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Ch. 15 - Structural Identification 2: Nuclear Magnetic Resonance Spectroscopy
Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Non è quello che usi tu?Cambia libro di testo
Capitolo 14, Problema 35b

Draw a spectrum for each of the following molecules, being sure to indicate the multiplicity, integration, and chemical shift of each peak. Label each signal based on the set of equivalent hydrogens to which it corresponds.
(b) Chemical structure of 3-pentanone, showing a five-carbon chain with a ketone group on the third carbon.

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1
Identify the structure of the molecule in question. Determine the number of unique hydrogen environments present in the molecule. Equivalent hydrogens will produce the same signal in the NMR spectrum.
For each unique set of equivalent hydrogens, determine the chemical shift. This is influenced by the electronic environment, such as the presence of electronegative atoms or π-bonds nearby. Use a chemical shift table to estimate the position of each signal.
Determine the integration of each signal, which corresponds to the number of hydrogens in each equivalent set. This is typically represented as a ratio in the NMR spectrum.
Identify the multiplicity of each signal, which is determined by the n+1 rule, where n is the number of neighboring hydrogens. Consider coupling with adjacent hydrogen atoms to determine if the signal is a singlet, doublet, triplet, etc.
Draw the NMR spectrum, placing each signal at the appropriate chemical shift, with the correct integration and multiplicity. Label each signal with the corresponding set of equivalent hydrogens from the molecule.

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NMR Spectroscopy

Nuclear Magnetic Resonance (NMR) Spectroscopy is a technique used to determine the structure of organic compounds by observing the behavior of nuclei in a magnetic field. It provides information about the number of chemically distinct hydrogen environments (protons) in a molecule, their chemical shifts, and the connectivity between them. Understanding NMR is crucial for interpreting spectra and identifying molecular structures.
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General NMR Features

Chemical Shift

Chemical shift in NMR refers to the resonant frequency of a nucleus relative to a standard in a magnetic field. It is measured in parts per million (ppm) and provides insight into the electronic environment surrounding a nucleus. Different functional groups and bonding environments cause shifts in the resonance frequency, allowing chemists to deduce structural information about the molecule.
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1H NMR Chemical Shifts

Multiplicity and Integration

Multiplicity in NMR describes the splitting pattern of a signal, which results from spin-spin coupling between non-equivalent protons. It indicates the number of neighboring protons and follows the n+1 rule, where n is the number of adjacent protons. Integration measures the area under each peak, corresponding to the relative number of protons contributing to that signal, helping to determine the ratio of different types of protons in the molecule.
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1H NMR Integration