Concept explainers
NMR spectra for four isomeric alkyl bromides with the formula
Assign structures to each of the alkyl bromides and assign the peaks in each spectrum.
Interpretation:
Structures of each of the isomeric alkyl bromides with the formula
Concept introduction:
In
Carbon atoms having equivalent environment will have the same chemical shift.
In simple molecules, equivalent carbon atoms can be identified just by inspection.
The number of signals depends on the number of distinct carbon atoms in the structure of the compound.
If the structure is symmetrical, the number of signals in the
The electronegative atom/group decreases the shielding of the carbon atom to which it is attached.
In
An
The chemical shift for methyl carbon atoms ranges from
The chemical shift for methylene carbon atoms ranges from
The chemical shift for methine carbon atoms ranges from
The chemical shift for aromatic carbon atoms ranges from
The index of hydrogen deficiency is calculated as follows:
Here
Answer to Problem 43P
Solution:
a)
b)
c)
d)
Explanation of Solution
a)
The molecular formula shows an index of hydrogen deficiency equal to zero. Thus, the compound contains ring or multiple bonds. All the carbon atoms must be
The signal at
Combining all this, the only possible structure for the isomer having the formula
b)
The molecular formula shows an index of hydrogen deficiency equal to zero. Thus, the compound contains ring or multiple bonds. All the carbon atoms must be
The signal at
The signal at
Combining all this, the only possible structure for the isomer having the formula
c)
The molecular formula shows an index of hydrogen deficiency equal to zero. Thus, the compound contains ring or multiple bonds. All the carbon atoms must be
The signal at
The signal at
The chemical shift values for the remaining two signals indicate two types of methyl groups. The signal at
Combining all this, the only possible structure for the isomer having the formula
d)
The molecular formula shows an index of hydrogen deficiency equal to zero. Thus, the compound contains ring or multiple bonds. All the carbon atoms must be
The signal at
The signal at
Combining all this, the only possible structure for the isomer having the formula
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Chapter 14 Solutions
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