Answered: Combine the chemical shifts, integrals,…

Physical Chemistry

2nd Edition

ISBN:9781133958437

Author:Ball, David W. (david Warren), BAER, Tomas

Publisher:Ball, David W. (david Warren), BAER, Tomas

Chapter16: Introduction To Magnetic Spectroscopy

Section: Chapter Questions

Problem 16.38E

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Question

Combine the chemical shifts, integrals, and spin-spin splitting patterns in NMR
spectra with information from infrared and mass spectra to determine the structures
of organic compounds

Expert Solution

Step 1

NMR explains structure in terms of chemical shift, spin-spin interaction

Chemical shift

All the nuclei of atoms having unpaired protons or neutrons have magnetic behavior and of all the atoms, highly magnetic active atoms are Hydrogen and Carbon which synthesize organic compounds.
When these organic compounds are kept in an external magnetic field then these magnetically active atoms show the difference in energy because of having an internal magnetic field and external magnetic field.
Different hydrogens have different surroundings and hence react differently towards the external field. This difference in the behavior of all hydrogen is called a chemical shift which is measured from a standard Tetramethylsilane (TMS) which shows the frequency at 0 ppm.
Different types of hydrogens have a different range of chemical shifts.

Like: Alkynyl hydrogen – 2.5-2.7, primary hydrogen of alkane – 0.7-1.3, hydrogen of alkyl halide – 2.5-4, Similarly different hydrogens of the different organic compounds have different chemical shifts which helps in identifying the functional group.

Step 2

Spin-Spin splitting

Since nuclides produce magnetic field means for 1 hydrogen there will be 2 fields. Applied field and field of neighboring nuclei.
Instead of having 1 signal from 1 hydrogen, splitting occurs because of neighboring hydrogen nuclei. And splitting takes place according to n+1 rule where n is the number of equivalent hydrogens. Also, equivalent hydrogens do not split one another signal.
If 2 different types of hydrogens are placed adjacent to each other then they split the signal independently into n_a +1 and n_b + 1.

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