How many equivalent hydrogens are there in each isomer of C3H7Cl?
1 Answer
There are three sets of equivalent hydrogens in 1-chloropropane and two sets in 2-chloropropane.
The two isomers of C₃H₇Cl are 1 chloropropane and 2-chloropropane.
1-Chloropropane
The molecule contains 7 H atoms. Some of them are different from each other.
For example, the three H atoms on the C-3 are attached to a carbon bonded to a C.
They are different from the H atoms on C-2, which is bonded to two C atoms.
And the two H atoms on C-1 are different again, because C-1 is attached to a Cl.
One way to check whether certain H atoms are equivalent is to replace each H atom with a group like Br and see if you generate the same compound.
Replacing any H atom on C-1 gives BrCH₂CH₂CH₂Cl
Replacing any H atom on C-2 gives CH₃CHBrCH₂Cl.
Replacing any H atom on C-3 gives CH₃CH₂CHClBr.
These are three different compounds, so there are three sets of equivalent H atoms.
The NMR spectrum for 1-chloropropane confirms this prediction.
Peak 4 at 1.0 ppm corresponds to the CH₃ group.
Peak 3 at 1.8 ppm corresponds to the H atoms on C-2.
Peak 2 at 2.5 ppm corresponds to the H atoms on C-1 (peak 1 is caused by the solvent).
2-Chloropropane
The H atom on C-2 is in a class by itself, and the 6 H atoms on the two CH₃ groups are equivalent.
So 2-chloropropane has two sets of equivalent hydrogens.
The NMR spectrum for 2-chloropropane confirms this prediction.
Peak B at 1.6 ppm corresponds to the two CH₃ groups.
Peak A at 3.8 ppm corresponds to the H atom on C-2.
