. These interactions, or coupling, amplify distinctions between different isomers in NMR analysis, manifested as peak splitting. The primary factors affecting coupling patterns are:
  • Nuclear Spin: Nuclei with non-zero nuclear spin interact with each other influencing the magnetic field.
  • J-Coupling Constant: This constant gives a measure of the splitting pattern in the spectra and varies based on the distance, angle, and surrounding atoms.
Analyzing coupling patterns allows for precise differentiation between similar compounds. Different isomers, due to their unique spatial configurations, exhibit distinct splitting patterns, making NMR a powerful tool for their structural elucidation.

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

(a) Discuss structural variation among the phosphorus(III) and phosphorus(V) halides, indicating where stereochemical non-rigidity is possible. (b) \(\mathrm{On}\) what basis is it appropriate to compare the lattice of \(\left[\mathrm{PCl}_{4}\right]\left[\mathrm{PCl}_{6}\right]\) with that of \(\mathrm{CsCl} ?\)

(a) We noted that \(\left[\mathrm{N}_{3}\right]^{-}\) is isoelectronic with \(\mathrm{CO}_{2}\) Give three other species that are also isoelectronic with \(\left[\mathrm{N}_{3}\right]^{-} .\) (b) Describe the bonding in \(\left[\mathrm{N}_{3}\right]^{-}\) in terms of an MO picture.

Draw the structures of the possible isomers of \(\left[\mathrm{PCl}_{2} \mathrm{F}_{3}(\mathrm{CN})\right]^{-},\) and state how many fluorine environments there are based on the structures you have drawn. At room temperature, the \(^{19} \mathrm{F}\) NMR spectra of \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\) solutions of two of the isomers exhibit two signals, while the spectrum of the third isomer shows only one signal. Account for these observations.

Comment on the fact that \(\mathrm{AlPO}_{4}\) exists in several forms, each of which has a structure which is also that of a form of silica.

\(25 .0 \mathrm{cm}^{3}\) of a \(0.0500 \mathrm{M}\) solution of sodium oxalate reacted with \(24.7 \mathrm{cm}^{3}\) of a solution of \(\mathrm{KMnO}_{4}, \mathrm{C}\) in the presence of excess \(\mathrm{H}_{2} \mathrm{SO}_{4} .25 .0 \mathrm{cm}^{3}\) of a \(0.0250 \mathrm{M}\) solution of \(\mathrm{N}_{2} \mathrm{H}_{4}\) when treated with an excess of alkaline \(\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-}\) solution gave \(\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{4-}\) and a product \(\mathbf{D} .\) The \(\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{4-}\) formed was reoxidized to \(\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-}\) by \(24.80 \mathrm{cm}^{3}\) of solution \(\mathrm{C},\) and the presence of \(\mathbf{D}\) did not influence this determination. What can you deduce about the identity of \(\mathbf{D} ?\)
See all solutions

Recommended explanations on Chemistry Textbooks

Ionic and Molecular Compounds

Read Explanation

Kinetics

Read Explanation

Nuclear Chemistry

Read Explanation

The Earths Atmosphere

Read Explanation

Physical Chemistry

Read Explanation

Inorganic Chemistry

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.