Concept explainers
Interpretation:
The structure for a compound with molecular formula
Concept Introduction:
Determination of structure of a compound from its proton NMR spectrum:
There are several steps to be followed for the determination of the structure as given below.
Step
Calculation of hydrogen deficiency index (HDI) from the molecular formula.
It can be formulated as given below.
Where,
If
If
If
Step
Consider the number of signals and integration of each signal. This gives the clues about the symmetry of the compound.
In order to convert the integration values into useful information, a smallest number should be chosen and then all integration values should be divided by this number. If the numerical values are not whole numbers, then in order to arrive at whole numbers all the numbers should be multiplied by a suitable integer.
Step
Analyze each signal and then draw fragments consistent with each signal. Consider chemical sift value, integration and multiplicity. If
Step
Assemble the fragments into a molecular structure.
Important chemical shift values and splitting patterns:
An ethyl group is characterized by a triplet of
Type of proton | Chemical shift |
Methyl group | |
Methylene group | |
Methine group | |
Allylic | |
Alkynyl | |
Aromatic methyl | |
Alkyl halide | |
Alcohol | |
Vinylic | |
Aryl | |
Aldehyde | |
Carboxylic acid |
Key point:
Methyl protons, methylene protons and methine protons attached to a carbonyl group give a chemical shift value of
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Organic Chemistry As a Second Language: Second Semester Topics
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